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reflection coefficient of PSA

Question asked by Achrononmaster on Feb 26, 2009
Latest reply on Mar 2, 2009 by dgun

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Suppose I want to measure the reflection coefficient, Gamma_L, of my measuring receiver.
I propose to connect the PSA to my calibrated VNA and perform a standard S-parameter measurement to determine Gamma.
Furthermore, I wish to measure Gamma_L for a whole bunch of different PSA settings and ranges, including configuration with "Range Hold" turned and the range held in Range 3 where the receiver is most sensitive.
My questions are:
(a) is there a better way to measure Gamma_L than this?
(b) how can I do this safely without damaging the PSA mixer or other elements, ie., what is the maximum power the mixer can take (given any possible PSA settings)?

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dgun Feb 27, 2009 11:46 AM

I'm not familiar with the measuring receiver, but I can tell you some things about typical PSA. The load match vs frequency will typically change every time you change attenuator setting and center frequency setting. In fact, above about 3.1 GHz, it will change as the PSA sweeps across the span. The reason for this is the tuned preselect filter.

If I wanted to measure a CW signal, I would use zero span (make sure to use 10 MHz ref between source and PSA) measure the load match at each center frequency and step through all attenuator ranges I might need (there can be a LOT of attenuator ranges on a PSA). If you want to measure harmonics, it gets even trickier, since setting the center frequency to the second harmonic can change the load match at the fundamental. Of course, if you have the attenuation set at 10 dB or above, the load match change will be very small between settings and gets progressively worse as you go from 10 dB to 0 dB.

For a standard PSA, the input damage level is on the front of the box near the connector. It is 1W for my PSA. This should apply to all settings.

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Achrononmaster Feb 28, 2009 4:30 AM

Thanks dgun.

For ref. our PSA is the E4440A N5531S Measuring Receiver System. I'll be making CW TRFL measurements, but for characterization and in-house uncertainty analysis I need the receiver Gamma as stated previously. So I think your suggestions are about spot on, thanks. It'd be cool if you could confirm that the damage limit is definitely 1W for all settings of this instrument. In the mean time I will be sure to stay well below that level. Thanks again.

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dgun Mar 2, 2009 10:41 AM

Based on the datasheet (see pages 13-16), the max power is +30 dBm w/pre-amp off and +16 dBm w/pre-amp on (pre-amp is option 1DS or 110).

Also, I found out that for measurements above 3 GHz, option 123 is required for TRFL (pages 2 & 17 of the datasheet), which bypasses the preselector. So the load match should not change as the PSA sweeps across the span (with measurement spans that do not cross bands).

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dgun Feb 27, 2009 11:46 AM
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I'm not familiar with the measuring receiver, but I can tell you some things about typical PSA. The load match vs frequency will typically change every time you change attenuator setting and center frequency setting. In fact, above about 3.1 GHz, it will change as the PSA sweeps across the span. The reason for this is the tuned preselect filter.

If I wanted to measure a CW signal, I would use zero span (make sure to use 10 MHz ref between source and PSA) measure the load match at each center frequency and step through all attenuator ranges I might need (there can be a LOT of attenuator ranges on a PSA). If you want to measure harmonics, it gets even trickier, since setting the center frequency to the second harmonic can change the load match at the fundamental. Of course, if you have the attenuation set at 10 dB or above, the load match change will be very small between settings and gets progressively worse as you go from 10 dB to 0 dB.

For a standard PSA, the input damage level is on the front of the box near the connector. It is 1W for my PSA. This should apply to all settings.
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Achrononmaster Feb 28, 2009 4:30 AM
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Thanks dgun.

For ref. our PSA is the E4440A N5531S Measuring Receiver System. I'll be making CW TRFL measurements, but for characterization and in-house uncertainty analysis I need the receiver Gamma as stated previously. So I think your suggestions are about spot on, thanks. It'd be cool if you could confirm that the damage limit is definitely 1W for all settings of this instrument. In the mean time I will be sure to stay well below that level. Thanks again.
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dgun Mar 2, 2009 10:41 AM
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Based on the datasheet (see pages 13-16), the max power is +30 dBm w/pre-amp off and +16 dBm w/pre-amp on (pre-amp is option 1DS or 110).

Also, I found out that for measurements above 3 GHz, option 123 is required for TRFL (pages 2 & 17 of the datasheet), which bypasses the preselector. So the load match should not change as the PSA sweeps across the span (with measurement spans that do not cross bands).
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reflection coefficient of PSA

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