[TowerTalk] decoupling

[Tom Rauch]

> If the coax feeds are brought up through the tower body and tied to
> one of the legs is there any or enough choking effect to preclude a
> coax choke at the top at the center insulator. Life would be a lot
> simpler if we didn't need the choke at the top.

You may not need a choke at each dipole, it all depends on many 
things. I use them just to be safe, because I like my antenna to do 
all the radiating!

> I seem to recall folks running coax through the boom to the DE and
> claiming a choke effect of the metal boom got them out of using a
> balun at the DE, urban myth?? 

Yep, that's mostly an urban myth!

The only way a sleeve works is if it is 1/4 wl long and open at the 
dipole feedpoint and grounded to the coax shield 1/4 wl from the 
feedpoint.

You also have to include the velocity factor change caused by the 
outside insulation of the coax and the spacers used. The coax has 
to be centered in the sleeve, and preferably the diameter ratio of 
coax OD to sleeve ID  should be large.



73, Tom W8JI
W8JI@contesting.com 

List Sponsored by AN Wireless:  AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 100 feet for under $1500!!  http://www.anwireless.com

-----
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com