QO-100 Build but rf issues stopping Rx during Tx

  • Hello,

    I've built a Pluto+ SDR QO-100 setup, typical design: Pluto+, CN0417, SG Labs PA, and ice cone to 80 cm dish. Then a bullseye LNB on receive, as below:



    I'm using SDR Console, but I've found when I transmit I stop receiving - the waterfall goes blank and I can't hear anything.

    I then tried using an external 12 V battery for the biased-tee and then everything was fine, I could recieve whilst transmitting, so I assumed the PSU maybe wasn't suitable.

    I then tried powering everything from the battery but the same issue returned. This leads me to believe there's 2.4 GHz rf coming back into the setup, entering the biased tee and causing interference in the Pluto+ (?).

    I checked the VSWR of the coax and ice cone downstream of the PA and it was 1.1 across 2400.000 MHz to 2400.500 MHz.

    I'm not sure what to check or test now - any suggestions?


  • Thanks Wilhelm, that is already set.

    The issue isn't SDR Console, but hardware side. As I said I've got it working when I have separate power supplies for the biased tee and the rest of the equipment, but when they share the same power supply I lose Rx on Tx.

  • Hi,

    I had the same problem.

    I use a 12V input to power the BiasT for the LNB, the preamplifier/PA stage, a fan, and the Pluto+ SDR with voltage converters. This setup has plenty of room for EMI/EMC issues.

    Initially, I had a cheap LSP-02G LNB, which sometimes kept losing the beacon stabilization during transmission, although RX worked visually fine during TX.

    I upgraded to a Bullseye LNB to fix the loss of beacon stabilization issue, but then I experienced only noise in the SDR console during TX. With a separate power supply for the LNB, both RX and TX worked perfectly.

    I believe the Bullseye LNB is more sensitive to power supply interference than the LSP-02G. Although this interference likely caused the beacon stabilization issues with the LSP-02G as well.


    I added a step-up converter before the BiasT for the LNB, and all problems disappeared. The step-up converter probably filters the interference at the input, preventing it from affecting the output.