I note my P3's amplitude readings are about 6 dB low-- that's with the IF output switched off. I'm not sure how to calibrate it.
Even so, the P3 gives great insight into signals and their amplitude. Let's say you calibrated your S-meter to read S9 with a 50 uV input signal. Fifty microvolts is -73 dBm in 50 ohms. A CW signal which is S9 on your S-meter should peak at around -73 dBm (plus or minus 3 dB) on the P3. But an SSB signal which is S9 on your S-meter will not. It will be several dB less than -73 dBm on the screen of the P3. Why? A CW signal is one pure tone, and all of the power is concentrated in that one tone, whereas the human voice contains many different tones or frequencies within the 2 or 3 kHz bandwidth of the SSB signal. To measure the power in the SSB signal requires integrating or summing all of the power of all those different tones to come up with the total. Any one frequency falls far short of -73 dBm, but the total is far greater and should approach -73 dBm. This is easy to see on the P3. As an example of the above, if you had (10) -100 dBm in-phase tones in a 3 kHz bandwidth, the total channel power would actually be -90 dBm, 10 dB higher due to the summation. If the number of tones is greater than 10 as it can be with the human voice, the total can be even higher, that is, the difference between any single frequency and the total becomes greater. Fascinating. One final thing: my son is studying for his Technician license, and I plan to show him some real AM, SSB and CW signals on the P3 to help him see the difference. Do you suppose I can write the P3 off as an education expense? :^) Al W6LX ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
