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Variations on the channel TRF AM tube tuner; and a question
Last night I posted a couple messages regarding the proposed "channel
TRF" AM tube tuner, focusing on the plug-in mini-board idea as one way among several possibilities to implement it. The idea underlying the channel TRF concept is to build bandpass tuning circuitry specific to, and optimized for, each frequency in the BCB, instead of fixing that circuitry to some "average" value and trying to vary it using a traditional variable air capacitor (or variable inductor) for continuous tuning. A switch would be used to select the bandpass circuitry for the particular frequency channel the listener wants to hear. This would allow, in principle if not in practice, the ability to very precisely optimize the bandpass circuitry (to maintain a quite constant bandwidth and shape) for every broadcast frequency in the BCB (from 500 khz to 1800 khz.) The "mini-board" variation of the concept would place the bandpass circuitry for each channel (frequency) onto a small plug-in PCB board. Depending upon the type and order of bandpass filter used, the number of components on the mini-board may be quite small, maybe a couple capacitors, a resistor or two, an inductor, etc., having the optimal values, and with one or more trimmers for fine adjustment of the center frequency. Clearly there are several implementations of the general concept, one of which is a well-known hybrid that allows continuous tuning in the more traditional and familiar way. The ones I think of at the moment a 1) Traditional continuous tuning: Divide the wide BCB into several sub-bands, such as 5 or even more, each sub-band having optimized bandpass circuitry for the sub-band, and then use the traditional variable capacitor or inductor to tune within the narrow sub-band. Although each channel will no longer have the most optimal bandpass configuration, it will be closer to optimal. 2) Single Board, True Channel: It may be possible, instead of having 120+ totally independent channel circuits each placed on a separate mini-board, to put them all onto one larger board, but still keep all circuits otherwise separate on the board. A lot of components, and probably a lot of trimmers. 3) Single Board, Shared Components: As a combination of items (1) and (2), channels which are adjacent to each other (in their own "sub-band") could probably share a lot of common bandpass components, thereby reducing the number needed on the board. Only the large number of trimmers for individual channel calibration will remain. The original idea of mini-boards is most advantageous when the user of the TRF tube tuner only plans to listen to 10-20 stations (such as local, higher-power stations). They only install the channel mini-boards they want to listen to. ***** I do have a couple questions of both John and Patrick (and anyone else caring to chime in) related to this. 1) In the single frequency TRF tube receiver (a TRF designed strictly to listen to a single frequency), is there a need for double tuned circuits? Or will singly tuned circuits be sufficient for excellent performance (audio quality, sensitivity and selectivity)? If not, how do double tuned circuits benefit the overall performance of the single frequency TRF receiver? 2) Let's assume that we decide to design a Mark I TRF AM tube tuner kit designed solely for more local, higher power stations (thus the sensitivity is less critical than a tuner to also be used for casual DXing.) How will this further simplify the optimal single frequency TRF receiver design? Will only one RF amp stage be necessary, or will we still need two? The focus now will be on very high-quality audio reproduction of local stations, which I believe tubeophiles will be most interested in. Thanks. Jon Noring |
How many stages you need depends on the selectivity you need because of your
geographic location and antenna Two stations close in frequency will interfere with each other unless you have enough selectivity. A weak local station that is strong enough to be heard may get splatter from a distance station close in frequency that has 50KW or more and a pattern that concentrates on your area! High Q, double tuning, addtional stages all add to selectivity. The spuerhet solved this problem. But if you want to satisfy your demons with a mdoular approach you might want to consider salvaging a couple of turret type tuners from 1950s TVs. These have clip in moddules with silver contacts and appropriate LC for each channel. With todays ferrites you should be able to squeeze-in a LC for AM BCB. Each tuner will give you 12 channels. -- 73 Hank WD5JFR "Jon Noring" wrote in message ... Last night I posted a couple messages regarding the proposed "channel TRF" AM tube tuner, focusing on the plug-in mini-board idea as one way among several possibilities to implement it. The idea underlying the channel TRF concept is to build bandpass tuning circuitry specific to, and optimized for, each frequency in the BCB, instead of fixing that circuitry to some "average" value and trying to vary it using a traditional variable air capacitor (or variable inductor) for continuous tuning. A switch would be used to select the bandpass circuitry for the particular frequency channel the listener wants to hear. This would allow, in principle if not in practice, the ability to very precisely optimize the bandpass circuitry (to maintain a quite constant bandwidth and shape) for every broadcast frequency in the BCB (from 500 khz to 1800 khz.) The "mini-board" variation of the concept would place the bandpass circuitry for each channel (frequency) onto a small plug-in PCB board. Depending upon the type and order of bandpass filter used, the number of components on the mini-board may be quite small, maybe a couple capacitors, a resistor or two, an inductor, etc., having the optimal values, and with one or more trimmers for fine adjustment of the center frequency. Clearly there are several implementations of the general concept, one of which is a well-known hybrid that allows continuous tuning in the more traditional and familiar way. The ones I think of at the moment a 1) Traditional continuous tuning: Divide the wide BCB into several sub-bands, such as 5 or even more, each sub-band having optimized bandpass circuitry for the sub-band, and then use the traditional variable capacitor or inductor to tune within the narrow sub-band. Although each channel will no longer have the most optimal bandpass configuration, it will be closer to optimal. 2) Single Board, True Channel: It may be possible, instead of having 120+ totally independent channel circuits each placed on a separate mini-board, to put them all onto one larger board, but still keep all circuits otherwise separate on the board. A lot of components, and probably a lot of trimmers. 3) Single Board, Shared Components: As a combination of items (1) and (2), channels which are adjacent to each other (in their own "sub-band") could probably share a lot of common bandpass components, thereby reducing the number needed on the board. Only the large number of trimmers for individual channel calibration will remain. The original idea of mini-boards is most advantageous when the user of the TRF tube tuner only plans to listen to 10-20 stations (such as local, higher-power stations). They only install the channel mini-boards they want to listen to. ***** I do have a couple questions of both John and Patrick (and anyone else caring to chime in) related to this. 1) In the single frequency TRF tube receiver (a TRF designed strictly to listen to a single frequency), is there a need for double tuned circuits? Or will singly tuned circuits be sufficient for excellent performance (audio quality, sensitivity and selectivity)? If not, how do double tuned circuits benefit the overall performance of the single frequency TRF receiver? 2) Let's assume that we decide to design a Mark I TRF AM tube tuner kit designed solely for more local, higher power stations (thus the sensitivity is less critical than a tuner to also be used for casual DXing.) How will this further simplify the optimal single frequency TRF receiver design? Will only one RF amp stage be necessary, or will we still need two? The focus now will be on very high-quality audio reproduction of local stations, which I believe tubeophiles will be most interested in. Thanks. Jon Noring |
Henry Kolesnik wrote:
How many stages you need depends on the selectivity you need because of your geographic location and antenna. Two stations close in frequency will interfere with each other unless you have enough selectivity. A weak local station that is strong enough to be heard may get splatter from a distance station close in frequency that has 50KW or more and a pattern that concentrates on your area! High Q, double tuning, addtional stages all add to selectivity. The superhet solved this problem. Hmmm, the "channel TRF" approach may help with one stage selectivity since it appears we can now use a perfectly optimized higher order tuned filter on the channel mini-board, while in a traditionally tuned circuit, implementing that same bandpass circuit to apply across the whole BCB will be much more difficult, and I would guess be near impossible (too many circuit components which need to be varied simultaneously as one varies the reception center frequency.) With the channel TRF approach, the tube-o-phile can mix and match bandpass filter types from station to station depending upon the circumstances. For example, they could use the default, wider-band, gentler, bandpass filter plug-in board (one which has better linear phase) for a local station which doesn't have adjacent interference, and for a more difficult station (with adjacent interference) they can use a bandpass filter plug-in board with a shape factor closer to unity (which probably has more ripple and worse linear phase). (Even for the default "wider-band" filter, because we can now use a frequency optimized higher order filter, we should be able to achieve reasonably good selectivity, at least sufficient for local station reception, even with one RF amp stage.) There appears to be a lot more freedom given to the circuit designer when the necessity of tuning a fixed set of tuning components over a frequency range is removed, such as using higher order bandpass filters. (Of course, this is one reason for IF, but even superhets have at least one tuned RF amp before the mixer, so the same issue applies to superhets, but is not as critical.) I now wonder that with a single TRF RF amp stage, and with a higher order bandpass filter optimized for a particular frequency, if we can now dispense with the RF transformer? Or does an RF transformer confer other benefits that it should remain? I thought its main benefit was for improved bandpass shaping, but then I may be wrong here (likely with high probablity -- RF transformers do help with isolation of stages for DC, so I've read, but don't know how that would benefit real tuner circuit design.) Jon Noring |
Robert Casey wrote:
Jon Noring wrote: I guess the question to ask is how much better can be done when continuous tuning is eliminated, and one uses an optimum bandpass circuit for each channel frequency? (It appears possible to get almost uniform bandwidth and shape across the entire BCB spectrum.) For high-fidelity audio purposes in the channel TRF concept, what order and type of RF bandpass filter circuitry suggests itself? The upside of several single channel TRF circuits is that each channel's TRF circuits can be custom tuned for frequency and bandwidth. The downside is that this will require a lot of parts for more than a few selected channels, and that if someone moves to another radio market a lot of retuning is required if all channels aren't built to begin with. Yes, this is a downside, but as I see it now, it may not be that much of a burden -- it depends upon the use. It also opens up many interesting opportunities for the hobbyist. There are two general approaches to wiring up the independent bandpass filters for some or all of the BCB channels: 1) Hardwire all the filter components for all the BCB channels onto one large board (we'd have an "American" board and a "European" board, both premade PCB.) This is not trivial, and we could have upwards of 1000 small RLC components needing to be soldered on the board, depending upon the order of the filter we want to use. That's a whole lot of work. It is also inflexible -- the whole board must be committed to one particular bandpass filter type and order (e.g., it must be a 4th order Butterworth -- bandwidth is adjusted by altering the values of the components soldered in as the supplied "chart" will indicate.) 2) The mini-board idea, where the filter components for a single channel frequency are put onto a small PCB mini-board. The user plugs the mini-board into a slot to connect it to the RF amp section (probably with antenna tuning as well.) We could imagine having a large PCB "motherboard" which has up to 130+ plugin slots (not unlike those used for PCs, but we need only have a small number of contacts per slot -- the number I can't guess at the moment.) A switch will also be needed (is an electronic switch a possibility?) Of course, a smaller board with 20 slots, with a twenty position switch, could be made for those who do not anticipate tuning anymore than 20 channels. For local listening (especially for the simple 1 RF amp stage tuner where it won't be very sensitive), this is probably more than enough channels. The advantage of this approach is that the user needs only to get boards for the BCB channels they will listen to, and will have the ability to alter the bandpass characteristics for a particular channel (just wire up a different mini-board tuned to that frequency.) For example, one could have a 7th order Chebychev for 1130 khz with a bandwidth of 15 khz, and a 4th order Butterworth for 750 khz with a bandwidth of 10 khz. At a later time, the user can change the bandpass filter used for any particular channel -- just swap mini-boards. Now how big does the mini-board have to be? I don't have a good feel for this, while the experienced radio builders out there will have a much better idea. But let's look at what the mini-board will contain. Essentially it will contain the RLC bandpass filter components (plus a trimmer or two for fine calibration of the center frequency). Depending upon the order of the filter used, it may have anywhere from 5 to 10 RLC components (again just a guess -- the very high order bandpass filters will have more.) So the mini-board will need to be big enough to hold these components. Again, I think most of them will be fairly small in size, so it is not inconceivable for the mini-board to be as small as, for example, 1" x 2" (again, only a guess -- anyone?) I also foresee that there will be a standard bandpass filter for the channel TRF tube tuner (a given type and order -- what would you use for a single RF amp TRF tube tuner for local listening?) One can have a large number of PCB boards made for that bandpass filter. Then, for a given channel frequency (e.g., 830 khz), and a chosen desired bandwidth, the kit-builder refers to the table of values for each component (e.g., this resistor will be 50 ohms, that capacitor 5 pf, etc.), solders them in, then fine calibrates the center frequency. I don't imagine these boards, when made in bulk, will be that expensive, neither the components be, nor will it take much time to solder the components onto the mini-board -- maybe only a few minutes. The biggest issue I foresee is the fine calibration of the bandpass center frequency -- can that be done independent of the tuner (thus allowing the kit-supplier to make them available on order) or must the mini-board be plugged into the tuner? Since there will be some distance between the RF amp tubes and the bandpass filter, with intervening wire, a switch or two, and slot connectors, there will be interwire resistance, capacitance, etc. For a real world tuner, how important will this be? As to the question of what the unused channels will do to the receiver, I'd do the switching such that all unused channel circuits are completely switched out, and maybe tied to ground. Agreed, although there are probably other possibilities. One interesting aspect of this design is that an enthusiast could add a more traditional continuous tuner if they wanted to (e.g. with a multiganged variable air capacitor or inductor -- just build it separately and plug it into one of the slots. I really do think there are other interesting things one might do with the "channel TRF" tuner concept. I think we have just scratched the surface. Jon Noring |
Henry Kolesnik wrote:
I haven't seen a technical reason whatsoever that a single channel TRF perhaps switchable would have any verifiable advantage over a superhet. But the thread continues to perhaps imply that there might be something. Did I miss something? I'd sure like to know. Patrick Turner noted the following in a thread from early this year, when someone asked about a single frequency BCB tuner: "Since you only want one channel, there is no need for a frequency converter or any IFTs or IF amps, and a TRF with four tuned circuits in the form of two critically coupled RF trannies will do nicely." My understanding of the primary reason why superhet was designed was to allow the most important amplification to be done at a single frequency (the IF frequency), so the tuning circuit can be optimized for that fixed frequency. (I'm sure Patrick and John Byrns will be able to more accurately explain the advantages of the superhet, but that's how I understand it in 10 words or less.) But if we already have a single-frequency tuner, there's no need for an IF stage since we can optimize the bandpass tuner sections for that particular frequency. So for a single frequency tuner, adding an IF stage only complicates the circuitry -- it is superfluous -- and will add more distortion to the final audio signal (albeit small, I assume, for a well-designed IF stage.) So why use it? (It's been said a superhet may confer better stability, whatever that means -- again a topic for Patrick or John to address.) Now, comparing a multichannel TRF tuner (with each channel having its own optimized bandpass filter circuitry) to superhet tuner, then one compares the complexity of switching individually tuned optimal RF bandpass circuits with the complexity of adding a multigang tuning capacitor (or inductor) and an IF stage. Also, there is the factor of audio quality. As I see it at the moment (subject to change as everything comes into better focus over time), a cross-over point between choosing the "channel TRF" and the traditional superhet for a tube-based BCB tuner appears to lie between: 1) Listening to local stations, wanting the highest possible audio quality, and 2) Casual to medium-serious DXing. For (1), the listener only needs 20 or so channels, and the number of RF amps can be kept to one or two (two for some added sensitivity to pull in fairly weak local stations), so the "channel TRF" is more attractive for this purpose (particularly for audio fidelity.) For (2), for a "channel TRF", there'd probably have to be three RF amps, with the full complement of optimized bandpass filters for all 130+ channels installed, so at this point a traditional superhet is strongly indicated. Nevertheless, even for DXing, the "channel TRF" is still intriguing for those who might want to experiment, especially for the ability to quickly swap bandpass filters (for changing the type and order, and not only the bandwidth.) Just my $0.02 worth. Jon Noring |
[Obligatory Telamon rec.radio.shortwave on-topic statement: The
following reply touches upon aspects of TRF design as they apply to MW DXing, particularly sensitivity and selectivity of tube-based TRF designs. MW DXing is on-topic to r.r.s. discussion. I appreciate Telamon's efforts to keep r.r.s discussion strictly on-topic per the written r.r.s. Charter.] Patrick Turner wrote: Jon Noring wrote: Patrick Turner noted the following in a thread from early this year, when someone asked about a single frequency BCB tuner: "Since you only want one channel, there is no need for a frequency converter or any IFTs or IF amps, and a TRF with four tuned circuits in the form of two critically coupled RF trannies will do nicely." The design I evolved for my variable frequency superhet leaves behind all of the many AM radios I have repaired as new and tested in my kitchen for comparison. Even an old Quad AM tuner I have is no better. Patrick, have you published the schematic for your radio? How amenable is your design for turning it into a kit? And what are its overall specs? It sounds like a good MW DXer combined with high audio quality. A TRF fixed F tuner with say two j-fets could be cobbled up with preset RF transformers, in the same format as the double tuned IFTs and with necessary couplings and input LC to broaden the pass band. Miniature sized coils and cans could be used and each module with the RF amps would fit on a board about 70mm x 40 mm, which is 2,800 sq.mm. Thanks. The single frequency tuning board you sized is somewhat close to the size I essentially guessed at. So we'll go with your estimate of 70mm x 40mm. 120 such modules could then fit on a board about 350,000 sq.mm, so that 10 boards would each be 35,000 sq mm, and about 190 mm x 190 mm, and thus all fit in a box the same size as a variable tuner radio from the 1940s. Chuck in an extra board with tubed detector and audio preamp, and 120 position switch, and a PS, and you're done. Another way to look at this is by a volumetric analysis, since one can take advantage of plugging modules in a motherboard-like fashion. Let's assume the modules will be 70 mm by 40 mm, and let's assume we have to space the modules 19 mm apart because of the height of the components soldered on. (Is this reasonable? -- 19 mm is the spacing between PCI boards on a PC MB.) This means each module must minimally take up a volume of 53,200 mm^3. 120 modules therefore will occupy a minimum of 6,384,000 mm^3 (6.4 liters). This works out to a cubic box 186 mm on a side, or in English units 7.3" on a side (alternatively, it works out to about 390 cubic inches for those not used to working in metric.) Of course, a cube is aesthetically and practically not the way the modules would be distributed. So let's assume we plug the modules into the "motherboard", with the long side (70 mm) sticking up. This would yield a single motherboard footprint of 142 square inches, or about one foot on a side, and about 3" tall. If we split it into two motherboards, each holding 60 modules, then the footprint would be 8.4" on a side, with a height of about 6". Yes, this is not an insignificant volume, but it is not a huge volume. I notice that the three gang tuning air capacitor on my Philco 37-670 occupies a space of 3"x4"x7", or about 84 cubic inches, about 1/5 the volume of the 120 module "box" (in a channel TRF, the tuning capacitor would not be used.) Also remove the small volume taken up by the IF section (no idea how much volume that typically takes up in a tube set, but it is not tiny.) Now, let's look at the 20 module motherboard. Here, the necessary one-level motherboard would have an area of 24 square inches. Thus, a 6"x4" motherboard (make it 7"x5" for some clearance) will hold 20 modules, plugged in. The height will be 3". Now this seems reasonable when the end-user only intends to tune in 20 local stations. It is smaller in volume than the 3-gang tuning air capacitor on my Philco. Of course, it will only tune 20 stations, and nothing in-between. From the perspective of tuners in general (not specific to tube type tuners, but also solid state and digital), the channel TRF does not make sense. But with respect to a tube-based tuner, it does seem to make sense for *some* applications. Since the only ones who will even buy or build an AM tube tuner are tube-o-philes or tube-o-holics (those who are attracted to tube-based equipment for whatever aesthetic reason), the aspect of "commercial application" as we understand it for ordinary radios does not enter the picture. Those who simply want to get some job done with a radio (listening to local stations, DXing, etc.), and are not overly enamored with any particular under-the-hood architecture, will certainly NOT gravitate to any tube-based tuner because of the much better and cheaper options out there in the marketplace (digital and SS designs -- I don't know of any tube-based high-end general coverage receiver being built today -- and I'd be surprised if someone is attempting it.) As Patrick noted, and which I agree wholeheartedly, pure digital is the future of radio for utilitarian purposes (if BCB and FM radio itself even has a future!) But that's the point. In this discussion we are not talking about building a radio for those who want to get a job done, but those who are enamored with tubes and want the best possible sound out of the AM tuner. For this purpose, the channel TRF is certainly a viable candidate, along with a tuned TRF (as John Byrns is apparently working on), as is the more traditional IF design (which Patrick says he is working on.) If the components for each tuner board cost $20, then about $3,000 for the 120 + PS, box, etc, all would be a steal, and a quite cheap sort of "high-end" price. An asian maker of boards might reduce the cost by 20 dB to $2 each. Obviously, the component cost is significantly higher than for a traditionally tuned circuit because one is using a larger number of components, most of which will not even be powered while the tuner is selected to a particular channel frequency. So in a sense, this is a significant inefficiency. But for a tuner intended to tune in local stations, the channel TRF tube tuner appears to have some things in its favor. As a tube-o-phile myself, one can make several strong arguments in favor of the channel TRF tube tuner: 1) the circuitry is "clean", no IM mixing, 2) the bandpass filters are *perfectly* optimized for each channel -- no compromises (this is a *huge* attraction), 3) provides the ability to plugin different bandpass filters for a particular station (if needed), and 4) *may* be more amenable to a kit than would a full- blown superhet design. Now, if a tube-o-phile wants a tube tuner for serious MW DXing (for whatever reason -- I would not use a tube tuner for *serious* DXing), then the channel TRF is not down and out, but certainly has its work cut out for it to try to compete with the continuously-tuned TRF, and of course with traditional superhet designs. The need to include all 120+ BCB channels does work against the "channel TRF". (On the other hand, I can see a serious MW DXer build a single- channel TRF design of three or four RF amp stages where the bandpass sections are "swappable" to tune the channel wanted to monitor. Here the design will simply have a single slots for each bandpass filter stage -- no channel switches. Just swap the mini-boards to retune to a different frequency.) I eagerly await your completion of a prototype of just one single iddy biddy TRF tuner board which has all the discussed and wanted capabilities with respect to audio BW, distortions, sensitivity, selectivity to allow local station listening where weak and powerful stations exist which are only 40 kHz apart, all without spurious noise, interference, cross modulation, etc. First, I assume that sensitivity is largely a matter of the RF amp itself (and number of RF amp stages), not the bandpass filter itself (although the filter should not overly get in the way of RF amp gain.) But if the bandpass filter plays a greater role in sensitivity than I realize, shouldn't an optimally tuned bandpass filter in the channel TRF concept significantly outperform the limited and sub-optimal single or double stage bandpass filters one is *forced* to use for continuous tuning? Second, each tuning module (for a single frequency) is, by and large, independent of all the other modules. Thus, this simplifies the design process since one doesn't have to share the same bandpass component values from channel to channel, except maybe the RF transformers. This should make it much easier, not harder, to achieve the performance goals. In the channel TRF, we are no longer constrained to single or double tuning -- we can, for example, have the equivalent of quintuple "tuning" for a 5th order bandpass filter if we want. I'm assuming that, for a given frequency, the designer will have full control over the values of all the LC components (and not just one or two, excluding the RF transformer, though) in the bandpass filter, thus making it much easier to achieve selectivity, distortion and other performance goals, all the while simplifying the main part of the circuit -- to make it cleaner -- fewer kludges needed. (I keep looking at advanced radio circuits and see such a spiderweb of wiring between the various stages, wondering why the hell it is all there -- I wonder how much of that complexity is due to not being able to properly optimize the RF bandpass filters for a given frequency, thus requiring all sorts of work-arounds to get good overall peformance.) It is a remarkable achievement for a radio designer to meet the several specification goals Patrick listed for an AM BCB tuner (his list appears to be an "all things for all users" dream list) and which is continuously tunable from 500 khz to 1800 khz (thus necessitating most of the tuning components be shared.) I have no doubts that Patrick has come up with a great design. Superhet definitely helps with accomplishing this feat, but from what I see, there are a lot of ****ty superhets out there, so if superhet alone were sufficient, the perfect radio would have been designed years ago. (Isn't the AA5 that perfect radio? -- it is, depending upon the definition of "perfect" -- it is "commercially" perfect for the masses.) IF is not the magic bullet (albeit it is a powerful one), but simply a nifty tool to get from here to there. But like all nifty tools, they have their limits and their place. One does not use a hammer to drive in a screw, for example. Almost the entire amount of AM radio reception theory that has ever filled the minds of conscious humans has been repeatedly explained so far in this thread, so you have all the knowhow you ever wanted, so what's the hold up? Stop dithering, and go to it man! Actually the know-how has not been explained in full! :^) Thanks for your feedback. It is definitely adding useful information to this thread. Jon Noring |
"Jon Noring" wrote in message ... snip (here and other places) Another way to look at this is by a volumetric analysis, since one can take advantage of plugging modules in a motherboard-like fashion. Let's assume the modules will be 70 mm by 40 mm, and let's assume we have to space the modules 19 mm apart because of the height of the components soldered on. (Is this reasonable? -- 19 mm is the spacing between PCI boards on a PC MB.) This means each module must minimally take up a volume of 53,200 mm^3. 120 modules therefore will occupy a minimum of 6,384,000 mm^3 (6.4 liters). This works out to a cubic box 186 mm on a side, or in English units 7.3" on a side (alternatively, it works out to about 390 cubic inches for those not used to working in metric.) Don't forget you will have to swich those modules in an out of circuit. The switch and all the associated wiring will significantly add to the space. The wiring for the switch will also probably affect the tuning of the modules forcing them to be tuning 'in place'. Of course, a cube is aesthetically and practically not the way the modules would be distributed. So let's assume we plug the modules into the "motherboard", with the long side (70 mm) sticking up. This would yield a single motherboard footprint of 142 square inches, or about one foot on a side, and about 3" tall. If we split it into two motherboards, each holding 60 modules, then the footprint would be 8.4" on a side, with a height of about 6". If the long end sticks up, you have the inout and output of the modules on the same end. This could result in unwanted coupling. Yes, this is not an insignificant volume, but it is not a huge volume. I notice that the three gang tuning air capacitor on my Philco 37-670 occupies a space of 3"x4"x7", or about 84 cubic inches, about 1/5 the volume of the 120 module "box" (in a channel TRF, the tuning capacitor would not be used.) Also remove the small volume taken up by the IF section (no idea how much volume that typically takes up in a tube set, but it is not tiny.) snip But for a tuner intended to tune in local stations, the channel TRF tube tuner appears to have some things in its favor. As a tube-o-phile myself, one can make several strong arguments in favor of the channel TRF tube tuner: 1) the circuitry is "clean", no IM mixing, Conceptually it may appear clean, but the proposed switiching of many modules adds a new complexity. All the wiring associated with a swicth will cause more problems that the design solves. 2) the bandpass filters are *perfectly* optimized for each channel -- no compromises (this is a *huge* attraction), If you are looking for broad band with reasonable attenuation of other stations, a superhet is much better as there is only one signal you are optimizing for. 3) provides the ability to plugin different bandpass filters for a particular station (if needed), and 4) *may* be more amenable to a kit than would a full- blown superhet design. I would think that a kit should be simple, the proposed solution is not. First, I assume that sensitivity is largely a matter of the RF amp itself (and number of RF amp stages), not the bandpass filter itself (although the filter should not overly get in the way of RF amp gain.) But if the bandpass filter plays a greater role in sensitivity than I realize, shouldn't an optimally tuned bandpass filter in the channel TRF concept significantly outperform the limited and sub-optimal single or double stage bandpass filters one is *forced* to use for continuous tuning? If you are only looking at a single aspect of the design (get all unwanted signals out at the earliest point in the radio) then you may be correct. But if you look at the overall design, then you will see there are tradeoffs that must be considered. If the front end can tolerate the unwanted signals, then IF filtering can deal with them and you have a workable solution that does not have the alignment problems you would look at with a TRF design. Second, each tuning module (for a single frequency) is, by and large, independent of all the other modules. Thus, this simplifies the design process since one doesn't have to share the same bandpass component values from channel to channel, except maybe the RF transformers. This should make it much easier, not harder, to achieve the performance goals. snip (I keep looking at advanced radio circuits and see such a spiderweb of wiring between the various stages, wondering why the hell it is all there -- I wonder how much of that complexity is due to not being able to properly optimize the RF bandpass filters for a given frequency, thus requiring all sorts of work-arounds to get good overall peformance.) I think you really need to understand that spiderweb before making that kind of statement. snip Almost the entire amount of AM radio reception theory that has ever filled the minds of conscious humans has been repeatedly explained so far in this thread, so you have all the knowhow you ever wanted, so what's the hold up? Stop dithering, and go to it man! Actually the know-how has not been explained in full! :^) And that know-how does not all need to be explained here. There are plenty of resources on the internet, look for them and study them. Thanks for your feedback. It is definitely adding useful information to this thread. Jon Noring IMO this thread and the related theads are more on-topic for rrs than much of the stuff posted by one of the people considering this to be off topic. craigm |
[Obligatory Telamon rec.radio.shortwave on-topic statement: The
following reply touches upon aspects of TRF design as they apply to MW DXing, particularly sensitivity and selectivity of tube-based TRF designs. MW DXing is on-topic to r.r.s. discussion. I appreciate Telamon's efforts to keep r.r.s discussion strictly on-topic per the written and published r.r.s. Charter.] craigm wrote: Don't forget you will have to switch those modules [all 120+] in and out of circuit. The switch and all the associated wiring will significantly add to the space. Granted, it will. Some of the wiring hassle is removed if we use a ready-made PCB motherboard (see, for example, the ST-35 clone board at http://www.diytube.com/ ). But, unless one can think of some clever electronic switching arrangement, there will be wires from the switch to the board. One would make sure the wires from the switch would solder on to pins along one side of the motherboard (and appropropriately shielded), but for 120+ channels could be 480+ wire connections (assuming we can get by with four wires per channel to feed the bandpass filter(s), which is unclear at the moment) -- definitely formidable, but not outside the realm of solvability by clever design and utilization of modern components. With 15-20 channels (for local listening purposes), however, the situation is much more reasonable all around. As I've noted recently (a shift in the requirements), the channel TRF concept makes the most sense for an audiophile-acceptable tube tuner to listen to strong, local stations. Even the so-called "RCA "high-fidelity AM tube tuner" is a TRF design, not an IF. Thus, having it optimally tuned for 15-20 stations (channels) will be acceptable for this purpose, and in fact may be a good selling point among these people. If one wants all 120+ stations soldered in, that means the user is interested in tuning the whole BCB, which automatically means DXing. Now we are in a different ballpark, and the user expectations are different. [Here, I would consider John Byrns advice and design a doubly tuned TRF design, such as his proposed "modernized" Western Electric 10-A. One interesting twist, to get more optimum bandshaping across the BCB, divide the wide-ranging BCB into five or more tunable bands; thus, for example, band 1 would tune from 500-650 khz, band 2 from 650-850 khz, band 3 from 850-1100 khz, band 4 from 1100-1400 khz, and band 5 from 1400-1800khz (or whatever makes sense.) Each band would have its own singly or doubly tuned bandpass circuitry, optimized to that band (but not optimized to any particular frequency). In fact, with a narrow enough sub-band, one should be able to get pretty good bandshaping with single tuning, I presume, which is a welcome simplification.] The wiring for the switch will also probably affect the tuning of the modules forcing them to be tuning 'in place'. Yes, that is definitely a consideration which I've noted before, the affect of the interwire/interconnect RLC on the tuning circuit. With continuous tuning, this is not an issue. With the 15-20 channel system for local tuning, it may not be a problem either if we add to the circuit some calibration indicator (like the tuning light of old.) For example, the user makes or buys a mini-board for 830 khz (a local station they want to listen to.) They plug it in. They then turn on the tuner (letting it warm up fully). Once sufficiently warmed up, they then calibrate the mini-board by turning a trimmer on the mini-board to fine tune the station, until either the station sounds as if it is "in tune", or the calibration indicator light shows it to be tuned to the correct center frequency. (Also as I've noted before, it will no doubt be important for there to be a fine tuning control on the tuner itself, to fine tune +/- 1 khz (or thereabouts) to account for warmup and for long-term drift of the component values inbetween calibrations. But many audiophiles and especially kit-building tube-o-philes love to tweak their stuff -- they'll enjoy this, and they will also be enamored in having the most optimum bandpass tuning circuitry for that frequency -- it's a performance/sound issue. Some may even wish to swap plugin boards, to try different bandpass types, order and bandwidth (for some stations they may have to because of adjacent interference.) In a sense, an IF design is boring when looked at from this angle. laugh/. If the long end sticks up, you have the inout and output of the modules on the same end. This could result in unwanted coupling. Granted. One of those problems which needs to be sorted out in the design of the whole "tuning box" architecture. It is a problem, but so far does not appear to be a show stopper. It's one of those items that still falls under the category "to be solved by appropriate board and wiring design". Conceptually it may appear clean, but the proposed switiching of many modules adds a new complexity. All the wiring associated with a swicth will cause more problems that the design solves. For 120+ channels, yes, it looks like a plumbing nightmare unless someone can come up with a clever idea (and that is certainly possible). But with 15-20 channels, it is entirely workable. Old TVs worked with 12 channel switches (channels 2-13.) And I'm not familiar with what could be done with modern electronic switches. If you are looking for broad band with reasonable attenuation of other stations, a superhet is much better as there is only one signal you are optimizing for. Well, the same applies to the channel TRF concept. When we switch in a particular bandpass tuning circuit, it is calibrated for a single center frequency, with the optimum tuning circuit for that frequency. Note again that Patrick himself said that IF is not needed when one is building a single frequency receiver -- and from his comments he is a very strong advocate of superhet design for a tunable receiver. That's all the channel TRF is: a single frequency receiver, duplicated n number of times (where n is the number of channels one wants to tune, which are switched in and out.) The downsides of a channel TRF are obvious: plumbing (wiring) complexity for an all-channel BCB tuner, and not being able to continuously tune all frequencies within the BCB. I would think that a kit should be simple, the proposed solution is not. At 120+ channels, the channel TRF is intimidating (the switch box and individual tuning circuits), but at 15-20, with the plugin architecture I am thinking of, it does not look that complicated, especially if a lot of the architecture and components we see used in PCs can be utilized. And that know-how does not all need to be explained here. There are plenty of resources on the internet, look for them and study them. I've definitely done that! IMO this thread and the related theads are more on-topic for rrs than much of the stuff posted by one of the people considering this to be off topic. I've put in the obligatory Telamon preamble stating this message is on-topic to r.r.s., so all should be fine with the Usenet gods (tm). Thanks for your informative feedback. Jon Noring |
Jon Noring wrote in message . ..
[Obligatory Telamon rec.radio.shortwave on-topic statement: The following reply touches upon aspects of TRF design as they apply to MW DXing, particularly sensitivity and selectivity of tube-based TRF designs. MW DXing is on-topic to r.r.s. discussion. I appreciate Telamon's efforts to keep r.r.s discussion strictly on-topic per the written r.r.s. Charter.] Telamon is being a petulant freak and the "usenet gods" as you mention are dealing with him. Meanwhile I'm thinking of killing this file too. So far I haven't cared to bother about finding out where your nonsense really emanates from either. Other people have some interest in the thread and it wouldn't be fair to them. My address is real though. You won't get any reply without one, even if you do try it. |
snip The design I evolved for my variable frequency superhet leaves behind all of the many AM radios I have repaired as new and tested in my kitchen for comparison. Even an old Quad AM tuner I have is no better. Patrick, have you published the schematic for your radio? How amenable is your design for turning it into a kit? And what are its overall specs? Overall specs are excellent as detailed in many previous postings. No, I havn't posted the full schematic, and no, I am not aiming to supply details to anyone else to make into a kit for sale. So you'll have to do your own R&D, at your own expense, using your time, not mine. It sounds like a good MW DXer combined with high audio quality. A TRF fixed F tuner with say two j-fets could be cobbled up with preset RF transformers, in the same format as the double tuned IFTs and with necessary couplings and input LC to broaden the pass band. Miniature sized coils and cans could be used and each module with the RF amps would fit on a board about 70mm x 40 mm, which is 2,800 sq.mm. Thanks. The single frequency tuning board you sized is somewhat close to the size I essentially guessed at. So we'll go with your estimate of 70mm x 40mm. 120 such modules could then fit on a board about 350,000 sq.mm, so that 10 boards would each be 35,000 sq mm, and about 190 mm x 190 mm, and thus all fit in a box the same size as a variable tuner radio from the 1940s. Chuck in an extra board with tubed detector and audio preamp, and 120 position switch, and a PS, and you're done. Another way to look at this is by a volumetric analysis, since one can take advantage of plugging modules in a motherboard-like fashion. Let's assume the modules will be 70 mm by 40 mm, and let's assume we have to space the modules 19 mm apart because of the height of the components soldered on. (Is this reasonable? -- 19 mm is the spacing between PCI boards on a PC MB.) This means each module must minimally take up a volume of 53,200 mm^3. 120 modules therefore will occupy a minimum of 6,384,000 mm^3 (6.4 liters). This works out to a cubic box 186 mm on a side, or in English units 7.3" on a side (alternatively, it works out to about 390 cubic inches for those not used to working in metric.) Of course, a cube is aesthetically and practically not the way the modules would be distributed. So let's assume we plug the modules into the "motherboard", with the long side (70 mm) sticking up. This would yield a single motherboard footprint of 142 square inches, or about one foot on a side, and about 3" tall. If we split it into two motherboards, each holding 60 modules, then the footprint would be 8.4" on a side, with a height of about 6". Yes, this is not an insignificant volume, but it is not a huge volume. I notice that the three gang tuning air capacitor on my Philco 37-670 occupies a space of 3"x4"x7", or about 84 cubic inches, about 1/5 the volume of the 120 module "box" (in a channel TRF, the tuning capacitor would not be used.) Also remove the small volume taken up by the IF section (no idea how much volume that typically takes up in a tube set, but it is not tiny.) Now, let's look at the 20 module motherboard. Here, the necessary one-level motherboard would have an area of 24 square inches. Thus, a 6"x4" motherboard (make it 7"x5" for some clearance) will hold 20 modules, plugged in. The height will be 3". Now this seems reasonable when the end-user only intends to tune in 20 local stations. It is smaller in volume than the 3-gang tuning air capacitor on my Philco. Of course, it will only tune 20 stations, and nothing in-between. From the perspective of tuners in general (not specific to tube type tuners, but also solid state and digital), the channel TRF does not make sense. But with respect to a tube-based tuner, it does seem to make sense for *some* applications. Since the only ones who will even buy or build an AM tube tuner are tube-o-philes or tube-o-holics (those who are attracted to tube-based equipment for whatever aesthetic reason), the aspect of "commercial application" as we understand it for ordinary radios does not enter the picture. Those who simply want to get some job done with a radio (listening to local stations, DXing, etc.), and are not overly enamored with any particular under-the-hood architecture, will certainly NOT gravitate to any tube-based tuner because of the much better and cheaper options out there in the marketplace (digital and SS designs -- I don't know of any tube-based high-end general coverage receiver being built today -- and I'd be surprised if someone is attempting it.) As Patrick noted, and which I agree wholeheartedly, pure digital is the future of radio for utilitarian purposes (if BCB and FM radio itself even has a future!) But that's the point. In this discussion we are not talking about building a radio for those who want to get a job done, but those who are enamored with tubes and want the best possible sound out of the AM tuner. Then the cabinet size for the tubed tuner will be enormous compared to using fets, and there will be 240 tubes in there for all the single channel tuner modules. A tubed tuner with 120 x two tubed modules is an absurd idea. Its a waste of time trying to suggest such a kit with tubes. So please try to be practical, instead of a perpertual waffler. I think practicalities will force you to abandon tubes, and adopt SS or go to a decent superhet. I am not sure you will figure this out, since you just don't seem to know enough, imho. For this purpose, the channel TRF is certainly a viable candidate, along with a tuned TRF (as John Byrns is apparently working on), as is the more traditional IF design (which Patrick says he is working on.) If the components for each tuner board cost $20, then about $3,000 for the 120 + PS, box, etc, all would be a steal, and a quite cheap sort of "high-end" price. An asian maker of boards might reduce the cost by 20 dB to $2 each. Obviously, the component cost is significantly higher than for a traditionally tuned circuit because one is using a larger number of components, most of which will not even be powered while the tuner is selected to a particular channel frequency. So in a sense, this is a significant inefficiency. But for a tuner intended to tune in local stations, the channel TRF tube tuner appears to have some things in its favor. As a tube-o-phile myself, one can make several strong arguments in favor of the channel TRF tube tuner: 1) the circuitry is "clean", no IM mixing, 2) the bandpass filters are *perfectly* optimized for each channel -- no compromises (this is a *huge* attraction), 3) provides the ability to plugin different bandpass filters for a particular station (if needed), and 4) *may* be more amenable to a kit than would a full- blown superhet design. Now, if a tube-o-phile wants a tube tuner for serious MW DXing (for whatever reason -- I would not use a tube tuner for *serious* DXing), then the channel TRF is not down and out, but certainly has its work cut out for it to try to compete with the continuously-tuned TRF, and of course with traditional superhet designs. The need to include all 120+ BCB channels does work against the "channel TRF". (On the other hand, I can see a serious MW DXer build a single- channel TRF design of three or four RF amp stages where the bandpass sections are "swappable" to tune the channel wanted to monitor. Here the design will simply have a single slots for each bandpass filter stage -- no channel switches. Just swap the mini-boards to retune to a different frequency.) I eagerly await your completion of a prototype of just one single iddy biddy TRF tuner board which has all the discussed and wanted capabilities with respect to audio BW, distortions, sensitivity, selectivity to allow local station listening where weak and powerful stations exist which are only 40 kHz apart, all without spurious noise, interference, cross modulation, etc. First, I assume that sensitivity is largely a matter of the RF amp itself (and number of RF amp stages), not the bandpass filter itself (although the filter should not overly get in the way of RF amp gain.) But if the bandpass filter plays a greater role in sensitivity than I realize, shouldn't an optimally tuned bandpass filter in the channel TRF concept significantly outperform the limited and sub-optimal single or double stage bandpass filters one is *forced* to use for continuous tuning? Second, each tuning module (for a single frequency) is, by and large, independent of all the other modules. Thus, this simplifies the design process since one doesn't have to share the same bandpass component values from channel to channel, except maybe the RF transformers. This should make it much easier, not harder, to achieve the performance goals. In the channel TRF, we are no longer constrained to single or double tuning -- we can, for example, have the equivalent of quintuple "tuning" for a 5th order bandpass filter if we want. I'm assuming that, for a given frequency, the designer will have full control over the values of all the LC components (and not just one or two, excluding the RF transformer, though) in the bandpass filter, thus making it much easier to achieve selectivity, distortion and other performance goals, all the while simplifying the main part of the circuit -- to make it cleaner -- fewer kludges needed. (I keep looking at advanced radio circuits and see such a spiderweb of wiring between the various stages, wondering why the hell it is all there -- I wonder how much of that complexity is due to not being able to properly optimize the RF bandpass filters for a given frequency, thus requiring all sorts of work-arounds to get good overall peformance.) It is a remarkable achievement for a radio designer to meet the several specification goals Patrick listed for an AM BCB tuner (his list appears to be an "all things for all users" dream list) and which is continuously tunable from 500 khz to 1800 khz (thus necessitating most of the tuning components be shared.) I have no doubts that Patrick has come up with a great design. Superhet definitely helps with accomplishing this feat, but from what I see, there are a lot of ****ty superhets out there, so if superhet alone were sufficient, the perfect radio would have been designed years ago. (Isn't the AA5 that perfect radio? -- it is, depending upon the definition of "perfect" -- it is "commercially" perfect for the masses.) IF is not the magic bullet (albeit it is a powerful one), but simply a nifty tool to get from here to there. But like all nifty tools, they have their limits and their place. One does not use a hammer to drive in a screw, for example. Almost the entire amount of AM radio reception theory that has ever filled the minds of conscious humans has been repeatedly explained so far in this thread, so you have all the knowhow you ever wanted, so what's the hold up? Stop dithering, and go to it man! Actually the know-how has not been explained in full! :^) Well then if you don't think you have bothered all of us for long enough to extract our knowledge to do anything, then try some study and in-workshop experiments to get yourself up to speed on RF designs. If you want it, then you do it. Thanks for your feedback. It is definitely adding useful information to this thread. Jon Noring I leave you to your AM tuner meanderings, and wish you well in your R&D. Patrick Turner. |
snip, Note again that Patrick himself said that IF is not needed when one is building a single frequency receiver -- and from his comments he is a very strong advocate of superhet design for a tunable receiver. That's all the channel TRF is: a single frequency receiver, duplicated n number of times (where n is the number of channels one wants to tune, which are switched in and out.) The downsides of a channel TRF are obvious: plumbing (wiring) complexity for an all-channel BCB tuner, and not being able to continuously tune all frequencies within the BCB. I would think that a kit should be simple, the proposed solution is not. At 120+ channels, the channel TRF is intimidating (the switch box and individual tuning circuits), but at 15-20, with the plugin architecture I am thinking of, it does not look that complicated, especially if a lot of the architecture and components we see used in PCs can be utilized. 120 separate AM channels with perhaps 480 discrete LCs and two tubes each is an entirely overcomplex and impractical idea. Pigs would fly before you make a profit selling any kits. You'd need a 6.3 volt x 72 amp power supply just for the filaments alone, as well as 2 amps x 300v for the B+. Please re-arrange your mind's thinking to permit practical and saleable and effective ideas only. Patrick Turner. |
Patrick Turner wrote:
Patrick, have you published the schematic for your radio? How amenable is your design for turning it into a kit? And what are its overall specs? Overall specs are excellent as detailed in many previous postings. No, I havn't posted the full schematic, and no, I am not aiming to supply details to anyone else to make into a kit for sale. So you'll have to do your own R&D, at your own expense, using your time, not mine. Is it because you plan to market the design? Or that you simply don't want anyone else to "profit" from your design? The trend these days is to open source software, and now there's a move to open source mechanical designs. I see the same for open sourcing electronic designs, such as radio receivers. Obviously, the designer of anything has the right to do with it as they please, but I find it perplexing that you have decided not to share your design with the rest of the world, and with posterity. But that's your choice. When you die (as we all must), does the design die with you? And about the so-called "kit", I myself know that it is not a money maker -- I'm sure you will agree with that. The goal is not to make money (which isn't there anyway), but rather to just get something out there for people to build and enjoy. So you would not be interested in your design to be "kit-i-fied", and called the "Turner AM Tuner"? The kit itself will essentially be like what diytube does: provide the PCB boards, a schematic, parts list and directions, and the kit builder has to wing it from there. If they don't want to even use the PCB boards, they have the schematic and parts list to work from. In fact, I would prefer to open source the schematic and parts list for the AM tube tuner if you agreed with that -- that way no one will make money from it in a proprietary sense. Then the cabinet size for the tubed tuner will be enormous compared to using fets, and there will be 240 tubes in there for all the single channel tuner modules. A tubed tuner with 120 x two tubed modules is an absurd idea. ??? Maybe I miswrote in my last reply, but that's NOT what I have in mind. All channels will share the same tubes and RF transformers -- only the rest of the tuned bandpass circuitry (mostly a few LC components) will be swapped between channels. You yourself sized it out in your prior reply, showing you understood this. [I'm just repeating this in case someone reading this message in the distant future, who does not have access to the other prior messages, will not be misled as to the design I am exploring.] For 15-20 channels, the design appears practical and doable. For 120+ channels, it's much more of a push. Maybe reality will get in the way of doability, but for the 15-20 channel design, no one has yet offered any show stopper reasons why it cannot work (both in a layout sense, and in an electronic sense.) That does not mean there aren't any hidden show stoppers lurking around the corner, but I've heard nothing yet which would make me say: "it will never work because ..." There is, of course, a difference between impractical and impossible -- I've not heard any reasons which fall into the "impossible" category yet -- I have heard reasons why it may be impractical. The bigger issue is if anyone is interested in building and using it for their audio system. That is the more valid question. I've covered my thoughts on this in prior messages -- and I am looking at this from the perspective of a tube-o-phile audio enthusiast where audio performance is everything, and not as a vintage radio collector, nor as a hobbyist who simply designs and builds radios as a hobby. I think practicalities will force you to abandon tubes, and adopt SS or go to a decent superhet. I am not sure you will figure this out, since you just don't seem to know enough, imho. One of the goals of this inquiry (the "channel TRF" is one side alley of this more general thread) is to come up with a high-audio-quality AM BCB tube tuner design suitable for building a kit, to be put together by experienced tube amp builders who want to add an audiophile-grade AM tuner to their setup. I've said this quite a few times. The key word is "tube". Not that tubes are better, not that they produce a necessarily better radio (you and I agree on this), but that there are those who want the aesthetics of tube-based equipment. Is anyone wishing for a tube tuner being rational? Yes and no -- it depends upon how one looks at it. Of course, the most obvious path to take is to investigate classic AM tube tuner designs from the golden years (mid 30's to the 1950's) and see if there is any particular design which is a good candidate to base the modern design on (e.g., it must use, or be adapted to use, tubes commonly sold today, can't be too complicated, fairly simple, etc.) TRF, rather than superhet, is repeatedly brought up as the best approach for the kit (even though superhets were the overwhelming dominant design of the golden era), particularly if the prime focus is on audio quality. But if a good superhet design comes along that appears to meet the spirit of the various reqs, I'll seriously consider it. Like the Turner AM Tuner. Btw, for real heavy duty DX work (shortwave and MW), I covet the WinRadio, so I'm not exactly out-of-step with the future of digital radio. Jon Noring |
Patrick Turner wrote:
Jon Noring wrote: Note again that Patrick himself said that IF is not needed when one is building a single frequency receiver -- and from his comments he is a very strong advocate of superhet design for a tunable receiver. That's all the channel TRF is: a single frequency receiver, duplicated n number of times (where n is the number of channels one wants to tune, which are switched in and out.) 120 separate AM channels with perhaps 480 discrete LCs and two tubes each is an entirely overcomplex and impractical idea. Sigh. It was a bad choice of wording on my part, since I assumed from what I previously wrote that what I intended was obvious: that the tubes and RF transformers remain the same, but the rest of the LC components of the bandpass tuning stages will be swapped out from channel to channel. This is functionally *equivalent* to having 120+ independent and optimized TRF circuits (one for each channel) -- that's what I intended to say. This is more than obvious, since in traditionally-tuned radios, nearly all the components remain the same except the tuning capacitor (or for a few radio designs, a variable inductor.) Same with the channel TRF: all channels use the same common components except those whose values/properties must change as a function of tuning frequency, which are the bandpass filter components. Thus the same tubes and RF transformers (as a matter of practicality) are intended to be commonly used for all the channels. Now, again, why use the channel approach when one can use either a single or double tuned bandpass filter? It's a matter of the degrees of freedom one is given in optimizing the bandpass characteristics. In the channel TRF we should be able to, in principle at least, assure that for each channel, from 500 khz to 1800 khz, we can have essentially the same exact bandshape: bandwidth, shape factor, etc. And higher order filters are definitely a possibility (if it makes any sense to use them -- delay/linear phase is an issue.) This degree of bandshape control cannot be accomplished by tuning one or two capacitors (or inductors) in the bandpass tuner. In the TRF as John Byrns is studying, simply adjusting the capacitance for tuning has the downside of increasing bandwidth for higher frequency (in a simple parallel RLC circuit, BW=(1/RC).) There are tricks that can be done within the limited parameter space to keep the bandwidth more constant, but it probably has a negative effect on the shape factor and degree of linear phase, and still does not give the degree of control preferred (of course, a variable inductor suggests itself.) Thus was born the "channel TRF", taking advantage of the fact that, for the BCB at least, all broadcasts are on pre-assigned frequencies (channels), so why care about being able to tune in-between these frequencies? (Now, as I think about it, it would be possible to build a continuous tuning system for these higher-order bandpass filters, optimally varying each of the LC components to their best values as a function of center frequency. It could be a "true quintuply tuned circuit" (or higher order.) But mechanically accomplishing this would get extraordinarily complicated: having to increase this capacitance a certain nonlinear way, decrease that inductance by its own function, slowly increase another capacitance, etc., all at the same time. This is much much much more complicated than even the all-channel TRF.) Jon |
Jon Noring wrote: Patrick Turner wrote: Patrick, have you published the schematic for your radio? How amenable is your design for turning it into a kit? And what are its overall specs? Overall specs are excellent as detailed in many previous postings. No, I havn't posted the full schematic, and no, I am not aiming to supply details to anyone else to make into a kit for sale. So you'll have to do your own R&D, at your own expense, using your time, not mine. Is it because you plan to market the design? Or that you simply don't want anyone else to "profit" from your design? In today's world there *is no* market for a tubed AM radio, and a kit would sell in such tiny numbers, that I was led to think there is no market, and I would never profit. Whether anyone else would make a profit is a moot point. They wouldn't need my design though. And if they did use my design, they'd still have to work hard at making a prototype free of bugs on their own. Have you ever run a business? The trend these days is to open source software, and now there's a move to open source mechanical designs. I see the same for open sourcing electronic designs, such as radio receivers. Obviously, the designer of anything has the right to do with it as they please, but I find it perplexing that you have decided not to share your design with the rest of the world, and with posterity. But that's your choice. When you die (as we all must), does the design die with you? I already have described my radio design in full in numerous postings. I really couldn't care less if I die taking knowledge and experience to the grave with me. The living better get busy if they want to build a decent AM tuner, and stop dithering about, if they want one by then end of next month! And about the so-called "kit", I myself know that it is not a money maker -- I'm sure you will agree with that. Well then just design and build your own. The goal is not to make money (which isn't there anyway), but rather to just get something out there for people to build and enjoy. But nobody does anything for nothing. If you want a kit for diyers then *you* better get busy. So you would not be interested in your design to be "kit-i-fied", and called the "Turner AM Tuner"? I am far to busy with projects that earn money to take the time to get a kitset prototype done for people like you who will not work it all out for themselves. The kit itself will essentially be like what diytube does: provide the PCB boards, a schematic, parts list and directions, and the kit builder has to wing it from there. If they don't want to even use the PCB boards, they have the schematic and parts list to work from. In fact, I would prefer to open source the schematic and parts list for the AM tube tuner if you agreed with that -- that way no one will make money from it in a proprietary sense. Then the cabinet size for the tubed tuner will be enormous compared to using fets, and there will be 240 tubes in there for all the single channel tuner modules. A tubed tuner with 120 x two tubed modules is an absurd idea. ??? Maybe I miswrote in my last reply, but that's NOT what I have in mind. All channels will share the same tubes and RF transformers -- only the rest of the tuned bandpass circuitry (mostly a few LC components) will be swapped between channels. You yourself sized it out in your prior reply, showing you understood this. [I'm just repeating this in case someone reading this message in the distant future, who does not have access to the other prior messages, will not be misled as to the design I am exploring.] For 15-20 channels, the design appears practical and doable. For 120+ channels, it's much more of a push. A 15 channel AM BCB radio is as useful as tits on a bull, imho. switching 120 sets of LCs to allow only 2 RF amp tubes to be used presents huge wiring problems, and is, unless *you* proove otherwise, a complete waste of time. Maybe reality will get in the way of doability, but for the 15-20 channel design, no one has yet offered any show stopper reasons why it cannot work (both in a layout sense, and in an electronic sense.) That does not mean there aren't any hidden show stoppers lurking around the corner, but I've heard nothing yet which would make me say: "it will never work because ..." There is, of course, a difference between impractical and impossible -- I've not heard any reasons which fall into the "impossible" category yet -- I have heard reasons why it may be impractical. The bigger issue is if anyone is interested in building and using it for their audio system. That is the more valid question. I've covered my thoughts on this in prior messages -- and I am looking at this from the perspective of a tube-o-phile audio enthusiast where audio performance is everything, and not as a vintage radio collector, nor as a hobbyist who simply designs and builds radios as a hobby. I think practicalities will force you to abandon tubes, and adopt SS or go to a decent superhet. I am not sure you will figure this out, since you just don't seem to know enough, imho. One of the goals of this inquiry (the "channel TRF" is one side alley of this more general thread) is to come up with a high-audio-quality AM BCB tube tuner design suitable for building a kit, to be put together by experienced tube amp builders who want to add an audiophile-grade AM tuner to their setup. I've said this quite a few times. The key word is "tube". Not that tubes are better, not that they produce a necessarily better radio (you and I agree on this), but that there are those who want the aesthetics of tube-based equipment. Is anyone wishing for a tube tuner being rational? Yes and no -- it depends upon how one looks at it. Of course, the most obvious path to take is to investigate classic AM tube tuner designs from the golden years (mid 30's to the 1950's) and see if there is any particular design which is a good candidate to base the modern design on (e.g., it must use, or be adapted to use, tubes commonly sold today, can't be too complicated, fairly simple, etc.) TRF, rather than superhet, is repeatedly brought up as the best approach for the kit (even though superhets were the overwhelming dominant design of the golden era), particularly if the prime focus is on audio quality. But if a good superhet design comes along that appears to meet the spirit of the various reqs, I'll seriously consider it. Like the Turner AM Tuner. The Turner AM tuner only exists in my kitchen. Try to concentrate on decisions about design that *you* will have to make, regarding the Noring Tuner. There is enough info available for you. Btw, for real heavy duty DX work (shortwave and MW), I covet the WinRadio, so I'm not exactly out-of-step with the future of digital radio. Jon Noring I leave you to create whatever you want to on your own. Continuing to type at the computer and at other hobbyists won't produce anymore fresh ideas about AM radio than the last 80 years has produced, and I suggest you spend time in your workshop rather than clutter the airwaves with petulant requests for more info. Nobody knows anymore than what they have said. Patrick Turner. |
Jon Noring wrote:
[Obligatory Telamon rec.radio.shortwave on-topic statement: The following reply touches upon aspects of TRF design as they apply to MW DXing, particularly sensitivity and selectivity of tube-based TRF designs. MW DXing is on-topic to r.r.s. discussion. I appreciate Telamon's efforts to keep r.r.s discussion strictly on-topic per the written r.r.s. Charter.] Jon (and patrick), with all due respect to the topic, getting your thoughts together before posting and knowing when to snip goes a long way. I don't think I'm alone in seeing that this topic just plain gets too windy in spite of its importance or relevance. I enjoy the subject but even I killfiled some of the initial topic titles because people were cluttering up my screen with megaposts of ways to kill a dead horse. If you want to avoid ****ing people off its easy enough to corral your thoughts and not spread the topic across multiple threads while musing at the keyboard. If you did the same at the coffee machine at the office they'd physically pitch you out the door. Be kind to us random readers or take it to personal email. -Bill M |
You got to know when to hold them and when to fold them. I've folded, ...
-- 73 Hank WD5JFR "Patrick Turner" wrote in message ... Jon Noring wrote: Patrick Turner wrote: Patrick, have you published the schematic for your radio? How amenable is your design for turning it into a kit? And what are its overall specs? Overall specs are excellent as detailed in many previous postings. No, I havn't posted the full schematic, and no, I am not aiming to supply details to anyone else to make into a kit for sale. So you'll have to do your own R&D, at your own expense, using your time, not mine. Is it because you plan to market the design? Or that you simply don't want anyone else to "profit" from your design? In today's world there *is no* market for a tubed AM radio, and a kit would sell in such tiny numbers, that I was led to think there is no market, and I would never profit. Whether anyone else would make a profit is a moot point. They wouldn't need my design though. And if they did use my design, they'd still have to work hard at making a prototype free of bugs on their own. Have you ever run a business? The trend these days is to open source software, and now there's a move to open source mechanical designs. I see the same for open sourcing electronic designs, such as radio receivers. Obviously, the designer of anything has the right to do with it as they please, but I find it perplexing that you have decided not to share your design with the rest of the world, and with posterity. But that's your choice. When you die (as we all must), does the design die with you? I already have described my radio design in full in numerous postings. I really couldn't care less if I die taking knowledge and experience to the grave with me. The living better get busy if they want to build a decent AM tuner, and stop dithering about, if they want one by then end of next month! And about the so-called "kit", I myself know that it is not a money maker -- I'm sure you will agree with that. Well then just design and build your own. The goal is not to make money (which isn't there anyway), but rather to just get something out there for people to build and enjoy. But nobody does anything for nothing. If you want a kit for diyers then *you* better get busy. So you would not be interested in your design to be "kit-i-fied", and called the "Turner AM Tuner"? I am far to busy with projects that earn money to take the time to get a kitset prototype done for people like you who will not work it all out for themselves. The kit itself will essentially be like what diytube does: provide the PCB boards, a schematic, parts list and directions, and the kit builder has to wing it from there. If they don't want to even use the PCB boards, they have the schematic and parts list to work from. In fact, I would prefer to open source the schematic and parts list for the AM tube tuner if you agreed with that -- that way no one will make money from it in a proprietary sense. Then the cabinet size for the tubed tuner will be enormous compared to using fets, and there will be 240 tubes in there for all the single channel tuner modules. A tubed tuner with 120 x two tubed modules is an absurd idea. ??? Maybe I miswrote in my last reply, but that's NOT what I have in mind. All channels will share the same tubes and RF transformers -- only the rest of the tuned bandpass circuitry (mostly a few LC components) will be swapped between channels. You yourself sized it out in your prior reply, showing you understood this. [I'm just repeating this in case someone reading this message in the distant future, who does not have access to the other prior messages, will not be misled as to the design I am exploring.] For 15-20 channels, the design appears practical and doable. For 120+ channels, it's much more of a push. A 15 channel AM BCB radio is as useful as tits on a bull, imho. switching 120 sets of LCs to allow only 2 RF amp tubes to be used presents huge wiring problems, and is, unless *you* proove otherwise, a complete waste of time. Maybe reality will get in the way of doability, but for the 15-20 channel design, no one has yet offered any show stopper reasons why it cannot work (both in a layout sense, and in an electronic sense.) That does not mean there aren't any hidden show stoppers lurking around the corner, but I've heard nothing yet which would make me say: "it will never work because ..." There is, of course, a difference between impractical and impossible -- I've not heard any reasons which fall into the "impossible" category yet -- I have heard reasons why it may be impractical. The bigger issue is if anyone is interested in building and using it for their audio system. That is the more valid question. I've covered my thoughts on this in prior messages -- and I am looking at this from the perspective of a tube-o-phile audio enthusiast where audio performance is everything, and not as a vintage radio collector, nor as a hobbyist who simply designs and builds radios as a hobby. I think practicalities will force you to abandon tubes, and adopt SS or go to a decent superhet. I am not sure you will figure this out, since you just don't seem to know enough, imho. One of the goals of this inquiry (the "channel TRF" is one side alley of this more general thread) is to come up with a high-audio-quality AM BCB tube tuner design suitable for building a kit, to be put together by experienced tube amp builders who want to add an audiophile-grade AM tuner to their setup. I've said this quite a few times. The key word is "tube". Not that tubes are better, not that they produce a necessarily better radio (you and I agree on this), but that there are those who want the aesthetics of tube-based equipment. Is anyone wishing for a tube tuner being rational? Yes and no -- it depends upon how one looks at it. Of course, the most obvious path to take is to investigate classic AM tube tuner designs from the golden years (mid 30's to the 1950's) and see if there is any particular design which is a good candidate to base the modern design on (e.g., it must use, or be adapted to use, tubes commonly sold today, can't be too complicated, fairly simple, etc.) TRF, rather than superhet, is repeatedly brought up as the best approach for the kit (even though superhets were the overwhelming dominant design of the golden era), particularly if the prime focus is on audio quality. But if a good superhet design comes along that appears to meet the spirit of the various reqs, I'll seriously consider it. Like the Turner AM Tuner. The Turner AM tuner only exists in my kitchen. Try to concentrate on decisions about design that *you* will have to make, regarding the Noring Tuner. There is enough info available for you. Btw, for real heavy duty DX work (shortwave and MW), I covet the WinRadio, so I'm not exactly out-of-step with the future of digital radio. Jon Noring I leave you to create whatever you want to on your own. Continuing to type at the computer and at other hobbyists won't produce anymore fresh ideas about AM radio than the last 80 years has produced, and I suggest you spend time in your workshop rather than clutter the airwaves with petulant requests for more info. Nobody knows anymore than what they have said. Patrick Turner. |
Patrick Turner wrote:
Jon Noring wrote: Is it because you plan to market the design? Or that you simply don't want anyone else to "profit" from your design? In today's world there *is no* market for a tubed AM radio, and a kit would sell in such tiny numbers, that I was led to think there is no market, and I would never profit. I agree with you the market is small, and not profitable. But people do things for reasons beyond just monetary profit. Whether anyone else would make a profit is a moot point. They wouldn't need my design though. And if they did use my design, they'd still have to work hard at making a prototype free of bugs on their own. O.k. Thanks for clarifying. Have you ever run a business? laugh/ I am very aware of business, thank you, having co-founded several startup companies and non-profit ventures the last few years, plus three sole proprieterships, one of which is still active in the ebook publishing industry. I already have described my radio design in full in numerous postings. O.k., I'll dig through Google and see what you've said on your tuner. Love to hear it. Have you made any recordings of received stations? The living better get busy if they want to build a decent AM tuner, and stop dithering about, if they want one by then end of next month! Well, maybe I seem impatient, but... smile/ And about the so-called "kit", I myself know that it is not a money maker -- I'm sure you will agree with that. Well then just design and build your own. I just might, or as part of a team of like-minded individuals. Even though the current focus I am taking is the channel TRF, I am not wedded to it even though it appears that way. John Byrns approach for an improved TRF is *very* intriguing. Maybe it's the rebel in me... But nobody does anything for nothing. This is very true, but there are rewards that go beyond strictly monetary. If you want a kit for diyers then *you* better get busy. Definitely! I am far to busy with projects that earn money to take the time to get a kitset prototype done for people like you who will not work it all out for themselves. So I should not embrace a classic design from the past, but to design it all from scratch? A 15 channel AM BCB radio is as useful as tits on a bull, imho. Your comment is noted. You definitely will not be interested in a 15 channel TRF kit, then, if it ever came out. smile/ switching 120 sets of LCs to allow only 2 RF amp tubes to be used presents huge wiring problems, and is, unless *you* prove otherwise, a complete waste of time. Agreed about the huge wiring problems, and agreed about having to prove it, or someone having to prove it. One reason for mentioning it as I have is to engage the collective creativity of the many people here in the newsgroups -- to think positive, and to think of a clever way to make it work. Or, it may catalyze some other idea leading to some improvement somewhere. Before going into the workshop, it is good to maybe run thoughts and ideas off of other experts. One doesn't build a bridge by going out to the site and start building. Rather, it is carefully planned to meet the specific requirements. Experts in bridge design are consulted, etc. And this includes for new bridge designs which have not ever been built before (there are new bridges now being built which push the limits, and doing it in unorthodox ways.) (I'm of the view that all ideas, even silly ones, may have value in unforeseen and unpredictable ways. I'm also of the view that one can think of a hundred ways why something will not work, while all one has to do is to think of one way to make it work. That's why I have no difficulty in proposing what may end up being silly ideas.) Of course, contingent on the whole channel TRF concept is that the RF bandpass filters can exactly be tailored for each frequency. One thing which has not been established is how important is this really? Will accomplishing this result in a noticeable improvement in audio and general performance over the better superhet or tunable TRF designs (and maybe allow a simplification of the rest of the circuitry)? Or, will it only result in a marginal improvement, maybe only measurable with equipment? If the latter is the case, then the channel TRF concept becomes less attractive, except maybe for some unusual circumstances. The Turner AM tuner only exists in my kitchen. Ah, the kitchen radio. smile/ I'm sure it is a great performer. Continuing to type at the computer and at other hobbyists won't produce anymore fresh ideas about AM radio than the last 80 years has produced, and I suggest you spend time in your workshop rather than clutter the airwaves with petulant requests for more info. Nobody knows anymore than what they have said. I am wondering if something like the channel TRF for BCB reception was ever proposed in times past, or used in some unusual application where it was called for? Anyone? Thanks, Patrick, for your frank feedback. It is welcome. Jon Noring |
Henry Kolesnik wrote:
You got to know when to hold them and when to fold them. I've folded, ... I wish that Jon could actually experience this and see that his thinking 'outside the box' isn't going to be an automatic revelation that 80 years of radio has simply overlooked. Thirty minutes on the bench could save 'light-hours' of ramblings. -BM |
"Jon Noring" wrote in message ... [snip] This is functionally *equivalent* to having 120+ independent and optimized TRF circuits (one for each channel) -- that's what I intended to say. [snip] How would each of the 120+ independent TRF circuits get optimized? With a scope and a sweep and marker generator? Any one of the channels might be easy enough, but 120 is asking alot. Even moreso, with the complication of Wide/DX option. And it's not like there a wonderful victory after the struggle. Wideband AM sometimes sounds very good, and sometimes not. Have you heard wideband AM? Frank Dresser |
In article , Bill wrote:
Henry Kolesnik wrote: You got to know when to hold them and when to fold them. I've folded, ... I wish that Jon could actually experience this and see that his thinking 'outside the box' isn't going to be an automatic revelation that 80 years of radio has simply overlooked. Thirty minutes on the bench could save 'light-hours' of ramblings. I don't follow your reasoning on this, what is Jon going to learn in "Thirty minutes on the bench"? I would venture next to nothing? Thirty weeks on the bench might be more like it, and even then there won't be time to explore all avenues. As far as 80 years of radio go, Jon's constraints are different than might have existed when tube radios were a mass application, he may be able to make different tradeoffs than were practical then. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
John Byrns wrote:
In article , Bill wrote: Henry Kolesnik wrote: You got to know when to hold them and when to fold them. I've folded, ... I wish that Jon could actually experience this and see that his thinking 'outside the box' isn't going to be an automatic revelation that 80 years of radio has simply overlooked. Thirty minutes on the bench could save 'light-hours' of ramblings. I don't follow your reasoning on this, what is Jon going to learn in "Thirty minutes on the bench"? I would venture next to nothing? Thirty weeks on the bench might be more like it, and even then there won't be time to explore all avenues. As far as 80 years of radio go, Jon's constraints are different than might have existed when tube radios were a mass application, he may be able to make different tradeoffs than were practical then. Regards, John Byrns Don't be silly just for the sake of being a 'devils advocate', John. If Jon can achieve his plug-in TRF boards with any semblance of a $1.95 flea-market AA5 selectivity then I would be pleased. What I haven't heard from Jon beyond musings that suggest that 80 years of radio have missed his point is a bit of actual soldering on the bench to make up these mythical circuits. At least Mr. Windbag No-Snip Patrick appears to have walked the walk before but Jon is reluctant to take your, my, Patrick's or anybody else's advice about how to meet his goal...and at this stage seems to be fishing without good bait for somebody who is in agreement. Jon's "tradeoffs" are ultimately the clue. Once presented with the facts and a million lines of newsgroup advice its time to go to the bench and actually MAKE one of these panacea BCB BP filters. I strongly suspect that this effort would clue Jon into some of the realities of how things work and no amount of chatter from us could be of further benefit other than our own wing flapping. -Bill M |
snip,
In today's world there *is no* market for a tubed AM radio, and a kit would sell in such tiny numbers, that I was led to think there is no market, and I would never profit. I agree with you the market is small, and not profitable. But people do things for reasons beyond just monetary profit. Whether anyone else would make a profit is a moot point. They wouldn't need my design though. And if they did use my design, they'd still have to work hard at making a prototype free of bugs on their own. O.k. Thanks for clarifying. Have you ever run a business? laugh/ I am very aware of business, thank you, having co-founded several startup companies and non-profit ventures the last few years, plus three sole proprieterships, one of which is still active in the ebook publishing industry. Try running a business which pays the bills and puts food on the table, and which makes you attractive to women, (or a man,whatever is your bent) Try doing it without capital. This makes you think twice about time wasting. I already have described my radio design in full in numerous postings. O.k., I'll dig through Google and see what you've said on your tuner. Love to hear it. Have you made any recordings of received stations? Nope. I don't believe recording and replaying it would convey the sound properly. AM is not regarded as hi-fi by all my friends, its just a tolerable midi fi medium, great for replays of the Goon show, and forms of music which don't need a hi-fi medium, like most pop and folk music. The living better get busy if they want to build a decent AM tuner, and stop dithering about, if they want one by then end of next month! Well, maybe I seem impatient, but... smile/ You seem to have all the time to discuss it all, and make nothing, like the original armchair solderer, and that's hardly impatient.... And about the so-called "kit", I myself know that it is not a money maker -- I'm sure you will agree with that. Well then just design and build your own. I just might, or as part of a team of like-minded individuals. When you have tested your first prototype, we might compare notes, but why before? You could proove you mean to contribute to the exercize by doing a lot on your own. snip, switching 120 sets of LCs to allow only 2 RF amp tubes to be used presents huge wiring problems, and is, unless *you* prove otherwise, a complete waste of time. Agreed about the huge wiring problems, and agreed about having to prove it, or someone having to prove it. One reason for mentioning it as I have is to engage the collective creativity of the many people here in the newsgroups -- to think positive, and to think of a clever way to make it work. Or, it may catalyze some other idea leading to some improvement somewhere. There is a point where *you* have to un-tether yourself from the crowd and do your own experiments, and make conclusions of your own. In the absense of anyone else volunteering to do the donkey work of R&Ding a test circuit, there is only yourself who is left to realize this dreamy obsession of yours. snip Good luck, Patrick Turner. |
Frank Dresser wrote: "Jon Noring" wrote in message ... [snip] This is functionally *equivalent* to having 120+ independent and optimized TRF circuits (one for each channel) -- that's what I intended to say. [snip] How would each of the 120+ independent TRF circuits get optimized? With a scope and a sweep and marker generator? Any one of the channels might be easy enough, but 120 is asking alot. Even moreso, with the complication of Wide/DX option. And it's not like there a wonderful victory after the struggle. Wideband AM sometimes sounds very good, and sometimes not. Have you heard wideband AM? I have, and its very much better than the low fi crap coming from most crummy receivers. Its not up to FM standards, but its very listenable for news, pop, rythym and blues, folk, interviews, etc. AM DX is a total waste of time for me. Patrick Turner. Frank Dresser |
John Byrns wrote: In article , Bill wrote: Henry Kolesnik wrote: You got to know when to hold them and when to fold them. I've folded, ... I wish that Jon could actually experience this and see that his thinking 'outside the box' isn't going to be an automatic revelation that 80 years of radio has simply overlooked. Thirty minutes on the bench could save 'light-hours' of ramblings. I don't follow your reasoning on this, what is Jon going to learn in "Thirty minutes on the bench"? I would venture next to nothing? Thirty weeks on the bench might be more like it, and even then there won't be time to explore all avenues. As far as 80 years of radio go, Jon's constraints are different than might have existed when tube radios were a mass application, he may be able to make different tradeoffs than were practical then. It took years' full of late nights to fully understand tube audio amps, and months of work to re-design my ex Trio AM/FM receiver, and then another month or two full time to build decent AM only radio, from antenna to speaker. 30 minutes is nothing. Patrick Turner. |
In article , Patrick Turner
wrote: John Byrns wrote: In article , Bill wrote: Henry Kolesnik wrote: You got to know when to hold them and when to fold them. I've folded, ... I wish that Jon could actually experience this and see that his thinking 'outside the box' isn't going to be an automatic revelation that 80 years of radio has simply overlooked. Thirty minutes on the bench could save 'light-hours' of ramblings. I don't follow your reasoning on this, what is Jon going to learn in "Thirty minutes on the bench"? I would venture next to nothing? Thirty weeks on the bench might be more like it, and even then there won't be time to explore all avenues. As far as 80 years of radio go, Jon's constraints are different than might have existed when tube radios were a mass application, he may be able to make different tradeoffs than were practical then. It took years' full of late nights to fully understand tube audio amps, and months of work to re-design my ex Trio AM/FM receiver, and then another month or two full time to build decent AM only radio, from antenna to speaker. 30 minutes is nothing. Earth to Patrick, that was exactly my point! Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
In article , Bill wrote:
John Byrns wrote: In article , Bill wrote: I wish that Jon could actually experience this and see that his thinking 'outside the box' isn't going to be an automatic revelation that 80 years of radio has simply overlooked. Thirty minutes on the bench could save 'light-hours' of ramblings. I don't follow your reasoning on this, what is Jon going to learn in "Thirty minutes on the bench"? I would venture next to nothing? Thirty weeks on the bench might be more like it, and even then there won't be time to explore all avenues. As far as 80 years of radio go, Jon's constraints are different than might have existed when tube radios were a mass application, he may be able to make different tradeoffs than were practical then. Don't be silly just for the sake of being a 'devils advocate', John. I'm not being the "devils advocate", I'm just saying that the problem is more complex than you are making it out to be and a mere thirty minutes on the bench is not going to resolve much. If Jon can achieve his plug-in TRF boards with any semblance of a $1.95 flea-market AA5 selectivity then I would be pleased. These threads have grown to a point where I have not been able to follow them all. I have been following most of the discussions like the superhet, TRF, and segmentation of the MW band posts, but I have not yet read the ones related to channel based receivers, which I hope to read through as time permits. Perhaps that explains my confusion with relation to the "thirty minutes on the bench", if you are referring to a channelized TRF approach to receive all 117 or so MW channels, then I would think you wouldn't need to go to the bench at all to realize it isn't practical. A smaller number of channels, say half a dozen or so might be practical. I think the best approach for the all out audiophile would be the one suggested by Randy, or was it Sherry? Gutting out a National NC-100, and rebuilding the band selection assembly with 5 sets of 3 optimized band pass filters to segment the MW band into 5 parts. Regards, John Byrns Surf my web pages at, http://users.rcn.com/jbyrns/ |
John Byrns wrote:
I'm not being the "devils advocate", I'm just saying that the problem is more complex than you are making it out to be and a mere thirty minutes on the bench is not going to resolve much. The suggestion was not that the issue would be resolved in 30 minutes but actually sitting down with a few components to make a plug-in BPF would be very enlightening. -BM |
[Comment and question on NC-100 toward the end]
John Byrns wrote: ...if you are referring to a channelized TRF approach to receive all 117 or so MW channels, then I would think you wouldn't need to go to the bench at all to realize it isn't practical. A smaller number of channels, say half a dozen or so might be practical. I think 15 or so channel slots will be fairly easy to implement, and nearly all metropolitan areas I know of probably don't have more than 15 stations of sufficient power and fidelity to make it worth tuning any more (or the end-user will not want to listen to conservative talk radio, but will listen to ordinary news, sports, oldies, and progressive radio stations, etc.) Again, the idea of the channel TRF approach is to be able to really fine tune the bandpass filters for each channel. Several here say it simply won't work, and I scratch my head on this one since the simplest is to take an existing working TRF circuit using a variable capacitor to tune the radio, remove the tuning capacitor, and replace each gang with a fixed capacitor of the right value (probably with a trimmer capacitor to fine tune the center frequency) -- it is now a single channel receiver, and should work identical to the original circuitry, but now it won't tune. Now, can't one now extend this, and alter that part of the circuity, adding LC components with the right value in the right ways to improve the bandpass shape and proper electronic interfacing with the properties of the RF section for that particular frequency? Obviously the problem is figuring it all out, but one now has a lot of degrees of freedom to work with -- no need to compromise any more as is needed whenever one tries to continuously tune the circuit. I assume if one can optimize it this way for one frequency (say the midpoint of the AM band, around 950 khz), then one can then optimize it for each channel in the 500 to 1800 khz range by simultaneously changing the values of all the LC components as needed. Of course, the question is how much is gained in performance taking this approach. If several here believe it will make little difference in real-world performance, then it makes no sense to even consider the channel TRF approach, at least for high-fidelity purposes. ***** Now moving to classic super-hets, the mention by John Byrns of the National NC-100. I think the best approach for the all out audiophile would be the one suggested by Randy, or was it Sherry? Gutting out a National NC-100, and rebuilding the band selection assembly with 5 sets of 3 optimized band pass filters to segment the MW band into 5 parts. I recall last year a few people mention the NC-100. Is this radio reputed to have excellent audio fidelity (I suppose when the variable bandpass control is set wide) in addition to excellent selectivity and sensitivity? And can the circuitry be modernized (e.g., modern tubes), etc.? The idea of making it a 5 band AM radio is certainly interesting. Jon Noring |
Jon Noring wrote: I recall last year a few people mention the NC-100. Is this radio reputed to have excellent audio fidelity (I suppose when the variable bandpass control is set wide) in addition to excellent selectivity and sensitivity? No - not at all - nor the point. What the NC-100 (and NC-120) have is a "sliding catacomb" band change mechanism. This is a cast metal box with three compartments front to back - duplicated five times left to right. Each compartment (front to back) houses the frequency critical coils (and trimmers); etc.) for each RF stage of the radio (the NC-120 has an additional one compartment deep five-wide box appended to the rear of the radio to add yet another tuned RF stage). Each compartment has five contacts that stick "up" towards the radio's chassis (15 total; 20 in the case of the NC-120). The band-change mechanism is a rack and pinion affair that "slides" the entire box left and right - so that one set of compartments (and their contact fingers) line up with the mating contacts sticking down from the chassis. In this way - each band has it's own complete set of RF coils completely isolated and brought into the circuit as needed. Much like a strip TV tuner - but done linear rather than turret style. The advantages are extreme shielding - and a good bit of room in each compartment to put all of the frequency determining components (note only the tuning cap and tubes are above chassis - and are the only "shared" RF components). I think Randy mentioned that the NC-100/120 have a product detector - but that's not to imply that the fidelity is any good - just that many usable parts and ideas are already in place (guess you could count the power supply and amplifier as well). They are communications receivers - first and foremost - but they do offer some intriguing possibilities for TRF or multi-band BCB experimentation. And can the circuitry be modernized (e.g., modern tubes), etc.? Nothing wrong with the tubes they have- you could go with miniature equivalents - but since the copper plated chassis is already huge - why bother? I don't believe any significant performance gains (in the BCB) would be realized by "more modern" tubes. The idea of making it a 5 band AM radio is certainly interesting. That's the point - whether it would be the BCB divided into 5 continuously tuned bands - each optimized as best fit in five segments - or 5 specific BCB stations... each tweaked to "perfection" - the foundation is all there. -- Sherry |
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