Goobay LNB mod, Rafael RT330 chipset

  • Hello folks. I've been assembling pieces for a QO-100 station and wanted to check here if anyone can confirm my plan for my LNB. I have a dual input Goobay LNB (bought about two years ago), and want to modify it to send a 25 MHz reference up one of the downlink cables. I'm using multi-channel SDRs for receive so want to hardwire each LNB output to a specific polarization to remove the need for sending a control voltage up.

    The addition of a diplexer to separate the 740 MHz RF from the external 25 MHz seems straighforward enough, but wanted to check if I could feed the 25 MHz directly into one of the RFIC's reference pins (if so, which pin?!), or if I'll need a transformer to create a differential signal. If so, can anyone recommend a small transformer?

    I haven't found any photos of the PCB of this particular model, so here's one. The RF section is very straighforward with a two stage LNA and some filtering.

    The output section of the PCB is also fairly simple, but there are a few details I wanted to check on.

    First is the question about the need for a transformer for the 25 MHz reference?

    Second, I'd like to hardwire each output to a single polarization. I can see the two (likely) control pins. I can probe around and figure out what voltage needs to be on each for V and H polarization selection, but while I'm here thought I'd ask if anyone knows already.

    Does anyone sell, or have design files for, a combined Bias-T and reference frequency injector? A simple circuit but I'd rather avoid recreating one if it's easy to get.

    Thanks! I'm excited to get up and running.