Receiver Performance Tests
The Sensitivity test is very simple to do on an HPSDR rig:
- Calibrate the level and frequency on the rig with the output of the signal generator using PowerSDR's Setup calibration at the test frequency using a -40 dBm signal.
- Set the panadapter to average the signals.
- Set the Mode to CWL, the bandwidth to 100, and the preamp to Off.
- Read the value of the noise floor with the PowerSDR meter set to "SigAvg", with the signal generator turned off. This value will be the minimum discernible signal (MDS).
- Obtain a MDS value with the preamp on at the same test frequency by repeating all the above steps.
SSB Phase Noise
The SSB Phase Noise tests require a very low phase noise oscillator to run the tests. Most synthesized oscillators will not be good enough. Before you choose an oscillator to do the testing, check its SSB phase noise specifications. If the oscillator has a worst case spec of greater than -130 dBc/Hz, find one that is better as your noise measurement results will never be better than the test oscillator noise level.
- Use the MDS obtained per the process above as A0, then tune away from the signal until you can't distinguish a tone in the noise or to your first defined offset frequency. At this frequency, increase the amplitude of the signal until the displayed amplitude (using the PowerSDR meter set to "SigAvg") is the same as A0 plus 3 dB (the MDS will be a minus number, so this number will be 3 dB lower in absolute value), note the frequency f1, and then go back to f0 and measure the amplitude A1 using the PowerSDR meter set to "SigAvg".
- To calculate SSB Phase Noise use this equation from KI6WX's March and April, 1988, QST article (The 2009 and earlier ARRL Handbooks have a missing minus sign in the equation): L(f)=A1-A0-10Log(BWnoise), Where L(f)= SSB phase noise in dBc/Hz; A1= The attenuation required at the offset frequency for the same noise level as A0 plus 3 dB; A0= MDS; and BWnoise= The CW bandwidth used during the test.
The ARRL handbook instructions (Page 25.43 of the 2009 handbook) says to use a weak signal at about a level of 110 dBm and a strong signal 20 KHz offset. The ARRL Lab procedures requires the weak signal level to be about 10 dB below where we detect the 1 dB of gain compression of the weak signal. On Mercury no detectable gain compression was measured on any level of weak signal with any level of strong signal below the A/D overload values at 4, 14, and 30 MHz with the PreAmp on or off.