On 8/15/11 9:20 AM, Cliff Hilty wrote:
Alittle off topic but thinking about mounting my Powerflare brick and
trying to keep GPS antenna away from each other, I was going to move one of
the antenna I have on the side of my glare sheild to the turtle deck and
velcro it to the top of the GFRP turtledeck in my Ventus B. Reading the
info about flarm antenna should not be installled "touching" the canopy
would or should this be a problem with normal GPS antenna?

Well that's what starting a new thread is for, I changed the topic.

Again the real concern (if any in practice) is unlikely to be "keeping
GPS antennas away from each other" it is more likely keeping GPS
antennas away from the FLARM transmitter antenna.

The concern with the FLARM vertical antennas touching or intermittently
touching the canopy is static electricity discharge. That requires the
canopy to charge to a significant level beyond the rest of the
fuselage--I would expect the PowerFLARM box and its antenna should be
sitting at that fuselage potential via ground wires and fuselage/panel
contact. It seems unlikely but I guess it is possible.

Having an antenna touch the fuselage under the turtledeck should not be
a problem and there are gliders with antennas mounted like this today.
Make sure it is not covered by carbon fiber. When attaching anything to
the main fuselage itself like under the turtle deck the static potential
should all be the same (the electrical system is going to be effectively
earthed at multiple places (e.g. avionics boxes mounts in the panel,
antenna ground planes, etc.)--at least as far as static electricity is
concerned.

Personally I would wait and see how the PowerFLARM works before doing or
even planning surgery moving things around--with the obvious exception
if the PowerFLARM box now is going to cover/obscure the sky view of your
current GPS antenna. There is a trade-off in running long remote GPS
antenna. Many installs like being discussed will have over 10' of coax
to the antenna and maybe 6dB or more of signal loss added to the GPS
signal. While these active (i.e. they have an amplifier in the antenna
powered by DC from the cable) GPS antennas tolerate longer cables
surprisingly well just be careful going crazy with long cables, and
avoid multiple connectors etc. e.g it may be better to get a custom made
longer single piece cable if possible. Also different GPS antennas have
different amp gains and some vendors tout their antennas higher gain, if
you do run a long cable and especially if using an older GPS antenna and
have problems then it may be worth trying a higher gain antenna.

Darryl