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  #1  
Old 08-25-2011, 08:51 PM
jeffsvan jeffsvan is offline
 
Join Date: Jul 2010
Location: detroit, michigan
Posts: 71
Default RG-400 vs RG-58

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
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  #2  
Old 08-25-2011, 09:48 PM
RV7ator RV7ator is offline
 
Join Date: Jan 2005
Location: Boise, ID
Posts: 751
Default

RG-58 is entirely adequate for RV purposes.

John Siebold
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  #3  
Old 08-26-2011, 12:48 AM
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tommylewis tommylewis is offline
 
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Posts: 551
Default my opinion

Is that rg400 is required only for the gps antenna, rg58 is okay for everything else
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  #4  
Old 08-26-2011, 05:57 AM
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Brantel Brantel is offline
 
Join Date: Mar 2006
Location: Newport, TN
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Default

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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Last edited by Brantel : 08-26-2011 at 06:04 AM.
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  #5  
Old 08-26-2011, 06:45 AM
jeffsvan jeffsvan is offline
 
Join Date: Jul 2010
Location: detroit, michigan
Posts: 71
Default 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
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  #6  
Old 08-26-2011, 07:16 AM
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Brantel Brantel is offline
 
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You as the builder decide that. There is no such thing as being IFR certified with an experimental.
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  #7  
Old 08-26-2011, 09:20 AM
vasrv7a vasrv7a is offline
 
Join Date: Jul 2006
Posts: 105
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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
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  #8  
Old 08-26-2011, 09:35 AM
molson309 molson309 is offline
 
Join Date: Jul 2009
Location: Bloomington, MN
Posts: 171
Default 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
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  #9  
Old 08-26-2011, 10:04 AM
aerhed aerhed is offline
 
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Location: Big Sandy, WY
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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.
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  #10  
Old 08-26-2011, 11:06 AM
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Mel Mel is offline
 
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Location: Dallas area
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Quote:
Originally Posted by aerhed View Post
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.
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