In article .com,
MRW wrote:

I forgot to mention that the radio station is not based under FCC
jurisdictions. It is used for a none government / non-profit
organization in another country.

Ah, OK. That clarifies things quite a bit. Just make sure that you
cover your bases with the other government's authorities... some of
them may be as humorless as the FCC.

First thing I'd do is suggest that you take a look at coaxial-cable
attenuation figures. http://users.erols.com/rfc/attenrat.htm has a nice
table which shows the attenuation in dB per 100' of cable, at various
frequencies. For a first approximation I'd suggest using the "100
MHz" column.

As you'll see, 100 feet of RG-58 coax has an attenuation of 4.5 - 5 dB
at 100 MHz. That means that almost 3/4 of the power is lost as heat
in the cable - only about a third of the power makes it up to the
antenna. If you *really* need a 100-meter run of cable, triple that
loss... only a single-digit percentage of your power will reach the
antenna.

Good RG-8-size cable is better. LMR-400 loses 1.2 dB per 100', which
means that you'd get almost half of your transmitter power up to an
antenna 100 meters away. LMR-600 is even better, at 0.8 dB per 100' -
you'd have more than half of your power left. Some of the really
fancy/thick/expensive hardline cables are even better - LDF5-50A
would have just a hair more than 1 dB of total loss in 100 meters,
which would really be negligible.

This suggests two things:

- It'd pay big rewards to see if you can route the cable as directly as
possible. I can't see any good reason to run 100 meters of cable
to go up a "three story" building!

- Don't use cheap, thin cable... don't use anything less than RG-8.

As I mentioned before, aluminum-jacketed cable-TV "hardline" may be a
choice to consider. It's often available in useful lengths, either
for free or for scrap value, from cable-TV operators - they buy and
install it in large quantities and often don't have a use for the
"cut-off" pieces at the end of the spool (and such "cut-off" remnants
may be 100' or more in length).

This sort of cable has a 75-ohm characteristic impedance. It might
actually provide a better match to a dipole antenna than 50-ohm cable
would (depending on the antenna type and mounting arrangement). The
modest SWR at the transmitter might or might not be an issue... if it
is, a simple two-component (one-inductor, one-capacitor) "L" matching
network can allow the transmitter to "see" a 50-ohm load even though
the antenna and coax are both 75-ohm.

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