Re: RF Metrology

On Sun, 29 Sep 2024 19:57:34 +0100, John R Walliker
<jrwalliker@gmail.com> wrote:

On 29/09/2024 19:02, Jeroen Belleman wrote:

On 9/29/24 19:14, Cursitor Doom wrote:

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?
>
Your pal,
>
CD.

 
Aren't we getting a teensy bit lazy?
 
Jeroen Belleman

>
I have seen transmission (S21) losses of around 1dB at about 1.2GHz
just from failing to tighten an N connector sufficiently.
We do need to know the magnitude and frequency of the problem in
order to give helpful comments!
John

Not really. If you just think of it as a slight impedance mismatch in
the cable between the SA and the signal generator. However, this model
has the facility to be able to save files of the screen display
(although I very much doubt it'll save a real-time video of the
sweep).
And John - it's the 'Ultra' version. I already had the base model and
this is a worthwhile upgrade.
Jeroen - it's more a problem of available time!