I have recently converted one of these sets for the 2 metre amateur band, and am very pleased with it's performance. It was also an enjoyable few hours in the workshop, the set is fairly easy to work on, and I only hit a few snags.....! (more on that later.)
Instructions.
Here is the transcript of modification details
sent by GWM Radio, who can supply these sets for conversion. (with improved
diagrams.)
Here are copies of the original documents ( approx. 60Kb each):-
Instruction Page 1
Instruction Page 2
Instruction Page 3
Instruction Page 4
Circuit Diagrams.
The following GIFs are a complete set of schematics for my version
of this transceiver.
(Each file is 80~100Kb each)
Circuit Diagram Page 1
Circuit Diagram Page 2
Circuit Diagram Page 3
Circuit Diagram Page 4
Circuit Diagram Page 5
Circuit Diagram Page 6
And here is a layout diagram for the PCB's.
My Experience
I enjoyed doing this conversion, and was rewarded by ending up with
a fine 2m FM transceiver for the car, at very little cost. (The extra components
required were sourced from the scrap box easily.) I have to say I was glad
to have a Weller desoldering station in the workshop, as I think it would
have been difficult (but certainly not impossible) to use a "solder-sucker"
device on some of the components.
I found that the transmitter PA section was not easy to align during
tuning. The cure was to adjust the number of turns on some of the coils.
I also replaced some of the compression trimmers, as I found them to be
VERY "gritty", and hence also cause problems with tuning. I ended up setting
the power output to about 18W, allthough the set would have certainly provided
more if required.
The receiver side aligned extremely easily, and resulted in a final
sensitivity of about .2uV.
I have also replaced the original GWM Radio EPROMS, so I now have 12.5KHz
channel spacing.
The Future
At present, the Dymar is set up in the shack as my 2m FM station. I
plan to install this into my car, and add a PYE
A200 amplifier to bring my mobile power output up to about 55Watts.
When? Who knows!