Don White wrote in
:

When our skipper bought a Mirage 33 sailboat, it came with a Garmin 75
(I believe a 1993 model) That thing was expensive in it's day...about
$1k CDN but you could unscrew the stubby antenna and hook up the unit to
a cable attached to a bigger antenna mounted on the stern rail while you
were in the cabin.



The "antenna" in the Garmin 75 series GPS wasn't just an antenna. DC power
is fed up the coax from the 75 to a microwave amplifier and downconverter
which makes a much-lower-frequency IF signal, properly amplified, before it
is fed down the same coax to the 75. There used to be an Xray picture of
the Garmin 75's grey plastic antenna on the net and I stored it showing the
helical dipole array actually made of flexible printed circuit board and
wrapped into a cylinder inside the plastic radome, but it is off the net,
google couldn't find it and my hard drive is long gone....

Because the RF between this antenna/converter and the GPS75 is a lower
intermediate frequency, not the 2400 Mhz microwaves from the birds, any
coaxial extension cord with a BNC male on one end and BNC female connector
on the other works great to move the antenna away from the GPS75, Same
old, cheap RG-58 from RatShack works fine.

Just make SURE the coax center conductor is ISOLATED from its shield or it
will burn up the tuning circuitry in the GPS-75 from the shorting of its
tuning voltage output!

I programmed a mint condition GPS75 for a visiting old sailor single-
handing a 28' sloop on our dock just yesterday! He'd had it for years and
NEVER USED IT! I gave him a little GPS/Garmin 75 school from what I could
remember about mine...(c;

--
Larry

You know you've had a rough night when you wake up and you're outlined in
chalk.