>From time to time a buddy will enlist my help in doing some signal strength monitoring. That can be a useful exercise when working with stable signals to compare various antennas at least over the path between that station and mine.
When I do that I turn off the S-meter because I turn the AGC off. I put a step attenuator in the antenna line and select some nominal amount of attenuation - say -20 dB. Then I connect my DMM or a 'scope to read the AC voltage at the speaker jack and note the audio his signal produces. That can be a tone transmitted by him SSB or, best, the beat not produced from his CW carrier. He makes a change and I adjust the step attenuator to regain the *same* voltage at the audio output. The attenuator shows me the dB change directly. I've considered building an appropriate audio voltmeter into a homebrew receiver but the need doesn't come up often enough to justify it. I have built step attenuators into my receivers at the antenna jack that I use for a RF gain control. I've often used 6 dB, since that is about the smallest definite change in gain one notices in normal operation with typical QSB, etc. A rotary switch attenuator is handy for that; just turn the knob. I used two separate -40 dB attenuators cascaded with it, each with a simple toggle switch, for a total of about 116 dB attenuator. Of course, it's necessary to pay attention to isolating the inputs from the outputs for the attenuation to be accurate, especially on the higher frequencies. With a rotary switch, that starts to get difficult above 40 dB, so I limit the range to that value and add to well-isolated single stage -40 dB attenuators in series with it. That attenuator at the antenna input become the main receiver gain control. Like days of old, the audio gain is adjusted to the level just below that at which the internal noise is audible, then the RF Gain - the attenuator - controls the loudness of signals heard. That makes for a lazy operator. If I notice that I have to switch in, say, another 6 dB of attenuation as the other station's signal builds up during a QSO, I can observe "UR SIG UP AN S UNIT HR OM..." during the next xmission. I suppose I could calibrate the attenuator in "S-Units". That's definitely not a new idea. A popular regenerative receiver from the 1930's featured direct signal strength readout. They calibrated the volume control! As the control was turned, the pointer passed "9" down near minimum gain and worked through 8, 7, 6...to "1" at maximum gain. One tuned in a signal, set the gain for comfortable listening, and then read the "S" report directly from the pointer on the gain control knob! Ron AC7AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
