80 and 160 m band

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  • Updated 3 years ago
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Why do I get this signal, sinusoidal, on 80m and 160m bands with my ZS6BKW/G5RV multiband antenna?
On all other bands the display is normal.
Is it propagation related?
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Roger Sjölin

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Posted 3 years ago

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Jim Gilliam

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Perhaps it is related to the impedance of your antenna and the signal strength varies in accordance to the amount of noise/signal arriving at the antenna terminals?
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Stan - VA7NF

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Most signals I see of this nature are EMI from switching devices.  In this case, with so narrow panadapter view, is a 40Khz driven source with a fundamental probably down around 200Khz.

The signals at 3.728 and 3.766 are similar, as are 3.722 (just out of view) and 3.762.

Switch to AM and listen to the signal.  Zoom in with the panadapter and measure the spacing; you will likely find it is 60 or 120Hz based(for 60Hz line frequency), or record with Audacity and expand the audio for a cycle "signature".  This is assuming it is an EMI signal.

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Stan - VA7NF

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Captured some live information relating to what I see:


EMI results on (suspected) Digital Balast as viewed:


  1. Top slice is on 160M AM Very tight zoom.  Visible are 60Hz spaced modulation that result in a 60Hz buzz

  2. Bottom slice is on the apparent source (or likely the 3rd harmonic of the source) showing its very wide modulation of the same 60Hz signal


Visible in the waterfalls is when the 160M pattern changes there is a corresponding in the source.  As the harmonics increase, by the 160M band it becomes a constant 60Hz buzz with groupings of stronger signals (not visible in this deep zoom)


There are many other EMI sources that are mixed into this view, of which the 270Khz source is the strongest.


The signal from 1.900 was recorded into Audacity, using DAX Audio RX 1, then expanded to view the audio signature of the EMI.  It can be seen the timing between each burst is 16.6ms or 60Hz.  That grouping contains 12 peaks, some muted by the ballast duty cycle, which represent a 720Hz modulation.  Not seen is each of these 1.4ms bursts are made up of square wave bursts (hundreds per 720Hz).  This square wave fundamental of 260Khz modulated by 720Hz and 60Hz parts creates a blanket of noise which is strongest in whatever wiring is resonant.  In my case it is carried on the power line and can be found on my power feed.  I happen to have ferrite beads on my power line into the switch box to reduce it to the S9 levels shown.

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Roger Sjölin

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Thanks
I found it.
It was my Newsky TV28T RTL 2832U/R820T RTL-SDR USB Stick that
coused the problem.
/Roger SA0AND

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