[ADXA] noise issue - take 2

[Mark Graves]

What does the audio component waveform look like? If line noise, it would most likely have 120 hz pulses well defined by some sort of arc on the positive and negative peaks. The long wavelength that you are tuned to could peak and null depending on how the signal is launching off the horizontal and vertical lines while traveling a wire for possibly thousands of feet. Think “long wire and traveling wave” antenna models. As you drive down a noisy line listening to an AM radio, often you see these peaks and nulls of noise. They become closer (faster) until it mixes to a steady signal. That’s when you just drove by the offense. Think something similar to Doppler effect.

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From: adxa-bounces at mailman.qth.net <adxa-bounces at mailman.qth.net> on behalf of Jussi Eloranta via ADXA <adxa at mailman.qth.net>
Sent: Monday, March 23, 2026 3:45:28 PM
To: 'ADXA' <adxa at mailman.qth.net>
Subject: [ADXA] noise issue - take 2

Hi,

Just recorded the 160m noise on the panadapter. I was expecting it to be
wide and all over the place. However, see attached. Bog is beverage on
ground (wideband resonant) and invL is my inverted L (narrow resonant;
SWR only OK at the bottom of 160m). You can see that both spectra are
surprisingly narrow. They have center around 1.840 MHz (FT8 160m
frequency, of course!) and extend to the sides by about 100 KHz. I was
initially looking at this with my inv L and thought that, OK, that must
be just the antenna response I am seeing. But now that I see the same
thing with the BOG, I am not so sure what to make of this. If I scan
more to the AM band, it seems that it is clear over there but then going
further down in frequency I find another similar spot that is noisy.

So, is this power pole noise after all? And if not, what on earth could
it be? It has the characteristic raspy tone with multiples of 60 Hz in
it. On AM it sounds like the typical power line hum. All that fit power
pole noise but the spectrum does not - I think. Furthermore, I do not
hear this noise at all on 80m. This is not from my shack as I have
turned off power and used the radio on battery power. I do hear
something weak on 6m from far away but I have no idea if this is the
same thing as what I see on 160m.

Jussi (aa6kj)
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