[TowerTalk] 40 Meter Yagi

[Jim Thomson]

Date: Sun, 18 Jun 2017 11:02:02 -0600
From: "Doug Renwick" <ve5ra at sasktel.net>
To: "'AB2E Darrell'" <ab2e at hotmail.com>, "'Kim Elmore'"
<cw_de_n5op at sbcglobal.net>, "'Gary'" <gary_mayfield at hotmail.com>
Cc: <towertalk at contesting.com>
Subject: Re: [TowerTalk] 40 Meter Yagi

<Hi,
<I junked my Hygain Discoverer and replaced it with the XM-240. The linear
<loading wires near a bend at the end would keep 'breaking'. Keep in mind the
<XM-240 balun is a piece of junk. The rest of the antenna is good value.
<Doug 

##  Linear loading is out of vogue these days.   But the coils used in the XM-240
leave a bit to be desired, too lossy imo.  They could have done the coils better. 
Still, its a proven performer.  

##  68 turns of 12 ga magnet wire, wound tight, on a 5.57 inch long  x  .75 OD solid fiberglass rod
results in a less than optimum coil Q...like Q = 81. http://www.qsl.net/ve6wz/CC_coil.html   Steve rewound the
oem CC  coils with hb coils made of .1875 AL tubing, air core. 
11.5 turns, 5 inch diameter, 5 inch long  x .1875 inch OD   Al tubing, 3003-H0 alloy.   Q=767

The complete unit weighs 12.1 oz.

The original CC coil weighs 11.4 oz.   

##  If made from  .1875  Cu tubing, the  tubing weight would have increased by aprx 2.76 X.   Q = 1200

##  If you use Termans  formulae, the coil Q is even less,  but this is all debatable.  

##  JK antennas  winds their 40m  coils from .25 inch solid  AL...then welds the ends. Zero ohm connections. 

https://jkantennas.com/manufacturing.html

Jim  VE7RF