[BVARC] 70cm J Pole SWR. Is it supposed to look like this?

[Daniel Poirot]

TL;DR  What does a 70cm VNA trace look like?


Howdy y'all,

The car is in the shop, so I had some time on my hands...

I took a 16 cm section of 450 Ohm ladder line, shorted one end, soldered on
a 32.5 cm length of wire and BOOM. I have another J Pole.

I tacked on a short length of RG-8x, 1.6 cm from the end, and put a female
BNC on the end. Closer still!

I calibrated my NanoVNA for 420-450 MHz and made a trace of SWR and
Resistance. I am looking to hit the 444.3 repeater.

[image: Screenshot 2025-10-15 at 4.16.08 PM.png]

This here is some messed up stuff. Do I have to tune to catch 50 Ohms as it
goes by?

The SWR minimum is to the left of 444.3, so my J Pole is long. I am about
to nibble away.

Should I expect a 25 MHz cycle like this? The middle of the cycle will be
crazy SWR and terrible resistance, right?

Comments welcome!

73
Dan KJ5IZK
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