[Hammarlund] Distortion in HQ-180 audio output

[Kenneth G. Gordon]

Robert:

OK. I found the article in ER Mag I remembered: it is in issue number 304, 
the September 2014 issue, beginning on page 12. Single issues are very 
inexpensive and I would advise you to get that issue before you start on your 
audio distortion problem.

Distortion on strong CW or SSB signals was a very common problem in 
many receivers of the period of the HQ-180.

The problem in the HQ-180 is caused by an incorrect or incomplete 
application of AGC.

In the case of the HQ-180, there are two AGC loops: 1) a delayed AGC for 
the 1st RF amp only, and 2) a "main" loop for the other controlled stages.

In the HQ-180, the 2nd loop controls the 455 KHz IF stage, and only ONE of 
the two 60 KHz IF stages, V-6.

The author of the article, Jeff Covelli WA8SAJ, connected the 2nd 60 KHz IF 
stage, V-7, to the AGC buss. This reduced the distorted audio very 
dramatically.

In the Heathkit Mohawk, there is NO AGC connected to either of the two 50 
KHz IF stages. He added those stages to the AGC buss, and the effect on 
that receiver was the same as for the HQ-180: dramatically reduced 
distortion of the audio on CW and SSB.

I strongly suggest that you contact Ray at www.ermag.com and buy that 
issue of ER magazine asap.

Those improvements that Byron mentioned should also be investigated, 
especially, IMHO, that one which improves the AGC attack-time.

Kenneth G. Gordon W7EKB

"Courage is being scared to death but saddling up anyway."--- John   Wayne