I tried Bud, W2RU's suggestion of switching the shunt capacitor, but it made
the receive level lower.
I moved the gamma tap to 70 feet. I connected the center conductor at the
top and the shield at the bottom of the coax gamma "rod" I am using, to
increase the series capacitance. That increased the receive level
substantially. I can hear all kinds of signals early in the evening. The
background noise is S-9 on SSB. This is as good as the receive gets on a
vertical here, but I am not getting a match.
Do I need to "bite the bullet" and move the tap up to 90 feet like Larry,
K4AB says? Or has someone used more capacitance with these approximate
heights? I feel I am close due to the good receive.
----- Original Message -----
From: "Larry K4AB" <email@example.com>
To: "Tower and HF antenna construction topics." <firstname.lastname@example.org>
Sent: Monday, February 15, 2010 10:50 AM
Subject: Re: [TowerTalk] Shunt Fed Tower - 160 Meter Gamma Match Question
> I've installed a lot of 160 shunt feeds. I would start by raising the
> attachment point.
> Usually 2/3 the height of the tower would be fine. In your case 90' should
> work well.
> Larry K4AB
> On Mon, Feb 15, 2010 at 10:35 AM, Chuck <email@example.com> wrote:
>> I am trying to shunt feed a tower for 160 meters. I have a 135' Rohn 55
>> tower with several good sized antennas on it. Guys are insulated. I
>> run an old piece of coax up 35' about 2' off the tower for a gamma. I
>> about a 150 pf variable in series and 200 pf to ground. Ground is 2 -140
>> foot radials, elevated 10' (In the past I think I have used larger
>> capacitors for this.)
>> I do not get any match on the series variable with 200 pf, 100 pf and 0
>> to ground.
>> What is the easiest thing to do now?
>> 1. Shorten the radials?
>> 2. Increase the series capacitance?
>> 3. Increase the capacitance to ground?
>> Is my gamma too short?
>> Chuck W5PR
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