[Collins] 75A4 SSB AGC...

[Jeff Anderson]

----- Original Message -----
From: "Bob Wilder" <bwild@earthlink.net>
To: <geraldj@isunet.net>; "Bill Russell" <wgr@adelphia.net>
Cc: <collins@mailman.qth.net>
Sent: Wednesday, April 30, 2003 1:58 PM
Subject: Re: [Collins] new subscriber with a 75A4


> Even 75A4's, new out of the box needed reduced RF gain to operate well on SSB.
Had
> two new ones for use with a pair of KWS-1's on a USAF SSB circuit and always
had to run
> reduced RF gain on SSB
>
> Bob, AF2HD

This has also been my experience with my 75A-4.  With the RF gain full-on, the
audio distortion introduced to the recovered SSB audio by the AGC is, to me,
both audible and annoying.

My KWM-2A and 75S-3 are not much better.  I find that I need to run the RF-gain
of both of these at reduced levels to keep SSB distortion to a level I consider
to be acceptable.  At first I thought this was a problem with my 75S-3, and I
spent a week trying to run down the source, believing that something had gone
out-of-spec, but without any luck.  Eventually, a friend brought over his 75S-3
so that I could run some side-by-side measurements.  Low and behold - his
receiver exhibited the same distortion!  Two receivers - same problem...I
decided to assume it was a design problem and not waste any more time on it.

Even modern transceivers can have AGC-induced distortion problems.  My FT-1000D,
in my opinion, has very annoying of distortion artifacts introduced by the AGC
circuit.  Unmodified, it sounds terrible (to my ears), given the big bucks
charged for it, even in the SLOW AGC position.

Do other receivers sound better with respect to this kind of distortion?
KWM-380 sounds pretty good, as does my 651S-1.  51S1, if I recall, is quite nice
(but I haven't listened to it in some time - it needs repairs).  Interestingly,
my favorite receiver (for its sweet sounding audio) is the Drake 2-B.

Admittedly, I'm very critical when it comes to audible distortion, and to others
the distortion I hear may not be perceptible.  A good friend who also has an
FT-1000D, can't hear its distortion.  It's all a matter of perception.

- Jeff, WA6AHL