Lowell,
Don is giving some good advice here, as usual. The circuit of
balun that I built is essentially identical to the BL2. I made mine
using two FT-240-43 toroid cores - I needed a balun in a watertight box
since it located outside in the rain and snow. I also wanted a balun
that can handle more power than the BL2, since I aspire to higher power
when I grow up. The one I made uses 12 bifilar turns of #12 wire, and
should easily handle a kW. A diagram of this two core balun is found on
page 26-24 of the ARRL antenna book (the same diagram is also in the
transmission line section of my 1999 edition of the ARRL handbook). I
mounted the two toroids in a plastic box from Radio Shack, with a coax
connector on one side and screw terminals for the ladder line on the
another side, plus a screw terminal for the ground connection for the
counterpoises. If you look at the schematic on the BL2, several of the
toroid leads go the switch. In place of the switch, I brought those
leads out to screw terminals and use one external jumper between screw
terminal for the 4:1 configuration, and two external jumpers between
from the other screw terminals for the 1:1 configuration. With wing nuts
on these jumper screw terminals, I can quickly switch between the 1:1
and 4:1 configurations (for my home setup, I just keep the balun in the
4:1 configuration - the quick change ability I use when I take the K2 on
the road with antennas that the characteristics will change depending on
the trees they're attached to) - of course, you can put the BL2 in a
watertight box, but then you don't have easy access to the 1:1/4:1
switch, which in a fix setup you probable don't need to change often
anyway.
73
Bob W1SRB
-----Original Message-----
From: Don Wilhelm [mailto:[EMAIL PROTECTED]
Sent: Thursday, February 22, 2007 12:44 PM
To: Lowell; Solosko, Robert B (Bob); elecraft@mailman.qth.net
Subject: RE: [Elecraft] Rf in the shack distorting audio - the results
Lowell,
Look at the Elecraft BL2 for a switchable 1:1/4:1 balun, it will handle
up to 250 watts. If you do not need the switchable arrangement, the BL1
can be constructed for either a 1:1 or a 4:1 configuration and its power
rating is 150 watts. A convenient ground lug is located on the balun
output side.
Look on the Elecraft website - click Our Products, and from there click
on Mini-module kits.
73,
Don W3FPR
> -----Original Message-----
>
> I found your solutions to curing RF in the shack very interesting. I
> have a similiar problem to yours and would appreciate info on the
> 4:1/1:1 Current
> balun. Thanks
> Lowell, W5FH
>
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