radio / vario interference - HELP!

[Chris Davison]

A problem with interference, all advice welcome.

..radio by itself works fine...but when I turn the
vario on I get huge amounts of noise (even some with
Squelch ON). Radio is a Dittel FSG50, vario is Cambridge
302/303.

Where do I start looking?

Chris

[Eric Greenwell]

In article >,
says...
> A problem with interference, all advice welcome.
>
> .radio by itself works fine...but when I turn the
> vario on I get huge amounts of noise (even some with
> Squelch ON). Radio is a Dittel FSG50, vario is Cambridge
> 302/303.
>
> Where do I start looking?

What did Cambridge tell you about the problem?

Is the vario connected to anything besides power, the GPS antenna, the
temperature probe, and the 303 display?

Does the cable to the 303 have the ferrite cores on it?
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Eric Greenwell
Richland, WA (USA)

[JJ Sinclair]

Hi Chris,
I just went through this (breaking squelch) problem with my Borgelt B-100 and I
found some very interesting things:

1. When the NMEA cable from the cambridge GPS was moved near the radio antenna
cable, I got full squelch. Move it away and the squelch went silent.

2. When the cable going to the LCD display was moved near the antenna cable, I
got full squelch. Move it away and the squelch went silent.

My fix was to move the antenna cable (RG-58) to the other side of the
instrument panel and routed it out the right side, about 12 inches AWAY from
all the other cables.
JJ Sinclair

[Richard Pfiffner]

Chris,

All cables are not equal. Make sure you have a shielded cable with ferrite
supressor.

Richard
www.craggyaero.com

"Chris Davison" > wrote in message
...
> A problem with interference, all advice welcome.
>
> .radio by itself works fine...but when I turn the
> vario on I get huge amounts of noise (even some with
> Squelch ON). Radio is a Dittel FSG50, vario is Cambridge
> 302/303.
>
> Where do I start looking?
>
> Chris
>
>
>

[HL Falbaum]

Solved same problem with 302/303 and Dittel FSG70M by rerouting the cable
from 302 to 303 (display). Turn everything on, squelch off and get teh
noise. Then start unplugging cables-start with the 302 to 303 cable. As soon
as the noise quits, you have found it!
Good luck!
--
Hartley Falbaum
ASW27B "KF" USA

"Chris Davison" > wrote in message
...
> A problem with interference, all advice welcome.
>
> .radio by itself works fine...but when I turn the
> vario on I get huge amounts of noise (even some with
> Squelch ON). Radio is a Dittel FSG50, vario is Cambridge
> 302/303.
>
> Where do I start looking?
>
> Chris
>
>
>

[Ian Forbes]

On Sat, 25 Oct 2003 18:15:54 +0000, Chris Davison wrote:

> A problem with interference, all advice welcome.
>
> .radio by itself works fine...but when I turn the vario on I get huge
> amounts of noise (even some with Squelch ON). Radio is a Dittel FSG50,
> vario is Cambridge 302/303.
>
> Where do I start looking?
>
> Chris

I had a similar, but much worse problem, with an early 2 channel Magellan
GPS about 10 years ago. The GPS was mounted in a bracket on the panel of
my Nimbus II. The antenna was remote mounted on top of the instrument
panel with a foot long extension cable. There was a power cable with an
integral DC regulator which plugged into a 12V power socket that I fitted
behind the panel.

The interference was so bad that it would break through the squelch on the
radio of the glider lined up behind me on the start grid!

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
place. The result was two rather ugly cables of nearly 1 inch diameter -
but no interference!

The 2 channel GPS had a habit of loosing the satellites in a thermal but
on the glides it would lock in and give a readout within a minute or so.
It cost me a small fortune at the time but was much less than price of a
more sophisticated unit. Compared to map reading it was great! I flew many
thousands of km with that setup.

Ian

[Eric Greenwell]

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
> place. The result was two rather ugly cables of nearly 1 inch diameter -
> but no interference!

Why did you choose steel wool instead of aluminum or copper foil?
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directly

Eric Greenwell
Richland, WA (USA)

[Richard Pfiffner]

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.

Richard

"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
> > place. The result was two rather ugly cables of nearly 1 inch diameter -
> > but no interference!
>
> Why did you choose steel wool instead of aluminum or copper foil?
> --
> !Replace DECIMAL.POINT in my e-mail address with just a . to reply
> directly
>
> Eric Greenwell
> Richland, WA (USA)

[Ian Forbes]

On Mon, 27 Oct 2003 20:47:48 +0000, Eric Greenwell wrote:

> Where did the idea for the steel wool come from?

I read a tip suggesting steel wool and shrink wrap, as a means of last
resort. I think it may have been in a Sailplane and Gliding magazine.

I experimented and it worked and so it stayed.

(I had already tried various coax cables and grounding arangements without
significant success.)

Ian

[Eric Greenwell]

In article >,
says...
> On Mon, 27 Oct 2003 20:47:48 +0000, Eric Greenwell wrote:
>
> > Where did the idea for the steel wool come from?
>
> I read a tip suggesting steel wool and shrink wrap, as a means of last
> resort. I think it may have been in a Sailplane and Gliding magazine.
>
> I experimented and it worked and so it stayed.
>
> (I had already tried various coax cables and grounding arangements without
> significant success.)

Fascinating! I never would have thought of trying it.
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!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

[Richard Pfiffner]

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)

[Eric Greenwell]

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)

[Simon Waddell]

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)

[Mark James Boyd]

>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.