[Hammarlund] HQ-180/HQ-170A audio comparison video

[Kenneth G. Gordon]

On 17 Dec 2014 at 22:07, Robert Sauvan wrote:

> Hi all,
> Everybody has been a great help in trying to troubleshoot my HQ-180 
> audio issue.
> In an attempt to find a cure for what I feel is a distortion problem on 
> my HQ-180, I decided to make a short video comparing my 180 with my 170A 
> since it is difficult to actually explain what I am hearing.The video 
> isnt quite as good as hearing the comparison in the shack, but Im hoping 
> for everyones opinion. Let me know what you think. Click the link below 
> to take you to a temporary page on my website.
> 
> Thanks-Bob-W0YBS
> 
> http://w0ybs.com/w0ybs_025.htm

First of all, it sounds as though you are not using the same loudspeaker 
for both receivers.

Secondly, if you want us to compare what you are hearing on the two 
receivers, you should try to set them both at the identical audio pitch. 
You have the 180 tuned to a much lower pitch than the 170. That makes it 
somewhat difficult to accurately compare the two receivers.

Thirdly, to me it is VERY obvious that the AGC is always on with the 180, 
but is turned off on the 170....OR, the AGC is working correctly in the 
170, but is not working correctly on the 180.

Lastly, what you are hearing on the 180 are what is called "popping on 
peaks" if it was listening to an SSB signal: this is due to the AGC 
allowing a very strong pulse from the signal to hit the receiver before 
the AGC can "grab" it and drop the receiver's gain. It sounds as though 
you have the AGC set to "Fast", but there is a slight delay before it 
activates. The attack-time of the AGC is a bit too slow.

What you are, essentially, hearing are receiver-generated key-clicks on 
the 180.

I suspect the problem is in the AGC circuitry.

THis would also explain why the RF gain control is not working the same 
way as it is on the 170: the 180's AGC is controlling the gain and, 
essentially, bypassing the RF gain control.

I think you need to take a very close look at the 180's AGC circuitry.

And, by the way, AGC circuits can be very difficult to troubleshoot. The 
180's is especially difficult because Hammarlund's schematic for that 
receiver is extremely "messy".

Ken W7EKB