The coax, unless it's defective, only adds loss (and rotation around the
Smith Chart) to the measurement of the antenna. It doesn't affect the
frequency response.
You could calibrate S11 with the coax connected and applying Short, Open,
Load at the far end of the coax with the antenna disconnected.
Or, just measure it as is - the Return Loss dips will be at the same
frequency as if you measured directly at the antenna. Just the depths of
the dips will be different.
Make sense?
73, Carey, WB4HXE
On Tue, Mar 31, 2020 at 1:30 PM Jeff W6FCC via Groups.Io <w6fcc=
[email protected]> wrote:
Setup: I have a 40 meter dipole at 30 feet. Feeding with 100 ft of RG8X
Measurement: 7.200 Mhz, SWR at RADIO end of COAX can be measured (For the
Analysis System -- coax + antenna)
Question: Can the Reference plane be "calculated" by software. It's the
location of the antenna at the END of the Coax, discounting the Feedline,
perhaps by entering the Feedline Impedance and Velocity Factor and Loss?
Asked a different way:
Can the NanoVNA be used to isolate the antenna at the far end of the COAX
and somehow IGNORE the impact of the COAX itself ?
I realize the best way to check the antenna is AT the feedpoint, but that
is not possible right now. I'm stuck at the Radio End of the COAX and
trying to determine of the DIPOLE is too long or short.
One possible "solution" IF I could take a second piece of 100' RG8X and do
the calibration at the far end (OPEN, SHORT, LOAD) and push the Reference
plane out to the 100' mark.
But can it be done without a second piece of COAX ??
Has anyone calibrated their NanoVNA using a long piece of coax and doing
the CAL at the end of the coax before attaching to an antenna to be tested ?
Jeff, W6FCC, 3-31-2020
--
Carey Fisher
careyfisher@...
