Ivan IonovParticipantIvan Ionov August 20, 2015 at 4:14 am
As I understand, in sweep mode with Spur Rejection turned on, I can’t see the frequency hopping signal, because SA44 samples a frequency region with LO 10MHz lower, than with LO 10MHz higher and shows the signal which presents in both samples (which is usually false for hopping signal). But when I turn Spur Rejection off, I get the mirrored signal (20MHz lower) with the same(!) amplitude as the real signal. And as a result I can’t collect correctly (with max hold) the hopping frequency range, can’t tell where the hopping range starts.
My suggestion here is to add an option to Spur Rejection algorithm so that it accumulates both regions (with “max hold” mode for hopping signal or “average” for other types of signal) for some time before merging both regions and filtering out spurs. For example, if I know for sure, that my radio transmitter repeats hopping pattern every 0.5sec, then accumulation of the signal for that time surely collects all hopping channels. So if I accumulate signal in 2 regions for 0.5sec and then combine them to reject spurs, I get clean and stable result in this 250KHz range. Repeating the same process, in 40sec I can get clean 10MHz sweep and see all hops in this range…
This feature can require long time for large sweep, but now SA44 simply useless in that case.
Second example, for the analog video signal (~10-20MHz band) the accumulation time can be much shorter (= 1/25sec, video frame of PAL signal) and can get me a much better and more stable graph (now it has many random dips).
Is this feature realistic, and can it be implemented?
Justin CrooksModeratorJustin Crooks August 20, 2015 at 9:35 am
Thank you for the suggestion. Our solution for frequency hopping spectrum analysis is the BB60C. It has hardware image rejection and very fast sweeps.
There are a number of solutions for frequency hoppers using the SA44B, but they are generally case-specific and do not work in the general case. If you can keep the hopping to a 20 MHz band, the SA44B can be used with image rejection off (disregard the image responses ~21.4 MHz away), or if the transmissions are long at each hop (>sweep time) you can keep image rejection on and analyze 40 MHz worth of spectrum.
Beyond this, the BB60C is required.
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