Lowering cockpit RF interference

wrote:
Thank you Dan for your article link

John DeRosa wrote:
Your question is less about "I have a problem and want to fix it." versus, "I don't want any problems in the first place.

Exactly.

Do late model sailplanes actually have a "factory" grounding point?

Certainly not when they are in the air!

OK, that's a joke, but it does bring into sharp
relief that the "ground" concept is a fiction
(except under limited circumstances that are not
relevant here). It is also a fiction on the ground
as well, particularly where RF is concerned (see
any book on antenna design).


Am I correct to assume the best grounding point
would be the heaviest metal frame work closest
to the instrument panel such as the control yoke
or the adjustable rudder pedal track?

I doubt it, but read the service manual and contact
a competent engineer/technician. I would be
very reluctant to allow electricity to be conducted
through any part of the airframe.

On 12/20/2012 9:17 AM, Tom Gardner wrote:
wrote:
Thank you Dan for your article link

John DeRosa wrote:
Your question is less about "I have a problem and want to fix it."
versus, "I don't want any problems in the first place.

Exactly.

Do late model sailplanes actually have a "factory" grounding point?

Certainly not when they are in the air!

OK, that's a joke, but it does bring into sharp
relief that the "ground" concept is a fiction
(except under limited circumstances that are not
relevant here). It is also a fiction on the ground
as well, particularly where RF is concerned (see
any book on antenna design).

How do you think we should be discussing the issue?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

Eric Greenwell wrote:
On 12/20/2012 9:17 AM, Tom Gardner wrote:
wrote:
Thank you Dan for your article link

John DeRosa wrote:
Your question is less about "I have a problem and want to fix it."
versus, "I don't want any problems in the first place.

Exactly.

Do late model sailplanes actually have a "factory" grounding point?

Certainly not when they are in the air!

OK, that's a joke, but it does bring into sharp
relief that the "ground" concept is a fiction
(except under limited circumstances that are not
relevant here). It is also a fiction on the ground
as well, particularly where RF is concerned (see
any book on antenna design).

How do you think we should be discussing the issue?

I don't really understand the question, but maybe
we shouldn't be discussing it here. Interference
arises due to many causes, is transmitted by many
means, and is received in different ways [1]. A specific
solution to one combination of source/route/destination
will not be effective for other combinations. I'm
sorry, but there aren't any generic solutions.

Probably the best general advice is to have good quality
equipment, cables and connectors, and to ensure the
connectors are properly tightened.

And even that won't prevent the "rusty bolt effect"


[1] as a single _simple_ example, given signals coupling
from one wire to another leading to interference, there
are two types of interference, near-end crosstalk and
far-end crosstalk. The causes are different and the
solutions are different.

RF introduces a whole slew of more subtle effects.
There are _many_ books on the topic, which is a good
indication that it isn't a simple problem with a simple
solution.

But of course one solution to one problem may well
be simple.

This is like posing a question to a lawyer: "It depends."

What might be helpful to non-experts is a typical step-by-step
approach to identifying the type and source of interference and then
addressing it. For you AI types (is that term still used?), an expert
system flow chart. EX: If it's a noise in the radio speaker, go to
step 2a. If it's a noise in the audio vario speaker, go to step 2b. If
it's a disturbance in the needle or indicator of an instrument, go to
step 2c. Etc. "It depends" covers too much ground.

I've chased interference before, the most maddening case being hearing
a French African channel on Voice of America non-stop thru the
aircraft radio years ago when flying at Caesar Creek, OH. It was my
brother's glider, actually, but we worked on it together. From memory:
capacitors, homemade high-pass, low-pass, and band-pass filters,
shieded cables, shielding around various components, etc. Eventually
we drove the trailer over to the VOA facility, parked on the road
outside, pulled the fuselage out, and started working. That got action
pretty fast. I didn't realize VOA had security guards. Once they
believed our story, and that the Komet trailer wasn't full of
explosives, we were actually invited in to meet the manager and get
info on freqs, antennas, power, etc. Pretty awesome numbers, as I
recall. I honestly can't remember what finally did the trick. Maybe it
was my brother moving to VA.

Chip Bearden
ASW 24 "JB"
U.S.A.