Michael D. Harmon wrote:
A fellow ham gave me 5 Icom U12 commercial radios, which I'd like to put
on the 440 MHz ham band. Upon inspection, they are dead ringers for the
old IC-4AT series of transceivers (even have silk-screened outlines for
the three mini switches on the back). I need a schematic and PCB layout
so I can move them down about 10 MHz.

Thanks,
Mike Harmon, WB0LDJ


I've found that if I want U12 information, it's more productive to ask for
U12 information. Only reason I found this is cause I accidentally
clicked the wrong link.

It matters which U12 you have. If it's the highband version, you can
move it to 440 by switching the input wires on the pLL to flip it down
by 2X the IF frequency.

To make the Icom U12 work on Ham band.
Start with highband version of U12
Cut pin 15 of IC201 to reduce count by 1000. Too tight to lift pin or
cut trace.
Swap pins 7 and 8 of IC202 to reverse sense of offset.
This can be easily done with cut and strap on backside.

Example:
rxfreq txfreq txofst
21.8 osclow osclow osclow
rxfreq 444.1 444.1 449.1
oscfreq 422.3 444.1 449.1
vco 140.7666667 148.0333333 149.7
3xvco 422.3 444.1 449.1
x202 47.3 49.722 50.278
3x202 141.9 149.166 150.834
mixout 1.133333333 1.132666667 1.134
-cnt 272.0106254 271.8506192 272.1706317
use 272 count
x201 8.533 8.533 8.533
x201/2048 0.004166504 0.004166504 0.004166504
stepsize 0.012499512 0.012499512 0.012499512
cnts/mhz 80.00312512 80.00312512 80.00312512
div N/3 90.67020847 90.61687305 90.72354389
divisor 272.0106254 271.8506192 272.1706317

Board layout he
http://nm7u.tripod.com/homepage/u12.jpg

If you have the lowband version...never mind.
mike

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