Metallic paint and composite antenna signal strength

On larger aircraft, there are very few antennas the manufacturer will
let you paint. You can get by with metalics on some such as the
comms, but not any of the L-band, TCAS, or other high frequency ones.
As a rule though, we won't cover the antenna manufacturer's paint with
anything else.

I recently had a new Gulfstream that the tail radome that covers the
satcom, Direct TV, and high-speed data antennas that had to be changed
because the paint was too thick and attenuated the TV and data
signals. The satcom worked fine.

Experience has shown me that with other than small metallic stripes on
the nose radome, they won't pass a transmissivity test on the range
and have to be stripped and re-painted. The white urethane base coats
don't cause a problem there.

"Don Hammer" wrote in message
news:1119738126.4b52018cd82f8bdc4b584a58e183d17a@t eranews...

On larger aircraft, there are very few antennas the manufacturer will
let you paint.

A holdover from the days when most paints had colors with pigments starting
with "lead", "cadmium", "copper" and the other heavy metals. With the EPA
ban on truly metal based paints as the pigment, why should the manufacturer
go back and redo the whole damned testing procedure with the new oxide based
colors.

Besides, at these speeds, there are some legitimate static buildups that
come in to play to require "furry paint". At Mach .25, these effects are
hardly noticeable.


You can get by with metalics on some such as the
comms, but not any of the L-band, TCAS, or other high frequency ones.
As a rule though, we won't cover the antenna manufacturer's paint with
anything else.

I don't have a problem with that. If you don't have an antenna pattern
range on which to "prove" your work, the best course is to avoid paint.
However, we were talking about an experimental here, and THIS is where we
prove the new concepts that eventually work their way into production
aircraft. How many production aircraft had Whitcomb winglets installed
until several thousand EZs proved the point?



I recently had a new Gulfstream that the tail radome that covers the
satcom, Direct TV, and high-speed data antennas that had to be changed
because the paint was too thick and attenuated the TV and data
signals. The satcom worked fine.

No problem. If I was working with submicrovolt signals, my advice would be
to save every tenth of a dB possible. Here we are talking noise margins of
forty to sixty dB and the dB or so that thin, thick, or semimetallic paint
would introduce is a second order effect at best.



Experience has shown me that with other than small metallic stripes on
the nose radome, they won't pass a transmissivity test on the range
and have to be stripped and re-painted. The white urethane base coats
don't cause a problem there.


And we both know that the "small metallic stripes" are there to conduct
lightning strikes from the epoxy to the metal airframe. Ever seen a radome
that takes a REAL lightning pop that goes through the epoxy before it gets
to the metal stripes? The sucker looks like it had a huge popcorn kernel
under the skin.

Jim

"RST Engineering" wrote

Why on earth would you bond a transponder antenna to the inside of the
fuselage? How do you get lower hemispherical (not biconical) radiation
from
something bonded to the fuselage?

Ahh, those pesky double meanings. Perhaps he means bonded - as in glued to,
instead of your EE, bonded - electrically.
--
Jim in NC

And we both know that the "small metallic stripes" are there to conduct
lightning strikes from the epoxy to the metal airframe. Ever seen a radome
that takes a REAL lightning pop that goes through the epoxy before it gets
to the metal stripes? The sucker looks like it had a huge popcorn kernel
under the skin.

Jim


All good points Jim.

Larger aircraft radomes have lightning deverter strips installed on
the outside of the glass. What I'm talking about is metalic paint
trim stripes. We try and keep all metallics off of the radomes
because it will attenuate the signal if it is anyway near the signal
path. The radome on the tail also has diverters. Their placement is
engineered to be out of the way of the signal.

Don

"RST Engineering" wrote:

Mark ...

I mean no offense, but anecdotal evidence about painting pagers doesn't take
the place of a controlled environment test when it comes to making general
pronouncements about antennas inside of one paint or the other.

Of course not, but the fact the paint DID affect the operation of the
pager shows that there WILL be an effect on the operation of the
antenna inside the painted radome. The controlled environmental
testing will determine the magnitude. Kinda like giving a dose of a
substance to a mouse. It squeaks, drops dead quivering ten seconds
later... it would be safe to say the substance wouldn't be good to
ingest, but you'd have to do more testing to find out just how
dangerous it is.

So far as I know, the paint could have leaked inside, the pager could have
crapped out from natural causes...

Nope - with a new pager case, the thing worked like new. And FWIW,
the testing of the pager did involve a radiation test fixture inside a
Lindgren screen room, and lotsa nice HP test equipment.

Mark "wouldn't have brought it up otherwise" Hickey

Jim


"Mark Hickey" wrote in message
.. .
"RST Engineering" wrote:

I have absolutely no idea. I can tell you how to run a test on it if you
would like.

Had a customer paint his pager case with metalflake paint - didn't
work worth squat when he was done. I suspect the effect would be the
same on any radome (since that's what a pager case is).

Darrel Toepfer wrote:

RST Engineering wrote:

Mark ...

I mean no offense, but anecdotal evidence about painting pagers doesn't take
the place of a controlled environment test when it comes to making general
pronouncements about antennas inside of one paint or the other.

So far as I know, the paint could have leaked inside, the pager could have
crapped out from natural causes...

They also operate in all the normal bands...
VHF Low/Hi, UHF, 800/900/1200 mhz and probably more...

The pagers we were working on at the time were almost all VHF or UHF
(this was quite a while ago).

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame

In that case I stand corrected ... for THAT brand of paint at the frequency
of THAT pager

{;-)


Jim


"Mark Hickey" wrote in message
...
"RST Engineering" wrote:


Nope - with a new pager case, the thing worked like new. And FWIW,
the testing of the pager did involve a radiation test fixture inside a
Lindgren screen room, and lotsa nice HP test equipment.

Mark "wouldn't have brought it up otherwise" Hickey

Jim

No, that wasn't the point. You CAN'T bond (as in glued to) a ground plane
type of transponder antenna to the plastic fuselage. If you were so ...
ummm ... thoughtless as to try and bond a dipole type antenna for
transponder use half your transponder power gets radiated into outer space.
Where, as I understand it, no ATC facilities yet exist.

Jim



"Morgans" wrote in message
...

"RST Engineering" wrote

Why on earth would you bond a transponder antenna to the inside of the
fuselage? How do you get lower hemispherical (not biconical) radiation
from
something bonded to the fuselage?

Ahh, those pesky double meanings. Perhaps he means bonded - as in glued
to,
instead of your EE, bonded - electrically.
--
Jim in NC

On Sun, 26 Jun 2005 07:41:15 -0700, "RST Engineering"
wrote:

No, that wasn't the point. You CAN'T bond (as in glued to) a ground plane
type of transponder antenna to the plastic fuselage. If you were so ...
ummm ... thoughtless as to try and bond a dipole type antenna for
transponder use half your transponder power gets radiated into outer space.
Where, as I understand it, no ATC facilities yet exist.

Jim



sounds like a good place to use Wier's foil antenna setup :-)

"Joe Camp" wrote in message
.. .

What about metal flake paint?

Metal flake paint has considerably more metal, and bigger pieces of
it. Wouldn't that block the signal to and from an embedded antenna?

I'm sorry to but in this late in the thread, and further since I have been
away from avionics for 20 years...and was almost exclusively a Comm
and VOR technicial at the time.

But I'm not sure that all metal-flake paint has any metal it it. As I
recall, a lot of is is/was "mylar". Back when I was last involved,
metal-flake was enjoying a resurgence of popularity (after a 15 to
20 year slump) and we were seeing King Air 200's with metal-
flake radome paint--which contained a small amount of added
conductive material, just like the plain radome paint...

Your local DuPont supplier of aircraft paint should be a good
information source. They have an outstanding product line and
are/were quite helpfull.

Peter