I just read a book by another Ham who tells how wonderful operating FM in the 29.nn megahertz band is. And it just happened that I was recently given several non-synthesizer, crystal mixing 23 channel CB radios. Perfect, EXCEPT that these are closely built with a lot of parts. That means that tracing out the circuit to see just where the changes go would be tedious and error prone..
Has anybody here actually done that??
AND, does anybody have the circuit schematic for a Lafayette HB525 radio ?? I do have another 23 channel radio, two crystals per channel. Changing that to FM and a bit higher would technically be simpler, except for having to create two stable oscillators and find a way to accurately tune them..OR, just one receive L.O and one offset oscillator for the simplex transmit frequency. Still a bit tedious.

 

I think the 23 channel CB Radios are AM devices. That being the case a conversion will be challenging.
OTOH, there may be 40 channel radios that have FM capability.

 

I do not know if it is the same, but here is the "E" version...
https://elektrotanya.com/lafayette_hb525e_sch.pdf/download.html#dl
The TX could be FMed by adding a vatactor diode to Xtal 12, the 11.730Mhz crystal. You would need to include some sort of FM discriminator for FM reception.
If I was trying it, all the crystals 1 to 10 would be replaced with an Arduino driving an Si5351 sig gen.
One of my VFO conversions that went well is here...
http://www.sadarc.org/xenforo/upload/index.php?threads/ax-144-cb-to-10m.488/
My first was a PCM Hawk Flying Doctor HF transceiver that I still use today. It goes very well. The sets modified include HF, 10M, 6M, 2M and 70cm.
http://www.sadarc.org/xenforo/upload/index.php?threads/pcm-hawk-arduino-vfo.36/
The Si5351 boards have been used by lots of folks in many sets to free them from the limitations of crystals. Have a look on line.

 

OK!! AND Thank You!! That site wants to add "an extension" prior to doing the download, and I am a bit cautious about add-ons.
I have already located a number of FM detector circuits that do not require that tapped transformer that the commonly available circuits always demand.
My one unknown is how many are active on the 29 MHZ segment.

 

Here is the circuit.

 

Thank You!!!This looks like what I need. Now to see how close they are.

 

In that stack of CB radios from the estate of a fellow club member, I found the ALLIED RADIO 23 channel crystal control RX and TX, that also has tunable receive. AND a 6.000 MHz first IF. So I can add a 6 mhz offset oscillator with FM and a buffer/booster/mixer and work simplex FM around 29.60. That was the 10m hot spot back when the book I read was written. And I found FM detectors in an RSGB book that avoid using the rare FM discriminator tapped transformer. WHY hasn't the ARRL published any of those circuits?? And I can save the AM detection system and modulator, alongside the FM option.


The really nice feature about this particular transceiver is the built in AC power supply

 

HAM is not an acronym. It is short for "amateur" and is typically written as "ham" or "Ham" (as in ursine farm animal).

 

So now there are two candidates for surgery. The crystal mixing Lafayette radio versus the "Allied" crystals per channel radio. For that radio I can just use a 6 Mhz oscillator that I can FM, which will be simple to add, and mix that with the tunable receive oscillator already provided for the receiver, to generate the transmit frequency. The receiver is double conversion, 6Mhz and 455 Kc second IF.
The challenge being that I do not know if it even works at all. So this project will have several stages, no matter which radio I use. Going from AM to FM transmit is not difficult. But a stable FM detector scheme might be a challenge. Has anybody used a CD4046 PLL IC to detect narrow-deviation FM at 455KHZ??

 

One BIG PUZZLE on that PDF of the Lafayette radio: The transistor type numbers have all been altered to read "2SCFand then a single digit. Obviously that is done to obscure the actual identity of the devices.
As for FM versus AM in the radio, that change is simple for both receive and transmit. The CA3089 is a single IC limiter and FM detector device in one package, VERY well documented and multiple sourced. No problem there. And FM transmit is even simpler.

 

No more comments. What is still unknown is how much activity is going on in that band.

 

Hi
Screenshot of current conditions.

 

Hi
Screenshot of current conditions.

Many Thanks, DbLoud! So there is activity.

OK, so there is some longer distance communication going on, and conditions must be OK. I am not sure how that will apply to a rig that I might be able to boost up to five watts. Of course I can always add a pair of 6146's since FM does not need a linear amplifier. An interesting thought.

 

OK, so now I have a bit of information.
Sorry about the extended time of no responses. I seem to have been guilty of a second violation of a rule that I was not aware of. A week later I was told, by an unmentioned individual, the nature of my offense. Many thanks for that warning.

The CB radio conversion to ten meter FM is still live, but no longer forefront.
An RSGB publication provided a lot of useful information about NBFM detectors, so many thanks to the RSGB!!!!
The RSGB "Radio Techniques" fifth edition is a very useful publication indeed!!

 

Evidently conversion of older CB radios to 29 MHZ FM is not a popular topic. Not terribly surprising, I suppose.