Poor Man's BFO                  

(Or how to receive SSB on an AM only rig)


Financially affluent people are often the envy of many people of lesser means. It seems that whatever it is that they want, an affluent person need only to effortlessly plunk down the cash and walk out with their newest toy. Whether it's a car, a boat, or a shiny new CB with all the fancy bells and whistles. It's all too easy for them. But being the guy who can have anything he wants, sometimes deprives him of some of life's better lessons in value,  humility, and creativity. I mean, would a rich person need to develop the skills to kludge together an antenna out of scrap aluminum? How about a power supply made from a Lionel train transformer? Or how about having to deal with "no-frills" or 2nd hand radios because that was all you could afford? Yes, a definite lack of funds is what often drove much of my experimentation.  In retrospect, I think I had a much more rewarding experience on CB thanks in part to me owning modest equipment, and having little choice but to build many things from the ground up.  In the process, I found that it was fun making junk work better. It also helped that I wasn't the only one though.  I guess it's true what they say about misery loving company......

It is with this spirit of creativity, fueled by perceived necessity,  that this featured project came to be.  It began sometime in 1975 and at the time, I was running my Lafayette Comstat 25 tube rig. I was generally happy with my somewhat modest setup at the time. My radio was a few years older than most but was generally comparable to the stuff that most of my other radio friends had, even if some of them were lucky enough to have had their parents foot the bill for it.  We were all pretty much on equal footing. But then a couple of the other teens made the next leap and traded in their Realistic Navaho's for SSB rigs (Royce 640's).  This seriously disrupted the harmonious balance which had existed on the channel, which quickly devolved into a feeling of pure envy. All was right in the world,  if we all had the same basic capabilities.  But if anyone got something significantly better, then the rest of us wanted it too (The CB version of "Keeping up with the Joneses"). The problem, of course, was that most of the rest of us didn't have the money to play in that game.  Things got worse when these guys started rubbing the rest of our faces in it by jumping to SSB to talk about the rest us knowing that we couldn't listen.  Needless to say, I wasn't happy about this flaunting of their newly found capability. I couldn't afford the $250+ that even a "basic" SSB rig cost new, and my mother wasn't about to kick in the extra cash to get me a SSB radio. So it looked like it would be quite a while before I could elevate my own status and join the ranks of the SSB crowd.  In the meantime, if I could find a way to at least receive these guys when they went to SSB, and make them realize that their "private" channel, wasn't so private anymore, they might quit doing it.  But nothing I could think of at the time would solve the problem without spending serious money. Then quite by accident, while one of these guys was talking on SSB, someone else keyed up on AM and just dumped a dead carrier. The carrier signal was very close to the signal that the SSB station put out and I could hear the guys on SSB through the carrier as it demodulated their signals. They sounded a little "Donald Duck-ish", but I could understand them fine.  Further experimenting, using my 100 mW walkie-talkie to provide the carrier, yielded similar results.  But it was not an easy task. I had a tough time balancing the signal of the walkie-talkie to match the signals of the guys on SSB, but with some effort, I could at least understand them.  It would have been more to my advantage if I would have kept quiet about my discovery, and used it to play some clever prank on them.  But no, it somehow felt better to immediately knock them down a few pegs by publicly deflating their idea that they had "private channels", and along with it the hope that they'd stop flaunting their capability.  But once they realized what I was doing (I couldn't keep anything secret then), they started going to channels where I didn't have corresponding crystals for the walkie-talkie, thereby negating my ability to listen in.  Rats! There had to be another way. I couldn't afford to buy crystals for all the CB channels just for this purpose.

The solution came one day when I was lamenting about the situation to Steve on the phone.  Steve suggested trying to make a B.F.O. (Beat Frequency Oscillator) for the I.F. frequency of my radio. At the time, I was not well enough versed in oscillator theory yet to build it myself, so he made me an oscillator circuit from a single 2N-2222 transistor , a couple of resistors and caps, a coil, and a variable tuning cap. The whole thing was built on a 4 lug terminal strip and mounted to a chunk of pegboard. It got its power from a 9V battery (And with several Radio Shack free battery of the month club cards, I was never short on batteries). This oscillator was tuned to run at 455 Khz, which corresponded to the I.F. frequency of my radio. Taking the "antenna" wire from the oscillator and inserting it down through the middle of one of the tall, dual slug I.F. tuning cans in my Comstat and then carefully adjusting the tuning cap would put a carrier on the radio which would then show up on ALL channels.  I now had a crude, but working, BFO which could demodulate SSB signals on any of the channels that these guys went to. By adjusting the tuning cap, I had a "clarifier" which allowed me to make them sound pretty close to normal. I could adjust the amount of carrier signal by how far I put the wire into the I.F. can. It took a little time and experimentation to find the optimal combinations, but I now had the ability to receive SSB on my AM-only rig.  I would use this circuit whenever anyone went to SSB, and I wanted to hear what was being said. Eventually the newness of their radios wore off and those guys calmed down and stayed with us on AM.  I would use the BFO for the next few months until a deal on a used and broken Realistic TRC-47 SSB rig fell in my lap, and I would finally have a SSB radio of my own.

Now, had I been someone of considerable financial means, I could've just bought a SSB rig of my own.  But I never would have learned how to make a BFO or felt that feeling of triumph which happens when you solve a problem through the results of your own efforts.