The steel table may have an effect. But based on your description, the antennas are some distance away from that table. The table will likely not have any impact on the antenna system if it's separated from the antennas by distance.
To prevent any possible interaction just put the NanoVNA on a non conductive insulator or surface like a piece of cardboard or plastic or rubber mat or something.
The radio is insulated from the table by its insulated feet on the case, so you want to mimic that to some extent if you are using the NanoVna to tune the antenna system from the radio end of the coax.
In the previous scenario, the OP was working in a mobile situation which has different variables to a fixed installation at home.
73
Colin, VA6GG
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On 2025-02-02 6:33 p.m., Jon via groups.io wrote:
I am waiting for NanoVNA to be delivered this week. My FT-710 radio is on a
steel table. I am planning to use an SMA to SO239 patch cable of 1m length
to connect NanoVNA to PL 259 of my antennas.
From this discussion, it seems that I will have to get a wooden table to
keep the NanoVNA?
I have not used NanoVNA yet.
73
Jon, VU2JO
On Mon, Feb 3, 2025 at 6:53?AM Colin McDonald via groups.io <colinrmcdonald=
[email protected]> wrote:
Put the NanoVNA on a non conductive surface well away from where the
antenna is mounted.
The reason you are getting different readings is because you are
changing the ground plain of the antenna system with your body or metal
surface or non metal surface. I would guess the antenna itself doesn't
have a sufficient ground plain to work off of and so any small changes
to the ground side of the system, IE where the coax is finding ground,
will alter the measurements.
When you say it's changing, how much is the SWR changing? If by a couple
points it's not a big deal. If it's changing from say 1.1 to 1 to 3 to 1
or 4 to 1 by placing the NanoVNA on the hood verses in your hand then
you've got a antenna ground issue.
You can try connecting a counterpoise to the ground side of the antenna
mount if you can't electrically ground it to the vehicle. That would be
a quarter wave of wire or so on the band you are trying to tune.
I would say that the most accurate reading will be the one where the
NanoVNA is on the insulated pelican case.
Is the radio you are using going to be chassis grounded to the vehicle
or floating inside or outside the vehicle during operation? If floating
you want the NanoVna to most accurately represent where the radio will be.
You can cross check this by tuning with the NanoVna, then checking the
swr with the radio itself. If they are close, within .5 or so, you'll
be good to go on SWR.
73
Colin, VA6GG
On 2025-02-02 6:04 p.m., Coyote via groups.io wrote:
When using my NanoVNA to adjust length of a 20m hamstick, the readings
kept changing depending on what the NanoVNA was sitting on (truck hood,
pelican case, my thigh, or in my hand).
How do I get a reliable reading that I can count on for a properly
adjusted antenna?
Thanks, Coyote
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