Thanks for your suggestion, Stan. I will attempt to reset the sweep range to a lower stop frequency, but it won¡¯t happen until tomorrow.
I did make return loss and characteristic impedance measurements and they look nominal for this coax. Zo=48.2 ohms tested at 9.8Mhz +/- 90¡ã and the return loss at 10Mhz is .99dB and 1.3dB at 30Mhz. Both of these figures seem reasonable for a 100ft chunk of RG-8X. But that big spike at 14.65m has me scratching my head. There are only minimal artifacts apparent on the display around 120nS which you can see in my original post. So maybe there is something hiding between sampling points.
By the way, I really love this new toy. I am trying to consume as much as I can from the various postings, discussions and videos to be able to use it to its fullest. What a fantastic invention! The guys who developed this tool should get an award for one of the most useful inventions for Radio Communications since the oscilloscope.
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On Jun 19, 2023, at 1:32 PM, Stan Dye <standye@...> wrote:
?Also, for a cable that long using the 101pt scan, you need to set your stop
frequency to about 70MHz to see the reflection from the whole length of the
cable. So what you are seeing now may be due to aliasing or something.
(I just experimented with the Transform settings with a 100ft length of
good cable on my -H4. When I had it at 400pt scan, 125MHz let me see much
longer than 100ft, but at 100pts I needed to set the frequency down to see
the reflection from the end of the cable. This is due to the "bin size"
used in the FFT.)
On Mon, Jun 19, 2023, 10:13 AM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:
On Mon, Jun 19, 2023 at 08:23 AM, RJOLLIS wrote:
Procedure. I have set up the VNA on Trace 0 in the Linear mode. VF is
set to
a nominal 80% for the 100 ft (30.5m) RG-8X coil of coax. The Transform
function is selected and Low Pass mode is on. I sweep from 500Khz to
125Mhz. I
get a spike at 14.79m. When I swap the inputs, the number doesn¡¯t
change. I
would expect that if there was a short in the coax, I would observe
15.21m
when I flip the ends.
Question. Am I doing something wrong here or do I have a defective nano?
I
haven¡¯t yet characterized impedance or line loss. Those come next.
Looking at your photo your yellow trace shows S21 linear instead of S11
Linear.
I don't know what revision of firmware you have but recent firmware has a
Cable Measure function built in. Have you tried that?
Roger
