[TowerTalk] To Choke or Not to Choke?

[Jim Brown]

The choke I've described IS a common mode choke, and far better than 
anything you can buy.

73,

Jim K9YC

On Sun, 15 Feb 2009 20:43:31 -0800 (PST), Edward Sylvester wrote:

>Jim:

>Will a common mode filter be as effective?


>--- On Sun, 2/15/09, Jim Brown <jim at audiosystemsgroup.com> wrote:

>> From: Jim Brown <jim at audiosystemsgroup.com>
>> Subject: Re: [TowerTalk] To Choke or Not to Choke?
>> To: "towertalk at contesting.com" <towertalk at contesting.com>
>> Date: Sunday, February 15, 2009, 8:14 PM
>> On Sun, 15 Feb 2009 17:58:56 -0800 (PST), Edward Sylvester
>> wrote:
>> 
>> >I have a LW/Inv L that I will feed thru an auto tuner
>> at the base, 
>> >with radials.  Was wondering if I should bother with
>> forming a 
>> >coaxial choke (12-15 turns at 6" diameter) before
>> it enters the 
>> >shack 30 feet away.
>> 
>> I coil of coax with no ferrite is a waste of coax -- it
>> will look 
>> inductive, the rest of the line will look capacitive, and
>> the result 
>> will be lots of feedline current. You DO want a choke on
>> the coax 
>> side of the tuner, but it needs to be 7 turns through five
>> Fair-Rite 
>> #31 1.4-inch i.d. cores (commonly advertised as FT-240-31
>> by those 
>> mark them up 4X their cost and resell them to hams). If
>> you're 
>> feeding with RG8, you will need to wind the choke before
>> you put the 
>> coax connector on -- you can fit 7 turns through those
>> cores, but 
>> only with no connector attached. 
>> 
>> For a tutorial on all the technical background on this see 
>> http://audiosystemsgroup.com/RFI-Ham.pdf
>> 
>> 73, 
>> 
>> Jim Brown K9YC
>> 
>> 
>> 
>> _______________________________________________
>> 
>> 
>> 
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk


>