Jim, the NANOVNAs I contend are highly useful for us amateurs and "top
level" professional applications and CERTAINLY for education. However, I
use mine where I can not carry the (100-lb.) 8753C with S-Parameter Test
Set. That and the price point is where the NANOVNAs shine for the amateur
and professional. Of course, Keysite has offered a portable VNA as does
R&S, but the price point(s) keep us amateurs away. Fortunately, at one
time (pre-Carley), HP encouraged dumpster dipping. For those of us who
practiced our skills on the hobby as well as on the job, that was quite a
priviledge!!!
Dave - WLEV
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On Thu, Aug 4, 2022 at 5:50 PM Jim Lux <jimlux@...> wrote:
On 8/3/22 4:38 PM, 0root via groups.io wrote:
Hey all, first post here.
I currently own and love the nanovna-h and h4, I was sure to buy them
from the alibaba store zeenko as this is apparantly hugens chosen
manufacturer.
However, if I wanted to get more precision - specifically in the areas
of Return Loss / VSWR and attenuation readings - what would be the next
device up to get - within the region of $100 - $2000 and no higher...
I see alot of siglent stuff, but the reviews are not too appetizing
One other thing..
The "raw measurement" that the NanoVNA makes is essentially a filtered
sum of 48 samples. The raw adc samples are probably about 1 part in 10^4
(call it 1E-4 fractional uncertainty) so 48 samples will be sqrt(N)
better, or 1.4E-5. (ignoring arithmetic precision).
That's voltage, not power, relative to full scale.
In reality, the input signal isn't full scale, it's more like 0.1 full
scale or 0.05 full scale, so the uncertainty is about 0.1%
The reflection coefficient is calculated as the algebraic combination of
two of those measurements, so the uncertainty is roughly doubled (0.2%)
So that really sets your accuracy - especially with a big signal (e.g.
the reflection of a short or open) - with a good load, the accuracy is
less, because reflection power is less, so the uncertainty of that
measurement is poorer. If the reflected power is -40 dB, then the
signal to noise of the measurement is 1/100th, so instead of a 0.1%
uncertainty, it's more like 10%
More expensive analyzers will have better SNR, from a larger stimulus
signal, a lower input noise floor, and a narrower detection bandwidth
(which reduces the noise).
--
*Dave - W?LEV*
*Just Let Darwin Work*
--
Dave - W?LEV
