Friday, April 17, 2020

nanoVNA and FieldFox VNA as seen by RSPduo in SA mode


The impressive accuracy of the nanoVNA compared to much more expensive VNA's had me wondering how the output of the device looked compared to the FieldFox I have access to. ("You ended that sentence in a preposition, John" - voice of 3rd grade teacher, Mrs. Rogers, in my head).

Once the return to normalcy occurs (if ever - I believe "normal" will be re-defined) I'll have access to a real spectrum analyzer - for now, the SA function/software for the RSPduo will have to do. At the very least it offers a comparison, if not absolute values, of what comes out of each VNA with a given sweep range programmed.

A step attenuator was used to lower the output of the nanoVNA. The FieldFox has two selectable output levels with the lower one being chosen for this test at three different frequencies.

In the case of both the nVNA and the FieldFox, a certain amount of time (5 to 30 seconds) was required to paint the resulting square wave that covers the 2 MHz-wide frequency range programmed in as a sweep. The FF did this much faster than the nVNA and also painted a more uniform square wave with less noise above and below the swept range.

The FF painted this range with what appeared to be a single narrow pulse; the nVNA did it with numerous simultaneous pulses of widely varying amplitudes.

In each of the images below, the nVNA result is on the left; the FF is on the right:
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49 to 51 MHz

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499 to 501 MHz

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999 to 1001 MHz

Despite the fact that the FF is much cleaner and more precise than the nVNA, the various other comparisons of these two VNA's are remarkably close in their measurements throughout the 3-1000 MHz range, as noted elsewhere on this website.
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2 comments:

  1. John-

    This is interesting — not surprisingly, it looks like the FieldFox has better filtering.

    I'm wondering how do the two versions of the nanoVNA compare, other than in their frequency ranges. Is the newer one more precise?

    73!

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    1. I haven't compared the two versions of the nanoVNA together but, based on how they both are so close to what the FF presents, I'm pretty sure their only difference would be the freq range. My plan with the lower range nVNA is to update it to the latest firmware and then sell it. I don't really need two of them.

      If anyone's interested, lemme know...

      73 - John

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