On Sat,9/12/2015 10:02 PM, Jim Thomson wrote:
Date: Fri, 11 Sep 2015 16:19:27 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Identifying Teflon Cable
On Fri,9/11/2015 3:17 PM, Richard (Rick) Karlquist wrote:
On 9/11/2015 1:24 PM, Jim Brown wrote:
Which is a terrible choke, because the Q of #61 material is far too
high.
73, Jim K9YC
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There is a tradeoff regarding power handling. 61 material will have
far less heating than, for example, 43, or 31. Depending on what
you are trying to do, 61 might make sense. I use it in my
50 ohm to 450 ohm bal-bal transformer.
You're talking about a TRANSFORMER to handle RF power, where higher Q is
desirable. My comment was on use of the core for a choke.
Important fundamental principle: Chokes want LOW Q material, lots of
resistance, transformers want HIGH Q if they need to handle power. #61
high Q below 10 MHz, low Q at UHF, so it is a good choke material at
UHF, a good transformer material below 30 MHz. This is true of nearly
all ferrite materials -- materials have low loss at lower frequencies,
so can handle power, much more loss at higher frequencies, so can't
handle power but are good as chokes. A key difference between materials
is WHERE they transition from low loss to high loss.
73, Jim K9YC
## Even then, you would still want to follow up immediately with a good CHOKE
balun.
IE: 1:1 choke balun using type 31....followed by the 1:9 xfmr using type 61.
Yes.
## same deal if a 1:4 xfmr used...like on a 200 ohm yagi. 1:1 choke 1st,
then the 1:4 xfmr.
Maybe it's semantics, but the correct arrangement is the 1:4 transformer
matching the 200 ohm Yagi to 50 ohm coax, then the choke in the 50 ohm
section.
I wouldn’t call any of the various xmfrs a choke.
RIGHT! More examples of why I strongly object to use of the word
"balun" -- it is used to describe nearly a dozen objects or products
that are VERY different from each other.
73, Jim K9YC
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