QO-100 Experiments – QRP Transmit Converter

Having spent some time listening to the QO-100 satellite using the Goonhilly WebSDR facility and my own temporary receive solutions, I decided it was time to try generating some RF and get a signal up to the satellite.

I was aware of stations transmitting using a number of 2.4GHz based modules available on various websites such as eBay. This looked an interesting approach and the modules could probably be repurposed if things didn’t work out or I decided to adopt a completely different route.

I decided to purchase the following modules:

This is a fairly conventional transmit converter setup. I did however want to use 144MHz as the IF rather than 432MHz. The reason for this being that I already have a GPSDO locked low power 144MHz IF setup that I use with other transverters. This choice of IF would mean that good filtering would be needed to ensure that the final output on 2,4GHz was acceptable and any unwanted spurs were well down on the wanted signal.

This photo gives an idea of the basic setup that has evolved so far:


If we follow the RF route, things start off with a 10MHz GPSDO derived source being input to the tin-box on the left. This box houses an Arduino Nano and the ADF4351 synthesizer board. This produces approximately +4dBm output at 2256MHz which is fed into the ADL5350 Mixer module. In addition to the 2256MHz input (via blue coax cable), 144MHz is input at +15dBm on the spare unterminated SMA socket. This results in the wanted 2400MHz output which is then fed into a 2400MHz BPF (bandpass filter). The output of the BPF is then fed via the long semi-rigid length of coax into a SPF5189Z Low Power Amplifier. These amplifiers seem to have a gain of typically +10dB. The output of the first amplifier is then fed into a homemade 2400MHz pipe-cap filter and then finally into a second SPF5189Z.

This current setup is at present far from being optimised in terms of physical layout and minimal losses. As a result of the numerous SMA connectors / adapters / interconnecting cables and filtering the final output power is approximately +7dBM (5mW) but it’s an acceptable 5mW at 2400MHz with all spurs as best as I can tell >55dB down on the wanted signal.

To be continued…

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