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forming precision detector brewing group
N9NEO wrote: Is anyone here interested in collaborating on a small pc board with a precision detector and an elliptic filter? and maybe even a small amplifier too. This would be a retrofit to existing radio. I have heard it is almost as good as a sync detector- better than some. I have heard others say it is smoke and mirrors so I expect to get to the truth here. I am looking for two other people to help out. Board will cost you maybe 30 bucks. I use PCB express. You get three small boards no silk no solder mask for about 60bucks. I am in-between consulting jobs now, so that I have a little time but watching my funds. I think with smd parts maybe only half a board is needed so that each will cost even less. Idea has been around for quite some time but recently brought to my attention by Terry. I am looking at that Redsun RP2100 unit as the platform to run with. regards, NEO For an interesting thread see: http://amfone.net/Amforum/index.php?topic=3857.0 Terry |
forming precision detector brewing group
For an interesting thread see: http://amfone.net/Amforum/index.php?topic=3857.0 Terry Yea, those guys over there got a lot on the ball with High Perfromance detectors and such. Frank, GFZ, is a friend of mine and does a lot with the Racal units. I'm not looking for anybody to do any hands on work that will take up a lot of time. Just a few who I can bounce Ideas off of and help if I get stuck. Like I said - I'm in between jobs so I got the time to lay out a board. When boards done whoever wants one can have. Looks like the board will have the detector, amplifier and filter on it. I want to drive a set of phones with the thing and am not really too concerned with driving a speaker. I will have a line out connector to drive directly into my Marantz so I don't think amplifier will be so critical for me. I notice that Dallas Lankford set up his filters to drive into 8 ohms. I think I'm going to drive into a higher impedance - probably near 100 ohms and then just a buffer to drive the phones. So question for now is about headphone impedance. I'll post that seperate and see what others are using for phones. Below is link to paper. it's the one about improved eliptic filters. I have the filters in switchercad just to see how impedance effects filter response. http://www.kongsfjord.no/dl/dl.htm 73 NEO |
forming precision detector brewing group
N9NEO wrote: For an interesting thread see: http://amfone.net/Amforum/index.php?topic=3857.0 Terry Yea, those guys over there got a lot on the ball with High Perfromance detectors and such. Frank, GFZ, is a friend of mine and does a lot with the Racal units. I'm not looking for anybody to do any hands on work that will take up a lot of time. Just a few who I can bounce Ideas off of and help if I get stuck. Like I said - I'm in between jobs so I got the time to lay out a board. When boards done whoever wants one can have. Looks like the board will have the detector, amplifier and filter on it. I want to drive a set of phones with the thing and am not really too concerned with driving a speaker. I will have a line out connector to drive directly into my Marantz so I don't think amplifier will be so critical for me. I notice that Dallas Lankford set up his filters to drive into 8 ohms. I think I'm going to drive into a higher impedance - probably near 100 ohms and then just a buffer to drive the phones. So question for now is about headphone impedance. I'll post that seperate and see what others are using for phones. Below is link to paper. it's the one about improved eliptic filters. I have the filters in switchercad just to see how impedance effects filter response. http://www.kongsfjord.no/dl/dl.htm 73 NEO I have found Dallas' LP fitle to be a very usefull addition to my system. When I first posted a link to his filter I took some hits because some people think that active is either easeier or better. An active fitler would clearly lend it self to easier adjustments. The active circuit at the link I posted has a slight advantage for those with radios will less then ideal IF filters. The 5KHz, 9KHz, and 10KHz notches will be very usefull. I built a set for my DX398 for use on mini-dxpeditions. For normal adjsutments I like the Tone Tilt that I first experienced in a Kiwa MAP SAD. One simple circuit for which I do not have a link is a "ear protector". I listen with earphones a lot of the time. My wife is very supporting but doesn't understand my fascination with utility reception. Nothing worse then trying to dig out a weak signal, with the AF gain cranked up, and a loud static "pop" rolls in. Or even worse, another signal comes on frequency. OUCH! My hearing has suffered enough and have no desire to damage them any more! So I built a device that consists of a series resistor, a pair of two 1N400X wired as a clamp to limit the voltage to a maximum of ~1.4V. Since my two choices of earhphones are a 40 year old set of Sennheiser HD424, 2K each side, and a set of Byer's with ~600 Ohms each side. The Sennheiser are of the "opne air" desing and I can wear them for hours.The Beyers are of the clsoe design and I were them when there is too much back ground noise. They also have a built in boom mic so on those odd occasions I actually use my ham gear, they are nice for hands free. A foot PTT or VOX are very usefull. The earphone protector has a Lo-Z to high Z (8:600 ohms) transformer, but it will work great with every radio I have tried it with without thetransformer. I use sereis resistors of 470 Ohms, and have a 1K pot across the diodes to allow the level to be adjusted. This pot is a screwdriver and even though the Beyers and the Sennheisers have over a 2:1 difference, the sound levels are matched to within a few dB. I can't measure earphone output better then about +/- 2dB. Terry |
forming precision detector brewing group
I have found Dallas' LP fitle to be a very usefull addition to my system. When I first posted a link to his filter I took some hits because some people think that active is either easeier or better. An active fitler would clearly lend it self to easier adjustments. The active circuit at the link I posted has a slight advantage for those with radios will less then ideal IF filters. The 5KHz, 9KHz, and 10KHz notches will be very usefull. I built a set for my DX398 for use on mini-dxpeditions. For normal adjsutments I like the Tone Tilt that I first experienced in a Kiwa MAP SAD. One simple circuit for which I do not have a link is a "ear protector". I listen with earphones a lot of the time. My wife is very supporting but doesn't understand my fascination with utility reception. Nothing worse then trying to dig out a weak signal, with the AF gain cranked up, and a loud static "pop" rolls in. Or even worse, another signal comes on frequency. OUCH! My hearing has suffered enough and have no desire to damage them any more! So I built a device that consists of a series resistor, a pair of two 1N400X wired as a clamp to limit the voltage to a maximum of ~1.4V. Since my two choices of earhphones are a 40 year old set of Sennheiser HD424, 2K each side, and a set of Byer's with ~600 Ohms each side. The Sennheiser are of the "opne air" desing and I can wear them for hours.The Beyers are of the clsoe design and I were them when there is too much back ground noise. They also have a built in boom mic so on those odd occasions I actually use my ham gear, they are nice for hands free. A foot PTT or VOX are very usefull. The earphone protector has a Lo-Z to high Z (8:600 ohms) transformer, but it will work great with every radio I have tried it with without thetransformer. I use sereis resistors of 470 Ohms, and have a 1K pot across the diodes to allow the level to be adjusted. This pot is a screwdriver and even though the Beyers and the Sennheisers have over a 2:1 difference, the sound levels are matched to within a few dB. I can't measure earphone output better then about +/- 2dB. Terry Ok on the phones. You had mentioned them in your email to me in September. You had also sent me a diagram of an op-amp with a pair of emitter followers that I could use to drive the filter. Like I said, I'm probably going to design the filter to run into a hundred or so ohms. I'll probably stick an op-amp on the output of the filter to act as a buffer - although 2k probably wouldn't move the filter response much. Then of course I'll have to have a baxandall /bandaxall style tone control so the project grows some. Yes, active filters would probably be ok and LT has some very nice filter chips that would work too - and I haven't ruled them out. More later. NEO |
forming precision detector brewing group
N9NEO wrote: Ok on the phones. You had mentioned them in your email to me in September. You had also sent me a diagram of an op-amp with a pair of emitter followers that I could use to drive the filter. Like I said, I'm probably going to design the filter to run into a hundred or so ohms. I'll probably stick an op-amp on the output of the filter to act as a buffer - although 2k probably wouldn't move the filter response much. Then of course I'll have to have a baxandall /bandaxall style tone control so the project grows some. Yes, active filters would probably be ok and LT has some very nice filter chips that would work too - and I haven't ruled them out. More later. NEO Before trying a baxandall /bandaxall tone circuit, you owe it to yourself to at least bread board the circuit at http://members.tripod.com/roymal/ReverbTone.htm. I like baxandall for "HiFi" audio but in 40+ years of SWL I have never needed to boast the highs, lows and mids seperately. I played with a professional 1/3 octave EQ unit, that had variable shelving etc last winter and except for the complexity it had some minor advantages. But all in all the single Tone-Tilt won the test. A tuneable AF notch is a nice addition. There have been times when I found a very sharp 60Hz notch filter to very usefull with older tube radios with less then perfect power supply filtering. These days I mainly operate radi from a well regulated and very well filtered 12V. [13.67V which is also the proper voltage to float charge a Gell Cell/PbSO4 battery] So 60/120/180 Hz hum is seldom an internal issue. At some point I am going to have to redesign my system to seperate the audio from the outboard detector. When I built it I didn't plan on adding radio that didn't have 455KHZ as the IF. Best laid plans and all of that. There are paradoxes or logical conflicts in my statements and the operation of my audio chain. I want smooth response out to say 15KHz. But I add filtering to chop out the highs and lows. I found it better to use a set of JBL speakers designed for "Home Theater" 5.1 (or 7.1) side speakers that naturally roll off at about 6K. By 10KHz they are mute. I found this works better then adding a low level AF filter. The Minimus 7's almost worked with the tweeter switched off. Then when I get the harmonic distortion during bad fades with ths SADs, I kick in Dalla's ELP AF filter. When an unwanted het pops up I use a low level tuneable notch. When I look at my system I sometimes want to scream. This was supposed to be simple! I designed and built a true hifi system that is flat, +/1 1dB from ~30Hz to above 20KHz. With the minimuis speakers and an added tweeter and subwoofer it is flat +/- 4 or 5dB from 60Hz to above 15KHz. [It is very hard to come up with accurate measurements that relfect reality in a room!] When doing serious, IE money making, audio work on the PC I really need the full bandwidth with the subwoofer. But for SWL I chop it to something like ~100Hz to maybe 7KHz. Simply nuts. No wonder my wife insisted on her own radio. Since my "far field"/ ISM/HiFer beacon is toast, lightning, I have to be content with running my test audio from a high bit rate MP3 into my system and mixing real radio background noise and measuring the result. Since I can't, and never could, really duplicate any of the effedts sfading and selective fading introduced, this isn't really that much different then my prior test. As a general rule, it is better to control BW with the correct IF filter, a speaker with natural roll off or lastly low level or high level filters. Conversly the more filtering you add, the quicker you get listening fatigue. Listening to AM through a 1.8KHZ SSB fitler will tire you out pretty fast. More later when my brain untangles. And this is all for fun. Terry |
forming precision detector brewing group
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forming precision detector brewing group
There looks like a typo in schematic.
http://www.amwindow.org/tech/htm/alowdisdet.htm Amplifier inputs have to be swapped at the two rectifiers. later NEO |
forming precision detector brewing group
There looks like a typo in schematic.
http://www.amwindow.org/tech/htm/alowdisdet.htm Amplifier inputs have to be swapped at the two rectifiers. later NEO |
forming precision detector brewing group
N9NEO wrote: There looks like a typo in schematic. http://www.amwindow.org/tech/htm/alowdisdet.htm Amplifier inputs have to be swapped at the two rectifiers. later NEO I don't remember any errors, but it has been 8 months since I built one of these. I will open up my outboard detector and verify the design. It will have to wait until Sunday night at the earliest. Terry |
forming precision detector brewing group
DUH!
You have to do full-wave rectification if you are going to use a avaraging type of filter. Think about it. The precision half-wave circuit that responds to peak should work well also. I'll probably stick em both on the board. 73 NEO N9NEO wrote: wrote: N9NEO wrote: There looks like a typo in schematic. http://www.amwindow.org/tech/htm/alowdisdet.htm Amplifier inputs have to be swapped at the two rectifiers. later NEO I don't remember any errors, but it has been 8 months since I built one of these. I will open up my outboard detector and verify the design. It will have to wait until Sunday night at the earliest. Terry No big deal there Terry, it's really a minor issue and probably would work no problem anyway. What I found is just that the way the detector is shown the output will be negative. I simulated it in SwitchercadIII. (That's my secret to designing pc boards that work without breadboarding.) I would appreciate if you look at and comment on a couple of things with the circuit though. I am a power supply guy and I don't know too much about detectors. Rob uses a RC filter on the output of this thing so that the output is an avaraging operation rather than responding to the peak of the waveform. It looks like the pole is set for near 5kHz so some phase distortion is going to be introduced - probably not a big deal. Rob goes out of his way to do a full wave rectification, but that doesn't make much sense to me with the filter he sticks on the end. What do you think about just doing a detector that responds to the peak of the waveform in a half-wave type rectifier? By the time this signal goes through a 4kHz elliptic filter there isn't going to be a microvolt of 455kHz signal to be found. Gain the IF signal up so that any error due to diode matching will be minimized. I have a circuit that uses 3 schottkys in Spice that should do a nice job. I can send it to you if you run Switchercad. It's a free download. regards, Bob |
forming precision detector brewing group
N9NEO wrote: DUH! You have to do full-wave rectification if you are going to use a avaraging type of filter. Think about it. The precision half-wave circuit that responds to peak should work well also. I'll probably stick em both on the board. 73 NEO Rob K2CU design goal limited the loading on the diodes. D800 goes to the non inverting, very hi z, D801 goes to the non inverting input of U6A and the gain is 1 so the non inverted, now low Z, output goes to the inverting input of U6A where the 18K resistor might give too much loading. I built a simple, U6A less, version but it had fairly high distortion. It sounded much worse then a single diode detector. In my wife's R2000 I went with a 0.001uF for the output filter cap. For most SW/HF signals the tansmitted BW will be 5KHz. To tell the truth the change from 0.0033 to 0.001 didn't make much audiable difference. I didn't bother to make any tests. For 455KHz IFs U6A/B will need to be changed. The LMC660 is just not up to that higher freq. They do work fine at 50KHz. The other improved AM detector with a single OpAmp works, but diodes must be very closely matched. A simple DVD diode Vforward will not suffice! Petes AD607 synch detector has to be the simplest way to get going. There are other approaches that might fare better. The SAD in the R8B is much better then the AD607 or the AO7030+. Better as in will never growl, and doesn't fo nuts with a strong adjacent signal. The AD607 OpAmp fitler I/Q combiner page that I refferenced is well worth the study. If done correctly, it is possible to exclude or reject everything except for the desired signal. The Synch detector group has some very interesting PDFs from older approaches that go into the mind numbing math. I never got the filter to work properly. There are no obvious typos, and the design looks sound. When I run out of other projects I intend to revisit this one because IF it can be made to work, the rejection would be very useful. My psuedo/quasi/faux "MAP"/SE-3 had several detectors. For reasons that escape me I decided to add FM with a crystal discriminator. Works great the 3 times I used it. Twice for 10M FM, and once for a Pirate on 6.925. The least usefull part of my oatboard detector. Terry |
forming precision detector brewing group
I might have to put hi perf detector project on the back burner for a
few weeks. Seems as though I've been called up by my next employer for a 90 day contract job. I think he wants to make sure that I'm somewhat sane before he takes me on full time. I can't really blame him - after all I do subscribe to rec.radio.shortwave. I really didn't want to go back to work till like March or April. I left my last job designing large inverters back in October. The place was a real pressure cooker and I needed some time off to figure out what is real and what is just a product of my own paranoia. Ya know, time for the voices in my head to subside. But feeling good enoughtnow and I don't have to report till January 7 I think. It's a dream job working for a govt contractor so lots of really cool test gear around. I'm thinking about goin over to the wrecking yard and picking up a 50 dollar car and heading south to Key Largo to do some snorklin for a few days. Maybe I'll take the plates off the car when I leave and set it afire on the beach and just stick out the thumb. Maybe stop by Cuhulin's place on the way down with a box of dog biscuits and a six pack of Old Milwaukee. 73 NEO wrote: N9NEO wrote: DUH! You have to do full-wave rectification if you are going to use a avaraging type of filter. Think about it. The precision half-wave circuit that responds to peak should work well also. I'll probably stick em both on the board. 73 NEO Rob K2CU design goal limited the loading on the diodes. D800 goes to the non inverting, very hi z, D801 goes to the non inverting input of U6A and the gain is 1 so the non inverted, now low Z, output goes to the inverting input of U6A where the 18K resistor might give too much loading. I built a simple, U6A less, version but it had fairly high distortion. It sounded much worse then a single diode detector. In my wife's R2000 I went with a 0.001uF for the output filter cap. For most SW/HF signals the tansmitted BW will be 5KHz. To tell the truth the change from 0.0033 to 0.001 didn't make much audiable difference. I didn't bother to make any tests. For 455KHz IFs U6A/B will need to be changed. The LMC660 is just not up to that higher freq. They do work fine at 50KHz. The other improved AM detector with a single OpAmp works, but diodes must be very closely matched. A simple DVD diode Vforward will not suffice! Petes AD607 synch detector has to be the simplest way to get going. There are other approaches that might fare better. The SAD in the R8B is much better then the AD607 or the AO7030+. Better as in will never growl, and doesn't fo nuts with a strong adjacent signal. The AD607 OpAmp fitler I/Q combiner page that I refferenced is well worth the study. If done correctly, it is possible to exclude or reject everything except for the desired signal. The Synch detector group has some very interesting PDFs from older approaches that go into the mind numbing math. I never got the filter to work properly. There are no obvious typos, and the design looks sound. When I run out of other projects I intend to revisit this one because IF it can be made to work, the rejection would be very useful. My psuedo/quasi/faux "MAP"/SE-3 had several detectors. For reasons that escape me I decided to add FM with a crystal discriminator. Works great the 3 times I used it. Twice for 10M FM, and once for a Pirate on 6.925. The least usefull part of my oatboard detector. Terry |
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