[TowerTalk] Ferrite Balun on a LPDA?

[Jim Chaggaris]

" With the LPDA the antenna boom is actually part of the feed system for
the elements."

Not always the case with every LPDA design.  Maybe with Tennadyne's LPDA
design it is.  My buddy Tim (N9IW) homebrewed his 14 element logs and a 1:1
balun is placed at the front of each LPDA.  All elements are insulated from
the boom and he uses a separate phasing harness. Works great!

Check it out at DX Engineering's Showcase
 
73,

Jim N9WW
 
James Chaggaris
President
PowerOne Corp.
1020 Cedar Avenue
Suite 110
St. Charles, IL 60174
Phn: 630-443-6500
Fax: 630-443-6505
Cell: 630-669-2241
www.pwrone.com

 
-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of R. Kevin Stover
Sent: Thursday, June 14, 2007 5:58 PM
To: n7ka at comcast.net
Cc: towertalk at contesting.com; Tom Rauch
Subject: Re: [TowerTalk] Ferrite Balun on a LPDA?

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Big difference between LPDA and mono bander.
With the LPDA the antenna boom is actually part of the feed system for
the elements. If you install the choke/balun at the feed point, then
tape the coax to the boom you have negated choke/balun at the feed point
because the cable is tightly coupled to the RF hot boom.

Not so with a mono bander like the OWA and others where the boom is
insulated from the driven element. Tape or clamp the balun/choke any
convenient spot.

n7ka at comcast.net wrote:
> Guess I need a bit of clarification on a point or two.  I am thinking
monoband yagi, not LPDA  for my questions.
> 
> 1.  You state
>      "the  coax needs to be routed down the boom tied to the shield."
> 
> I take this to mean the shield of the coax should be connected to the boom
close to the feed point.  
> 
> 2. You state
>     "If you tape the coax to the boom  the balun needs to be at the point
where the coax leaves the boom to go to the tower, not out at the feedpoint"

> 
> I take this to mean placing rhe balun after the 90 degree turn from the
horizontal boom to the vertical mast.  Will taping the balun and coax down
the mast have detrimental affects?  Will the balun need to be spaced from
the mast and if so how far?
> 
> In the case of an OWA type antenna with split dipole feed(dipole insulated
from the boom), would the coax shield get grounded to the boom near the feed
point and the balun placed after turning down the mast?
> 
> Arne N7KA
> 
> 
> -------------- Original message -------------- 
> From: "Tom Rauch" <w8ji at contesting.com> 
> 
>>> I am close to putting my Tennadyne T-6 back up. When I took 
>>> it down it had the prescribed Coax Balun on it and it 
>>> showed it's age. For the last month or so I have had the 
>>> antenna on a short perch in the yard with a Ferrite Bead 
>>> Balun on it and it sweeps fine using an analyzer and I have 
>>> even made a few DX contacts on it. The balun I am using is 
>>> a W2AU by Unadilla. I have searched different archives and 
>>> the only one with any significant information is one I 
>>> started on eHam some years ago.The old Tennadyne maker 
>>> specifically said he had not tested a ferrite balun and did 
>>> not recommend them. The reasons I would like to use the 
>>> Ferrite Balun are: 
>>
>> Watch how you run the coax. If you use a balun and then tape 
>> the coax to the boom (which is hot) you totally defeat the 
>> reason for having a balun. If you tape the coax to the boom 
>> the balun needs to be at the point where the coax leaves the 
>> boom to go to the tower, not out at the feedpoint, and the 
>> coax needs to be routed down the boom tied to the shield. 
>>
>> 73 Tom 
>>
>>
>> _______________________________________________ 
>>
>>
>>
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> _______________________________________________
> 
> 
> 
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> 

- --
R. Kevin Stover, ACØH
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