Re: ND6T AGC Troubleshooting

Don, ND6T

Just to make sure, I opened up my uBIITX and checked voltages. With a 50 uV (S9, -73 dBm) there was about 1 to 2 millivolts RMS on the top of my volume control. But with 1,000 uV (about S9+27, -46 dBm) there was a substantial .6 VRMS at the top of the volume control. That gave a nice 1.1 VDC at the AGC bias with it active. This is the dual mosfet model so it was giving me a pleasant output. That will hold up to nearly 4 volts before it runs out of control headroom and cannot attenuate any more at around S9+50! Your single mosfet should hold it up to S9+20 at which point that test point will read about 4 volts DC. Those measurements were taken with the signal about 1 KHz from the displayed frequency, just a constant CW tone. That allows the digital meter to track without resorting to peak holding.

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