help on coax runs

[shiney]

I'm just starting work on my coax run into the sub panel area (comm & trans) There's lots of wires in there now, should I avoid running coax too close to wire runs or is it safe to get close?

Martin

 

[AFulmer]

Coax near other "stuff"

Here is Bob's response to a similar question I posted on the Aeroelectric List:

--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <[email protected]>

At 11:38 AM 1/27/2009, you wrote:
>--> AeroElectric-List message posted by: "Allen Fulmer" <[email protected]>
>
>Bob,
>
>One possible route for multiple coax cables from belly mounted COM and XPDR
>antennas would require them to pass within a couple inches of and parallel
>to the electric fuel pumps. Airplane is all electric so one or both pumps
>would be running.
>
>Would that likely create an antagonist for the radios and/or transponder?

No, the respective spectrums of interest for both
pumps as potential antagonists and the radios as
potential victims are very widely separated. Further,
the really magic thing about a properly terminated
transmission line (coaxial cable) is that isolation
between the outside environment and itty bitty signals
within is huge.

Not to worry.


Bob . . .

 

[Rainier Lamers]

You are correct in a perfect World.
But our's is somewhat less than that.
We can safely assume that our antenna termination is at best approximate (and varies with frequency) and that our cable, despite the manufacturers best intentions is not perfect and even worse, typical radios have only very approximately 50 ohms output and input impedance.

This means that it is indeed a good idea to seperate the coax cable somewhat from any other signals that could be compromised by VHF emissions or that could carry signals that could interfere with your radio's receiver.

It's easy to do and certainly does not harm anything.

Rainier
CEO MGL Avionics

Here is Bob's response to a similar question I posted on the Aeroelectric List:

--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <[email protected]>

At 11:38 AM 1/27/2009, you wrote:
>--> AeroElectric-List message posted by: "Allen Fulmer" <[email protected]>
>
>Bob,
>
>One possible route for multiple coax cables from belly mounted COM and XPDR
>antennas would require them to pass within a couple inches of and parallel
>to the electric fuel pumps. Airplane is all electric so one or both pumps
>would be running.
>
>Would that likely create an antagonist for the radios and/or transponder?

No, the respective spectrums of interest for both
pumps as potential antagonists and the radios as
potential victims are very widely separated. Further,
the really magic thing about a properly terminated
transmission line (coaxial cable) is that isolation
between the outside environment and itty bitty signals
within is huge.

Not to worry.


Bob . . .