[TowerTalk] Shunt Fed Tower - 160 Meter Gamma Match Question

[Chuck]

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.

Chuck W5PR
----- Original Message ----- 
From: "Larry K4AB" <larry.k4ab at gmail.com>
To: "Tower and HF antenna construction topics." <towertalk at contesting.com>
Sent: Monday, February 15, 2010 10:50 AM
Subject: Re: [TowerTalk] Shunt Fed Tower - 160 Meter Gamma Match Question


> Chuck,
>
> I've installed a lot of 160 shunt feeds.  I would start by raising the 
> gamma
> attachment point.
>
> Usually 2/3 the height of the tower would be fine. In your case 90' should
> work well.
>
> GL!
>
> 73,
> Larry K4AB
>
> On Mon, Feb 15, 2010 at 10:35 AM, Chuck <w5pr at swbell.net> 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 
>> have
>> run an old piece of coax up 35' about 2' off the tower for a gamma.  I 
>> have
>> 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 
>> pf
>> 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?
>>
>> Thanks!
>>
>> Chuck W5PR
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