On 6/28/23 3:30 PM, Pedro Madeira CT7AHV wrote:
Hello to all,
Thanks for all your inputs, I made a few searches and I saw the devices you
told.
Actually, I just need to work up to 150MHz, I build solid state amplifiers
and I need to tune the low pass filters. I also build antenna transformers,
Baluns, Ununs and RF chokes and need to measure them.
I have a nanoVNA S-A-A-2 which is useless because it doesn't measure Rs or
Xs independently in S21 mode, only measures impedance complex.
Isn't complex impedance Rs + Xs j?
But you said S21, which is also complex (although often displayed as magnitude and phase). But convertible to equivalent series R and X, with some math. There's been some discussion of this on the list, and it's not "instrument" dependent.
Tuning low
pass filters with this nanoVNA is also not possible because the measurements
are not accurate enough as my other VNA. I performed some comparisons and
the Transmission Loss in dB is very different, and yes I made proper
calibrations. The nanoVNA I have is just good enough to do SWR
measurements...
That seems odd.. how much rejection do you need to measure? (I'm assuming the passband isn't a problem). The little original NanoVNA does just fine at 60dB down, although I don't know that I'd want to commit to 1 dB uncertainty in the stop band.
The NanoVNA is probably not the right tool for aligning a 6 can diplexer for 2 meters.
My goal is to have a VNA independent of the use of a computer, that's why
I'm looking for a VNA with screen bigger than 3 inches! Which model should
be the most accurate? I know all these are Chinese devices, but maybe I can
find a reliable one for my works...
Well, yes - the tiny screen is a pain. I was checking some feedlines earlier this week outdoors and not only is the 3" screen hard to see, it's hard to take a picture of.
But if you're tuning something on a bench, it seems a computer isn't a deal breaker. I use a RPi to talk to a NanoVNA using NanoVNA-Saver, and it will display on as large a screen as you can plug in.
Thanks, best 73
Pedro Madeira
CT7AHV/C91AHV
