[Boatanchors] antenna question

[Glen Zook]

A 4:1 balun is going to be needed.  However, you can make one from a piece of coaxial cable for less than $1.00.  That is what I have on both yagis with folded dipole driven elements to match the 200-ohms balanced to 50-ohms unbalanced.

I can't remember if attachments make it through on this reflector!  However, attached is a diagram showing a 4:1 coaxial balun using 50-ohm coaxial cable for a 200-ohm to 50-ohm match.  You can use RG58/U, RG213/U, RG214/U, RG8X, RG8/U, etc.  To match 300-ohms to 75-ohms, use 75-ohm cable (RG59/U, RG-11/U, RG6/U, etc.)
 
Glen, K9STH


Website:  http://k9sth.com



On Thursday, January 16, 2014 2:57 PM, RAY FRIESS <rayfrijr at msn.com> wrote:
 
a folded dipole will need a 4:1 balun for feeding with coax ... or just straight coax feed?



________________________________
Date: Thu, 16 Jan 2014 12:43:25 -0800
From: gzook at yahoo.com
Subject: Re: [Boatanchors] antenna question
To: jack at n7oo.com; rayfrijr at msn.com; boatanchors at puck.nether.net


OO:

The entire driven element.


ITZ:

My 2-meter yagi started out as a Cush-Craft and the gamma match got into very poor condition.  I replaced the driven element with a folded dipole with the 2:1 rod diameter ratio.  My 222 MHz yagi still has the original gamma match.  Basically, the type of match used on the driven element really doesn't matter.

I obtained my 6-meter beam, along with other things, and there was no indication of the manufacturer.  It resembled the Cush-Craft but there were a few things different.  The driven element was in very poor condition and the gamma match was in even worse condition.
 
Glen, K9STH


Website:  http://k9sth.com



On Thursday, January 16, 2014 12:43 PM, Jack Taylor <jack at n7oo.com> wrote:
 
Glen, which horizontal element are you referring to, the gamma rod or the 
DE?

Jack - n7oo


-----Original Message----- 
From: RAY FRIESS
Sent: Thursday, January 16, 2014 11:15 AM
To: Glen Zook ; BoatAnchors
Subject: Re: [Boatanchors] antenna question

Actually, I
 misspoke...   My two meter antenna is the Cushcraft just like 
yours.   Two 11 element phased.  I have them
vertically mounted and phased for FM.  It's the driven elements on them that 
are gamma matched and kind of in
crummy shape.  I thought instead of rebuilding the gamma matches, I'd just 
build a different kind of driven element
that can be attached to the boom, or a type that I can insulate from the 
boom with a small plastic block mounted to the boom itself.

Date: Thu, 16 Jan 2014 10:03:54 -0800
From: gzook at yahoo.com
Subject: Re: antenna question
To: rayfrijr at msn.com; boatanchors at puck.nether.net

Generally, the type of match on the driven element doesn't matter.
On both my 6-meter yagi and 2-meter yagi, I have changed the driven element 
to a folded dipole.  This was done because I was having problems with the 
gamma match on both antennas.
If you make one of the horizontal sections half the diameter of the other, 
the impedance will be close to 200-ohms instead of the 300-ohms when both 
sections are the same diameter.  Then, matching to 50-ohm coaxial cable only 
requires a simple coaxial cable balun.
My 6-meter yagi and my 2-meter yagi can be seen in the second photo at:
http://k9sth.com/uploads/Antennas_At_K9STH.pdf Glen, K9STH

Website:  http://k9sth.com

     On Thursday, January 16, 2014 11:03 AM, RAY FRIESS <rayfrijr at msn.com> 
wrote:
    First of all ... let me take a moment to express sadness at the loss of 
Glen's fellow author, Glen W6ISQ.  While he was not a "technical" author 
like Glen, it was always a real joy to read his stuff, just like it was to 
read Glen's stuff in the magazines.Now ..  I have an antenna technical 
question.I have a HyGain 11 element two meter beam that uses gamma matching. 
The question I have is, does the type of drivenelement matter on a given 
beam as long as the driven element is adjusted for the best match at a given 
frequency?In other words, I am refurbishing the beam and have given some 
thought to redoing the driven element and usinga dipole, folded dipole or 
hairpin, or a Y match driven element.Ray  WA7ITZ


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