> Has anyone tried mounting the GPS antenna on the centerline of the
aircraft
> at the top of and within the instrument panel? This is only a few inches
> below the windshield (windshield mounts reportedly work well in glass
> airplanes). Should be easy to approximate by putting the antenna on top
of
> the glareshield temporarily. Seems like inside the panel would be a very
> simple installation if it works out.
>
> John A044
John --
It may be a few inches from the windshield, but also a few inches from some
healthy RF noise makers. Besides the DC motor in a turn coordinator, and
avionics with neon displays, your transponder has a step-up transformer that
converts 14v to about 1500v, so it can squirt out 250 watt pulse trains to
keep ATC controllers happy. A real noisy sucker. These RF interference
effects are inherently noticeable only at very short distances, because the
receiver (e.g., handheld GPS) is affected by only what harmonics of interest
it can pick off from RF noise which is not harmonic-rich (only square waves
contain the fundamental frequency plus all harmonics thru near infinity).
Conversely, your other avionics are generally immune, because the antennae
are remotely located (plus they're well shielded). Note also that while a
handheld GPS may work OK on the top of a panel, that panel top is usually
made of aluminum, which helps shield it a bit.
My Garmin GPS III Pilot works OK even inside my house; works great on my
other plane's panel top, except after engine startup and avionics master
switch flip, she sometimes immediately goes out for coffee. Placing it then
on the right seat, coffee break over (despite overhead aluminum).
You might want to test it out in flight testing first, if you'd still rather
not site the antenna just about anywhere else.
Regards,
Fred Fillinger, A063
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