After finishing the initial “smoke tests” on the 5.6-5.9 GHz receiver setup – in particular the KU LNC 5659 C PRO down converter, we decided to measure the sensitivity of the WBX receiver over the whole range. We define sensitivity in this respect as the weakest CW signal that:
- Gives an SNR of at least 5dB on the spectrum scope in GNU Radio (before filtering)
- Produces a clearly audible signal in the speaker
This corresponds roughly to the weakest Morse code signal we could decode using the receiver and while it is definitely not a universal measure for the performance of the receiver, it is a good figure to compare with other ham radio equipment. Noise figure and IP measurements are available from Ettus Research.
I already had some very good results on the air with the WBX receiver and transmitter but I was excited to put some numbers on this “goodness”.
The USRP/WBX receiver was connected directly to a well calibrated signal generator using 50 cm of AIRCELL 5 coax cable. The computer was running the Simple CW Receiver V0.3 🙂
We found that a -130 dBm signal is clearly detectable over the whole range, which is quite good. The screenshots below were all taken using a -130 dBm signal, except the 70 MHz measurement, which was taken using -133 dBm. As you will see, we increased the RF gain at the higher frequencies to get a better SNR. Click on the images to get a full resolution screenshot.
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| 70 MHz using a -133 dBm CW signal. | 145 MHz using a -130 dBm CW signal. |
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| 435 MHz using a -130 dBm CW signal. | 1296 MHz using a -130 dBm CW signal. |
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| 1.6 GHz using a -130 dBm CW signal. | 2.1 GHz using a -130 dBm CW signal. |
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| 2.2 GHz using a -130 dBm CW signal. |