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I am in the process to do the following on my "original" BITX40 (yes I got one from Farhan):
use an opamp with a gain of 10 (20 dB) and an audio AGC system using a SSM2166.
Fortunately I purchased a pcb from ZL1CVD with the DIL chip via ebay years ago... Unfortunatley he does not sell this pcb any more...
The SSM2166 has a dynamic range of 60 dB, the opamp in front of it instead of the first discrete amp aftger dthe demod will amplifiy the audio into a range the SSM2166 can handle.
Also the SSM2166 has a provision of outputtting a AGC voltage -- may be used for driving an S-meter.
Let´s see what comes out.
Am 10.12.2017 um 21:33 schrieb Jerry Gaffke via Groups.Io:
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
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?