[Elecraft] Possible doublet configuration

[qrp_1 at juno.com]

Following this thread with much interest. I need a stealth antena and
a doublet may do the job.
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? [[snip]]

Sure you can do it that way, but the ATU may or may not tune it on all
bands - depends on that matching range of the ATU and the impedance of
the antenna system at each frequency.  Impedance does change with
frequency, and as long as it stays within the matching range of the ATU,
it should work just fine.  But I think you would have much greater
success with a non resonant length for the doublet - say an 88' doublet
for 10 thru 80 meter coverage, or a 44' doublet for 10 thru 40 meter
coverage.  These lengths aren't carved in stone either, the theory is to
stay away from 1/2 wavelength per side of the doublet to avoid extremely
hig impedance.  You might even want to look into an off center fed
doublet fed with balanced feedline with the balun at the end of the
balanced feedline and a short run of coax coming into the shack.  The
idea behind the off center feed is that the impedance stays fairly close
to the same (around 200 to 300 ohms)  over a wide frequency range and
allows a 4:1 balun to convert it down close to 50 to 75 ohms (or
thereabouts).  Do a google search for the FD-3, or FD-4 antenna to get a
better idea of what I mean.
 
Is it OK to bring ladder line into the shack? [[snip]]

Sure !  Just keep it clear of long runs that are parallel to large metal
objects and it will work just fine.

73 - Rick McKee, KC8AON
Southern Ohio - EM88sn
www.angelfire.com/electronic2/qrp
With God all things are possible ~ ><(('> ~