A long time ago, Heathkit made a balun like this. I have
one I bought on ebay, more as a curiosity than anything
I would ever actually use.
Rick N6RK
hanslg@aol.com wrote:
> Hi,
>
> I used a rather large, 4" diameter, 12" long solenoid with two parallell
> windings as a common mode choke for the ladder line to my windom antenna.
> Worked OK for my purpose. Kept the RF out of the shack. Used #14 wire with a
> little space between the wires. Have no idea how it affected the "SWR" in/on
> the line, but who cares. It is a ladder line after all.
>
> I don't see a practical solution to put a ladder line through a toroid core
> unless it is incredible large. It should be possible though even if it will
> be heavy. :-)
>
> 73 de N2JFS Hans
>
>
>
>
>
>
>
> -----Original Message-----
> From: jimlux <jimlux@earthlink.net>
> To: Jim Brown <jim@audiosystemsgroup.com>
> Cc: chas <chasm@texas.net>; towertalk <towertalk@contesting.com>
> Sent: Tue, 5 May 2009 10:27 pm
> Subject: Re: [TowerTalk] Ladderline - what are the facts??/
>
>
>
>
>
>
>
>
>
>
> Jim Brown wrote:
>> On Tue, 21 Apr 2009 00:14:50 -0500, chas wrote:
>>
>>> WHERE are the facts about ladderline??
>> Ladderline does not radiate differential mode current (the power it
>> carries from the transmitter to the antenna). Ladderline DOES
>> radiate COMMON MODE current. So does coax.
>>
>> Common mode current is the result of imperfect balance at either end
>> of the feedline. Nearly all practical ham antennas are unbalanced by
>> their surroundings. Common mode current causes radiation, and
>> antenna imbalance causes common mode receive current.
>>
>> An important difference between coax and ladder line is that coax
>> can be CHOKED to kill common mode current, but ladder line cannot.
>
>
>
> Just wondering out loud here.. If I put a twisted pair (unshielded) or
> ladder line through the center of a ferrite toroid, would it not choke
> the common mode currents? I can see this being somewhat impractical for
> ladder line, although with some sort of appropriate spacers to make sure
> it's perfectly centered, and the toroid would have to be big enough that
> it didn't intercept much of the differential mode field.
>
> (that is, with 1" wide ladder line, you'd probably need a ferrite with a
> 6-8" hole )
>
> (hmm, one could design a common mode choke for a balanced transmission
> line. they're pretty common for switch mode power supply inputs, so the
> challenge is designing one for HF.)
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