CB to 10 ?
Inspired by the Soldersmoke blog:
I got out a Johnson Messenger 4135 CB I was given in the 20th century.
Looking around on the internet there aren't any ready-made mods to move to 10. The PLL is a MSC42502P which apparently is a custom made chip for EF Johnson that uses BCD programming:
from the 4135 schematic:
I can see that the PLL is driven by 5.12 MHz crystal which as we know with the VE3DNL Marker Generator:
http://wb9kzy.com/ve3dnl.htm
divides down to 5 or 10 kHz with a binary counter. There are two other crystals on the schematic, a diode switched transmit crystal is 21.275 MHz. And another diode switched receive crystal is 30.820 MHz. The difference between these two is 9.545 MHz but that doesn't really sound right. The schematic shows an IF filter at 455 kHz. 455 + 9545 = 10000 ? I will have to think about it.
I'll have to do some investigating to see if the PLL can be uplifted into the 10 meter band. I did try powering the unit and it does seem to transmit. One bonus is that while it's in PA mode, the PLL is active so the transmit frequency can be spotted at low power on another receiver.
However the receiver doesn't seem to hear anything. The squelch doesn't work and the volume control doesn't raise or lower the volume. So some troubleshooting and probably contact cleaner are in order.
Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm
