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Joining RG58 to RG400

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allthegooduseridsaregone(
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Posted: Wed Jun 02, 2010 7:42 am Post subject: Joining RG58 to RG400

I constructed my empennage in 2003 (hard to believe it's been that long!)

from fiberglass with four internal RST copper foil antenna (COM1, COM2, VOR,

ELT) plus a MB antenna running down the fiberglass dorsal fin.  I used Radio

Shack RG58 coax at the time 'coz it was conveniently available as I was

closing out the empennage -- following the RST directions for baluns on the

connection between foil and coax.  I used 40-ish foot lengths of the RG58

from each antenna (coiled up for now) to leave me plenty to reach the back

of the instrument panel without any break.



A year-ish later, I learned via this forum of the much lighter, slimmer, and

more elegant RG400 coax.  I bought five 15-foot lengths of RG400, with male

BNCs attached on each end, through a "bulk purchase" offered in this forum

in 2004 (hard to believe it's been that long!).



So now, as I'm finally getting around to routing my wires and coax forward,

I'd like to cut off each of the RG58's just behind the rear seats (where I

can still easily reach them) and connect to the RG400's for the remaining

14-ish foot trip forward to the rear of the panel.



Should I install a female BNC connector on the RG58 for connecting to the

mail BNC on the RG400, or can I directly splice the RG58 to the RG400 ...

while doing my best to maintain a continuous outer shielding across the

transition?  



Or would I be asking for trouble (e.g. mismatched impedance reflections) by

mixing RG58 with RG400 ... so just continue with the RG58 all the way

forward? 



Thanks,

  Greg

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 02, 2010 7:53 am Post subject: Joining RG58 to RG400

 	  Quote: 	
		  

Or would I be asking for trouble (e.g. mismatched impedance reflections) by

mixing RG58 with RG400 ... so just continue with the RG58 all the way


	


   The performance difference between the two materials is slight.

   Your VHF radios are not going to work better in any observable way.

   I think the drive is going to be parts count. The act of splicing

   the two feeders together adds a handful of parts with the

   additional risk of future failure.  If it's not practical to

   replace the 58 with contiguous lengths of 400, I think I'd

   opt to leave the 58 in place. But a cable male/female joint

   would be quite acceptable too.



http://www.aeroelectric.com/Pictures/Connectors/Coax/BNC_Cable_Female_1.jpg



http://www.aeroelectric.com/Pictures/Connectors/Coax/BNC_Cable_Male.jpg



   Bob . . .

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longg(at)pjm.com
Guest

Posted: Wed Jun 02, 2010 11:50 am Post subject: Joining RG58 to RG400

Greg,



Welcome to 2010  Hey, time to get building. I did the same on my NAV

(joined it with a female) and found no difference in quality. They are

all rated at 50 ohms. Truthfully, I've never been able to justify the

added cost of the pure RG400 plumbing over the RG58 plumbing. I've also

got 142 plumbing. The RG58 radios work just as well as those with the $$

wire. Of course we could also open a thesis on location, type and

quality of antenna installations. Oh boy.



The more technically wire adept will differ but if you sat in my plane

you'd never know the difference. 



Glenn



--

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