Cool Radios from the N6QW Laboratories!
2/4/2017 ~ Request for AGC circuit being used. This was supplied to me by PD7SSB who came up with modification to my 20M Shirt Pocket Transceiver Project. It is an audio derived circuit. I have no details for implementing an RF/IF derived circuit such as the W7ZOI Hycas.
2/5/2017 ~ More on the AGC
Tribal knowledge here. The 4.7K Ohm Resistor connected to the output and feeding the diode was replaced by a 25K trim pot in series with a 3.3K fixed resistor. I found that there was too much "AGC" action with just the 4.7K ohm as shown on the schematic. The 25K pot was wired as a variable resistor (If you have to ask how to do that --turn off your soldering iron). Thus the range is 3.3K to 28.3K --now giving you a span of adjustments. Hold off sending me an email as there will be some who suggest just using the 25K pot with one end to ground and the center wiper to the diode and the other end connected to the LM386 output. That is not what I did and I leave that to others for experimentation. The photo below the schematic is actually what is on the schematic including the microphone amplifier, audio amp, AGC and S Meter circuitry.
2/5/2017 ~ More on the AGC
Tribal knowledge here. The 4.7K Ohm Resistor connected to the output and feeding the diode was replaced by a 25K trim pot in series with a 3.3K fixed resistor. I found that there was too much "AGC" action with just the 4.7K ohm as shown on the schematic. The 25K pot was wired as a variable resistor (If you have to ask how to do that --turn off your soldering iron). Thus the range is 3.3K to 28.3K --now giving you a span of adjustments. Hold off sending me an email as there will be some who suggest just using the 25K pot with one end to ground and the center wiper to the diode and the other end connected to the LM386 output. That is not what I did and I leave that to others for experimentation. The photo below the schematic is actually what is on the schematic including the microphone amplifier, audio amp, AGC and S Meter circuitry.
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| N6QW Two Band XCVR: Mic Amp, Audio Amp, AGC, and S Meter Board |
73's
Pete N6QW