Broken RFX1200 and more sensitivity measurements

I went to OZ7SAT today to do some measurements on the receiver boards. I wanted to see how the sensitivities compare to that of the WBX receiver that I have measured earlier using a CW signal and SSB receiver. The criteria was again to find the weakest signal that I could both hear and see on the spectrum scope and that I would be able to decode if it was a Morse code transmission. The limiting parameter is actually the spectrum scope, because I can hear tones much weaker than what is visible on the 512 channel FFT scope.

Getting ready to make some measurements on the USRP daughterboards.

My measurements started with some bad news: My RFX1200 appears to be broken. When I start the software it can not tune to the target frequency.

My RFX1200 is broken! Receiver can not tune any more.

The other daughterboards behaved much better. I measured both the TVRX and the LFRX receivers. I was very curious about the LFRX since it contains no active elements. Still, I could hear signals between -95 and -102 dBm depending on the frequency. This corresponds to 1.8 to 4 µV and that’s not bad for an ADC+PGA (yes, the gain was at the maximum 20 dB).

LFRX receiving a 5 µV signal at 48 MHz.The signal is the larger peak just above 48.

The TVRX did good too, in fact much better than I expected. I had no trouble hearing signals at -125 dBm that is 0.12 µV. I used a gain setting of 71 dB, which seemed to give best SNR.

Author: Alexandru Csete

Embedded software engineer in the satcom industry during the day. Radio amateur and SDR hacker during the night.