[HomeBrew] CB radio to 10M conversion for beacon

[Steven Weber]

>Anyway, NOW I want to convert this critter to a CW only transmitter in the 
>frequency range of 28200-28300KCs.  An extensive "Google" hasn't 

I don't know why people want schematics for these things, thier sooo simple
to figure out! The transmitter chain is obvious, as is most of the
receiver. The only place it gets a little complicated is in the T/R
switching and audio. What you really want to know is how the PLL works. 

A few basics: Standard generic CB set

Tuning range 26.965 MHz to 27.405 MHz
1st IF 10.695 MHz 2nd IF 455 kHz

That means the VCO tunes 16.27 to 16.71 MHz on receive. using 5 kHz steps.
VCO is doubled for transmit, so it tunes 13.4825 to 13.7025 MHz, in 2.5 kHz
steps. This scheme is used as it keeps the VCO swing from Rx to Tx within
reasonable bounds. 

Since the PLL reference frequency is 10.240 MHz, the same frequency used as
the 2nd LO to convert from 10.695 MHz to 455 kHz, the reference divider is
4096 to get 2.5 kHz steps. 

Since you'r only instested in transmit, the /N ratio for transmit is 5393
on CH1 and 5481 on CH40. The /N numbers don't go in quite constant interal
spacing, since the channels aren't all 10 kHz spaced, there are a few 20
kHz jumps here and there. 

Anyway, say you want to move the transmit frequency to say 28.100 MHz. Here
you'd want the VCO to be 14.050 MHz. Using the CH1 /N number the new
reference frequency would be 2.605 kHz. Multiply that back up by 4096 and
you get the new reference oscillator crystal frequency needed, 10.671018
MHz. Opps, your not going to find an off the shelf crystal with that
frequency. Lets see what happens if we use one we can get which is close. 

Mouser lists a ECS HC49 crystal for 10.738635 MHz. That would give a 2.622
kHz reference, pretty close to want you need. Now, 2.622 kHz times 5393
gives a VCO frequency of 14.139028 MHz and a final Tx freq of 28.2780 MHz.
Using CH2 /N would put you at 28.291 MHz. Basically, those are your two
transmit frequency choices which fall in the beacon sub band, using an off
the shelf crystal frequency. If you make the reference oscillator a VXO,
you could pull it a little one way or the other. 

The only other option is to make your own PLL with a programmable chip, so
you can put the VCO where you want it. Non-SMT, generic PLL chips are
pretty hard to find these days and you'd need to control it with a
microprocessor, so that option starts to become a real project! 

Now, for some final comments. Boosting the power from 3-4 watts to 10 is
not easy. There is not enough drive. You might get an extra watt or two by
tinkering with the LPF so it does some impedance matching for you. I'd
recommend doing this with a spectrum analyzer, so you know the transmitter
is still legal when your done. 

Use a pentium PC for a keyer? What a waste of electricity! Spend $5.00 and
get a memory keyer chip. Speaking of keying, you will have to do something
to get proper wave shaping of the keyed transmit signal. Simply tuning the
driver on and off or using the PTT switch will produce key clicks, annoy
people and possibly get a nasty gram from the FCC. 

Good luck, a little more complicated than you thought, eh?

72,
Steve, KD1JV
"Melt Solder"
White Mountains of New Hampshire
http://www.qsl.net/kd1jv/
http://kd1jv.qrpradio.com