Re: ubitx AGC?

Jerry Gaffke
 

No AGC on the production uBitx.

The original schematic for the uBitx here:  http://www.phonestack.com/farhan/ubitx/ubitx.html
shows the second half of the TDA2822 used as an AGC amp, attenuating the audio through the 2n7002 nfet.

Apparently Farhan found that he preferred using the rig without that particular AGC scheme.

As Henning/DK5LV has shown in the distant past, that npn audio pre-amp stage for rx is a dynamic range bottleneck.
if AGC is applied after it around the volume control as the above AGC scheme does.

I think something like the original uBitx AGC level detect could work, but we'd be better off if the attenuation occurred 
somewhere prior to the npn audio pre-amp:    https://groups.io/g/BITX20/topic/5913954

Jerry, KE7ER


On Sun, Dec 10, 2017 at 12:01 pm, <jettoblack@...> wrote:
Does the uBitx have AGC? It was discussed in some of the previous threads, but the website only has this comment: "The audio amplifier uses one section of the TDA2822 – a quieter device compared to the LM386. It has two audio channels, the second channel is kept free for use as an AGC audio amplifier."  I am not sure if that means an AGC can be added later, or is it already present?

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