Receiver Performance Tests

Instruments required

1. Two (2) Signal generators
2. Hybird combiner
3. Audio AC voltmeter
4. Distortion meter (FM Only)
5. Noise figure meter (for noise figure measurements only)
6. Two (2) step attenuators with 10dB and 1dB steps

Top to bottom, HP 3406A Broadband Sampling voltmeter, Tektronics TAS 465 Two Channel 100MHz Oscilloscope, HP 3586B Selective Level Meter, and HP 8656B Signal Generator

The signal generators at the W9KFB lab are as follows:

1. HP 3586B Selective Level Meter (dBm measurements are calibrated for 75 Ohm characteristic impedance, signal is 0 dBm out only at the level measurement frequency)
2. HP 8656B Signal Generator 0.1-990 MHz (dBm measurements are calibrated for 50 Ohm characteristic impedance)

Formulas and Values for a 45 Ohm Hybrid Combiner

Homebrew 45 Ohm Hybrid Combiner

The Hybird combiner was made from an old PC network splitter. The device was found in an used PC warehouse. It was a four port device with 4 BNC jacks on it. On inspection of the device, we found that it was a resistive splitter with four 39 Ohm resistors connected to each BNC center contact and a common point. These were removed and replaced with 15 Ohm 2 Watt 2% resistors metal film resistors (NTE 2W015 Flameproof Resistors).

To design you own splitter/combiner see this web site for a calculator[1]

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 AGC to "Fixed" and set the AGC-T to a set value to hear the demodulated tone ("78" works). Set the panadapter to average the signals.
3. Set the Mode to CWL and the bandwidth to 25.
4. Reduce the signal to where the signal disappears into the noise. Then raise the signal up until the peak, still in the pass band, is 3 dB above the noise floor. This value will be the minimum discernible signal (MDS).
5. Obtain a MDS value with the preamp on and off at the same test frequency by repeating all the above steps.

SSB Phase Noise

Block Diagram of MDS and SSB Phase Noise Measurement Setup

1. Record the signal level of the MDS as A0, then tune away from the signal until you can't distinguish a tone in the noise. At this frequency, increase the amplitude of the signal until the displayed amplitude is the same as A0, note the frequency f1, and then go back to f0 and measure the amplitude A1.
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; A0= The attenuation required to raise a signal 3 dB off the noise floor; 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 10/25/2009

Actual measurement of the SSB Phase Noise on a HPSDR Mercury with the Pre-Amp ON, CW BW=100 by W9KFB 10/26/2009

Dynamic Range

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