Difference between revisions of "Receiver Performance Tests"

Revision as of 19:36, 28 October 2009

Instruments required

Tests

Sensitivity

The Sensitivity test is very simple to do on an HPSDR rig:

1. 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.
2. Set the panadapter to average the signals.
3. Set the Mode to CWL, the bandwidth to 100, and the preamp to Off.
4. 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).
5. Obtain a MDS value with the preamp on at the same test frequency by repeating all the above steps.

SSB Phase Noise

Block Diagram of MDS and SSB Phase Noise Measurement Setup

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.

1. 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".
2. 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.

Actual measurement of the SSB Phase Noise on a HPSDR Mercury with the Pre-Amp OFF by W9KFB 10/26/2009. Note the output limit for the oscillator was reached at an ofset of 1KHz.

Actual measurement of the SSB Phase Noise on a HPSDR Mercury with the Pre-Amp ON, CW BW=100 by W9KFB 10/26/2009. Note the the A/D Overload limit was reached at an offset frequency of 1 KHz.

Measurement of Mercury's SSB Phase Noise by Marco IK1ODO / AI4YF and some comparables

Dynamic Range

40 dB Step Attenuator purchased at the 2009 Indy Radio Club Ham Auction for 25 Cents

This test has been difficult to repeat following the ARRL handbook instructions (Page 25.43 of the 2009 handbook). The Handbook says to use a weak signal at about a level of 110 dBm. The ARRL Lab procedures require this level be about 10 dB below where we detect the 1 dB of gain compression on a test frequency. If there is no AGC turn off (which is the case for PowerSDR) a signal level 20 dB above the MDS value shall be used. Best results on a HPSDR Mercury in the W9KFB lab indicates that a higher signal level is required, as signals below about 30 db above the MDS are very sensitve. All tests in this section will set the low signal to 30 dB over the MDS level.

Two-Tone IMD Test

Third-Order Intercept Tests