Receiving SSB on a 27 MHz AM CB radio

[@acestudioscouk-Ace-G0ACE]

This series is both fun and informative. Thanks.

[@BoB4jjjjs]

That is brilliantly simple.

[@coblecam]

Great video Peter (as always). I have been snagging a few CBs as I find cheap ones and this is a perfect project for fun and learning. Thanks! 73

[@peterarmitage5357]

Good video peter as always, good idea to keep these cb radios alive, some times if i come across one that is completely burnt out i use them for other homebrew projects, i recently bought a MDT and a MST3 from ozqrp, so i will be using what i have, some of the old 23 channel rigs i have made a simple circuit with a 20mhz osc to bring them to 40 meter band, good listening, keep up the good work i enjoy your videos.

[@BoB4jjjjs]

Why don't you do a video on that. I am sure others will be interested to see it and might even try it themselves.

[@wadepatton2433]

Peter, and hams who don't know this already, the biggest bunch of "power users" of CB in America are on 27.025 mHz (I think channel 6) also known as "the Superbowl". I tuned my fancy HF rig down there for a listen yesterday, and they where going at it per usual. Right now there is zero cw activity on 12, 10, or 6m (and none expected today), but those guys were getting some propagation with their AM signals running hundreds if not thousands of watts on 11m. Yes, under our FCC rules, 4 watts is maximum for CB. But then unless they cause harmful interference the FCC pretty much lets them run rampant. And a lot of us hams were on the CB freqs doing about the same thing, before we became hams. So it's neat to go listen to those guys for a few minutes--gets old pretty quick, sounds exactly like it did 20 years ago (and further back I'm sure). Some have fantastic AM audio and signals, but mostly it's a mish mash of guys simply trying to talk over each other- or a heterodyne hell. When propagation comes back around next solar cycle, I'm sure you'll hear some of these yanks if you tune there now and then. Heard a Golden Eagle in there yesterday, they had some E-skip going. Signals are weaker today-but present.

[@BoB4jjjjs]

Have you heard this crowd from Francisco Bay area? kzbin.info/door/Q27TShT08IUwSjjtlikBXw They go out live on KZbin.

[@orsonsegura8605]

Is a hard electronic work...

[@vk3ye]

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[@georgealbertacanadaeh1038]

hello Peter, could you please send me the design wiring diagram? Did you ever build one of these to receive and transmit? And lastly do you have any CB mods for 40 Cobra 29 Classic I could try. Thanks George

[@vk3ye]

Hi George - The circuit diagram is in the video. I've done no wiring diagram. I didn't build one for transmit. Sorry can't help re the CB mods.

[@stephenwalters4798]

It might be more useful to get the radio on to 10m and convert to dsb?

[@vk3ye]

This would be extremely difficult to do and it would be easier to build a 10m rig from scratch. Conversions to 10m were common with 1970s/1980s SSB CBs that used chips like the PLL02A which was easier to convert. Modern ICs are much harder. Plus you'd need to convert the power amplifier chain to linear. And AM only CBs like this have much less room inside the case than AM/SSB CBs.

[@vk2ig]

@@vk3ye Peter, I remember looking inside some AM-only 27 MHz CB transceivers years ago when I was looking for a radio to convert to 10m. All of the AM-only sets I looked at used high-level modulation. They would've been fine for converting for CW operation, but modifying the transmit signal chain to ensure the linear characteristics needed for SSB or DSB would've been a much bigger job. Cheers, Mike VK2IG

[@vk3ye]

@@vk2ig Agree. Back in the valve days one option could have been to modify a push pull linear amp to operate as a high level balanced modulator. Then you could run 4 watts carrier in and get more out - as DSB. From memory use was made of the screen grid. This was used around 1960 when DSB was (briefly) popular amongst those who wanted to convert old AM gear and couldn't afford crystal/mechanical filters. I have yet to see high level balanced modulators (ie >1w) using FETs etc.

[@vk2ig]

Peter, did you notice any desensing of the receiver due to the BFO signal? During my SWL days, I built a 455 kHz BFO for the National Panasonic receiver that I described in my comments against another of your recent videos. (I didn't dare modify the radio, as it wasn't mine, so I couldn't make any connections into the IF strip.) The radio had a non-metallic case, so placing the BFO immediately beside the radio allowed sufficient coupling into the IF strip to achieve product detection. However, I did note that the receiver desensed ... Max VK4MD told me this is due to the AGC being derived after the envelope detector. But at least I could hear SSB and Morse code properly. Cheers, Mike VK2IG.

[@vk3ye]

Mike - desensing can happen if the BFO is strong (eg a transistor oscillator putting out maybe 1mW). It doesn't happen here as the signal is coming from a passive diode mixer with significant loss. Also having the BFO outside the CB's shielded box cuts the signal compared to if it was internal.

[@guillermosempron5776]

Better use 455Khz local oscilator to mix.

[@vk3ye]

I considered that but wanted something that would work on any CB, with any IF, and didn't require any internal modifications or connections.