CQ-Contest
[Top] [All Lists]

Re: [TowerTalk] Modeling antenna traps

To: Timothy Holmes <taholmes160@gmail.com>
Subject: Re: [TowerTalk] Modeling antenna traps
From: Don <k9muf@comcast.net>
Date: Sun, 5 Jun 2016 17:41:32 +0000 (UTC)
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Hi Tim,

I haven't seen any replies to your question so perhaps I can give you a few 
clues.
I can't help you with modeling the traps, but you can do it by experimenting.
First of all you should determine what frequency you want the traps to be 
resonant at. 
It might seem that they should be resonant in the higher frequency band that 
you want to
separate from the lower band but that can cause high losses. This was discussed 
in an article in Ham Radio magazine of August, 1987 by Yardley Beers, W0JF and 
also by w8ji. For the lowest loss, the trap should be resonant at a frequency 
about midway between the bands.
I have build a trapped Yagi beam by measuring the trap frequencies with a grid 
dip oscillator.
This can be a little tricky and requires some practice if you haven't used a 
GDO before. When measuring the trap, it should be disconnected from other 
elements of the antenna and should be separated from other metal objects. There 
may be other ways to measure the frequency, but I haven't tried them. You can 
also calculate the inductance and capacitance required to the resonate the 
trap, but then you have to have a way to measure those values. If you are using 
old trap assemblies, you are pretty much limited by the capacitance built into 
the trap, but you can adjust the inductance by changing the number of turns in 
the coil. Once you have the trap made, you should make arrangements to adjust 
the lengths between the trap and the antenna elements.You can then adjust the 
frequency of each band by using an SWR meter or an antenna analyzer starting at 
the highest frequency band first.

Good luck.

Don,  K9MUF

----- Original Message -----From: Timothy Holmes <taholmes160@gmail.com>To: 
Tower Talk <towertalk@contesting.com>, cq-contest@contesting.com 
<CQ-contest@contesting.com>Sent: Wed, 01 Jun 2016 20:52:27 -0000 (UTC)Subject: 
[TowerTalk] Modeling antenna traps

Hi folks ...

Bit of an off topic here.

I want to model a vertical made from old tribander parts. Its easy to getthe 
length and diameter measurements, but I dont know how to measure ormodel the 
traps. I am using MMANA, but I also have a demo of Eznec anyinput would helpful.

ThanksTimW8TAH_______________________________________________



_______________________________________________TowerTalk mailing 
listTowerTalk@contesting.comhttp://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>