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VHF Aviation Receivers
I'd like to build some homebrew VHF-AM receivers - specifically a receiver
for the VHF 108-118 Mhz band. I've found lots of great ideas and reference designs out there but they're all constructed of parts made from "unobtainium" (e.g. old MC13135/6, MC1350, etc., etc.)... Can anyone on this group point me to some designs/ideas for how to construct something made from "actually available" components??? Thanks for any help... |
I'd like to build some homebrew VHF-AM receivers - specifically a receiver for the VHF 108-118 Mhz band. I've found lots of great ideas and reference designs out there but they're all constructed of parts made from "unobtainium" (e.g. old MC13135/6, MC1350, etc., etc.)... Can anyone on this group point me to some designs/ideas for how to construct something made from "actually available" components??? The band in question is AM and the 13135 is an FM chip with discriminator. A perfectly fine lineup for your needs is any of the DBM's from Mini Circuits Labs or build you own with a few diodes and a couple of ferrite beads, the MC 1496/1596 is still very much available, even made the transition to SSOP if your tastes run to small and surface mount. Low side injection with an AD 9851 or high side with a 9951 DDS. With the channel spacing up there, a selection of an inexpensive Murata filter will do your selectivity, and audio is a VERY wide selection. W4ZCB |
Get youself an inexpensive collection of readily available parts from
rallies and car boot sales and then ask yourself what you can make out of it. ---- Reg. |
Netgeek wrote:
I'd like to build some homebrew VHF-AM receivers - specifically a receiver for the VHF 108-118 Mhz band. I've found lots of great ideas and reference designs out there but they're all constructed of parts made from "unobtainium" (e.g. old MC13135/6, MC1350, etc., etc.)... Can anyone on this group point me to some designs/ideas for how to construct something made from "actually available" components??? Thanks for any help... Kits: http://www.hamtronics.com/r121.htm http://www.vectronics.com/products.php?prodid=VEC-131K http://www.hobbytron.net/R-AR-1.html http://www.ramseyelectronics.com/cgi...ction&key=AR1C schematic and other info on one of the kits: http://www.uoguelph.ca/~antoon/circ/aviarx/aviarx.html kits are an easy way to get those Unobtainium plated parts in small quantities. |
Thanks for the suggestions. I ordered the Ramsey kit as a way to have
something to play with for now. Next step is to lash together either a PLL-VCO combo or DDS to control the tuning from a cheapo processor (e.g. PIC). Any suggested starting points for this would be much appreciated (for example "National LMX2xxx plus Minicircuits xx" or "forget that, AD DDS is better because.......")....8-). The guts of the Ramsey widget consists of an SA602 and an MC1350 (single conversion with 10.7 Mhz IF). Potential ways to "improve" upon this??? Thanks again. Bill (RF Newbie - but willing to learn 8-)... "bigamps" wrote in message ... Kits: http://www.hamtronics.com/r121.htm http://www.vectronics.com/products.php?prodid=VEC-131K http://www.hobbytron.net/R-AR-1.html http://www.ramseyelectronics.com/cgi...ction&key=AR1C schematic and other info on one of the kits: http://www.uoguelph.ca/~antoon/circ/aviarx/aviarx.html kits are an easy way to get those Unobtainium plated parts in small quantities. |
It would be easier to convert an old AM/FM tuner or AM/FM stereo and you can
get them all over the place for a few bucks. Tube types are collector items but the older SS ones with discreet components and ICs are considered pretty much obsolete. Find one with an open tuning cap and remove a plate or two, or rewind the coils (too much work) or replace the enclosed tuning cap with an open one. Add an 11 mhz osc and use the 455Kc IF stage and AM detector. -- 73 Hank WD5JFR "Netgeek" wrote in message ... I'd like to build some homebrew VHF-AM receivers - specifically a receiver for the VHF 108-118 Mhz band. I've found lots of great ideas and reference designs out there but they're all constructed of parts made from "unobtainium" (e.g. old MC13135/6, MC1350, etc., etc.)... Can anyone on this group point me to some designs/ideas for how to construct something made from "actually available" components??? Thanks for any help... |
From: "Netgeek" on Sun, Mar 13 2005 4:42 pm
I'd like to build some homebrew VHF-AM receivers - specifically a receiver for the VHF 108-118 Mhz band. I've found lots of great ideas and reference designs out there but they're all constructed of parts made from "unobtainium" (e.g. old MC13135/6, MC1350, etc., etc.)... Can anyone on this group point me to some designs/ideas for how to construct something made from "actually available" components??? Firstly, 108 to 118 MHz is the international civil aviation radionavigation band. It's not all that interesting to listen to unless a local tower is also repeating voice comms over a VOR or Localizer radionav transmitter nearby on the ground. The civil aviation voice band is 118 to 137 MHz. Secondly, the MC1350 gain block is available from Jameco (it is still made after buying all the masking and stuff from Motorola). You can get MC1349s, a slightly higher gain version from Dieter Gentzow at Kitsandparts.com; I got 18 of them just before Christmas along with some other good parts. Good service from Kitsandparts, great source of toroid cores. There's still lots of legacy ICs available out there but you may have to search for sources. If you are trying to build something at VHF, you will need some reasonably accurate signal sources to check out the receiver. That's not a trivial task unless all you want is to carbon-copy some regen or super-regen tuned-by-a-single-variable sort of receiver. Jameco sells the MC145151 PLL IC (On Semiconductor the Motorola spin-off still makes them) which, with a prescaler, can make a good, stable LO that is channelized at 50 KHz increments for precise tuning. MC145151 is parallel-load for division, no extra IC needed to get the right division ratio as in some serial-input PLL or DDS chips. Lots of inexpensive "all-band" radios off the shelf include the aviation band, those in addition to all the available VHF scanner receivers. Those all work better and more reliably than simple regens and super-regens in my observation. |
Len,
Thanks for the input and observations! Comments follow: wrote in message oups.com... Firstly, 108 to 118 MHz is the international civil aviation radionavigation band. It's not all that interesting to listen to unless a local tower is also repeating voice comms over a VOR or Localizer radionav transmitter nearby on the ground. The civil aviation voice band is 118 to 137 MHz. Agreed - not that interesting to listen to, but the NAV channels are exactly what I'm interested in - (both VOR and LOC). The "experiment" I have in mind is a processor controlled scanner of sorts that tracks multiple VORs and performs as a backup to GPS. Hence the need for fast/agile tuning (either PLL or DDS). As you may have gathered - I'm not an "RF guy" by any stretch - but I'm attempting to learn (out of sheer necessity 8-)..... Secondly, the MC1350 gain block is available from Jameco (it is still made after buying all the masking and stuff from Motorola). You can get MC1349s, a slightly higher gain version from Dieter Gentzow at Kitsandparts.com I'm not locked in to the MC1350 - it just happens to be what's used in the "ultra-cheap" kit I ordered. As it turns out, there's a company (Lansdale.com) that seems to be forming a business model around buying "obsolete" IP from Motorola et.al. and keeping the parts available. Interesting idea. As it happens, NTE has a drop-in replacement part for the MC1350 in their "NTE746" - available from Mouser. May be of interest to some on this group??? If you are trying to build something at VHF, you will need some reasonably accurate signal sources to check out the receiver. That's not a trivial task unless all you want is to carbon-copy some regen or super-regen tuned-by-a-single-variable sort of receiver. Well, even though (as I said) I'm not an RF-type I do have quite a bit of test equipment laying around that I've collected over the years. Among that stuff is an HP8654A good to about 520 MHz that I've never used (and for the life of me can't figure why I bought 8-)........ Jameco sells the MC145151 PLL IC (On Semiconductor the Motorola spin-off still makes them) which, with a prescaler, can make a good, stable LO that is channelized at 50 KHz increments for precise tuning. MC145151 is parallel-load for division, no extra IC needed to get the right division ratio as in some serial-input PLL or DDS chips. Thanks for the tip - I'm concerned about how long such a thing might be available though. For now the safest bet seems to be the National LMX series (or the Analog Devices equivalents) - and adding a processor for control is not a problem. Thanks again for your input - it is appreciated!!! Regards, Bill |
Netgeek wrote:
Len, Thanks for the input and observations! Comments follow: wrote in message oups.com... Firstly, 108 to 118 MHz is the international civil aviation radionavigation band. It's not all that interesting to listen to unless a local tower is also repeating voice comms over a VOR or Localizer radionav transmitter nearby on the ground. The civil aviation voice band is 118 to 137 MHz. Agreed - not that interesting to listen to, but the NAV channels are exactly what I'm interested in - (both VOR and LOC). The "experiment" I have in mind is a processor controlled scanner of sorts that tracks multiple VORs and performs as a backup to GPS. Hence the need for fast/agile tuning (either PLL or DDS). As you may have gathered - I'm not an "RF guy" by any stretch - but I'm attempting to learn (out of sheer necessity 8-)..... snip Neither the range nor the accuracy of VORs is all that great on the ground. What do you intend to do with this doo-dad other than experiment if I may ask? -- Jim Pennino Remove -spam-sux to reply. |
"Netgeek" writes:
Len, Thanks for the input and observations! Comments follow: Agreed - not that interesting to listen to, but the NAV channels are exactly what I'm interested in - (both VOR and LOC). The "experiment" I have in mind is a processor controlled scanner of sorts that tracks multiple VORs and performs as a backup to GPS. Hence the need for fast/agile tuning (either PLL or DDS). As you may have gathered - I'm not an "RF guy" by any stretch - but I'm attempting to learn (out of sheer necessity 8-)..... HAH! I did **EXACTLY** that project back in 1996 or so. Used the 145151 PLL that someone else reccomended. The RX was the ... crud .. can't remember the part number ... That motorola 3300 part that was so popular. 3356 maybe? Used a cheap 567 to track the FM part of the signal, and a simple envelope detector for the AM part. It was barely adequate for close-in stuff, and for long range stations, the noise performance was terrible. The outputs of the two detectors went into a two-channel 8-bit ADC and were read by the CPU. Used a 68HC000 for the CPU, and had a database of VOR stations burned into the ROM. The cleverest piece of code was the CW decoder that was used to ID the stations. It would tune around, listening to IDs and take a best-guess at where it was, then build a list of stations to scan, stopping on each one for a second to get a RMI fix. (There was a little crude LPF to help with the noise performance. Not that it did much good... ) I found some nice 4-line x 20 char LCD displays at a local junque shop, with ENORMOUS characters. 0.6" I Think .. Just HUGE for LCDs .... It would do a scrolling display of the form SJC 025 nm @ 036 OAK 044 nm @ xxx etc. All in all it was a fun project -- with lots of cool learning experiences. In terms of practicality, the performance was never spectacular, RF noise from the CPU section would get into the IF (21.4 MHz)... it made a neat cockpit toy, but I would **NEVER** have considered it even a backup aid to navigation. Just writing about this is making lots of little details come back to me. Feel free to e-mail and I'll bend your ear. -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- Lawrence Statton - m s/aba/c/g Computer software consists of only two components: ones and zeros, in roughly equal proportions. All that is required is to sort them into the correct order. |
Firstly, 108 to 118 MHz is the international civil
aviation radionavigation band. It's not all that interesting to listen to unless a local tower is also repeating voice comms over a VOR or Localizer radionav transmitter nearby on the ground. The civil aviation voice band is 118 to 137 MHz. Firstly, the tower does NOT repeat voice comms over a VOR. The local Flight Service Station MIGHT, but in the days of crystal controlled navcoms, the amount of voice traffic on a VOR is next to nothing. Secondly, the tower/FSS will never in HELL repeat something on a localizer frequency. You are correct; the civilian aviation voice band is 118.000 to 136.975 MHz. Jameco sells the MC145151 PLL IC (On Semiconductor the Motorola spin-off still makes them) which, with a prescaler, can make a good, stable LO that is channelized at 50 KHz increments for precise tuning. MC145151 is parallel-load for division, no extra IC needed to get the right division ratio as in some serial-input PLL or DDS chips. The 145151 is OK if you don't mind spurs every 25 kHz. from dc to daylight. The 145152 is a much better dual-modulo prescaler that gets rid of a lot of trash and garbage from single modulo prescaling that you probably don't want. Jim |
I'm not locked in to the MC1350 - it just happens to be what's used in the "ultra-cheap" kit I ordered. As it turns out, there's a company (Lansdale.com) that seems to be forming a business model around buying "obsolete" IP from Motorola et.al. and keeping the parts available. Interesting idea. As it happens, NTE has a drop-in replacement part for the MC1350 in their "NTE746" - available from Mouser. May be of interest to some on this group??? The absolute minimum operating voltage for the MC1350 is 12 volts. Not 11.9, 12. If this is a mobile application, then figure on a switching power supply to get you up to 15 volts or so. Among that stuff is an HP8654A good to about 520 MHz that I've never used (and for the life of me can't figure why I bought 8-)........ Oh, I'll take it off your hands for $20 or so {;-) Jim |
From: "RST Engineering" Mon, Mar 14 2005 8:11
pm Firstly, 108 to 118 MHz is the international civil aviation radionavigation band. It's not all that interesting to listen to unless a local tower is also repeating voice comms over a VOR or Localizer radionav transmitter nearby on the ground. The civil aviation voice band is 118 to 137 MHz. Firstly, the tower does NOT repeat voice comms over a VOR. The local Flight Service Station MIGHT, but in the days of crystal controlled navcoms, the amount of voice traffic on a VOR is next to nothing. Now, now, Jim. They do. My residence is a mile and a half from BUR, roughly eight miles from VNY here in the San Fernando Valley area of Los Angeles. Agreed, tower operators SELDOM repeat their transmissions over the VOR but it is there in case it is needed. I've heard them often enough. VOR has an almost enormous bandwidth between 30 Hz and the 9.96 KHz subcarrier phase reference...which was INTENDED to carry voice as a conventience to the tower. BUR, now the Bob Hope Airport, USED to carry the taped weather broadcasts over their VOR but stopped several years ago. Secondly, the tower/FSS will never in HELL repeat something on a localizer frequency. Calm down. I may still vote for you next election, but not if you act like Arnie... :-) Hokay, I may have spoken hastily on the voice over Localizer. Color me "probably wrong" there. You are correct; the civilian aviation voice band is 118.000 to 136.975 MHz. Thank you. Sigh, I was only in the business of making civil avionics and their test sets once. :-) Jameco sells the MC145151 PLL IC (On Semiconductor the Motorola spin-off still makes them) which, with a prescaler, can make a good, stable LO that is channelized at 50 KHz increments for precise tuning. MC145151 is parallel-load for division, no extra IC needed to get the right division ratio as in some serial-input PLL or DDS chips. The 145151 is OK if you don't mind spurs every 25 kHz. from dc to daylight. Sorry, I don't agree there. "Spurs" with an ordinary PLL happen when the loop filter component values are incorrect...and/or a higher frequency pole is used (via an extra R and C in loop filter)to reduce higher frequency components out of the PFD. I've made a few PLLs with that MC145151 for homebrew projects and not had any spurs from "DC to daylight" or within the band of interest. The 145152 is a much better dual-modulo prescaler that gets rid of a lot of trash and garbage from single modulo prescaling that you probably don't want. I've not tried the 145152 but, back a number of years before On Semi split from Motorola Semi, a Motorola factory person said the 152 is essentially the same as the 151 except for the serial data interface. I can't vouch for that but that's what I remember. Single modulus prescaling (putting a simple divide by 8 or divide by 10 in series with the VCO and PLL IC signal input) doesn't produce any more #$%^&!!! stuff than going direct into the PLL IC signal input. That is said PROVIDED the loop filter output line to the VCO it is controlling is "clean" and doesn't pick up other circuit signals. Such garbage pickup is the common cause of "spurs" and is layout dependent, NOT dependent on whether or not any prescaling is done. There's some dependency on proper supply rail decoupling for the phase-frequency detector and any active op-amps used between the loop filter and VCO control input. By the way, I've used the MC1350 down to 10 V supply rails with no problem although I do agree with it running optimally (for gain and noise figure) at 12 V supply. There's a lot of internal constant current sources on that IC and that causes the dependency on supply voltage. The same with the MC1349 which I'm working with now as both gain blocks and as mixers. I've worked with the MC1590 metal can original 34 years ago and the plastic package 1350 since 31 years ago. I like it as a little block of gain which has low distortion when running balanced input to balanced output...on up to 70 MHz with hardly any gain rolloff. |
On Sun, 13 Mar 2005 16:42:18 -0500, "Netgeek"
wrote: I'd like to build some homebrew VHF-AM receivers - specifically a receiver for the VHF 108-118 Mhz band. Note that the FM broadcast band is just below that band with lot of strong transmitters, so any configuration with low side local oscillator injection and the more or less standard 10.7 MHz first IF is most likely going to give image frequency problems from FM broadcast stations in the 86.6 .. 96.6 MHz range. To avoid this, a good narrow tunable filter is required in front of the first mixer, which can be a problem if good frequency agility is required. One approach would be to use a much larger first IF or put the local oscillator above the desired band (which also swaps the sidebands) with image responses in the rest of the aviation band. One idea would be to use a fixed downconverter e.g. with a 98 MHz crystal frequency, mixing the VOR band down to 10-20 MHz, filter out the strong mixing products from the FM broadcast band that is on frequencies below 10 MHz and use a DDS with I/Q outputs to get I/Q demodulation of the signal. Paul OH3LWR |
wrote in message Neither the range nor the accuracy of VORs is all that great on the ground. What do you intend to do with this doo-dad other than experiment if I may ask? For now it is strictly entertainment/education. If it works out, however, I plan to use it as part of a complete FMS for something like this: http://members.eaa.org/home/homebuil...ng%20flea.html Good point about the range/accuracy on the ground - I'll do a special version for Moeller and Bede products 8-)..... |
From: "Lawrence Statton N1GAK/XE2"
HAH! I did **EXACTLY** that project back in 1996 or so. snip Used a 68HC000 for the CPU, and had a database of VOR stations burned into the ROM. All in all it was a fun project -- with lots of cool learning experiences. Sounds like a cool project! *MANY* years ago (circa 1984 or so?) I had a plan to tear off the front panel of an RST radio I built and replace it with a display, some controls and a zillion parallel bits to replace all the thumbwheels switches - all driven by a Z80. I eventually decided it would take way too long and didn't accomplish much, besides just being a generally stupid idea 8-).. So I sold the radio... Now, twenty years later I'm playing with *this* project! All of which proves that I now have way too much time on my hands and I'm getting more stupid as I age 8-)...... Would like to hear more about your experiences. So, what would you do differently if you were starting over? I'm thinking that something like a cheapo DSP (or one of the new dsPIC widgets) might be real handy. But first - I have to get past the part where I have a reasonable RF front end! I really doubt that the $40 Ramsey kit is going to do much but I bet I'll learn a few things 8-)........ |
"RST Engineering" wrote in message The absolute minimum operating voltage for the MC1350 is 12 volts. Not 11.9, 12. If this is a mobile application, then figure on a switching power supply to get you up to 15 volts or so. Thanks for that tip - it will be the first "improvement" to the cheapo Ramsey receiver (which runs off 9 volts). The power supply is something I *can* handle easily 8-)... Among that stuff is an HP8654A good to about 520 MHz that I've never used (and for the life of me can't figure why I bought 8-)........ Oh, I'll take it off your hands for $20 or so {;-) Jim Well, give it a few weeks! Once the frustration level gets high enough and I realize that I'm really a bit-banger and not a radio-head I may be tempted to toss it (and anything else RF related) out the window - in which case I'll pack it up and donate it to you 8-)... In the meantime, any other suggested improvements or hints are most appreciated (e.g. "up the IF from 10.7"?)...! Thanks, Bill (Who still thinks the universe *IS* digital - but infinite resolution 8-) |
"Paul Keinanen" wrote in message One idea would be to use a fixed downconverter e.g. with a 98 MHz crystal frequency, mixing the VOR band down to 10-20 MHz, filter out the strong mixing products from the FM broadcast band that is on frequencies below 10 MHz and use a DDS with I/Q outputs to get I/Q demodulation of the signal. Thank you Paul - I'd like to look into this. Can you point me to some practical examples or reference materials to start with? Quite some time ago I ran across the articles from the flex-radio.com guys and was very interested in their approach. It's my understanding (and I mean a fairly fuzzy understanding) that direct conversion has many benefits but is limited to lower bands (unless you're the military with a big budget)??? What are the trade-offs in doing a downconversion followed by DDS-based conversion? |
On Tue, 15 Mar 2005 12:49:01 -0500, "Netgeek"
wrote: It's my understanding (and I mean a fairly fuzzy understanding) that direct conversion has many benefits but is limited to lower bands (unless you're the military with a big budget)??? What are the trade-offs in doing a downconversion followed by DDS-based conversion? My suggestion of using a DDS for direct conversion in the 10-20 MHz range is based on the assumption that DDS chips running with 50-60 MHz clock frequency should be available at a quite a reasonable price, compared to similar chips running at 400 - 500 MHz, which would be required for direct synthesis in the VHF band. However, translating the whole band down to HF requires a strong down converter, especially due to the nearby strong signal broadcast band. Some flimsy NE602 type converter will not survive very well in such environment, but a high current preamplifier followed by a diode ring mixer might be a better converter. Paul OH3LWR |
From: "Netgeek" on Tues, Mar 15 2005 12:49 pm
"Paul Keinanen" wrote in message One idea would be to use a fixed downconverter e.g. with a 98 MHz crystal frequency, mixing the VOR band down to 10-20 MHz, filter out the strong mixing products from the FM broadcast band that is on frequencies below 10 MHz and use a DDS with I/Q outputs to get I/Q demodulation of the signal. Thank you Paul - I'd like to look into this. Can you point me to some practical examples or reference materials to start with? Quite some time ago I ran across the articles from the flex-radio.com guys and was very interested in their approach. It's my understanding (and I mean a fairly fuzzy understanding) that direct conversion has many benefits but is limited to lower bands (unless you're the military with a big budget)??? What are the trade-offs in doing a downconversion followed by DDS-based conversion? Direct conversion (DC) won't be effective on this application for reasons of the civil aviation band being AM with no pilot carrier or other reference. Look into the allowed carrier tolerances and you will see that, unless you can definitely LOCK onto the incoming carrier, there will be a great change in the modulation information, both in frequency and phase. That is particularly true with VOR. The ground station antenna pattern is (now) electronically rotated at 30 Hz and the reference phase (representing magnetic north) is FM on the 9 KHz subcarrier. Without a proper phase relationship, the bearing signal will be very inaccurate. The VOR system was designed/innovated/invented over a half century ago and was elegant in simplicity for simple circuitry in vacuum-state hardware. The first lightweight VOR receivers in light aircraft used a (very old technology) small goniometer as part of the OBS or Omni-Bearing Selector and their accuracies were dependent on how well the goniometer was designed and manufactured. [a goniometer is a coaxial spherical toroid pair, best illustrated in "Lowfer" or low frequency - below AM BC band - small handbooks and some websites] More modern versions use an electronic equivalent of phase shifting at 30 Hz as part of the OBS subsystem. A VOR antenna pattern rotation results in about 30% AM at a 30 Hz rate. The magnetic north phase reference is 30 Hz FM on the 9960 KHz subcarrier. The FM demodulation will have a limiter stage ahead of it to effectively wash-out the 30% AM of the ground station antenna pattern rotation. In between the 30 Hz of the ground antenna pattern rotation and about 8 KHz or so of the lower limit of the 30 Hz FM on subcarrier phase reference is "empty space" that was reserved for optional AM from a local Flight Service Station (FSS) or tower transmission. In short, the elegance of the concept was ideally suited to vacuum tube circuitry, that being an almost ultimate simplicity at the time...and very light weight necessary for aircraft. The "big bucks" of military electronics doesn't go wild over fancy schmancy arrangements of the very "in" modern complications. Those "big bucks" are spent in making the hardware work over the totally gargantuan range of temperatures and physical shock and vibration that would tear apart consumer electronics style structures. The civil avionics market is not, nor has it ever been, large compared to consumer electronics products, hence their costs appear high. There IS room for experimentation in ways to demodulate the VOR information, don't get me wrong. What you must do is to FIRST concentrate on the characteristics of how the bearing information is conveyed...along with all the problems introduced by multi-path distortion from ground objects around you. Those problems aren't there in the aircraft flying a few thousand feet above all those reflecting objects. [an exception is a VOR in a helicopter and its own rotors...but that is another story in itself] Just because the FM BC band upper end is at 108 MHz doesn't automatically mean there WILL be RFI to the receiver. That's a matter of checking a local area to find where all those fixed FM BC carriers are and how strong they are. Aircraft VOR receivers have been overflying all sorts of FM BC stations for a half century all over the world and there aren't any stories (except invented horror tales) of terrible interference from FM. Simpler civilian receivers, not the "big bucks" of military aircraft. Just offhand, I'd say a simple, even tube-based, bearing information receiver can be hacked together to get +/-5 degrees accuracy using the simplest circuitry with minimum test equipment to check it out. Anything better is just finesse, bottoming out at the basic accuracy of whatever VOR ground station is used. That would be +/-1 degree but worse from any ground reception multi-path effects. VOR (Very high frequency Omnidirectional radio Range) was designed only for aircraft obtaining bearing information to a fixed ground station. That's a limited application although extremely important to pilots. A half century ago it was a quantum leap above older raw-DF-style radionavigation. GPS it ain't, nor never was... |
I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF
frequency) or 70 MHz. (satellite IF frequency), and then downconvert to either 21.4 or 10.7...there are cheap crystal filters at both frequencies. Jim In the meantime, any other suggested improvements or hints are most appreciated (e.g. "up the IF from 10.7"?)...! |
Netgeek wrote:
snip But seriously - let's look at the potential utility of a fairly "mindless" NAV receiver as it might apply to the non-instrumented-rated, day-VFR "Sport" or "Recreational" pilot. First off, these guys believe that GPS coupled to a simple moving map display represents not only the holy grail - but they'd be willing (foolishly) to bet their lives on this sole-source nav capability (never mind simple "dead reckoning" or other elementary - e.g. "follow roads" forms of navigation). If the batteries run out on the GPS - or the guys at Cheyenne Mountain pull the big red lever marked "scramble GPS" for whatever reason - they're in big trouble. If that happened, and that's a pretty big if given the US government is forcing GPS as the defacto navigation standard for just about everything, the accuracy would be reduced to such that it would be impossible to make a precision approach. The remaining accuracy would be more than enough to find an airport, especially since Sport and Recreational are limited to day VFR. Standard VOR-based equipment would give them a way out - but they don't have it ('cause it costs too much) and they wouldn't know how to effectively use it anyway ('cause they aren't instrument rated). Some form of relatively simple (albeit far from accurate) NAV capability would at least give them a last chance to drag out the sectional and try to determine roughly where they are - hopefully close enough to find a place to put down. Sporty's sells the SP-200 NAV/COM handheld for $299.00 with a $14.95 rebate if you use your AOPA credit card. It has VOR and LOC with a digital CDI display and 2,280 channel COM. You still would have to know what 235 FROM means. IMHO anyone not flying a big turbine with multiple redundent everything that doesn't have a handheld just in case is foolish. My ridiculous little experimental project is to try and come up with a "poor man's" (and perhaps "stupid man's 8-) nav capability based on VORs which is inexpensive and SIMPLE. There's no OBS nor any other "normal" features (e.g. ability to drive a CDI) - but it kicks out enough info relative to a few nearby VORs so that you can at least determine what planet you're on 8-).... and provide a few hints as to *where* you are on that planet... GPS replacement? Absolutely not. TSO'd NAV receiver replacement? Nope - not that either. Inexpensive (enough so that you might actually install one) and simple (enough so that you could derive some useful info with little training) - that would be the goal. In the meantime, it's really a personal educational and entertainment toy to play with, and nothing more ("amateur", "homebrew", etc. - so it's relevent here, right?)......8-) I appreciate your thoughts and comments, Len! You obviously have a wealth of experience to draw upon and I thank you for sharing it. Despite more than 25 years in product development, most of this is new territory for me (and I'm enjoying the learning experience!). I've never done an RF design - well - at least not "deliberately"!!! Regards, Bill Decoding the bearing can be done with a PLL running as a 360X frequency multiplier on one 30 Hz signal and using the other to gate a counter which is feed the multiplied signal. I built such a beast in '75 as a senior project with a NIXIE tube display. Available compenents have improved a lot since '75. If I were to do something like this today, I think I would look for someone's receiver module and use a microcontroller to control the receiver and do most (maybe all with DSP) the decoding, feeding it all to a PDA with a database of VOR frequencies and locations and use the PDA to generate a map display. It would be a fun project. -- Jim Pennino Remove -spam-sux to reply. |
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Parts are on the way...
First IF = 45 MHz Second IF = 10.7 MHz Any point in going further to 455 KHz for a third IF or just stick with the 10.7 - (MC1350 plus IF transformer) scheme? Bill "RST Engineering" wrote in message ... I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF frequency) or 70 MHz. (satellite IF frequency), and then downconvert to either 21.4 or 10.7...there are cheap crystal filters at both frequencies. Jim In the meantime, any other suggested improvements or hints are most appreciated (e.g. "up the IF from 10.7"?)...! |
I would go directly from 45MHz to 455kHz..............this is typical in HF
receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz crystal used with the on-board oscillator allows you to derive your 2nd I.F. Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator. This is also a good system and it will give you fairly good strong signal handling capability. Pete "Netgeek" wrote in message ... Parts are on the way... First IF = 45 MHz Second IF = 10.7 MHz Any point in going further to 455 KHz for a third IF or just stick with the 10.7 - (MC1350 plus IF transformer) scheme? Bill "RST Engineering" wrote in message ... I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF frequency) or 70 MHz. (satellite IF frequency), and then downconvert to either 21.4 or 10.7...there are cheap crystal filters at both frequencies. Jim In the meantime, any other suggested improvements or hints are most appreciated (e.g. "up the IF from 10.7"?)...! |
The Mini-Circuits SRA-2H comes to mind...............Level 17, which
requires 50mW of LO injection. Pete "Paul Keinanen" wrote in message ... On Tue, 15 Mar 2005 12:49:01 -0500, "Netgeek" wrote: It's my understanding (and I mean a fairly fuzzy understanding) that direct conversion has many benefits but is limited to lower bands (unless you're the military with a big budget)??? What are the trade-offs in doing a downconversion followed by DDS-based conversion? My suggestion of using a DDS for direct conversion in the 10-20 MHz range is based on the assumption that DDS chips running with 50-60 MHz clock frequency should be available at a quite a reasonable price, compared to similar chips running at 400 - 500 MHz, which would be required for direct synthesis in the VHF band. However, translating the whole band down to HF requires a strong down converter, especially due to the nearby strong signal broadcast band. Some flimsy NE602 type converter will not survive very well in such environment, but a high current preamplifier followed by a diode ring mixer might be a better converter. Paul OH3LWR |
"Pete KE9OA" ) writes: I would go directly from 45MHz to 455kHz..............this is typical in HF receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz crystal used with the on-board oscillator allows you to derive your 2nd I.F. Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator. This is also a good system and it will give you fairly good strong signal handling capability. Pete I'd hesitated to post since I wasn't sure of the sort of selectivity needed. But yes, if the selectivity is available at 455KHz, there's no need to have something in between that and 45MHz (or for that matter, if the right selectivity can be had higher, gain is the only reason for going down to 455KHz. Old cellphones, the big and bulky kind, have IFs in the above 30MHz range (the exact frequency has varied, but I think the majority of those that I've stripped have had 45MHz IFs. And they tend to drop down to 455KHz after that, meaning a scrap cellphone (the older the better because they are cheaper and the parts are bigger) will generally provide a "roofing filter" and the crystal to get down to 455KHz from there, and even the 455KHz filter if it doesn't have to be narrow. Michael VE2BVW "Netgeek" wrote in message ... Parts are on the way... First IF = 45 MHz Second IF = 10.7 MHz Any point in going further to 455 KHz for a third IF or just stick with the 10.7 - (MC1350 plus IF transformer) scheme? Bill "RST Engineering" wrote in message ... I'd probably jack the IF up to 45 MHz. (use TV parts; this is the TV IF frequency) or 70 MHz. (satellite IF frequency), and then downconvert to either 21.4 or 10.7...there are cheap crystal filters at both frequencies. Jim In the meantime, any other suggested improvements or hints are most appreciated (e.g. "up the IF from 10.7"?)...! |
From: "Pete KE9OA" on Fri, Mar 18 2005 6:36 am
I would go directly from 45MHz to 455kHz..............this is typical in HF receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz crystal used with the on-board oscillator allows you to derive your 2nd I.F. Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator. This is also a good system and it will give you fairly good strong signal handling capability. Pete "Netgeek" wrote in message ... Parts are on the way... First IF = 45 MHz Second IF = 10.7 MHz Any point in going further to 455 KHz for a third IF or just stick with the 10.7 - (MC1350 plus IF transformer) scheme? Bill As a suggestion (too late if parts are incoming), a single conversion to a 21.4 MHz IF is quite suitable. Using a monolithic quartz crystal filter (available from DigiKey for about $15 a pair of two) between the mixer and first IF could eliminate ALL tuned circuits in the IF following the 1st IF amplifier. Those are available in 12.5 KHz bandwidth which will be fine for a VOR signal. [DigiKey has a link to download specs for the ECS-made monolithics] This is now common in mobile radios, both new and retrofit of older ones. If a single-conversion scheme with 21.4 MHz is done, the LO can be 86.6 to 96.6 MHz with an image at 65.2 to 75.2 MHz. That is a low enough frequency to allow a simple L-C "top coupled resonator" fixed bandpass filter for the front end at 108 to 118 MHz (8.9 % bandwidth). Doing double conversion with a first IF of 45 MHz is, by itself, no problem. However the 2nd IF image is a bit too close to the nominal bandwidth of any 45 MHz 1st IF tuning (it's only 0.91 MHz away). With the second's image (on either side depending on 2nd LO above or below 45 MHz), there's still a chance to pick up part of the FM BC band locally. To avoid that, the 2nd LO should be on the high side of 45. Second IF image would then fall into the low end of the 118 to 137 MHz comm band (also AM) and those transmitters are much lower powered ones than BC stations. With a 10.7 MHz 2nd IF, its image would be 21.4 MHz away and rather easy to attenuate in the 45 MHz 1st IF. There's only a slight problem using stock 10.7 MHz IF components: Bandwidth of the whole 2nd IF might be around 160 KHz; less discrimination to nearby VORs and Localizers. A study of FAA sectional charts might be called for to check on potential interfering stations although those are assigned in regards geographic locations to minimize normal interference. |
On Fri, 18 Mar 2005 06:36:33 GMT, "Pete KE9OA"
wrote: I would go directly from 45MHz to 455kHz..............this is typical in HF receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz crystal used with the on-board oscillator allows you to derive your 2nd I.F. Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator. This is also a good system and it will give you fairly good strong signal handling capability. Pete it is almost like the gunnplexer RX units we made around 1978-80, wonder if the pcb's still exists for such receivers? JM --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/c.htm |
I agree about the 21.4MHz I.F. in a single conversion scheme. If the
required gain is achievable, this is a very good way to go. I remember one of the Rockwell-Collins ADF receivers that had this setup. As far as a 45MHz 1st I.F.............. these crystal filters seem to be designed with a 455kHz 2nd I.F. in mind because a 910kHz rejection spec is given. I have used that scheme over the years with a diode ring mixer as the 1st mixer. I follow the mixer with a series L, shunt C as the second leg of a diplexer that matches the 50 ohm output of the mixer to the crystal filter............ The first leg being is a parallel LC tuned circuit that is in series with a 50 ohm idler resistor. With a reactance of the LC elements of around 47 ohms, the selectivity at 6 db is approximately 15kHz. The (2 time 2nd I.F. image rejection ) is about 60dB when using four poles at 45MHz. I haven't done any in-band spur calculations with this scheme for the aircraft band but I think that with high-side injection it would be ok. Of course, if a 25kHz tuning step is used I am not sure how it would affect the phase noise of the synthesizer if a Fractional N topology wasn't used. I an NE602 is used as the 2nd mixer and just the I.F./ demodulator sections of a TDA1572 were used, the only adjustment required would be a trimmer adjustment of the 2nd LO in order to have a symmetrical adjacent channel response. Pete wrote in message oups.com... From: "Pete KE9OA" on Fri, Mar 18 2005 6:36 am I would go directly from 45MHz to 455kHz..............this is typical in HF receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz crystal used with the on-board oscillator allows you to derive your 2nd I.F. Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator. This is also a good system and it will give you fairly good strong signal handling capability. Pete "Netgeek" wrote in message ... Parts are on the way... First IF = 45 MHz Second IF = 10.7 MHz Any point in going further to 455 KHz for a third IF or just stick with the 10.7 - (MC1350 plus IF transformer) scheme? Bill As a suggestion (too late if parts are incoming), a single conversion to a 21.4 MHz IF is quite suitable. Using a monolithic quartz crystal filter (available from DigiKey for about $15 a pair of two) between the mixer and first IF could eliminate ALL tuned circuits in the IF following the 1st IF amplifier. Those are available in 12.5 KHz bandwidth which will be fine for a VOR signal. [DigiKey has a link to download specs for the ECS-made monolithics] This is now common in mobile radios, both new and retrofit of older ones. If a single-conversion scheme with 21.4 MHz is done, the LO can be 86.6 to 96.6 MHz with an image at 65.2 to 75.2 MHz. That is a low enough frequency to allow a simple L-C "top coupled resonator" fixed bandpass filter for the front end at 108 to 118 MHz (8.9 % bandwidth). Doing double conversion with a first IF of 45 MHz is, by itself, no problem. However the 2nd IF image is a bit too close to the nominal bandwidth of any 45 MHz 1st IF tuning (it's only 0.91 MHz away). With the second's image (on either side depending on 2nd LO above or below 45 MHz), there's still a chance to pick up part of the FM BC band locally. To avoid that, the 2nd LO should be on the high side of 45. Second IF image would then fall into the low end of the 118 to 137 MHz comm band (also AM) and those transmitters are much lower powered ones than BC stations. With a 10.7 MHz 2nd IF, its image would be 21.4 MHz away and rather easy to attenuate in the 45 MHz 1st IF. There's only a slight problem using stock 10.7 MHz IF components: Bandwidth of the whole 2nd IF might be around 160 KHz; less discrimination to nearby VORs and Localizers. A study of FAA sectional charts might be called for to check on potential interfering stations although those are assigned in regards geographic locations to minimize normal interference. |
And how, pray tell, do you get rid of the image with reasonable Q
components? Jim "Pete KE9OA" wrote in message ... I would go directly from 45MHz to 455kHz.............. |
On Sat, 19 Mar 2005 08:36:17 -0800, "RST Engineering"
wrote: And how, pray tell, do you get rid of the image with reasonable Q components? like Hi-Q resistors or was it condensers...? --- J. M. Noeding, LA8AK, N-4623 Kristiansand http://home.online.no/~la8ak/91n.htm |
As a follow-up - I bought and assembled the really simple kit sold
by Ramsey - and described in detail he www.sentex.ca/~mec1995/aviarx/avrxkitc.html I wasn't expecting much - but was really surprised! It works really well and has provided a platform that I can hack to death without feeling bad about destroying it if it comes to that... I'm about 8 miles from Washington National (DCA) with alot of "stuff" in between. With a lousy 21" wire, I have no problems picking up both Potomac Departure and Potomac Approach (with the first I heard being Air Force One coming in to Andrews AFB). The only modifications I've made are to increase the supply to 12V (from 9V - per Jim Weir's comments) and to replace the worthless 10k varactor tuning pot with a 3-turn widget salvaged from some old Tektronix gear. The thing works great! Now I'm looking for suggestions on how to "improve" it. My list includes: Replace NE 602 with SA612A mixer and add "real" tuning via National PLL and Minicircuits VCO. Replace 10.7 Mhz. ceramic filter with 4-pole Xtal-based filter. Replace MC1350 with MC1349 (per Len Anderson) and rework AGC. Add serious LP audio filter to output of AM detector diode. Throw away or rework "squelch" circuit - as it is makes lots of noise and is annoying (loud pops when switching in and out)... Get a decent (e.g. dipole 1/2 wave antenna). It seems to me that after attempting to improve the RF section the biggest gains are to be had in tweaking the audio stages - so that's what I'm focusing on. Just for fun - alot of filtering, noise gate, compression, limiting, etc. seem to be areas where I can really play with the thing and improve the performance. I've been looking at both Analog Devices and THAT components as a step short of going to DSP. I think some real improvements can be made. The basic signal is there (certainly at levels which are "good enough") even with such a simple receiver. I'd like to see what can actually be done (keeping in mind that this is a "learning exercise"..).... Any suggestions appreciated! (And, yes, there are plans to tweak the IF per previous suggestions!)... Thanks, Bill wrote in message oups.com... From: "Pete KE9OA" on Fri, Mar 18 2005 6:36 am I would go directly from 45MHz to 455kHz..............this is typical in HF receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz crystal used with the on-board oscillator allows you to derive your 2nd I.F. Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator. This is also a good system and it will give you fairly good strong signal handling capability. Pete "Netgeek" wrote in message ... Parts are on the way... First IF = 45 MHz Second IF = 10.7 MHz Any point in going further to 455 KHz for a third IF or just stick with the 10.7 - (MC1350 plus IF transformer) scheme? Bill As a suggestion (too late if parts are incoming), a single conversion to a 21.4 MHz IF is quite suitable. Using a monolithic quartz crystal filter (available from DigiKey for about $15 a pair of two) between the mixer and first IF could eliminate ALL tuned circuits in the IF following the 1st IF amplifier. Those are available in 12.5 KHz bandwidth which will be fine for a VOR signal. [DigiKey has a link to download specs for the ECS-made monolithics] This is now common in mobile radios, both new and retrofit of older ones. If a single-conversion scheme with 21.4 MHz is done, the LO can be 86.6 to 96.6 MHz with an image at 65.2 to 75.2 MHz. That is a low enough frequency to allow a simple L-C "top coupled resonator" fixed bandpass filter for the front end at 108 to 118 MHz (8.9 % bandwidth). Doing double conversion with a first IF of 45 MHz is, by itself, no problem. However the 2nd IF image is a bit too close to the nominal bandwidth of any 45 MHz 1st IF tuning (it's only 0.91 MHz away). With the second's image (on either side depending on 2nd LO above or below 45 MHz), there's still a chance to pick up part of the FM BC band locally. To avoid that, the 2nd LO should be on the high side of 45. Second IF image would then fall into the low end of the 118 to 137 MHz comm band (also AM) and those transmitters are much lower powered ones than BC stations. With a 10.7 MHz 2nd IF, its image would be 21.4 MHz away and rather easy to attenuate in the 45 MHz 1st IF. There's only a slight problem using stock 10.7 MHz IF components: Bandwidth of the whole 2nd IF might be around 160 KHz; less discrimination to nearby VORs and Localizers. A study of FAA sectional charts might be called for to check on potential interfering stations although those are assigned in regards geographic locations to minimize normal interference. |
I can comment on the filter change.............the 10.7MHz ceramic filters
that are being used right now have an IN/OUT Z of 330 ohms.................a crystal filter will have an IN/OUT Z of 3000 to 6000 ohms. It will work, but you will need to match the impedances. If the crystal filter is not properly matched, you will experience a deep nose in the response in the center of the passband, and your insertion loss could rise sharply. If you are interested, e-mail me directly and I can send you an Excel spreadsheet that will calculate the values needed for a series L, shunt C type of matching network. Pete "Netgeek" wrote in message ... As a follow-up - I bought and assembled the really simple kit sold by Ramsey - and described in detail he www.sentex.ca/~mec1995/aviarx/avrxkitc.html I wasn't expecting much - but was really surprised! It works really well and has provided a platform that I can hack to death without feeling bad about destroying it if it comes to that... I'm about 8 miles from Washington National (DCA) with alot of "stuff" in between. With a lousy 21" wire, I have no problems picking up both Potomac Departure and Potomac Approach (with the first I heard being Air Force One coming in to Andrews AFB). The only modifications I've made are to increase the supply to 12V (from 9V - per Jim Weir's comments) and to replace the worthless 10k varactor tuning pot with a 3-turn widget salvaged from some old Tektronix gear. The thing works great! Now I'm looking for suggestions on how to "improve" it. My list includes: Replace NE 602 with SA612A mixer and add "real" tuning via National PLL and Minicircuits VCO. Replace 10.7 Mhz. ceramic filter with 4-pole Xtal-based filter. Replace MC1350 with MC1349 (per Len Anderson) and rework AGC. Add serious LP audio filter to output of AM detector diode. Throw away or rework "squelch" circuit - as it is makes lots of noise and is annoying (loud pops when switching in and out)... Get a decent (e.g. dipole 1/2 wave antenna). It seems to me that after attempting to improve the RF section the biggest gains are to be had in tweaking the audio stages - so that's what I'm focusing on. Just for fun - alot of filtering, noise gate, compression, limiting, etc. seem to be areas where I can really play with the thing and improve the performance. I've been looking at both Analog Devices and THAT components as a step short of going to DSP. I think some real improvements can be made. The basic signal is there (certainly at levels which are "good enough") even with such a simple receiver. I'd like to see what can actually be done (keeping in mind that this is a "learning exercise"..).... Any suggestions appreciated! (And, yes, there are plans to tweak the IF per previous suggestions!)... Thanks, Bill wrote in message oups.com... From: "Pete KE9OA" on Fri, Mar 18 2005 6:36 am I would go directly from 45MHz to 455kHz..............this is typical in HF receivers. An NE602 mixer can be used for the 2nd mixer and a 44.545MHz crystal used with the on-board oscillator allows you to derive your 2nd I.F. Alternatively, you can use a TDA1572 as the 2nd mixer/I.F./ demodulator. This is also a good system and it will give you fairly good strong signal handling capability. Pete "Netgeek" wrote in message ... Parts are on the way... First IF = 45 MHz Second IF = 10.7 MHz Any point in going further to 455 KHz for a third IF or just stick with the 10.7 - (MC1350 plus IF transformer) scheme? Bill As a suggestion (too late if parts are incoming), a single conversion to a 21.4 MHz IF is quite suitable. Using a monolithic quartz crystal filter (available from DigiKey for about $15 a pair of two) between the mixer and first IF could eliminate ALL tuned circuits in the IF following the 1st IF amplifier. Those are available in 12.5 KHz bandwidth which will be fine for a VOR signal. [DigiKey has a link to download specs for the ECS-made monolithics] This is now common in mobile radios, both new and retrofit of older ones. If a single-conversion scheme with 21.4 MHz is done, the LO can be 86.6 to 96.6 MHz with an image at 65.2 to 75.2 MHz. That is a low enough frequency to allow a simple L-C "top coupled resonator" fixed bandpass filter for the front end at 108 to 118 MHz (8.9 % bandwidth). Doing double conversion with a first IF of 45 MHz is, by itself, no problem. However the 2nd IF image is a bit too close to the nominal bandwidth of any 45 MHz 1st IF tuning (it's only 0.91 MHz away). With the second's image (on either side depending on 2nd LO above or below 45 MHz), there's still a chance to pick up part of the FM BC band locally. To avoid that, the 2nd LO should be on the high side of 45. Second IF image would then fall into the low end of the 118 to 137 MHz comm band (also AM) and those transmitters are much lower powered ones than BC stations. With a 10.7 MHz 2nd IF, its image would be 21.4 MHz away and rather easy to attenuate in the 45 MHz 1st IF. There's only a slight problem using stock 10.7 MHz IF components: Bandwidth of the whole 2nd IF might be around 160 KHz; less discrimination to nearby VORs and Localizers. A study of FAA sectional charts might be called for to check on potential interfering stations although those are assigned in regards geographic locations to minimize normal interference. |
I guess it would have been handy if I'd posted the *correct* link
to the kit and schematic...8-) The kit was from Ramsey and it is identical to the design and schematic posted he www.uoguelph.ca/~antoon/circ/aviarx/aviarx.html As you can see it's surprisingly simple (and surprising how well it actually works). Thanks again for all suggestions! Bill "Netgeek" wrote in message As a follow-up - I bought and assembled the really simple kit sold by Ramsey - and described in detail he www.sentex.ca/~mec1995/aviarx/avrxkitc.html |
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