C-Quam AM Stereo Part 15 transmitter kit on eBay

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C-Quam AM Stereo Part 15 transmitter kit on eBay

Build your own FCC Part 15 compliant 100 mW Motorola C-Quam AM Stereo transmitter. This is Sean Cuthbert's latest PLL version with pushbutton digital tuning (previous versions had DIP switches or analog tuning):



There will be a few members excited about this kit. It will fill a void where, from what I having been reading, no 100mW AM stareo transmitter has been available.

Looking forward to hearing about experience with this.

Carl Blare

What Carl said!

I am very tempted to snag that unit and see what is all about.  AM stereo is a goal of mine here at the Jacksboro Radio Network.  Alas, I do have many goals.

Someone with some time to build a kit and a few extra bucks, needs to bring this unit into the fold with a report!

Working on getting our small town of <4000 local programming.

Like to see how this does. 

Like to see how this does.  Does it cover the whole band or only part like the old digital C-Quam AM Stereo one did?

Progressive Rock (Album Rock, Deep Tracks), Classic Rock

More Power for Hobby Broadcasters

Great! I've been seeing

Great! I've been seeing transmitters that look like this for a few years, same cases and knobs, with the perf board experimenter's board being used. They should consider getting fibre boards made, it's pretty cheap to do that these days, and much easier for the builder!

It came out a few years ago, and I saw the video that shows the evolution of the circuit on the guy's bench, to the final product. The first transmitters came from outside of the US, but now they've been coming from the West coast for the past year.

I notice his synthesizer is an older chip, the big chip by Motorola. I guess he has a reason for using it, but I didn't know those were still being produced.

I've wanted to experiment with AM stereo too, and I've tried to find a schematic for a real working unit to get started, but haven't been able to find anything solid state or IC based, just one done with tubes by a clever technician!

Where are circuit diagrams for transmitters like the old Alfredo Lite and others that have come out since then? Circuit diagrams for everything seem to be posted, and there are schematics for so many AM transmitters, but why not AM stereo ones?

Looks good

Looks good and a whole lot less $$$ than others. $129 and a whole lot of bang for the buck.

Not good for me here in Canada as it is not certified, just "meets" rules...not good here. I asked Industry Canada(IC) about this and got in writing that if it doesn't have an IC label and number it has to be tested by a IC approved test facility. You can be told you can't use it even if you are obeying all ground and antenna rules and power limits. Same with FM. Wonder how this would stand up against others like the Procaster?




I have the dip switch version

I have the dip switch version of that c-quam transmitter, and i also have the Aspisys ASMAX 1 transmitter, and today just received the Cyprus c-quam transmitter.

Regarding the perf board transmitter from california, the major problem i have with it is microphonic phase mod from the coil of the vco.Also the agc circuit is basic, and audio is fairly low, but sounds ok.Also the phase modulator looks not to be the full vector modulator, as in the proper c-quam spec, but seems to work ok.

The ASMAX 1 has no microphonics, but the pilot tone is poorly filtered, and this adds lf noise to the audio on my hifi setup, so i have added a 25hz bandpass filter to improve it.

On both above units i bypass any audio filtering, as i am using proper c-quam based audio processing in to the transmitters, also both these transmitters tested here have some modulation evelope assymetry on the scope.

The Cyprus c-quam exciter here, I will test this tx and offer my results.



What About Receivers

With revived AM stereo activity it's time to wonder about AM stereo receivers.

What is the low down on them? Are they available either from dealers or on-line?

Carl Blare

I also have the DIP Switch

I also have the DIP Switch version of this transmitter, not sure how old or new mine is compared to Boardmaker's. It isn't a bad unit, sound quality is somewhere between a TH and SSTran. Not bad but my Rangemaster sounds better, that being said the AM Stereo works and does sound quite good. The internal AGC does a good enough job at keeping the audio and modulation where it needs to be. None of these units tune the whole band, the Dip Switch models tune 1024-1750. The pushbutton tunes 1024-1710.

To answer Carl's question, you can find AM Stereo tuners on eBay quite often. I got my JC Penny MCS AM Stereo tuner for $20 off eBay. I'm unaware of any current manufactures of AM Stereo capable radios, nearly all the ones you will find will be of 80s or very early 90s vintage. Some early HD radios could decode AM stereo, albeit with the channels reversed.

Carl,I am presuming you were

Carl,I am presuming you were asking for new c-quam capable receivers only.Over at your end of the pond, i assume hd receivers are the only route left for possible new c-quam stereo decoding ?

The problem with used c-quam portable receivers, in my experience, are most are faulty due to scratchy potentiometers and switches, as well as dried out/leaked capacitors.

I have bought numerous c-quam receivers, over the last 18 months, and most needed refurbing.

Typical used portable receivers are Sony srf-a100, and the Sony srf-a1 walkman.

Typical used tuners are the Denon tu-680nab, and the Carver tx-11a.

More rare used c-quam receivers are the Sony st-jx220a and Sansui tu-d/tu-s amx variants.

Kevin is your man to talk about a wider list of receivers.



More Worry

Getting a stereo AM transmitter on the air is only half of the solution.

Thank you BOARDMAN for the briefing on stereo AM radios.

So what are stereo stations going to do about the receiver problem?

Not only will listeners probably not have AM stereo radios, they'll need to be convinced to buy one and good luck on that.

Anyway, it's a worthwhile pursuit. AM stereo should never have died and we are probably the best ones to bring it back.

This may be over-ambitious, but we could buy up AM stereo radios, refurb them, and either give or sell them to potential listeners.

Maybe the secret for a part 15 station is to buy listeners just like another piece of equipment.

Carl Blare

Yeah Carl, that's right, AM

Yeah Carl, that's right, AM stereo receivers are a problem here in the US, though old cars and trucks with factory radios can have them, and some HD radios added on C-Quam.

Instead of the whole transmitter, I'd like to see technicians come out with just a plain exciter for Am stereo, that you could apply to any transmitter, commercial or homebrew, so you could retrofit the transmitter you have, you might have spent a lot of money on it, or it gets out well already.

My idea would be the exciter, that also comes with schematics for a one stage final, or higher power transmitter if you can use one in your situation. If you have a transmitter, you could just add it to your unit, with instructions on how to do that.

Looking up outboard stereo exciters in commercial radio, like the unit I saw from Delta, it was a rack unit that takes left and right audio inputs, and bypasses the transmitter's oscillator with its own, replaces it as the station's frequency standard.

For example, if you're on 1190, then the stereo exciter produces that 1190 signal instead, and that signal now contains the phase modulated stereo information (left minus right), and 25 hz pilot tone.

Also coming from the box is left plus right, or mono audio that goes to the station's main modulator for mono radios. In the exciter, the L+R and L-R audio take separate paths, but are processed together in some ways, tied together, then there's a time delay adjustment on L+R to account for the small differences in delay of the L-R through the transmitter's RF section. I'm learning this part right now, but that seems to be it.

The problem I see is that all the AM stereo rigs that have come out in hobbyist circles contain the transmitter, often at low power, and need a linear amplifier, which is more wasteful than a class C or higher stage. In Part 15 it uses up your allowed input power, if you're lucky, you'll get 25 milliwatts out.

Great active testing

Great active testing BOARDMAKER! Wow, that Cypress transmitter is expensive for 100 milliwatts and a refurbished unit, let's hope you make a monetized Yutube unpack and use video to make some of that money back :)

Ramsey Kits' AM-100 I think it is, the PLL mono TX has a similar VCO oscillator with a coil, and I didn't find microphonics as much as modulated RF feedback causing FMing. I could see that being a REALLY big problem in a stereo transmitter, because the feedback would be causing phase modulation too!

How much phase change is required for stereo, isn't it less than 45 degrees? I'm guessing the phase modulator is based around the NE602?

I see linearity problems in so many AM transmitter circuits, where they just can't make it to 100 percent either way, especially negative.

Possible Solution

Nate Crime there is a guy named Dave Schmarder who might be able to solve the problems you have detailed.

Link to the Link

Carl Blare

Thanks for the link to the

Thanks for the link to the interesting site, Carl. I wonder how far a box loop like that would transmit? Since it's a loop, it might get out farther for apartment dwellers like Legacy and Friar Bruce of Dogradio, than a long wire antenna.

See, I've tried it on a Ferrite loopstick, long ago and it didn't work well because apparently the stick absorbs all the power, where an open loop wouldn't have that core loss, and it's bigger.

Is It Learning Yet?

Nate, your statement about trying a ferrite loopstick for transmission has me digesting thoughts, but I'm not sure if I'm learning or just building a bigger question.

Based on your discovery that ferrites absorb rather than radiate, perhaps that explains how they contribute to reception. As the ferrite absorbs medium wave energy from the air, the loopstick gathers some of the RF as it passes through.

If ferrite is unable to radiate RF energy it has no use in the transmission of radio waves. It's only purpose is to act as a "soak", which also would explain it's usefulness in filter circuits.

Is that a smart statement, or one that misses the point (?)

Carl Blare



I have the ase2 exciter, and you are quite right, the output replaces the main rf frequency at ttl level, and it phase modulates the carrier frequency, in quadrature.

I am going to feed this ttl level in to the amt5000, in place of the amt's synth output.

I can get the AMT5000 to output flat wideband am mod, on the bench, by feeding the output through a series 47pf cap, in to a 50 ohm dummy load/attenuator.I can sweep the audio in, and monitor the attenuators output on the scope for modulation envelope, and it is flat, and i mean flat between 20hz to 15khz+, we are talking 0.2db or better here !Of course i have bypassed the audio processor ic, as discussed before.Also do get it super flat i used a small cap to compensate the amt's modulator, to get it ruler flat.

It is a lot harder to do a c-quam add on for existing transmitters, as it requires some knowledge to apply it.

Also to get the phase/amplitude to match over the entire band, as in the Aspisys AMAX-1 requires the phase modulator/osc to be at a fixed frequency, and then mixed with a synth oscillator to produce the final frequency.

The upshot of this is that it does tune the entire band without peaking circuits, and the phase/am mod is consistent to give the same channel seperation.

Btw i have fired up the Cyprus C-Quam exciter, all i can say is it is total crap, power varies across the band dramatically, and the am envelope is badly distorted, and the 25hz pilot is a squarewave from a 555 ic !

The ASMAX-1 pilot tone is at least a dds squarewave with basic rc filtering, so i added a bandpass filter to make it resemble a decent sinewave.


The Sony SRF-42, SRF-A1, and

The Sony SRF-42, SRF-A1, and SRF-A100, Realistic TM-152, and MCS-3050 AM Stereo tuners are all common finds on eBay, although some sellers ask much more than what they're worth. The controls on top of the SRF-A100 are a dust magnet, but just pull off the knobs and spray some contact cleaner into them, and that'll get rid of the scratchiness. 

Many HD Radios also support C-Quam, but not all, and this feature was never officially promoted by the manufacturers, so you have to do some Internet searching to find out which models support it. Many HD Radios do not give any visual indication of when a C-Quam broadcast is being received and they can take anywhere from 10 to 30 seconds to begin decoding, so you just have to be patient and listen for the stereo separation to open up.

Also HD Radios tend to be picky about the C-Quam pilot tone. If it's not exactly dead on 25 Hz and 5% modulation they often will stay in mono. However I was able to get my Directed Electronics HD Radio to decode 890 WLS in AM Stereo via 700-mile skywave under pretty poor signal conditions:


CQuam Coverage -- 1988!

Curious about coverage of Am stereo back in it's heyday? Here's a coverage map of C-Quam stations from 1988!



1988 coverage..

I remember that year.  And I remember the promos from a couple of local stations in Wichita Falls running A.M. Stereo.   But, I didn't listen to them because they carried a format I didn't like at the time.  One was the old KNIN 990.  It was a fairly nice "powerhouse" that had been on the air for years.  I believe it went dark in the 90s.  The call letters moved to FM 92.9, not sure now if they are in use.  I will have to look. 

Regardless, things have definately gone downhill for A.M. stereo and A.M. in general.

Working on getting our small town of <4000 local programming.

Hey Tim?

So what breally happened to Stereo AM? Looks like a lot of staions invested and then stopped?

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

The sharpest decline happened

The sharpest decline happened in the mid to late '90s when Clear Channel was buying stations by the hundreds, and they had a policy of turning off the AM Stereo at any station they acquired, even if it had a music format.

And then another decline happened in the early to mid 2000s when IBOC DAB (HD Radio) was the hot new thing, and since C-Quam and IBOC are incompatible with each other, numerous big-market stations switched off their C-Quam "in preparation for upgrading to HD Radio", regardless if they ever actually implemented HD Radio or not.

Thus, with a few exceptions like 890 WLS in Chicago, most stations using AM Stereo today are small-market stations which were able to escape corporate takeover and never had the budget to use HD Radio.



That is good info. Makes sense. I guess CC thought that AM stereo was competing against their FM stations?

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

Interesting to see a few

Interesting to see a few stations missing from that map that I know were running C-QuAM in '88 in Texas. 820 WBAP at 50kW, 1400 KGVL at 1kW. Eventually KAAM/KMKI 620 would run AM Stereo as well.

Texas Stations..stereo Dallas Fort Worth

I had forgot that "K double A M" went stereo back when they were on 620.  I still listen to them these days on 770.   I wasn't aware of 820 being in stereo since they have been news talk since the early 80's (I think).  I remember the day they switched.  I was not impressed as a listener.

Working on getting our small town of <4000 local programming.

Stereo talk is effective if

Stereo talk is effective if the staion is doing live talk with two persons, one on each channel.

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  

What Happened to Quad?

Wasn't there talk in the 1970s of some stations going Quad (4-channel)?

Maybe that was just for FM, but I don't think it ever happened.

Quad LPs were on the market for a year or two.

Then more recently we heard big talk about 5.1 sound.

They always want to load us down with big box appliances.

Carl Blare

Stereo Talk Radio..

Very interesting.  I don't listen to talk radio, I have enough opinions of my own without getting upset about other peoples opinions.  But it makes sense. 

Working on getting our small town of <4000 local programming.

Quad Radio

Interesting, short bit on quad broadcasting, with an interesting list of recordings as well:


And of course, since all the trendsetting in broadcasting is done here in Minnesota, details on a quad broadcasting project:


I still have some Quad LP's.  And I remember a classmate in high school did his science project on quad sound, and had set up a booth with a speaker in each corner and sound effects of trains, airplanes, some symphonies (much like early stereo demonstration records) where those interested could sit in the center and hear the train, etc actually go around them from speaker to speaker. 


Hi, are you able to rerun

Hi, are you able to rerun that map for 2016, I'd like to see the stereo landscape of today.

Not a map but...

Druid Hills Radio AM-1710- Dade City, FL. Unlicensed operation authorized by the Part 15 Department of the FCC and our Resident Hobby Agent.  


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