This is what feedback is for.
>? I'm not sure how you design an agc amp to work against two such different slopes.?
If the audio is not loud enough then increase the control voltage, up to a max of 10 or 12v.
Should be easy enough with an op-amp.
Though I have not done this, or ever designed an AGC system.
So take this advice with a large grain of salt.?
If for some reason you can't use the 10v swing, then could add a 5dB amp prior to the attenuator.
Or maybe goose up the bidi amps for a little bit more gain.
Farhan's notes here:??
say that the front end LPF has 1dB loss, the mixers 7dB loss, the bidi amps 16dB of gain.
I'm not sure exactly what the loss is through the crystal filters, let's assume 4dB.
So the front end up lines up as follows from antenna to the input of the demodulator:
-1dB -7dB + 16dB -4dB -7dB +16dB -4dB? = +9dB
I guess the demodulator is going to be something like another 7dB loss, as it's just another mixer.
So the entire receiver up to the audio pre-amp has very close to zero gain.
I'm thinking the attenuator should be in series with R37,?
the BAP64Q is designed for use in a 50 ohm environment.
Jerry, KE7ER
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On Mon, Mar 26, 2018 at 09:32 pm, Tim Gorman wrote:
Jerry,
Looking at Figure 6 the useful part of the graph is from about .3v to
2v for control voltage. That gives you a swing of 60db loss to about
5db loss, about 3db per tenth of a volt of agc. You need a swing of 2v
to 10v to get from about 5db loss to 2db loss or about .03db per tenth
of a volt. I'm not sure how you design an agc amp to work against two
such different slopes.
The lines on Fig 4 are like elevation lines on a topographic map. When
lines are close together you have a steep slope and when they are
further apart you have less steep slope. Designing an agc amp to work
with two such different slopes, one slope before a threshold and a
different slope after the threshold is probably not a trivial thing to
do.
I'm not saying you can't do it. I just can't get my head wrapped around
how you do it at 11:20pm at night!
tim ab0wr
