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RG-400 vs RG-58

jeffsvan

Well Known Member
Hi,
I did not know I would end up with Garmin equipment, so when I wired
the plane I installed new antennas and new RG-58 cables.

The Garmin equipment reccomends RG-400.
Must I switch out the RG-58 or is it ok to leave and use?

Jeff
 
RG58 will work for anything in an RV. It works for the GPS too. Matter of fact it takes less RG58 to get the minimum dB loss required.

I used RG400 since that is the modern way but RG58 works...

RG58 has a loss of around 13.2-14 dB/100ft
RG400 has a loss of around 9.6 dB/100ft.

Now there is the issue with the fact that Garmin specifies RG400 for the GPS antenna on the WAAS panel mounts. This is needed to meet the TSO installation requirements. This is an area where you will need to decide on which direction to go.
 
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more...

The rg-58 is only attached to the radio antennas.
I do have a fresh rg-400 for the gps waas antenna as it was just installed.

So the last big question:
For the Garmin 430W is it (legal) and ok to have rg-58 for the comm radio
antennas and the rg-400 for the GPS antenna only?

The 430W manual is asking for all rg-400 on everything if i am reading it correctly?

I worry about being legal for IFR
 
You as the builder decide that. There is no such thing as being IFR certified with an experimental.
 
Jeff,

If you choose to experiment by using the RG-58 which you currently have installed, any problems or issues with your equipment will require time, effort and cost trouble-shooting the problem. And, when you do find the problem, the resolution may or may not point to the need for RG-400. I ran into this problem once before... I recommend that you replace all of the RG-58 with RG-400 and eliminate any problems or issues that may one day point to which cable was installed.

Good Luck.

Victor
 
Differences between the two cables

RG 58 has a plastic dialectric and RG400 has a PTFE (Teflon) dialectric.
RG 58 has single shielding and RG400 has double shielding.
RG 58 has a solid center conductor (some versions have stranded) RG 400 has stranded.
RG 58 has a plastic outer sheath, RG400 has a high temp FEP sheath.
RG 400 is more expensive than RG 58.

Summary:

Both cables will work fine in the short lengths used in aircraft applications, but the polyethylene dialectric in RG 58 does not handle elevated temps well and the single shield will allow more leakage. Also there seems to be a lot of quality variation in RG 58 construction. The jacket of RG 58 is also less able to handle higher temps, will chafe more easily, and AFAIK is also prone to generate more smoke/toxic fumes if it burns. I don't like the solid center conductor either, it's more prone to break under vibration/flexing than is the stranded center conductor of RG 400.

I'd use RG400 if possible as it won't degrade due to high temps - especially if used in the firewall forward area. It also has lower loss and less signal leakage than RG 58.

Mark Olson RV-7A F1-EVO AA0MH
 
Airplane makers have always used a stranded core RG58. If you see a solid core one its because someone replaced it with "TV coax".
RG58 is smaller diameter and more flexible than RG400. For com & vor use with runs under 20 feet I can't see a problem. As for flammability, I'd bet half of the guys are running this RG400 through polyethylene conduit anyway.
 
Airplane makers have always used a stranded core RG58. If you see a solid core one its because someone replaced it with "TV coax".
RG58 is smaller diameter and more flexible than RG400. For com & vor use with runs under 20 feet I can't see a problem. As for flammability, I'd bet half of the guys are running this RG400 through polyethylene conduit anyway.

I sincerely hope that no one is using "TV" coax. TV coax has an impedance of 75 ohm. Everything in you airplane uses 50 ohm cable.

Your avionics would not play well with "TV" coax.
 
Airplane makers have always used a stranded core RG58. If you see a solid core one its because someone replaced it with "TV coax".
RG58 is smaller diameter and more flexible than RG400. For com & vor use with runs under 20 feet I can't see a problem. As for flammability, I'd bet half of the guys are running this RG400 through polyethylene conduit anyway.

FYI: RG58u does have a solid center conductor variant though I doubt any certified aircraft would have ever used it....
 
FYI: RG58u does have a solid center conductor variant though I doubt any certified aircraft would have ever used it....

Certainly not any certified aircraft! But RG58 is available many places, such as Radio Shack, and you never know what you're getting in terms of quality. That's why I recommend RG400.

Mark Olson RV-7A F1-EVO AA0MH
 
I sincerely hope that no one is using "TV" coax. TV coax has an impedance of 75 ohm. Everything in you airplane uses 50 ohm cable.

Your avionics would not play well with "TV" coax.

Yep. "TV coax" I think is RG-59 which is 75 ohm impedance. RG58 is 50 ohms.
 
Jeff,

FYI... you might want to consider RG142 instead of RG400 or RG58. That was what I installed in my RV. See notes below in this narrative from another web board:


"I used either RG 400 or RG142 for all of my coax installations.

RG 400 and RG 142 are both superior to RG 58 in performance and material. RG400 has a multistranded core and RG142 has a solid core. Some people favor RG400 over RG142 because of the greater flexibility and resistance to flexing fatigue failure. RG 142 is a bit easier to work with when installing connections such as BNC. There are avionics shops that will refuse to install RG 58 in your airplane -- with good reason I think
."


Just a little something else to consider...

Victor
 
Fire and chaffing

are important considerations. The vinyl (or whatever it is) outer sheath of RG-58 will make bad smoke. I've seen issues with the sheathing which looks the same on the 4-conductor shielded "Belden" cable that is supplied with Whelen strobes. The stuff chaffes easily, and would burn in a fire. I don't know how Whelen ever got that TSO'ed.


Anyway, I used rg400 because of the better fire resistance.
 
I was kinda kidding about the TV coax, although I have seen it in an airplane before. You're right about the RG58U (solid core) as opposed to RG58CU (I think thats right).
 
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