[Elecraft] Possible doublet configuration

[Craig D. Smith]

<> Could I feed my K3/100 with ATU into a BL2 right at the antenna
<> connector, the output of the BL2
<> to home made ladder line, (2 to 4 inch spacing) to a doublet approx
<> 1/2 wavelength on the lowest
<> freq?  Is it OK to bring ladder line into the shack?

This might work, but I think you will be better served with a few
modifications.  First of all, stay away from 1/2 WL on the lowest freq band,
as higher bands will be harmonically related and can give you difficult to
match impedances.  I use 105 ft for my 80 thru 10  contest antenna.
Secondly, stick with the published ideal feedline lengths and impedances,
for example 30 ft of 300 ohm line for the 105 ft doublet.  Ladder line can
be brought inside, but coax is MUCH more user-friendly and can avoid lots of
problems.  Keep it as short as possible.  Here, I use 6 ft of RG-213 to go
from the K3 to the window termination with the ladder line.  I've tried the
BL2, and it worked OK most of the time but sometimes got quite warm - not a
good sign.  Instead I made a choke balun consisting of 4 turns of LMR-240
wound on two of the Fair-Rite type 31 big clamp-on ferrites (Mouser PN
623-0431177081).  This unit works GREAT based on both impedance measurements
and my actual experience.  It sits right in the window opening and
interfaces the ladder line with the RG-213.   The K3 internal tuner works
just fine with this setup on 80, 40, 20, 15 and 10.  Haven't really tried
the WARC bands.

         73        Craig   AC0DS