radio / vario interference - HELP!

All the cables in a glider I was having RFI problems with were shielded
with aluminum foil. The RFI continued, as evidenced by squelch on the
Becker Radio 123.3, 123.5 & 123.0. Added more foil around the power
converters, radio, GPS cables, radio antenna cables, power supply cables
etc. the RFI continued. So oviously the foil is not the answer. Unplug any
of the following instruments and the RFI stopped, Ipaq, L-NAV, either CAI
GPS Nav (there were 2). Finally traced the problem to a power converter,
replace it with a PWR-5b that I sell on my website and the problem was
solved, with no aluminum.

Richard
www.craggyaero.com


Richard
"Eric Greenwell" wrote in message
.. .
In article ,
says...
I have head that when you start with the aluminum foil, that soon the
entire
cockpit, all the cables, boxes etc will be covered, and the interference
will remain.

Foil covered bundled wires are standard for protecting instrumentation
from electrical noise. It's not quite the same to wrap existing cables
with foil, but it's close. Where did the idea for the steel wool come
from? I'm really curious, because I've never heard of this before.
Generally, steel isn't used as electrical shielding because of it's
relatively poor conductivity.

"Eric Greenwell" wrote in message
.. .
In article ,
says...
I eventually fixed it by wrapping both the antenna cable and the
power
cable with steel wool (the stuff Grandma used for cleaning pots in
the
kitchen). I pulled a large size shrink wrap over the wool and shrunk
it
in


--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

In article ,
says...
All the cables in a glider I was having RFI problems with were shielded
with aluminum foil. The RFI continued, as evidenced by squelch on the
Becker Radio 123.3, 123.5 & 123.0. Added more foil around the power
converters, radio, GPS cables, radio antenna cables, power supply cables
etc. the RFI continued. So oviously the foil is not the answer. Unplug any
of the following instruments and the RFI stopped, Ipaq, L-NAV, either CAI
GPS Nav (there were 2). Finally traced the problem to a power converter,
replace it with a PWR-5b that I sell on my website and the problem was
solved, with no aluminum.

It's always best to eliminate the source! And, of course, if the noise
is being transmitted through the cables instead of radiated into them,
shielding won't help. Filtering usually will, such as the ferrite
cores seen on many cables.
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

In the case of radiated interference, all the shielding on the world -
aluminium, copper, foil, wire wool etc - is of no use unless it is correctly
earthed (grounded) by a low-impedance at a single point.

Filtering is the correct approach for conducted interference. In most case,
a device that puts HF noise into the power feed (e.g. a swiching power
supply) is radiating as well, so correct screening is also required.


"Eric Greenwell" wrote in message
.. .
In article ,
says...
All the cables in a glider I was having RFI problems with were shielded
with aluminum foil. The RFI continued, as evidenced by squelch on the
Becker Radio 123.3, 123.5 & 123.0. Added more foil around the power
converters, radio, GPS cables, radio antenna cables, power supply cables
etc. the RFI continued. So oviously the foil is not the answer. Unplug
any
of the following instruments and the RFI stopped, Ipaq, L-NAV, either
CAI
GPS Nav (there were 2). Finally traced the problem to a power
converter,
replace it with a PWR-5b that I sell on my website and the problem was
solved, with no aluminum.

It's always best to eliminate the source! And, of course, if the noise
is being transmitted through the cables instead of radiated into them,
shielding won't help. Filtering usually will, such as the ferrite
cores seen on many cables.
--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

In article ,
says...
I have head that when you start with the aluminum foil, that soon the entire
cockpit, all the cables, boxes etc will be covered, and the interference
will remain.

Foil covered bundled wires are standard for protecting instrumentation
from electrical noise. It's not quite the same to wrap existing cables
with foil, but it's close. Where did the idea for the steel wool come
from? I'm really curious, because I've never heard of this before.
Generally, steel isn't used as electrical shielding because of it's
relatively poor conductivity.


When I replaced an alternator cable on my 172, I had them use a shielded
cable. The outer coat of shielding then was attached to ground (important).
All the radio interference after that was gone.

If you don't ground the shielding (electrically attach it to a
known ground point), I'm not certain you'll
get the result you want.