This turn out to be a very interesting thread. I recently inserted some
information about my inverted L antenna for
160 with 4 elevated radials on my qrz.com profile.
EC1CT, Fernando
73s
-----Mensaje original-----
From: Dave Sublette
Sent: Saturday, August 29, 2020 8:23 PM
To: kj6y--- via TowerTalk
Subject: [TowerTalk] Antenna and Radial current
Having followed the Inverted L discussion and learning lots, I decided to
document my 160 elevated ground plane antenna. It has been up for thirty
years. I replaced the feedline last year. It is 200 feet from the shack
and I ran a new run of half inch superflex through an underground conduit.
I have been very happy with the performance of this antenna. I work the
CQWW160CW contest QRP, an honest five watts output and place in the top ten
in North America and top 20 in the world. If I weren't too old to stay
awake a little longer, I might do better. Hi
I hate long detailed emails, but I think you should have an idea of how the
thing is made before I ask for your advice. The tower is Rohn 45 with a
length of four inch irrigation pipe at the top to adjust for best SWR. SWR
at the moment is 1.6:1. The feed point is a Rohn Broadcast antenna section
with the insulators at 27feet. Eight Radials are attached to an aluminum
plate which is insulated from ground also. The SO239 connector has three
#12 wires, one to each leg. The radials are each tied off with an
insulator and the pigtail fastened to the aluminum plate with threaded, #10
screws and terminals. The radials are #13 from Davis RF, insulated.
So I took my KX3 and a battery pack up to the feed point and took data in
each wire, while transmitting with 5 watts. I expected to find the RF
current to be divided in thirds in the radiating element and by 8 in each
of the radials. I had previously calibrated my RF current meter at five
watts to a dummy load on the bench.
On my RF Current meter, 5W to a dummy load yields 41 micro amps on the
meter.
If the system works as I expected, I should see13.66 microamps in each wire
to the tower and 5 microamps + in each radial.
What I measured was unequal currents in the three wires to the tower, 13.1,
9.8, and 15.6 microamps. Close on the total, but not equal.
The Radials measured, 9.8, 6.4, 0,1.8, 26.2, 0, 1.9 and 0 microamps.
My first thought is to go back up and clean up all connections, replace
crimp terminals on the radial ends and re-measure.
Additionally, I should be able to take an antenna analyser up (VA-FA5) and
measure the behavior of each radial. I expect to see differences because
of variations in droop angle, nearby objects (barn), etc. But I don't know
what to think about the radials that measure 0 and less than 2 ua.
Does anyone have any further suggestions for how I should go about testing
and troubleshooting this system?
I am totally surprised by this result, since this antenna works (but we all
know that this is an inaccurate and unscientific statement).
Thanks for your patience, if you made it this far.
73,
Dave, K4TO
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