1. Elecraft-K3
  2. Messages

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

Al N1AL
 

Hi Mel,

I'm trying to understand the test conditions. Are the 100W SSB signal and the 1 kW AM signal transmitted from the same station on the same antenna? If not, then no direct comparison can be made.

I can easily believe the sidebands of the AM signal are 20 to 30 dB below the carrier. Say the audio has a 10 dB peak-to-average ratio. Right away that puts the average power of each sideband at 6 + 10 = 16 dB below the carrier, assuming 100% peak modulation.

Furthermore, if the P3 span is 20 kHz, then each display point is roughly 40 Hz wide, perhaps 1/100 of the total sideband, assuming 4 kHz audio. That's another 20 dB.

Here's something to try: Turn on peak hold on the P3 and watch the AM signal for awhile as the program content varies between music, voice announcements, ads, etc. You'll probably notice the sidebands are much flatter and higher in amplitude on the peak trace than on the real-time trace.

Alan N1AL

On 07/02/2015 12:36 PM, farrerfolks@... [Elecraft_K3] wrote:


Yes, Alan, I understand all of that.

Here is the question. Why is the sideband power on AM on the same band,
75 M, less than the displayed signal on SSB.

An example. Watching the 100 watt signal on 3963 KHz SSB signal on the
P3, the envelop of the energy fills the IF KHz window and is smooth in
the display, if the audio is flat, to the top of the same RF level as
CW. With audio frequency variances allowed. While on the same settings
on a AM signal at 3870 KHz at 1KW carrier the sideband are 20 to 30 dB
lower and ragged in display.!!!!!!!!!!! All P3 settings the same......

If my math is correct, 100 w SSB and 1KW AM should have within ~3 dB the
same displayed sideband power level????? Where is my reasoning wrong???

Mel, K6KBE
Join Elecraft-K3@groups.io to automatically receive all group messages.