[TangerineSDR] Getting rid of magnetometer-related RF noise

Bill Engelke bill.engelke at ua.edu
Wed Jun 30 14:24:20 EDT 2021

To all:

You might recall that a few weeks ago I discovered some RF noise appearing on 160 M and 80 M when the magnetometer was hooked up. This was wideband noise on 80M and a birdie on 160M.

Note that I have been using shielded CAT6 cable between the magnetometer base (a Pi-Hat) and the in-ground magnetometer. The noise could be seen clearly in the waterfall on my FlexRadio 6600 connected to my 80M dipole; it was only 1 to 2 s-units, but this might be an issue for DXing.

It required 2 steps to eliminate this noise:

  1.  The ground plane of the R-Pi needs to be connected to an earth ground. This eliminates the birdie on 160M and cuts the 80M noise about in half. Do this by grounding the sleeve of the R-Pi audio jack.
  2.  The remaining 80M noise is due to the Canakit switching power supply that comes in a Raspberry Pi kit. To eliminate that, you must replace the switching power supply with a linear power supply. I found a 4.5 amp linear supply (Pyramid brand, on Amazon $55.79) that has 2 USB jacks (each able to supply 2 amps) plus 13.8 V terminals.*

-73- Bill,  AB4EJ

* There are cheaper linear power supplies, but R-Pi recommends a supply able to provide 3 amps. Linear power supplies able to provide 3 a are not plentiful or cheap. I measured the actual current pulled by a R-Pi 4 B+, and it is around 1 amp. With the Pyramid supply I am powering two R-Pi 4 B+ computers with power to spare, and the switching noise is gone.
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