Date: Mon, 19 May 2014 23:54:57 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@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
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