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I have made a Maxwell choke for my ladder line feed to my doublet. I would like to check the common mode impedance with the nanovna. Do I just use one of the wires for the reading or both? A diagram of it is in the photos section. It looks like this....
/g/nanovna-users/album?id=301856

John K0JHL

I do a 'loss' measurement rather than an impedance measurement. To do this, do a 'through' measurement (S21), either on a single wire, or both wires together, connected to the center pins of the nanovna leads - either measurement method should show you the same results. The ground (shield) of the leads to the nanovna should be connected together. A good choke should give >20dB of S21 loss across the frequency range of interest - the more loss (attenuation) the better.

Since the center conductor closes fields to the interior surface of the
coax shield, it does not interact with external fields. Therefore, it's
only necessary to connect the outer shield between the two ports of the
NANOVNA. Don't be concerned about the center conductor.

Yes, you should measure S21 at something greater than -20 dB (more negative
is more better).

Dave - W?LEV

On Mon, Apr 14, 2025 at 12:47?AM Stan Dye via groups.io <standye=
[email protected]> wrote:

I do a 'loss' measurement rather than an impedance measurement. To do
this, do a 'through' measurement (S21), either on a single wire, or both
wires together, connected to the center pins of the nanovna leads - either
measurement method should show you the same results. The ground (shield)
of the leads to the nanovna should be connected together. A good choke
should give >20dB of S21 loss across the frequency range of interest - the
more loss (attenuation) the better.

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*Dave - W?LEV*


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Dave - W?LEV