Re: Getting started with the nanoVNA guide

Jerry Gaffke
 

Yes, a good start.
I definitely learned some stuff about the user interface on this thing.

I especially liked these few words about the Smith chart:
This is just a polar plot with our received signal plotted as an amplitude and phase.
The outside circle represents a situation where we have received a signal of equal amplitude
to the transmitted signal. The centre of the plot shows where the received signal is near zero.
Short and concise. A very good beginning.
Add a few more paragraphs about pure resistance, inductive and capacitive reactance,
what happens over frequency, how to use it assuming a 50 ohm environment.
It's a subject that is seldom presented in a way understandable to somebody
who does not know what a Smith chart is.

I'd assume 90% of the market for a $50 VNA would be looking for
a quick start on how to plot the SWR of an antenna.
Should be possible to do that in the first few paragraphs, maybe
using a dummy antenna of a cap and resistor to demonstrate
in a way that the reader can duplicate with their own measurements.
Then start talking about how much more information you get when
it is plotted as a complex impedance (and what a complex impedance is).
How to add a series cap or coil to make the antenna a pure resistance.
How to measure a cap or coil across frequency, seeing what
happens at self resonance and beyond.
How to design a matching network to transform any load to 50 ohms.
How to perform a 2 port measurement to see the passband of a filter.

Only then start talking about Smith charts and S parameters
and reflection coefficients and exactly what the heck a reflection is.
I doubt many readers who need an explanation of S paramenters
will ever get around to using them in a formal manner.
But that material should be included, it's impossible to make sense of
any other documentation on VNA's without knowing about S parameters.
Or to make sense of this groups.io forum, for that matter.

Regarding this passage:
Connect your cables/Define your reference plane.
Unfortunately, it never says what a reference plane is.
Perhaps start by saying that you should calibrate using the same cables that you plan
to perform the test with. And then a few pictures of S11 and S21 test setups
with arrows pointing to this reference plane.

Maybe I'll write my own nanoVNA introduction someday,
but first I'll have to figure out how to use it.
I've got much to learn, and your document helps considerably.

Jerry, KE7ER


On Mon, Sep 2, 2019 at 05:52 AM, BruceN wrote:
Very helpful. Just what I was looking for in my long post. When you get done
with Part 2,
can you post PDF versions in the FILES folder too? With the docs already
there, a good
foundation for a library can be formed.

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