Terry
My tower is 116 high , plus 10 ft of mast with a top hat, and the HWF. I
never had any problem on 80m because the antenna is too long and near 1/2
wave vertical for 80m, my Vertical WF is 60 ft from the tower and I never
noticed any degradation on the irradiation diagram measured with polar plot.
My friend Peter N8PR used to have the K8UR four square for 80.. It worked
very well on 80m, however the dipole side connected to the coaxial braid,
connected to the phase box than connected to another coaxial and the other
dipole connected to the braid, all this connected forms a 1/2 wave on 160m.
Peter antenna on 160m is very similar to my but his signal was always 10 db
lower than my on 160m, the 1/2 wave formed by the 80m dipoles was changing
the irradiation patter on 160m, simulating on EZNEC we found that the signal
was going up and not low angle as it should be on 160m. Peter disconnected
the 80 dipoles from the phasing box and immediately his 160m signal become
very similar to my signal on all RBNs that we were able to check.
Saying that, John K9UWA detuned his tower and his 4 square improved a lot.
The way to find the capacitor value is using a small variable capacitor in
series with a MFJ 259, adjust the capacitor for zero ohms reactance on the
MFJ meter.
Luis IV3PRK has on his site a detailed description how to detune the tower
using antenna analyzers, here
http://www.iv3prk.it/detuning-tx-ant..htm
http://www.iv3prk.it/user/image/site2-rxant.prk_detuning-tower.pdf
73's
JC
N4IS
-----Original Message-----
From: Topband <topband-bounces@contesting.com> On Behalf Of John Kaufmann
Sent: Saturday, December 22, 2018 7:12 AM
To: 'terry burge' <ki7m@comcast.net>; topband@contesting.com
Subject: Re: Topband: capacity needed for Deturning tower
On 160 I've used a vertical wire of 20 feet with a 1000 pF variable
capacitor to detune a tower at its base. You can scale that to 80.
73, John W1FV
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of terry
burge
Sent: Friday, December 21, 2018 9:22 PM
To: topband@contesting.com; terry burge
Subject: Topband: capacity needed for Deturning tower
Hi again,
This may not be possible to answer with anything like 10% accuracy but can
someone give me an idea just how much capacitance I need for putting up a
50-55' vertical wire up the lower half of my tower to detune it on 75 meters
around the DX windown (3790-3800 Khz). The tower is Rohn 55 with 117' above
ground. A 3 element 20-6 mtr Steppir at 118', a GP6 at the very top with
peak at 134' and a 40 meter dipole (63' or so) at 104'. I have my K8UR style
4-Square around the tower with the lower half of the slopers pulled in
towards the tower.
Since I've not been able to get a beverage or bog to work due to a lot of
noise I'm going to run a detuning line up to below my Comtek unit at 64' and
try detuning the tower. But I just don't know what to expect to need for
capacitance to detune the tower.
Terry
KI7M
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