[R-390] AGC problem

[Bill Abate]

Ed,

My AVC voltage at 5 and 10 mv does not agree with yours.  Its less. 
10mv shows -0.25.  Can't figure anything to increase it.  The high end 
is OK.  Resistors and caps have been replaced.

SSB reception is still distorted but not as bad as when I was running 
255 VDC B+.  My friends 390A receives SSB at full RF gain and sounds 
good.  Maybe I can swap radios when he isn't looking! :)

I won't bother you guys further with this as I think this is as good as 
I'm going to get it.  At least I was able to get the radio to meet the 
AVC spec in the manual so something was accomplished.  I may experiment 
with the gain adjustment pot to see if that helps.  I believe it is IF 
gain causing the problem and not RF gain.  Next year's problem.  On to 
the Cosmos PTO!

73,

Bill, K3PGB

DJED1 at aol.com wrote:

> I made a few measurements on my receiver to see what the AVC characteristic 
> was.   I got the following curve, which shows pretty good AVC action:
> 
> microvolts in          AVC volts          audio level
> 5                         -1.0                    -5 dB
> 50                         -4.0                    -3 dB
> 500                    -7.0                    -2 dB
> 5,000                    -9.4                    -2 dB
> 50,000                    -12.3                    -3 dB
> 
> 
> I was also curious about the input impedance match to the generator, so I put 
> my MFJ antenna analyzer on the receiver input.   Interestingly, all readings 
> at center frequency were in the range of 25 to 50 ohms, with the reactance 
> being tuned out by the antenna trimmer.   I suspect I may have a bad measurement 
> because the signal level is so high.   Has anyone done a similar measurement?  
>  Is the receiver input really 100 ohms or so, or have we been worrying about 
> generator mismatch for nought?
> Ed   WB2LHI
>