QO-100 Station Build Journal

  • Hi everyone,

    I've started to put together a station for the QO-100, and since I don't have a personal blog, or a personal web page, I'll try to document my progress here. Hopefully it's OK with everyone.

    The setup will be based on an Adalm Pluto.

    I have couple useful LNB's at hand, that I will modify for an external 25MHz reference.

    First step, I made a board that serves three functions.

    1) Bias-T injection for the LNB DC

    2) 740 MHz RX filter

    3) Source for the 25MHz LNB reference

    Just as a personal preference, I didn't choose to use GPS locked PLL. Instead, I decided to use a OCXO for the LNB 25 MHz, and another OCXO for the Pluto.

    Picture of my bias-T/OCXO/filter board.

    Frequency response of the 25 MHz LPF, and the resulting waveform.
    (notice that in the oscilloscope FFT, the y-axis is 20dB per division, so most harmonics are about -70dBc)

    Mikko, AB6RF

  • It was the Thanksgiving holiday here in the US, so I had time again to work on this stuff.

    Today I tested my “EBay amplifier”.

    Very low cost, and has a nice and solid machined aluminum housing, but no heatsink.

    So my first step was to find suitable heatsink stock and drill the mounting holes.

    I don’t have metal machining tools, just hand saws and drills etc. so the heatsink machining is not pretty but it works.

    The amp works fine, and puts out good power.

    With 26 volt VDD, I measured 30 W out at -8dBm in.

    The amplifier is not tuned for 2.4 GHz. It’s best at 2.25 GHz, where it has 3.5dB more gain.

    But it’s fine, this is already more than I’ll need, so I'm not going mess the with the matching.

    (The amp also has an internal isolator that is not designed for 2.4 GHz, it would be easy to remove the isolator and get more gain, but there’s no need)