What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Antenna routing

R

redrv6

Active Member
I've just received a copy of plans Section 31B. On page 3 it tells us to route the comms antenna and the transponder antenna cables through separate snap bushings in the panel base. The original Section 31 didn't state that, though looking back at the diagrams it did imply that!

For some reason that I can't recall, I ran both cables through the larger snap bushing. Can anyone shed any light on why it's important to have them in separate bushings? Is it to keep them apart to prevent interference? They get together quite closely once over the rudder pedals and into the tunnel.

If it is going to cause electrical interference, I will pull one of the harnesses out and reroute one of the cables, but I'd rather not go to all that effort if it's not a significant problem.

Any thoughts?
 
If you're using RG400 (or better) you should be fine, if you're using RG58 then seperating them is probably a good idea.
 
:) Joe It would be easier to fix it now, with easy access to the harnesses. Just want to know if it is likely to be a problem. One thing that drives me nuts is radio problems!

Walt, I'm using the supplied cables and hardware. Please excuse my ignorance but what is RG400/ RG58? I need to learn this stuff!
 
redrv6 said:
:) Joe It would be easier to fix it now, with easy access to the harnesses. Just want to know if it is likely to be a problem. One thing that drives me nuts is radio problems!

Walt, I'm using the supplied cables and hardware. Please excuse my ignorance but what is RG400/ RG58? I need to learn this stuff!
Click to expand...

These are the part numbers of the most common coax cables, if it's supplied with the kit I would imagine its the RG400 coax. The 400 is brown and 58 is black.
 
Hi Walt - I think the cables are black. So if that's the case, what's the likely result of routing them too close together? As I said earlier, after passing through the panel base, the cables end up close together in the tunnel so I can't really see the point in putting them through separate snap bushings. Vans must have a reason for specifying separate bushings in the updated plans - or are they just messing with my head? :D
 
Check the cables, I would be very surprised if they supplied RG58 with the kit, Garmin does not approve RG58 for use with the transponder any longer due to the high losses and inferior shielding.
 
Will do. So am I right that the problem of close proximity is lack of shielding and therefore possible interference? If that's the only issue, I don't see the need to reroute the cables through the panel base, since they lie together in the tunnel.
 
big spikes of RF from transponder...

The transponder puts out BIG spikes of RF power (200 watts nominal) that will be picked up by the antenna wire, if they are closely coupled, in the form of audio clicks... RG400 is much better shielded than RG58 but it is not magical. Try to route the two with a minimum of several inches separation everywhere you can.
 
Subject: Re: Routing Antenna Leads
Hello Bob & List,
I'm installing my Garmin panel mounted GPS/Comm (GNC 250-XL) with
Perihelion's RG+142 coax in a tube & fabric aircraft. The two antennas are about 5' apart. The installation manual says to route the GPS cable 'as far as possible' away from the Comm cable. Before reading that part I was inclined to route them right next to each other. Now I don't really know what to do.
I couldn't find anything on this specific question in the archives. Is
there a minimum distance for good radio performance?
Thanks,
Grant Krueger

REPLY:
Date: Aug 16, 2005
From: "Robert L. Nuckolls, III"
If they're both modern coax (RG400 or RG142) you can
run them right together with any wires in any system.
Bob . . .
Click to expand...
http://www.matronics.com/archive/archive-get.cgi?AeroElectric-Archive.digest.vol-es
Robert Nuckolls is my mentor. I highly respect his opinion.
Unfortunately, if I recall correctly, the coax supplied with the RV-12 kit is RG-58, NOT RG400 or RG142. However there are many RV-12s flying that have been wired according to the plans with all of the wires and cables bundled together, including audio cables. Theoretically the coaxial cables should be separated. But in practice, it does not seem to be a problem in the RV-12. I do not think it will be a problem running both coax though a single bushing.
On the other hand, you can not go wrong following the plans and you will feel better too.
Joe Gores
 
I'm reminded of my father's (a lawyer) admonition: "Son, always hire a lawyer with one arm."

"Why's that, dad?"

"So he won't always be telling you 'On the other hand' and charging you top dollar for it too."

Bob Bogash
N737G
Both antenna cables currently through the same grommet, and likely to stay that way unless I have a problem.
 
Good advice, Bob!
I put the question to Vans and the response was that it should not be a problem, so I'm leaving it as is.
 
You must log in or register to reply here.
Back
Top