[Elecraft] Balanced solution for KAT500 tuner?

[Robert G. Strickland]

Jim...

Thanks for your reply. I think I've been unclear in my question. I'm not concerned as 
to what "it" is called, how to build "it" or what "it" costs. These things can all be 
agreed upon and implemented.

What I'm curious about is whether some such device, at the feed point of a doublet, 
in turn fed by window line is of any use [assuming an appropriate tuner at the radio 
end of the line]. You have said, accurately so, that a current choke at the feed 
point of a dipole [let's leave off-center fed antennas out of it at this point], in 
turn fed by coax, keeps RF from flowing on the outside of the coax and subsequently 
becoming "part of the antenna" and in turn picking up noise/etc. Another way of 
phrasing my question is, does the coax situation apply to open feeders, also?

For example, let's say we have a Johnson Match Box with balanced output, connected to 
open feeders, running up to a doublet antenna; is there any point in putting some 
sort of coupling device at the feed point between the line and the antenna? Still 
another way of asking this is: assuming a real antenna will be unbalanced due to all 
the usual factors, is there any way, and is there any RF benefit, in forcing a 
current balance into the open wire feeder?  Thanks for your patience and input.

...robert

On 9/29/2012 21:43, Jim Brown wrote:
> On 9/29/2012 11:26 AM, Robert G. Strickland wrote:
>> Is there anything to be gained in putting a 1:1 "balanced isolator" at the feed point
>> of an antenna that is fed by a "parallel wire" feed line? Does such an arrangement
>> achieve feed line isolation while preserving the ability of such an antenna to be
>> driven on various bands other than its resonant frequency? Thanks for your input.
>
> Phrases and words like "balanced isolator" and "balun" are not only
> confusing, they are used to separate people from their money.  The
> chokes described in my RFI tutorial can be built for the price of a
> single #31 core, a few yards of THHN wire, and a couple of connectors.
> You can put it in a box if you like, but it's only cosmetic.  These
> chokes will handle legal power IF the antennas are not badly
> unbalanced.  Off-center feed creates massive imbalance, and will fry
> even the best of chokes.  The relatively small imbalances created by
> surrounding objects will not -- they simply couple noise.
>
> #31 cores cost about $4.50 in 1,000 lots, about $7 if you buy 100, and
> $15 from the rip-off vendors who advertise in QST.  It's become fairly
> common for ham clubs to get together and make a group purchase. Over a
> period of about 8 years,  I've been part of several at the 1,000-piece
> level.  There are guidelines in Appendix One of the tutorial about how
> and where to buy.  It's worth buying in quantity, because these 2.4-in
> diameter cores are almost universally useful for RFI suppression.
>
> 73, Jim K9YC
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-- 
Robert G. Strickland, PhD, ABPH - KE2WY
rcrgs at verizon.net
Syracuse, New York, USA