20 June 2019

Thermal isolation for HB100 transmitter

The actual frequency of an "HB100 10 GHz radar doppler HAM RTX module" is very sensitive to external factors: supply voltage, proximity, temperature.

Voltage is easy to stabilize. Proximity too, and if the IF port it becomes less sensitive.

On the other hand, temperature has a devastating effect, both on short and long term. On the long term, the frequency will drift until the HB100 reaches a constant temperature. But even a quick breeze will produce a snake on the waterfall. So, in order to minimize the effect, I found my way to add short-term thermal inertia to my 10 GHz transmitter:

Transmitting end on 10 GHz, modulated on the IF port.

Variations on long term ("minutes") will still occur, but at a slower pace so that it's easy to do a manual AFC on the receiving side. And the trick is to let it reach a "working" temperature before use and avoid variations over the whole QSO.