[TowerTalk] 43' vertical mod for true resonance on 80M

[Mark Robinson]

----- Original Message ----- 
From: "Rick Karlquist" <richard at karlquist.com>
To: "Jim Brown" <jim at audiosystemsgroup.com>
Cc: "Tower Talk List" <towertalk at contesting.com>
Sent: Tuesday, 17 February, 2009 6:18 PM
Subject: Re: [TowerTalk] 43' vertical mod for true resonance on 80M


> Jim Brown wrote:
>>> My 160M antenna is 86 ft vertical with a lot of top loading and 60+
>> radials. People tell me I'm loud. My top-loading makes it electrically
>> longer than a quarter wave so that it looks inductive (50 + j200 or so),
>> and I tune the j200 out with capacitance.
>>
>> 73,
>>
>> Jim K9YC
>>
>
> Just wanted to second what Jim said.  I also have a 90 ft vertical
> (for 160 meters) with top loading that is resonant a little below the band
> edge and tuned upward with a series capacitor.  It is over a 230 foot
> diameter ground screen.  I also have people tell me I'm loud.  The top
> loading increases the radiation resistance about 50%.  By using more
> top loading than is necessary to attain resonance, I move the current
> maximum up above ground and further increase driving resistance.
> This same antenna on 80 meters has about 1000 ohms drive impedance
> at the bottom.
>
> The top is guyed with four pieces of baler twine coming down
> at about a 45 degree angle.  The top loading wires are 30 feet long
> and are ty-rapped to the guy ropes.
>
> If you only have 43 feet, by all means add top loading if you can.
>
> It is easy to model top loading with EZNEC.
>
> Rick N6RK
>
> _______________________________________________


I am planning something like this. What sort of capacitor do you need to use 
as the series feeding element.......a vacuum capacitor?


Mark N1UK