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RG-58, RG-400 and connectors

N999BT

Well Known Member
Patron
I was looking through a catalog and noticed that some BNC connecters say they are made different for types of cable:

One connector description says: Right angle, BNC connector plug for use with Belden 9907, Belden B7806A, LMR-195, RG-141, RG-303, RG-58, RG-58A, RG-58B, RG-58C coaxial cable.

and another that says: RF CONNECTOR/BNC male straight crimp plug for use with RG-58, RG-142, RG-400, 50 Ohm.

Two questions:

1) The first connector does not mention RG-400, but does mention RG-58. Does this mean that the connector should not be used on RG-400, and if so why?

2) How big is the performance difference between RG-400 and RG-58? When I built my plane 17 years ago, I'm not sure RG-400 even existed.
 
RG-400 has a thicker OD and needs a larger crimping sleeve. I suspect that the nipple extending under the braiding is also a different size. Usually those for 400 don't also support 58. I guess some are designed to support both, but would look at the data sheet to be sure it's not an error.

Larry
 
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RG-400 is much superior to RG-58. RG-400 is double shielded and the insulation is PTFE vs PVC.
The diameter of the inner conductor and insulation on RG-400 is just slightly different from RG-58.
I have found that crimp connectors for RG-58 will generally work fine for RG-400. As you noticed, some companies list both cables for a particular connector. Worth a try. The impedance mismatch will be undetectable between the two, it is more physical size of the shield sleeve, center pin wire hole, etc.
 
I recently had to return 90 degree connectors advertised to fit both RG-58 and RG-400. The 400 is a bit thicker, as others have mentioned. It was a tiny bit but enough of a difference the sleeve wouldn't go over the nipple and brading. My crimper from Stein works great on the 400.
 
I used a heat gun to warm the jacket on the last RG400 cable I assembled. It didn?t soften much, but eventually I was able to get it assembled.
 
I've found there is a wide range of quality and fit among BNC and TNC connectors, strangely enough. My recommendation is to purchase a handful of different ones and try them all out. When you find the one you like, buy more and use that for the real connections.

Also try buying from folks who use a lot of connectors, like Stein or Aerotronics.

I don't recall the ones I settled on otherwise would post here.
 
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Just looking at several vendors mainly Amazon for RG-400 cable. There is a huge price difference between Amazon and Spruce for example. Are all RG-400 the same or are there different qualities??
Thanks guys
 
Connectors

I just used these on RG-400. Stein also sells the same but Digikey shipping is cheaper.

The 90s are pricey but eliminate a 90 degree coupler type connector. They also are small. It keeps coax and conenctors away from other stuff. I used three of the BNC 90s on Antennas.

90 BNC

90 TNC

Straight BNC

Straight TNC

SteinAir published a really nice guide. Its dead on accurate.
Coax Stripping Guide

Every connector snapped perfectly into place. Crimp ring slides over the braid perfectly. I have a set of dies for my crimper. It works well.
I do things slightly different.
Slip a piece of heat shrink on. Slip the crimp sleeve.
Mark per the drawing. Trim the jacket. Mark the braid. Trim the braid. I use precision sissors. Mark the insulator. Trim with a set of wire strippers on 18AWG. Slip the pin over the center conductor. Check the witness hole. Crimp.
After crimping the center pin, I heat it with the soldering iron and wick a tiny bit of solder into the witness hole. Just a tiny bit. Not enough to go anywhere else. Cool. Assemble with a nice click confirming the connector is in correct position. Slide the ferrule up. Crimp. Slide the heat shrink up. Heat. Check with an ohm meter to insure there's no short.

RG-400 is expensive. Stein is cheapest. I bought 50' and had a tiny bit left after running three runs. Two to the area near the gear towers and one to the center tunnel between the seats.
RG-400
You want Mil-Spec cable. MIL-DTL-17-128B
 
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RG-400 is double shielded and the insulation is PTFE vs PVC.
Double shielding is a plus in aviation applications that could be electrically noisy, that's a good reason to choose RG-400 over RG-58.

I always buy Amphenol crimp connectors - Stein sells 'em, as does Digikey and other electronics parts vendors. Maybe a little more expensive than generic crud from Amazon, but worth it.

HTH

Dave
 
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Just looking at several vendors mainly Amazon for RG-400 cable. There is a huge price difference between Amazon and Spruce for example. Are all RG-400 the same or are there different qualities??
Thanks guys
 
Just looking at several vendors mainly Amazon for RG-400 cable. There is a huge price difference between Amazon and Spruce for example. Are all RG-400 the same or are there different qualities??
Thanks guys

If you buy ‘mil spec’ RG-400 then in principle it should all be the same. But you can buy non-mil-spec cable, in which case you have little idea about the quality of what you have.
In case people were wondering, the 50 ohm impedance comes from several parameters: diameter of the inner conductor, inner diameter of the shield, what is used as a dielectric in between the two. Then you can improve the shielding with multiple layers, solid metal foil, etc. Which is why you can end up with 50 ohm cable of widely varying diameters. Yes, you need to check that any given connector will work with your cable type.
 
Just looking at several vendors mainly Amazon for RG-400 cable. There is a huge price difference between Amazon and Spruce for example. Are all RG-400 the same or are there different qualities??
Thanks guys

Not sure I'd be willing to buy "mission critical" stuff from Amazon. They are getting a bad reputation for fake/counterfeit products. I spun the roulette wheel a few months ago and bought a starter solenoid through them that ended up DOA. Things like cargo nets and camera mounts: fine. Nobody dies if they're fake or out of spec.
 
Things like cargo nets and camera mounts: fine. Nobody dies if they're fake or out of spec.

Think carefully. If a camera mount or cargo net fails in an ‘off airport landing’, do you want to get hit in the head by a camera or toolbox going 60 MPH?
 
There is a huge price difference between Amazon and Spruce for example. Are all RG-400 the same or are there different qualities?? Thanks guys
They all may be labeled RG-400, but my experience with buying coax is you usually get what you pay for. I bought mine from Stein - not the cheapest, but not the most expensive either. Last I looked, DigiKey and Mouser were somewhere in the middle.

HTH

Dave
 
I just ordered some RG400 from Stein. They have a reasonable price. I saw lower prices at other locations, but I'd prefer to know that I have quality cable.
 
I'm planning to use RG400 for my comm antennas and transponder (I may even use something better for the transponder if it turns out to need longer than 8.8 ft), but was wondering if I need to use it for VOR/GS? I'm putting an Archer antenna in the wingtip, or possibly both wingtips. Toying with the idea of something cheaper for the VORs. Does anyone have thoughts or experience on this? Thanks.
 
I'm planning to use RG400 for my comm antennas and transponder (I may even use something better for the transponder if it turns out to need longer than 8.8 ft), but was wondering if I need to use it for VOR/GS? I'm putting an Archer antenna in the wingtip, or possibly both wingtips. Toying with the idea of something cheaper for the VORs. Does anyone have thoughts or experience on this? Thanks.

Well, in fact there are a lot of old Cessnas with RG58 running from a VOR/GS antenna high up on the tail all the way forward to the instrument panel. Biggest problem seems to be that over time (years) the inner conductor, if under stress from, say, a bend, can migrate thru the dielectric (or maybe the dielectric ‘flows’ around the wire) and you end up with the center wire not in the center, causing an impedance bump, or, extreme worse case, a short to the braid. So if you’re careful to minimize any bends, RG58 is probably good enough. Logistically, you now need different connectors for RG58 and 400, maybe different crimp tools, etc. I am curious: Why would you want two VOR antennas?
 
Well, in fact there are a lot of old Cessnas with RG58 running from a VOR/GS antenna high up on the tail all the way forward to the instrument panel. Biggest problem seems to be that over time (years) the inner conductor, if under stress from, say, a bend, can migrate thru the dielectric (or maybe the dielectric ‘flows’ around the wire) and you end up with the center wire not in the center, causing an impedance bump, or, extreme worse case, a short to the braid. So if you’re careful to minimize any bends, RG58 is probably good enough. Logistically, you now need different connectors for RG58 and 400, maybe different crimp tools, etc. I am curious: Why would you want two VOR antennas?

Thanks Bob for the quick and knowledgeable answer.

If I have dual comm/nav units I was thinking I need two VOR antennas. But maybe a splitter is sufficient and less weight? Wouldn't I get better signal strength with two antennas? Perhaps you are about to say that if I am worried about signal strength I shouldn't be thinking about RG58...
 
It’s seldom an issue. Remember high flying jets expect to get a useable signal at twice the distance that we do, due to the line of sight restriction. Also, to the extent that you’re worried about externally generated noise, a splitter cuts that in half as well as the signal! Very few production aircraft with two navs use two antennas. It’s cheaper, easier, and lighter to use a splitter. But, otoh, if you find yourself trying to bring in a vor at extreme range, and the VOR is off to the, say, right, you might get a bit better performance from the right wing antenna (if you had a choice of two). Here in the US some have gone to gps-only navigation and now have no vor capability.
 
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