Re: RF Metrology

On Mon, 30 Sep 2024 05:40:39 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Sun, 29 Sep 2024 18:14:53 +0100) it happened Cursitor Doom
<cd@notformail.com> wrote in <mu1jfjtd6521pp9nb0kubcorkkkdh20gu3@4ax.com>:
>

Greetings, gentlemen,
>
I bought one of those TinySA Ultras recently and have spent some time
testing it today. I have to say it's amazing what they've done for the
price. I mean, truly amazing. I do have two other 'proper' lab-grade
RF spectrum analyzers, but I think I'm going to be mostly using the
TinySA in future as it's just *so* convenient and doesn't weigh a ton.
Anyway, to get back to the point of this post, having checked out the
TSA and establishing I didn't buy one of the fake versions that are
out there, I turned my attention to my mid-level RF SA, an HP who's
model number escapes me (not the 8566B I've posted here about before
which is now fully working, but a newer model that's about 1/3 as
heavy. I say I can't recall the model number but it's not relevant to
this question anyway. "So what is the fucking question, CD??" I hear
you not unreasonably cry. Well, it's this:
When I'm feeding an RF signal into the SA, I'm seeing differing
amplitudes at different frequencies. So I've programmed in a sweep
from 10Mhz to 5.4Ghz at -49dBm using my Aeroflex RF signal generator
and I'm seeing the displayed amplitude vary as it sweeps through the
range. But this only happens when I'm using a cheap, Chinese N-type to
SMA adaptor at the signal generator output. Would I be right to
suspect some imperfection in the manufacturing of the adaptor could
cause such an effect? I do have a VNA I could characterize the adaptor
with but it's a bit of an effort to do. It would seem like the SA is
showing the adaptor's shortcomings in the frequency domain. But is
that a feasible hypothesis?

>
I duuno, do not have that thing,
but reflections in cable + connector could create dips and mountains?
That is quite a sweep width!
 

Yes! That is what I believe is happening. Nothing much occurs between
1Mhz and 100Mhz, but it becomes more and more apparent as I go from
1Ghz to 2Ghz, 2 to 3, 3 to 4 and so on - as does the attenuation. You
can't expect miracles from cheap Chinese crap, but even crap works
well up to high VHF/low UHF.