Active monopole + RTL SDR + RPi Spyserver experiment

A brief experiment was conducted of a remote HF receiver using:

  • 1m active monopole;
  • RTL-2832U v3 SDR dongle;
  • RPi 3B+ running Spyserver; and
  • SdrSharp client.

Above is the active whip antenna. Not optimal mounting, but as you can see from the clamps, a temporary mount but one that does not confuse results with feed line common mode contribution.

Above is the remote electronics, the RPi 3B+ and RDL SDR dongle, and underneath the power supply for the active monopole.

The initial trial was on 7MHz, and was a total failure due to extreme level of RFI from the RPi itself. The two RPi power supplies tested were noise tested on a dummy load and were OK, the noise comes from the digital signals on the RPi board. A Kenwood R-5000 receiver was connected to the active antenna, and noise floor was relatively low until the RPi was plugged in.

Above is the SdrSharp screen, extreme noise level and no signals could be heard (though a local transmitter on low power verified that the receiver was working).

The emissions from the RPi, were so high that it is really unsuitable for this purpose, it would be very difficult to reduce emissions by the needed more than 40dB.