On Sat, 17 Feb 2007 15:49:51 -0600, "Pete KE9OA"
wrote in
:


Sounds like it might be a little too hot for the band.....

I am not sure what you mean.


I have found that it's sometimes better to DE-sensitize the receiver
front-end on a noisy band. Tends to improve S/N.


I do have the service
manual, but I have never seen this kind of problem.


Never assume the manual is correct. Establish a baseline by injecting
a single tone post-AGC, run it up to 100% and measure. Then re-align
the AGC to your mic according to that baseline.

I might inject the signal right at the audio amplifier and work backwards.


Same difference.


For testing purposes, I am using a CT Systems Model 3000B Communications
Test Set. For the brief time that Tx audio is present, the modulation
envelope looks fine. This unit has a built in 100W dummy load.
RF output is flat across the band, at 4.5W, so it doesn't look like
somebody
tried to align the exciter/output stages.


Sounds like it may have an RF limiter. If you have a pulse generator,
hit the audio with 0.1ms spikes. That will also tell you if the audio
limiter has been disabled.

I'll give that at ry.


It looks like I will have to do some signal tracing with an o'scope.
Hopefully, I will be able to find that 5-pin mic plug so I can make up a
test cable. Thanks again for the advice!


No problem. If you ever get around to scanning the manual I wouldn't
mind having a copy.

I will do that. I only can scan up to 11 X 14 size, so the schematics will
be broken pages,but that should be fine.


No hurry. I only get a couple CB radios a year, so it's hard to tell
if or when I'll run across this model. There really should be a public
CB manual repository like BAMA..... maybe some day.