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M0VGA's picture
Sat, 28/01/2017 - 12:02 -- M0VGA

Testing Three Antennas Simultaneously using WSPR with WSPRlite

As someone already interested in WSPR and running a WSPR RX station 24x7 I bought a Sotabeams WSPRlite and really enjoyed experimenting with QRP TX using various antennas. I then decided to buy two more and assign one of my three call signs to each in order to allow testing of three antennas simultaneously at the same QTH here in IO93fx, 170m ASL. No A/B (or even A/B/C!) switching here, just a simple, flexible and relatively cost effective solution given the good value of the WSPRlite beacons that can be used for more test scenarios in the future.

I set up all three WSPR beacons on 40m using 200mW power over a measurement period of 6 days with antennas assigned as follows:

  • M0VGA – OCFD (Aerial-51 404-UL) in “inverted-V” formation, external.
  • 2E0WFM – OCFD (Aerial-51 404-UL) loosely strung around loft space.
  • M6WFM – Magnetic loop (AlexLoop) inside conservatory.

The two Off Centre Fed Dipole antennas have the Sotabeams Low Pass Filter (LPF) inline to filter erroneous transmission of harmonics, the mag loop doesn’t require that due to it’s high “Q” factor.

It comes as no surprise that the external dipole (M0VGA) fares much better than the compromised dipole in the loft (2E0WFM), or the mag loop (M6WFM) in the metal-framed conservatory at ground level! What might be surprising though it that the magnetic loop did OK at all (especially on 40m) and tracked the loft dipole fairly closely on the DX10 graph. I’ve not managed to make a voice QSO with the mag loop ever, and the graphs show why that’s much less likely than with the external dipole, at least on 40m during this measurement period which is probably typical. I’d love to try a mag loop like the Cirro Mazzoni but there are XYL, QTH and £ constraints there L

Pictures attached show amongst other things the “DX10 graphs” (calculated as a mean average of the 10 furthest spots) on the Sotabeams website.

You can see my original review of the Sotabeams WSPRlite on my club’s website here, and my WSPRlite LPF build here.

Next steps for me: now I have a baseline for all three antennas on 40m, I can go on to measure their relative performance on other bands (20m might help close the performance gap between my antennas given their sweet spots due to arrangement at my QTH) and can also be used to monitor propagation across three different bands simultaneously to see real-time QSO opportunities.


28 January 2017