----- Original Message -----
From: <n3eu@comcast.net>
Subject: Re: Europa-List: Antenna help
|
| Steve -
|
| Especially the xponder antenna cable should not be run in bundles
containing other wires running 14V power; avoid on VHF. Installing shops
and even factories do it all the time and often get away with it, but I'd
still separate them. COM may affect NAV only on xmit if their coax bundled
together, but I'd still separate them too. Takes only an inch or two.
|
| The tips of a dipole are the worst place to have metal anything. It
should be separated by 24" as best you can. Although in a sense the tips do
no work at all, the length of the element is what tunes it, and nearby metal
detunes it. Also, the distance you have between nav and comm may be
evidenced on the nav display when you key the mike.
|
| Energy radiates at 90-deg. to an antenna element, so curvature affects its
radiation pattern. I think what Archer is saying is that no practical
antenna installation has produced a perfect radiating pattern from Marconi's
day forward, so a little added curvature is not too bad.
|
| This will sound like the other advice you got, but the NAV antenna on the
bottom may be noticeably worse than mounted on the top of the fuse, due to
proximity of the pitch tube and rudder cables, aggravated by its curvature.
VHF nav has the annoying problem where the avionics mfr need only provide
enough sensitivity to meet FAA requirements for "service volume," relating
to reception distance. Else there's potential for interference from VORs of
the same frequency if too sensitive. Design is then further premised upon
an antenna installation of typical adequacy. I'd either install it so it
can be easily moved later if need be, or just plan to affix it later to the
top. Needs only blobs of RTV if Archer permits and duct tape to hold it
while curing, with access through the "D" panel.
|
| Regards,
| Fred F.
Steve,
We hear your anguish. Antenna tech is NOT black magic although
when it's unresearched it may seem so. If it's any consolation I agree with
Fred. Nothing in this small size aircraft will be perfect. If you use a
dipole and have to be near wires, it's best if the wires are perpendicular
to the dipole and passing through the point where the cable attaches.
There's more space on top than on bottom - smaller antennas can
be closer to others than large ones - so start with the biggest one and work
down in size. I agree that you should not run a transmit cable alongside a
similar receive cable (VHF/VOR or VHF/Transponder). Worst case - if it don't
work don't sweat it. Chances are you can reposition it later, although not
so easy. Some of this pooh can be used later - VOR ain't necessary to test
the aircraft, etc.
Good luck!
Ferg
A064 914 mono
|
| > I've had it with these antennas. I don't know much about them and
| > every time I tell someone how they're going in, I get, "whatever
| > you do don't do that"....nav and com wires, (RG 400) run down the port
| > side. The transponder wire runs down the starboard side with the
| > battery wires. The Nav has one tip running under the battery wires.
| > Is that going to mess up reception? The com is mounted to the port
| > side wall. It's curved, I know, but Bob Archer said that was ok.
|
| > http://idisk.mac.com/sdunsmuir/Public/bob1.jpg
| > http://idisk.mac.com/sdunsmuir/Public/bob2.jpg
| >
| > Thanks,
| > SteveD.
| > P.S. It's a radish... Don't ask....
|
