Lots of good wisdom in issue 21 of the digest, on
this topic. I won't attribute them here, as I mention
them...but I'll outline my approach to a 2nd floor shack.
* Earth ground vs. RFI. Absolutely true...Earth Ground is
for lightning protection...by the time you get to second floor,
you're not at "ground" potential at your equipment, but an
appreciable fraction of a wavelength away.
* Pin 1 audio problems...comments were correct...noted.
may vary by radio/sound gear models, as internal gnd
treatments vary between equipment. Too complex to deal
with in a generalized way. (although I've never had it,
using Icom gear.)
* I have always separated the problem of bringing the shack
itself to a unipotential, from the lightning protective ground.
i.e. run a good ground buss on the operating table, and tie
all chassis to it. That'll stop annoying RFI. Resonant antennas,
or ferrite decoupled feedlines to non-resonant antennas will help keep
rf out of the shack.
* I prefer a single point ground for lightning protection
but often find it hard to achieve. At a minimum, I ground the
tower base, and all feedlines to it. Then, I provide a ground
rod outside the house entrance, with all feedlines tied to it.
* Small second floor shack approach: ic706-II and R7000 vertical.
The R7K mounts on a 30' radshack pushup pole, behind a chimney,
adjacent to the shack. The pole strap-mounts to the chimney, and
is grounded at its base by 1" strap to an 8' rod. Coax exits the pole
at shack height, via a 2 turn drip-loop/choke, which further has
6 type 73 ferrite clip-ons, prior to house entry. Interior run is 6'
to the radio.
Is it perfect? No. Only marginally acceptable, in fact. A direct
hit, or even a nearby hit which induces secondary current in the vertical
will wipe out the radio, and probably everything connected to it.
Consequently, the antenna is disconnected whenever radio is not in use.
The pole makes antenna installation easier, and protects the chimney from
strike damage. (hopefully).
* Could I expand this concept to include my main shack-kw station?
Perhaps.
But I would move the vertical away from that location. I would route all
coaxes to ground level, and tie all shields to dissipative grounds at
whatever
common point I select, plus at the point where the coax and other cables
have to
run up to the second floor. (try and keep these OUTSIDE the structure, if
you
can.)
Visit http://www.radioworks.com . They had a treatise on second floor
shacks
worth reading.
N2EA
jimjarvis@ieee.org
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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