[TangerineSDR] Magnetometer RF testing, additional results

Bill Engelke bill.engelke at ua.edu
Tue Jun 1 12:15:00 EDT 2021

Here is a follow-up to my last email regarding possible RF interactions with the magnetometer.  A couple of suggestions came in from the community:

  1.  Ward Silver, N0AX, recommended to test by transmitting with a dipole near the magnetometer in several configurations, on 2 meters with 50 w.
  2.  Tom McDermott, N5EG, recommended to look for RF noise being generated by the magnetometer that might get into your station receiver.

Here are results of doing such tests:

  1.  I built a 2-m dipole specifically for this so that I could test with the antenna (a)broadside to the magnetometer, (b)vertical to it, and (c) pointed towards it. (photos) The antenna was located about 10 feet from the magnetometer, which is buried at 2 feet in the soil (its standard installation as tested by Jules and others), and connected to the station with shielded CAT-6.

Broadside configuration

[cid:image004.png at 01D756D6.2EB4CD30]

Vertical configuration:

[cid:image005.png at 01D756D7.049AA500]

Straight-on configuration

[cid:image006.png at 01D756D7.049AA500]

The antenna was connected via a new 50 foot RG-8 cable to an Icom IC-706MKIIG, set to high output (50 watts), 145 MHz. I did my best to do what Ward suggested.

Results: I never saw the magnetometer readings change when I keyed the rig; this was the same for the 3 different antenna angles. I have to conclude that the magnetometer is not sensitive to 2 meters.

  1.  Using the FlexRadio 6600, I looked for noise being generated by the magnetometer on all ham bands from 160 m to 10 meters. I looked for wide band noise by watching the waterfall and turning the magnetometer on and off. If I saw noise appear, I tried turning the magnetometer off and on to see if the noise would come and go with being connected to the magnetometer base card on the Raspberry Pi. I used the appropriate antenna for each band (i.e., the one I use for my station), as follows:  (160 M) - multiband vertical, (80M) halfwave dipole at 15 ' (20 feet away) and also multiband vertical about 50' away, (60M) multiband vertical, (40 M) double bazooka inverted vee, (20M through 10 M) DX Engineering Hexbeam on 50' tower.

Results: First the good news: I never saw wideband noise attributable to the magnetometer on the bands 60 meters and higher in frequency.   I did see noise on 80M and on 160M.  The magnetometer does generate noise of about 0.4 db as shown on the FlexRadio s-meter on 80M. (Note that this is a severe case, as the 80 M dipole is only up 15' and about 20' away from the magnetometer - but this is probably a typical situation). On 160 M, the magnetometer generated 1 db of noise.

Screenshot of 80 M result using dipole

[cid:image001.png at 01D756D4.9FD34E80]

Screenshot of 80 M on multiband vertical

[cid:image002.png at 01D756D5.12202BC0]

Screenshot of 160 M, multiband vertical

[cid:image003.png at 01D756D5.6F866360]

I suppose that we would recommend turning off the magnetometer if you are working DX on 80 Meters; possibly separating the magnetometer from the antenna might also help, but I was not able to test that.

-73- Bill,   AB4EJ
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