[TowerTalk] Common-mode choke

[Jim Thomson]

Date: Mon, 19 May 2014 23:54:57 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Common-mode choke

On 5/19/2014 6:19 PM, Jim Thomson wrote:
> use 2 foot of the large diam type 43 beads  slid over  213u  or  393 coax.

Sorry, Jim, but string of bead chokes using #31 or #43 simply are not 
very effective on the HF bands because their resonance is at VHF, and 
their resistive component at HF is very low. Study k9yc.com/RFI-Ham.pdf 
to understand why resistance is good and inductive reactance is bad.

73, Jim K9YC

##  per steve hunts charts, they, bead baluns, depict a large resistive component. 
Thats his black line on each chart. 

##  if any choke is high resistance, it will work..provide the Z is sky high. 
Power is still I squared x R. 

##  If you really wanted a sky high Z... a physical  quarter wave of coax...
or a  3 quarter wave of coax.....  minus 2-3%.... with the braid bonded to
the top of the tower, works extremely well.  Then no ferrite required at all. 

##  The fellow wanted a choke balun for the 10M band.    24 inches worth of large diam
beads slid over 213 or 393 will easily suffice on 10m band. 

##  4 turns of 213 u  around 4 x 2.4 inch od  type 31 cores will also work.

##  If its just a 10m yagi on a tower....a  physical quarter wave.. minus 2-3 %
will do the job very readily. 

Jim   VE7RF