In article . 196,
Ed wrote:

As far as the roof goes, it is a FLAT rubber covered metal roof on a
large 1 story building.... 14 feet above ground. The roof extends for
at least 50 feet beyond the ends of the antenna, and appears to be well
grounded at a number of points.

Ed,

I hope that once you figure out a more efficient matching system
(traps, or feedpoint coils, or whatever) and get your TX power up to
where you want it to be, you don't regret having succeeded :-)

Our ARES/RACES group has its shack located in our city's police-and-
fire admin building, which also hosts the city's 911 dispatch center.
We have a 40/80-meter trap dipole, mounted perhaps 20' above the roof,
running the length of the building.

We haven't had any matching problems with it.

What we *have* had, is a severe problem with RF incursion into the
building's phone system, including the 911 lines. At first we thought
it might be due to RF on the outside of the coax feedline (which runs
near the phone wiring) or RF leakage from the shack into the phone
wiring in the closet next-door. Feedline chokes didn't help,
unfortunately.

In the end, we ran a test in which we opened up the feedline near the
base of the central antenna tower (disconnecting the antenna from the
shack and from all of the in-building coax), and transmitted through
the antenna using a portable HF radio on battery power. The phone
lines still picked up the signal. Grounding or "floating" the HF
radio made no difference at all. The problem is apparently due to RF
near-field pickup by the phone wiring.

Unfortunately, the city comms folks weren't interested in making the
large effort (and handout of cash) needed to actually diagnose the
deficiencies in their in-house phone system, and install filters and
ferrites on the lines to choke off the RF pickup. Our only practical
solution was to limit our TX power to below the point which causes RF
incursion (varies by band... 20 watts usually seems to be safe).

I can't really blame the city folks, as our HF setup is used only
infrequently and is about a sixth-level backup to the city's other
communication systems. If we were operating independently, out of a
non-city-owned building using non-city equipment, we could make the
case that the incursion is their problem, not ours (according to the
FCC), but since they own the building and the gear we can't do that.

If you're lucky, your increased TX power won't cause you any such
problems... but you might want to consider the implications of having
this sort of incursion problem.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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