Please appreciate that my technical knowledge is limited and I have no microwave experience at all.
I have been putting together a QO-100 system centered around a LimeSDR mini. The receiving part works fine. The transmitting part doesn't. The LimeSDR does transmit (checked with 145 MHz receiver) but no real power comes out of the 2.4 GHz system.
The TX chain begins with the LimeSDR, followed by a 100 mW F1OPA amplifier, followed by an EDUP "8 watt" final and a filter finally into a dual patch.
The EDUP amplifier has the TX modification, so when powered is permanently switched on TX.
Since I don't have either a 2.4 GHz receiver or a power meter, my investigation is limited to measuring current drain.
1. F1OPA and EDUP amplifiers draw 380 mA on standby. This is entirely due to the EDUP standby current drain, as per specifications.
2. Putting LimeSDR in TX, current draw only goes up to 410 mA.
3. Disconnecting the EDUP from 12 v supply, current drain goes to 0 on standby. It would appear the the F1OPA standby draw is very low.
4. Putting LimeSDR in TX with only F1OPA module connected to 12 V supply DOES NOT change the 0 current draw.
The only conclusion I can draw is that, although the "on" led is lit, the F1OPA module is defective. The 30 mA increase in draw under TX conditions is - I think - the attempt of the EDUP circuit to amplify the minuscule power coming from the LimeSDR.
Is there any other explanation?
Thanks in advance.