This can be improved by adding a small Common Mode Choke at the VNA end to
help isolate the coax from the case of the device. The frequency being
measured also has an impact.
*Clyde K. Spencer*
On Wed, Apr 23, 2025 at 1:28?PM Kenneth Roberts via groups.io <kenr313=
[email protected]> wrote:
Yes, I have noted that the SWR changes when holding the VNA vs. not
holding it, and touching the SMA connector vs. not touching it. The
readings generally are better when touching vs. not touching.
Ken, W4KRR
On 4/23/2025 12:20 PM, Manfred Mornhinweg via groups.io wrote:
I have a whole load of rubber duck antennas that I'm checking so see at
what range they should work best.
Ken,
the behavior of rubber duckies depends significantly on the radio they
are attached to. So, to get reasonably accurate results when measuring them
with the nanoVNA, I suggest that you build a metal bracket about the size
of a typical HT, covered with some insulation to mimmick the plastic body
of an HT, mount the nanoVNA in that bracket, its measuring port bonded to
the bracket, and then hold that contraption in your hand like you would
hold an HT, while making the measurements.
You could even use a plastic box the size of an HT, covered with
aluminium foil on the inside, properly bonded to the nanoVNA's port.
Of course you need to run the nanoVNA without an USB cable connected.
You will see that depending on how you grab that test contraption, the
measured values will shift somewhat. If you mount the antenna directly to
the nanoVNA, they will shift more, since the nanoVNA is a lot smaller than
an HT, at least the 2.8" screen version. I haven't compared the size of the
H4 version to that of an HT. It should be closer, but maybe not close
enough.
Perhaps someone else can comment on how accurate the measurements come
out when mounting a rubber duckie directly on an H4?
Manfred
