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For filter design and performance, you might try Elsie:


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It's good for lumped element filters. My first knee jerk reaction to your
requirements is that you may need to go to a cavity filter to obtain the
harmonic and spurious suppression you require to be "legal". Hi-Q helical
filters might also get you there.

I can't speak for the FCC, but once worked at the very beginning of the
RFID craze (right off "The Hill" from Los Alamos) before we went public.
RFID was originally developed to track radioactive transport trucks. We
had an experimental license from the FCC for the 900 and 2.4 GHz ISM
bands. You are likely treading on thin ice with any amount of power,
however, even 3 decades ago, FCC (unofficially) considered the 902 to 928
MHz ISM band the new "junk band" (their words). Even in my relatively RF
isolated location, I have quite a number of 900 MHz ISM band emissions
detectable on the spectrum analyzer with nothing more than a short clip
lead as an antenna.

Take your chances with unlicensed emissions of any significant amount of
power / antenna gain.

Dave - W?LEV

On Wed, Oct 6, 2021 at 11:43 AM msat via groups.io <msatoria=
[email protected]> wrote:

Hello everyone!

RF newbie and first time poster here. Recently purchased a NanoVNA-H for a
specific experiment I'd like to perform. Without going into the unnecessary
details of the experiment itself, what I'd like to do is use the nano as a
fixed RF frequency gen, probably in the ~900MHz ISM band, to be fed to an
amp and transmitted via an antenna. A probe on S21 will then be used for
obtaining relative phase angle measurements.

I know the nano generates a square wave output, thus the dominating
frequencies are the fundamental and odd order harmonics, along with some
even order and spurious frequencies. I also know that the nano will rely on
the 5th harmonic of some fundamental in order to reach my desired fixed
frequency. Since not only would it be irresponsible to transmit those
various other frequencies, but I also think my experiment would be better
served by having as spectrally pure signal as is reasonably possible. To
avoid any confusion, my intended TX signal chain is as follows:
nanoVNA S11 -> bandpass filter (probably LC?) -> RF amp -> antenna

So my question is this: how sophisticated does the filter realistically
need to be? Would a 1st order LC bandpass do, or do I need something else?
Are there any common "gotchas" that trip up newbs that I should be aware of?

Thanks!
Mark

--
*Dave - W?LEV*
*Just Let Darwin Work*