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RG142 vs. RG400

H

HighSchoolBuilders

Well Known Member
Hi all,

I am on my antennas section of the build now, and could not understand what is the differences between RG400 and RG142. Seems like everyone is talking about RG400, and from Aircraft Spruce, RG400 has multistrand core while the RG142 has a solid core, but what does that mean in terms of usability and installation?

Can I use RG142 for all my coax need? I am able to source RG142 easier here in Hong Kong and if I can get away with that, I then don't have to wait too long to ship the RG400 from AS.

Many thanks!
Hank
 
Typically, any solid core wire is not used in aircraft. It tends to be more stiff and brittle. Vibrations over time tend to caused fatigue and wire breakage. Stranded wire is much more flexible.
 
Hank,

Check around for ham radio operators in your area. Aircraft Spruce would be trailing the pack of places I would order coax cable from. RG400 is good low-loss coax, but I wouldn't be afraid to use most good quality 50 Ohm cable. You shold not have much trouble finding something suitable that's available locally.
 
I've used both and would be fine with RG142 if its all that was available, they actually have the exact same bend radius. It's important that you use a good crimped connector with both.
 
As mentioned RG400 has a stranded center conductor and RG142 is solid. RG 142 should not be used where there would be flexing of the cable while in use but is commonly used for aircraft. Both are aircraft approved under Mil-C-17/ Minor flexing during installation and removal of the connector from an antenna isn't a problem. RG400 has a lower loss at transponder frequencies and denser shielding to prevent leakage into adjacent cables. This is important when cables are bundled tightly together. Otherwise both will work well at com frequencies and RG142 is fine for transponder/UAT's for lengths under 6 ft or so. Both have fire resistant insulation and won't be a fire hazard.

BTW, you should make sure it is Mil-C-17/ cable as some of the commercial variants might not be as good (although some low loss commercial versions can be better than RG400).
 
Thanks

Thanks for all the reply!

I am buying the RG142 from the aircraft maintenance facility, they are the only place I can get mil-spec cable. But for some reason, even the Boeing wiring manual doesn't list RG400, so they don't stock them.

So am I right to say RG142 is good enough if I secure it on the aircraft and keep it away from other wiring?
 
RG-142 will work just fine as long as you don't wiggle it around a lot where the connectors are crimped on.
 
100m?!!

I was a bit annoyed they don't have RG400 in Hong Kong. After few days of research, I finally found a place that export these cables and willing to sell me a reel of them....100 meter (328 feet) per reel!!

As always, there's a catch: I only need 20 meters and if I buy it from Spruce, it's almost $270 with shipping and it would take 2-3 weeks to arrive; versus $340 if I buy the 100 meters reel.

Question: Do you ever find yourself need these cables anywhere else in the project? I am planning to use these for my NAV, 2 VHF, ADSB, XPDR. I don't want to have 80 meters sitting at home if I have no further use for them, but on the other hand, extra $70 for 80 meters is almost too good to pass on.
 
Can you find out what shipping cost to England is .. lets say in units of 10 meters ...

I see lots of people from HK selling stuff on eBay ... I am in need of some .. not sure how many meters ... I am in Penang at the moment ... will be back in UK next week
 
Certification issue

Hi digidocs,

I wish I can use other substitute but because it's the first experimental in Hong Kong, I am limited to either manufacture provided/specified components, or certified parts/components. Everything has to be traceable and documented.

They got some weird requirements that I don't have much liberty to debate with. I can write a book on this subject....

Jan: Yeah, I saw them too on eBay, but I refrain myself from getting from them for the same reason mentioned.
 
Last edited:
You could use RG-58. It was used extensively in aircraft installations up to just a few years ago. The cable losses in short runs will not make a significant difference in the reception or transmission of the signals.
 
HighSchoolBuilders said:
I wish I can use other substitute but because it's the first experimental in Hong Kong, I am limited to either manufacture provided/specified components, or certified parts/components. Everything has to be traceable and documented.
Click to expand...

So LMR-400 would be out of the question... that's too bad. Skygeek says they have RG400 for substantially less than Spruce (or will have, it's out of stock) with a 100' (30.5M) minimum. If they are ridiculously expensive on shipping, let me know - I may be able to help, I ship internationally all the time.
 
Hank

How about this? I'm pretty sure that's what Mendelssohn supplied me with my avionics. Certainly, they were not picky about giving me the lengths and spare that I wanted which I doubt they would have done with RG400 at 20x the price. What I have has a stranded core so if this is it, it may well me suitable.

http://www.gps.co.uk/rg58-cu-co-axial-cable/p-320-322-1056/

Give Danny a call at the shop - he is the technical man. I'm pretty sure they will ship VAT-free to Hong Kong. If not, let me know and I can bring it back for you. I am on leave in UK and returning to Hong Kong at the end of the month.

Good luck with the CAD negotiations!

Paul
 
RG58 was used for years in aircraft but has the following short comings:
1. Insulation and dielectric is PVC and burns quite well which should be a concern for aircraft.
2. The attenuation (loss) at com freq's is OK but at transponder freqs not so good.
3. The shield braid density is poor, which means signal leakeage, potentially coupled to to other wiring.

It is generally not considered to be qualified for aircraft use today, but in the past has served ok. The main problem with generic RG58 is that the quality can vary widely. Most of us probably remember Radio Shack (Tandy Aerospace) RG 58 with some pretty poor sheilds. Cheap for for around the house but can be the source of reliability issues in aircraft.
 
Using a good quality RG-58 would work quite well. The losses even at the transponder frequencies would still be acceptable. I agree that the cheap stuff is good for clothes lines but it stretches too much. As for the fire rating of the wire, not to worry. If it ever gets that hot in the cabin or aft fuselage you won't be alive to notice the extra gassing off of the plastics. Yes the double shielded wire is a bit better for keeping the signal in the cable but. When using RG-400 on transponders they want you to use a minimum length not a big concern using RG-58.
 
DaleB said:
So LMR-400 would be out of the question... that's too bad. Skygeek says they have RG400 for substantially less than Spruce (or will have, it's out of stock) with a 100' (30.5M) minimum. If they are ridiculously expensive on shipping, let me know - I may be able to help, I ship internationally all the time.
Click to expand...

Umm...neither of those two places are particularly well known for aircraft electronical supply. Ever thought of buying stuff from some place that is good priced and has no minimums?!?! :)

I'll just get Hank taken care of with the right stuff tomorrow!

Cheers,
Stein
 
Hank, I hope Stein gets you fixed up. Something I have not seen mentioned is that RG 400 is double shielded.
If you still have a problem maybe you could call Van's and get them to ship you some. That might solve the manufacturer supplied requirement.
 
Problem solved

Someone saw the post and offered the leftover he had from his build. Very generous and true spirit of VAF! Along with Stein, I think I am all set! Thanks everyone for the reply and offer to help!
 
Another consideration is that the steel core in RG142 can interfere with compasses and other items sensitive to having ferrous materials nearby. All my coax is RG142, but a few lines had to be rerouted due to magnetism issues.
Trying RG400 next time.
 
N91CZ said:
...the steel core in RG142 can interfere with compasses...
Click to expand...
I never thought about that. The RG142 coax to my comm antenna pases probably 12" away from my magnetometer back in the tail cone. I haven't noticed any problems so I guess that's enough separation.
 
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