Thanks to everyone who posted a reply. I should have said that we operate
VHF-High band. After reading the posts, I began to inspect my office. My desk
backs up against an interior wall separating me from a room containing a bunch
of filing cabinets. I drilled though the wall, ran some coax through and
mounted a mobile mag mount on the side of of one of the filing cabinets,
horizontally, about three feet off the floor. My antenna was a simple 1/4-wave
VHF whip, which I had in my home garage with all the other old stuff. The
filing cabinet made an amazingly effective ground surface and I was able to
tune the antenna to an fairly low SWR.
I dialed the Kenwood TK-760 mobile back as far as I could so I was measuring an
not-precise 3-4 watts at the unit's antenna connector. The installation works
perfectly and my users have commented on the better audio quality.
Thanks again for all the good advice.
Robert Koblish <[EMAIL PROTECTED]> wrote: Chris,
Assuming that you've got a suspended ceiling with steel grid, just get
a mag mount antenna and stick it upside-down to the grid. Attach the
feedline to the grid for a couple of feet so it's perpendicular to the
radiator for 1/4 wavelength or so. And turn down the TX power. That
close to the repeater, you could even do without the PA, I suspect. So
if your radio shop has a mobile with a blown PA you might be able to
give it a home.
I used to operate indoors at home by sticking a mag mount to the top
of the fridge; a metal file cabinet would serve equally well as a
groundplane. But you'd have to be careful not to transmit when anyone
was near the file cabinet.
You could also make a ground plane with an SO239 female connector and
five 1/4 wavelength scraps of AWG14 solid copper house wire (one for
the radiator and four as radials). Put a loop in the top of the
radiator and suspend the antenna from the ceiling grid (or a hook)
with monofilament line.
Take a piece of coaxial cable, strip the jacket for something over 1/4
wavelength, spread the shield braid and fold it back over itself, and
over the jacket. You've got a coaxial dipole. You need to strip more
than 1/4 wavelength because the braid shortens as you spread it. Trim
the braid and the exposed center conductor to 1/4 wavelength each,
apply tape or shrink tubing, and hang as above. The end of any antenna
will be a high impedance (hence high voltage) point, so use several
inches of monofilament to suspend it.
If your office has a window, you may have enough room to make a J-pole
out of burglar-alarm or copper foil attached to the glass.
Just some ideas.
Bob N3HAT
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