Here's some antiqueradio guys talking about AVC, it is all about controlling RF and IF gain:
This is now commonly called AGC.
    https://www.antiqueradios.com/forums/viewtopic.php?f=6&t=263244
    http://www.johnsvintageradio.com/notes03.html
    https://www.radioremembered.org/detector.htm
    https://www.radiolaguy.com/info/AVC.htm

That last link mentions rheostats on filaments to control gain, though this was not commonly done.
See the final post here:  https://www.vintage-radio.net/forum/showthread.php?t=60467
 
I doubt there are many radios with AVC/AGC that ever did other than adjust the gain of RF and/or IF stages.
There's no real advantage for AGC to mess with the audio stage gain, and it has the disadvantage 
that this does not solve signal overload in earlier stages.  The uBitx and Bitx40 AGC schemes in the forum
often adjust the audio gain, but only because it's the easiest thing to slap in there as an add-on.

Can somebody point to a passage somewhere that claims AVC and AGC are different animals?
Not that it matters much, but I don't want future discussions of AGC schemes on the uBitx/Bitx40
to spend days arguing about the rather silly distinction of whether the controlled gain stage
happens to be operating at 1khz or 12mhz.   

Jerry, KE7ER


On Sat, Apr 20, 2019 at 08:32 AM, Joe Puma wrote:

I’m taking this discussion in and learning. Jerry you always find a way to educate the group when topics fly by. As I’ve been learning I understood that there is automatic volume control and automatic gain (RF) control. I learned that RF gain control is better to use. For me I just want to be able to hear weak stations and clamp down on the real close ones.  But as to your AGC AVC discussion and why we don’t properly label the two. Show my a radio that has AVC on the knob. I’m a relatively new ham but all I’ve ever seen is AGC. Maybe some of the older tube boat radios used AVC, I don’t know but it’s easy to label it all AGC because I’ve never seen a AVC lable on a radio knob. 

 

The AGC/AVC thing probably can’t be resolved at this point, but it would be unambiguous to me if folks just called their AVC/AGC IF-derived or audio derived.

Virus-free. www.avg.com

And because I’m a dinosaur I want to believe a decent IF-derived system is better, though I have to admit the ubitx audio-derived stuff is pretty good. :)

 

On Apr 20, 2019, at 2:52 PM, Sam Tedesco <stedesco619@...> wrote:

On the pspectrum page, tm0 and tmrDisplay populate the empty boxes that show up on full display. If you go thru the nextion code for those two, you'll see a few commands 'fill' and 'xstr' followed by comma delimeted sets of numbers. The main command structure for 'fill' is (x,y,w,h) and the fifth num is a color code. You'll have to run the 2.4" hmi in the editor and figure out the smaller horizontal boxes above and below the graph area. From there, you'll have to calculate your new dimensions based on the 480x320 pixels and subtract out your existing controls to get your new coordinates.

I have to look up the parameters for the 'xstr'...but, probably similar
PITA, but not bad at all. I don't have the i2c setup on my machine so I'm running blind. It's all Nextion code.