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Author Topic: BIFET Compressor Mic and IC-718 by WA7JHZ  (Read 31130 times)
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Steve - K4HX
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« on: October 30, 2018, 02:24:25 PM »

The attached JPG shows what I've been doing with my BIFET compressor mic and Icom IC-718. Followed by a decent linear amplifier, it is hard to tell the difference between it and a modified broadcast AM transmitter.


* IC-718 AM Modulator and BIFET Compressor Mic 10-19-2018.jpeg (429 KB, 1820x1140 - viewed 1591 times.)
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Steve - K4HX
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« Reply #1 on: October 30, 2018, 02:26:18 PM »

The attached JPG shows a reversed order between the 4 kHz LPF and AGC/peak-limiter on my proposed compressor mic circuit. The complex phase shift of the LPF occurs before the AGC/peak-limiter, and its noise and distortion are low enough to allow this. Note that I've also added a positive modulation control circuit (U12).


* BIFET Compressor Mic with no Boost Pos+Neg dynamic 10-30-2018.jpeg (298.18 KB, 1920x1080 - viewed 1519 times.)
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ab3al
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« Reply #2 on: October 30, 2018, 05:48:00 PM »

does this improve the audio bandwidth of the transmitter or just controll the agressive agc. looking at it from my phone cant see to well
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Steve - K4HX
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« Reply #3 on: October 31, 2018, 11:07:51 AM »

This circuit is to control modulation levels. There is a 4 kHz lowpass filter to limit higher frequencies.

In general, the only way to improve the audio bandwidth of a transmitter is to modify the transmitter, not with external boxes. Yes, an equalizer can overcome some inadequacies but there are limits to this approach.
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