Difference between revisions of "Receiver Performance Tests"

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=== [[Instruments required]] ===
  
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=== Instruments required ===
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=== Tests ===
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==== Sensitivity ====
  
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#Two (2) Signal generators
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The Sensitivity test is very simple to do on an HPSDR rig:
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#Hybird combiner
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#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.
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#Audio AC voltmeter
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#Set the panadapter to average the signals.
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#Distortion meter (FM Only)
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#Set the Mode to CWL, the bandwidth to 100, and the preamp to Off.
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#Noise figure meter (for noise figure measurements only)
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#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).
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#Two (2) step attenuators with 10dB and 1dB steps
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#Obtain a MDS value with the preamp on at the same test frequency by repeating all the above steps.
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[[Image:W9KFBinstrumentstack.jpg|thumb|300px|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]]
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The signal generators at the W9KFB lab are as follows:
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#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)
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#HP 8656B Signal Generator 0.1-990 MHz (dBm measurements are calibrated for 50 Ohm characteristic impedance)
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[[Image:45 Ohm combiner.jpg|thumb|300px|Formulas and Values for a 45 Ohm Hybrid Combiner]]
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==== SSB Phase Noise ====
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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).
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[[Image:Stepattenuator.jpg|thumb|300px|40 dB Step Attenuator purchased at the 2009 Indy Radio Club Ham Auction for 25 Cents]]
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==== Sensitivity ====
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[[Image:MDS & SSB Phase Noise Test.jpg|thumb|300px|Block Diagram of MDS and SSB Phase Noise Measurement Setup]]
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[[Image:HPSDR SSB Phase Noise.jpg|thumb|300px|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 offset of 1KHz.]]
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[[Image:HPSDR PN.jpg|thumb|300px|Measurement of Mercury's SSB Phase Noise by Marco IK1ODO / AI4YF and some comparables]]
  
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==== Dynamic Range ====
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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. Also note that in choosing a test oscillator for SSB Phase Noise measurement, 10 MHz should be avoided as there is usually a 10 MHz signal from the Mercury clock source that will interfere with measurement of SSB Phase Noise close to the 10MHz carrier signal.
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#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".
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#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.
  
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==== Two-Tone IMD Test ====
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==== Blocking Dynamic Range ====
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[[Image:HPSDR Blocking test block Dia.jpg|thumb|300px|A block diagram of the blocking dynamic range test setup]]
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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.
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==== IMD Dynamic Range ====
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[[Image:Image-HPSDR IMD DR test block Dia.jpg|thumb|300px|A block diagram of the IMD dynamic range test setup]]
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IMD Dynamic Range measures the effect of two-tone IMD on a HPSDR receiver. IMD is the production of spurious responses that results when two or more signals mix. IMD occurs in any receiver when signals of sufficient magnitude are present. IMD Dynamic Range is the difference, in dB, between the noise floor and the strength of two equal incoming signals that produce a third-order product 3 dB above the noise floor. For more information on IMD Dynamic Range measurement, see the 2009 ARRL Handbook, Test procedures, Chapter 25, page 25.43.
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''Important note: To get good performance with respect to the IMD Dynamic Range tests, be sure to check "Dither Enabled" and "Random Enabled" in the Setup > HPSDR > Mercury Options panel''. If this is not done your IMD Dynamic Range will be reduced by about 50%. Reference:[[Mercury - intermodulation (IMD) tests]].
  
 
==== Third-Order Intercept Tests====
 
==== Third-Order Intercept Tests====
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The recommended method of calculating the third-order intercept going for HPSDRs is as follows:
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IP3=(3*(Input Level)-(IMD Level))/2
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Where IP3 is the level where the desired response and the third-order IMD would theoretically be the same, if extended beyond their linear regions (In reality these levels would be a Mercury A/D overload level... positive dBm values). The values are considered a figure of merit.
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The "Input Level" is the dBm value of the two signals of equal level that provides a given third order product level.
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The "IMD Level" is a target level of -97 dBm for all HPSDR receiver designs.
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This file compares measurements taken at W9KFB's lab, Walter, HB9AJG's lab, and the ARRL Lab (Flex 3000 data) [[media:ARRL FLX3000&HB9AJG tests.pdf ]].
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[[Category:Mercury]]

Latest revision as of 10:35, 26 January 2010

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
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 offset of 1KHz.
Measurement of Mercury's SSB Phase Noise by Marco IK1ODO / AI4YF and some comparables

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. Also note that in choosing a test oscillator for SSB Phase Noise measurement, 10 MHz should be avoided as there is usually a 10 MHz signal from the Mercury clock source that will interfere with measurement of SSB Phase Noise close to the 10MHz carrier signal.

  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.

Blocking Dynamic Range

A block diagram of the blocking dynamic range test setup

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.

IMD Dynamic Range

A block diagram of the IMD dynamic range test setup

IMD Dynamic Range measures the effect of two-tone IMD on a HPSDR receiver. IMD is the production of spurious responses that results when two or more signals mix. IMD occurs in any receiver when signals of sufficient magnitude are present. IMD Dynamic Range is the difference, in dB, between the noise floor and the strength of two equal incoming signals that produce a third-order product 3 dB above the noise floor. For more information on IMD Dynamic Range measurement, see the 2009 ARRL Handbook, Test procedures, Chapter 25, page 25.43. Important note: To get good performance with respect to the IMD Dynamic Range tests, be sure to check "Dither Enabled" and "Random Enabled" in the Setup > HPSDR > Mercury Options panel. If this is not done your IMD Dynamic Range will be reduced by about 50%. Reference:Mercury - intermodulation (IMD) tests.

Third-Order Intercept Tests

The recommended method of calculating the third-order intercept going for HPSDRs is as follows: IP3=(3*(Input Level)-(IMD Level))/2

Where IP3 is the level where the desired response and the third-order IMD would theoretically be the same, if extended beyond their linear regions (In reality these levels would be a Mercury A/D overload level... positive dBm values). The values are considered a figure of merit.

The "Input Level" is the dBm value of the two signals of equal level that provides a given third order product level.

The "IMD Level" is a target level of -97 dBm for all HPSDR receiver designs.

This file compares measurements taken at W9KFB's lab, Walter, HB9AJG's lab, and the ARRL Lab (Flex 3000 data) media:ARRL FLX3000&HB9AJG tests.pdf .

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