As others have already posted, the log will show wild SWR curves even when
high in the air, altho should show decent freq/SWR response within the band
segments it's designed for (in our case, the ham segments). On or near the
ground, meaningful measurements of the antenna are nearly impossible to
achieve.
I put up a Tennadyne T10 years ago (it's still up there and doing a good job
BTW), and tried measuring it pointed to the sky, and also set up on
sawhorses. The measurements were interesting (and pretty terrible), but
proved nothing. I decided to put it on top of the tower anyway, and it
started to measure & perform as I'd hoped.
If your log is a commercial design of known-good specs and performance in
the amateur segments, AND you're certain you've built it correctly, with
correct choke & feed, then you're probably safe to put it in the air and
then see what measurements you get. If it's a homebrew design, you're kind
of on your own!
GL es 73
dan
k0dan
-----Original Message-----
From: Doug Ronald
Sent: September 25, 2015 20:16
To: TowerTalk@contesting.com
Subject: [TowerTalk] Expected VSWR of antenna near the ground
I have assembled my 19 element LPDA with the front 12 elements about 3 feet
off the ground and parallel to the ground. The back elements are laying on
the ground, but electrically connected in the usual LPDA way. Today, as a
check before I erect it, I swept with a VNA, the antenna from 1 MHz through
32 MHz. The VSWR is horrible! It has peaks and deep dips at the low end, and
then at 14 MHz or so, rises to over 5:1 and stays there. Now I didn't
expect even 2:1 over the range, but I expected the VSWR on the high end to
be at least reasonable, because the front shorter elements are off the
ground.
Anyone care to weigh in with an opinion? I hoping an expert says this is
perfectly normal for an antenna just a few feet off the ground. If not, I'm
kind 'a stuck as I have checked all the connections with an ohm meter, and
they are all okay.
Thanks,
W6DSR
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