[ARC5] AGC in the AN/ARC-5 receivers.

[Kenneth G. Gordon]

On 3 Nov 2013 at 15:38, Mike Hanz wrote:

> > particularly effective, and I was simply wondering why. Call it
> > another example of my inordinate curiousity, I guess.
> 
> Okay, thanks very much for the elaboration...I see where you're coming
> from now.  Please understand that I wasn't being critical...just
> simply seeking the background behind your question.

Oh, I understood that OK, Mike. No offense taken at all.

> > at least for AM work.
> 
> I couldn't agree more.  Of course, the AN/ARC-5 receivers were
> designed to be connected to a plethora of control boxes which had
> audio gain controls, some of which had *both* audio and RF gain
> controls - like the C-38/ARC-5.  I assume you were talking about using
> the receiver by itself.

Yes. As most hams would have done. I doubt if many had control boxes.

> Well, it may or may not be a bit high at 30uV for _ham_ use /in that
> particular receiver design/, as you suggested above.

Actually, I don't really think it is at all. I think it is probably just about right, in 
fact.

>  It all gets back
> to what results are to be expected.  I've never owned one of the
> modern Japanese receivers, which may provide the benchmark that you
> are using for defining "particularly effective" AGC,

No. Not at all, in fact. In my opinion, most Jap transceivers have AGC's that 
are not particularly good for much. They have too many compromises built 
into them.

The BEST AGC I have seen in many years of looking was one designed by 
Chuck Hatch for his R-390 and implemented very simply. It has almost 
instant attack, no overshoot at all, and is easily controllable to any setting 
one could desire. It was written up in ER magazine some time ago.

> so I don't have a
> particularly good idea what perfection really is.   I notice the AVC
> curve for the SX-28-A below, for example, has its knee close to
> 1,000uV!

Gee...!!!!! 

>  My other thought is that some tuning of the circuit might be
> done with tacked on components to lower that threshold if so desired. 
> It couldn't hurt a hacked receiver any further...

Well, what I have been doing it taking ARC-5 receivers which have been so 
badly hacked that they are now literally unusable, "restoring" them to useable 
condition, and then experimenting with some ideas for them.

Those that I have left here are literally junk, usable by anyone less stubborn 
than I am for nothing but parts.

Just FYI, I have even had to replace ball-bearings in tuning capacitors, both 
those little tiny ones and the larger ones.

It IS fun, though, to take a total piece of junk and make a working receiver 
out of it.

Ken W7EKB