yo3fffParticipantyo3fff October 3, 2019 at 4:57 am
I have a SA44B analyzer and I need to know how to setup the detector type.
Under Spike software it isn’t clear for me what the Acquisition control menu do. I see there a “Detector” drop down list with only two options: min/max an average.
Except the “average” option which looks familiar to me as a detector type, I’m wondering if this analyzer is capable of using a +peak, -peak, V(RMS), QP, etc.
Please let me know what detectors are available and how to setup theme on Spike.
AndrewModeratorAndrew October 3, 2019 at 9:30 am
You can use the video units and detector to accomplish a number of detector types. Our min/max is the same as plotting peak+ and peak- on the screen at the same time. When average detector is selected, the video units determine whether power averaging, voltage averaging, log power averaging or no averaging (sample) occurs. The only quasi peak detector we have in our software is in the EMC precompliance mode which is not compatible with the SA44B. It is a single frequency QP detector. Due to the FFT based approach in our analyzers, you may not see a difference between some detector settings (because the RBW/VBW specifies only a single FFT to occur). Lower RBW/VBWs will change this.
yo3fffParticipantyo3fff October 9, 2019 at 8:34 am
Thank you for the answer.
I try to evaluate what this analyzer measure with different detector types. I did 4 measurements with the analyzer’s input closed to 50ohm termination.
Here are the results:
Max Hold [dBm]= -122.98
AVG [dBm]= -130.93
delta [dB]= 7.95
Max Hold [dBm]= -126.42
AVG [dBm]= -137.17
delta [dB]= 10.75
Max Hold [dBm]= -128.66
AVG [dBm]= -134.14
delta [dB]= 5.48
Max Hold [dBm]= -127.69
AVG [dBm]= -137.62
delta [dB]= 9.93
As can be seen, there is big inconsistency between Sweep and Realtime Analysis Modes ranging between -0.97 to +6.24dB such as:
delta maxRT_Max-AVGRT_Max [dB]= 5.68
delta maxRT_AVG-AVGRT_AVG [dB]= 3.21
delta maxSW_Max-AVGSW_Max [dB]= 1.27
delta maxSW_AVG-AVGSW_AVG [dB]= 0.45
delta maxRT_Max-maxSW_Max [dB]= 3.44
delta maxRT_AVG-maxSW_AVG [dB] 6.24
delta AVGRT_Max-AVGSW_Max [dB] -0.97
delta AVGRT_AVG-AVGSW_AVG [dB] 3.48
How can you explain this behavior?
From my perspective, one cannot use the analyzer for consistent measurements with different modes and detectors having more than 7dB tolerance.
In the specs the analyzer amplitude precision readings is less than 2dB so what is wrong?
Look forward hearing from you.
Justin CrooksModeratorJustin Crooks October 9, 2019 at 10:42 am
There are several factors that go in to why these measurements are different. These include the software image rejection algorithm, the noise floor / sensitivity of the SA44B in the selected mode, and the effective video bandwidth and averaging method based on detector settings.
If your goal is noise spectral density measurements, the preferred instrument is the BB60C or SM200A. This is because the SA44B does not have hardware-based image rejection, so there is noise present from both sidebands (even if the signal from one sideband is rejected in software).
That being said, real-time mode, power average is a good way of measuring the noise energy (sum of energy at desired frequency and image frequency–subtract 3 dB typically for noise at desired frequency only).
For a lower noise floor, using sweep mode (image rejection ON), power, average, VBW <= 1/10 RBW, will use a more sensitive detector circuit and provide a lower noise floor than real-time mode.
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