it is indeed in that radio.
at this point i dont see much point in having you go through any antenna testing, as you have just stated the cause of your problem!
your radio is going off frequency when you speak into the mic.
no this is not normal, and your RF frequency should not change when you speak into the mic.
that is known as FM (frequency modulation).
there is a chance that speaking into the mic causes your freq counter to read erratically even though the actual carrier frequency is not changing, but with the problems you are having, it seems more likely that the frequency is actually changing.
so, lets eliminate the possibility of the freq counter getting freaked out by your modulation.
i know you said that the VCO seems to be working properly, but i want you to try something for me in order to illustrate the point im making.
get both of your 959's on the bench with the bottom covers off in order to do some A/B testing.
first, connect your freq counter to TP3 of the WORKING 959, mirror board removed.
once again, ch. 20, AM mode, clarifier centered, but this time with the mic gain up.
once you have the counter connected and are reading 16.5100mhz in receive; key the mic, and speak in to it.
did the VCO frequency change when you spoke?
it should not.
now do the exact same thing to the NON-WORKING 959.
did the VCO freq change when you spoke?
my guess is that it did, base upon your earlier statement.
if this all worked the way i think it will, you have just found your problem.
something inside your radio is causing the VCO to deviate off freq. when you are modulating.
the bad news is that there could be quite a few causes for something like this.
biggest possibility is that the voltage feeding the VCO is dropping with modulation.
so, first test would be to connect your DC voltmeter to TP2.
if your radio is still on channel 20, you should be reading pretty close to 3 VDC here.
now, key the mic and talk into it with the DC meter still connected to TP2.
did the voltage change?
if it did, we need to find out why.
if it didn't, you need to find out which signal/ voltage is dropping out on the VCO chip.
put the DC meter on each pin of the VCO chip, and try to find the one that is dropping out or freaking out with modulation.
right now i am thinking that with the dual finals, there is something in the radio that can't keep up with the additional current requirement of your modulated audio, and is in turn causing an unstable voltage at the VCO.
this would cause the problem you are having.
so next step is to find out where this dropping voltage is sourced from.
well, it's definitely going to come from a voltage regulator seeing as it's the PLL and voltage stability is critical here.
one example: your radio pulls so much current on modulated TX that the input voltage to the regulator is dropping so low as to cause the output to be erratic.
this is where my mind is at right now.
we are getting closer!
don't give up, your tenacity is admirable.
let me know what you find, and take full advantage of having a working radio to compar against.
any time you measure something that you don't understand; check the same thing in the working radio.
LC
