LNB locked to 25MHz, but tune frequency seems off....?

  • I am experimenting with a ready modded LNB from qro.cz that can be locked to a 25MHz reference up the one RX coax to the LNB. It seems to work well, but there seems to be a frequency offset. I have, in the below the dish cabinet, a Leo Bodnar GPSDO with 2 outputs. One at 40MHz is an external reference to my PlutoSDR, and one at 10MHz that goes to the qro.cz combined injection box and BiasT. Inside this box from qro.cz I assume there's some form of multiplication up to 25 MHz. There's certainly a chip in there.

    However, in use, whilst TX frequency is perfect, (measured with a GPS locked, and in calibration frequency meter), the RX is off a tad, compared to the QO-100 beacons. I am not sure why and am currently using SDR Console's Geostationary Beacon locking ability to correct this. I had expected locking the LNB LO to a GPSDO would not require this, am I missing something here please?