On 5/5/2023 9:28 AM, jim.thom jim.thom@telus.net wrote:
Several folks told me that the Tiny SA was useless for IMD testing, due
to it's 3 khz resolution. Apparently somebody listened, and the newer /
bigger version, with it's 200 hz resolution, should fare better.
That's quite coarse. The Elecraft P3 can get down to a few Hz; the SVGA
card, which does a higher res FFT of the same data, gets down to
fractional Hz. This is the sort of resolution needed to measure
transmitted bandwidth.
Some measurements I did about ten years ago are shown in these pdf
files. The first, for a talk by Elecraft engineer Bob Wolbert, K6XX,
was done before the SVGA card was developed.
http://k9yc.com/K6XXAmpTalk.pdf
The second file, which uses Power Point as a convenient means of showing
graphical data, was not intended for presentation to a club or at an
event. The measurement method is mostly described with text slides.
http://k9yc.com/P3_Spectrum_Measurements.pdf
The P3, with or without the SVGA board, measures 100 dB of dynamic
range, but can display only 80 dB on the screen at a time. It turns out
that 80 dB is more than enough for even the best rigs I've measured, but
if a cleaner rig showed up (or perhaps with Pure Signal), the bottom 20
dB could be displayed simply by changing the zero reference for the
display.
The various SDRs shown in the talk and text pdfs on chasing RFI by
studying their spectra, mostly have very good frequency resolution.
NR0V, who authored both Pure Signal and computer software for ANAN
radios, told me that the little 10W Anan rig is good for fractional Hz
http://k9yc.com/KillingReceiveNoise.pdf Text
http://k9yc.com/KillingRXNoiseVisalia.pdf Slide show
I used the P3 and SVGA board because they could do the job and I had
them. Both are discontinued by Elecraft. If I were doing those
measurements today, I'd probably use the ANAN.
I own both HP8590D and Rigol spectrum analyzers. Their frequency
resolution specs are comparable, MUCH to wide (at least two orders of
magnitude) for transmitted bandwidth measurements of transmission modes
used by hams.
73, Jim K9YC
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