Interesting P3 Observation


Bob McGraw - K4TAX
 

With recent communications and observations with my P3, I see lots of SSB signals that contain a lot of information below 300 Hz.  Much is centered around 200 Hz or so.   The point is, the fact this consumes a lot of nonessential transmit energy by worthless signal occurring in the less than 200 Hz frequency range.

One of the fellows commented to me:   " In your second point, {Still, it is representative of the TX BW and audio response.}  it seems that the majority of SSB signals do not come anywhere close to filling their passband.  Most of the energy is crowded up against the suppressed carrier frequency [low frequency audio], which is not real effective in communications.  In the "Olden Days," we'd tailor the speech amp and "build-out" the modulation transformer to get a good AM communications response.  Today, my radio has a TX equalizer and I don't have to plug the soldering iron in."

I know Jim, K9YC, has strongly advocated attenuation the three lower bands of the TX EQ as much as -16 dB each with the 4th band attenuated -9 dB to -12 dB.     I find this to be correct and does add a lot of "cleanliness" and articulation to ones transmitted audio.  And it does not affect the natural sound of the male voice.

I have attached a P3 capture of one of the represented signals.   Note the first peak to the right of the carrier frequency is 200 Hz and is clearly the most dominant part in the audio spectrum.  The green vertical bar represents the receiver bandwidth of 2.7 kHz.

73
Bob, K4TAX


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