[Qcwa] "Hidden" HF antenna

[Allan Henry Kaplan]

Keith, 
We all wish you good luck!  It is very hard to predict what effect your
foil-wrapped duct will have on your proposed zig-zag attic dipole,
except that it will almost certainly screw up the tuning of a dipole
built to formula!  The foil is every bit as good a conductor as a solid
metal duct would be, thanks to RF skin-effect.  At HF, the current stays
near the surface of a conductor.  If it were possible to strip off a
circumferential stripe of foil near the center of the duct run, you
could even try feeding it with coax -- braid to one side of the cut and
center conductor to the other.  I would sure keep the power low, because
it's possible you could start a fire!   It is wishful thinking that the
metallic duct would act as a 75-meter reflector, though!  It is probably
much too close to the proposed dipole proper to be a reflector.  Normal
spacing for a reflector is 0.15 to 0.2 wavelengths...

We are all sorry to hear of your all-too-common predicament in an
antenna-restricted development, and wonder if you have written the ARRL,
who has been collecting anecdotal evidence of how such restrictions
hamper our amateur radio service.   They will use what they learn of
amateur hardship in this area to counter the FCC's ill-considered
concept that we do not need to operate from the comfort of our homes,
'cause we can always go mobile!  The more pieces of ammunition ARRL has
in this skirmish, the more convincing they will be to the dumb
bureaucrats in Washington.   It's all too easy and glib to tell you to
go mobile, or move onto 30 unzoned acres as I did in my retirement.  

73, Allan, W1AEL, QCWA #13059