Re: [Elecraft_K3] K3/P3 video display on AM vs SSB

David McClain

… I’d love to hear the answers from somebody who really knows… by my speculation is that they need to drop the power output on AM because it emits a steady carrier, while in SSB mode those peaks are ms duration peaks, and can be easily handled by the instantaneous power available from capacitors and with endurable dissipation in the final transistors. But for those power levels under steady carrier conditions it would be intolerable to the finals and the power supply is insufficient.

- 73 de Dave, N7AIG

On Jul 3, 2015, at 10:29 AM, farrerfolks@... [Elecraft_K3] <Elecraft_K3@...> wrote:

OK, Alan, Thanks for the input.

Here goes.  I am monitoring a friend near by, 15 miles.  I took care to have him set up the 100 W SSB station and his 1KW AM station like this.

In CW mode, send a 100 W measured carrier.  I recorded the level on the P3.  Then had him transmit normal voice levels and the peak SSB audio components reached the same level as the CW signal on the P3.  

Then I had him set up his RCA AM transmitter to monitored 1 KW carrier on the bird.  I recorded the level on the P3, ~1-2 dB of 10 dB more than the CW signal.  Same antenna on both.

I had him transmit a 1 KHz tone 100 % modulated and yes, the 1 KHz was 6 db below the carrier at 1 KW on the P3.

Now I had him talk to the 100% modulation point on the AM transmitter.

With the Peak averaging set to max, the side band AM signals were 20-25 dB down from the carrier.

If the premise is that a 100% modulated AM signal has 50% of the power in the sidebands and 25% on each side, that is 500 watts total audio and 250 watts on each side.  So the level should be only 6 dB down from the carrier.

The only difference is the complex audio components vs the signal tone.  So why is the SSB signal peaking at the 100 watt level and the AM signal 10 to 15 dB lower?

Comments appreciated....

Mel, K6KBE

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