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BNC connector question

Paul 5r4

Paul 5r4

Well Known Member
I bought some BNC connecters from Radio Shack. It says on the package they are for RG 58 cable. I was under the impression the RG 400 and RG 58 were the same sizes and all except the 400 was braided and just a better cable. These connectors are the screw on type. My question is this: The RG 400 cable "center" conducter, (which is not a solid wire but braided), seems too large to fit in the tiny hole inside the BNC connector! I've tried everything I know but if I'm even remotely successful it just looks all messed up and I certainly don't have any confidience in the joint/connections. I have to be doing something wrong. I've read all the other threads I can find and looked at other sites for info. No place seems to mention the diameter of the inner wire not fitting the hole. Are those from spruce or stein different?

Thanks so much in advance!
 
Yep, BNC connectors should fit either RG58 or RG400. Can you give us a photo of the problem, coz there shouldn't be one.
 
Sounds like the connector is made for RG58 with the solid center conductor. In this case the hole will be too small for the stranded center conductor of the RG400.

I've had some luck with carefully enlarging the hole using small drills in succession.

In my opinion the quality of Radio Shack connectors is questionable, you'd probably be better off in the long run using a different supplier.

Mark Olson N407V RV-7A; flying
N16XV F1 EVO; almost flying
 
Thanks

Thanks guys... I've been thinking about this for a couple hrs and have gone to stein's site and spruce. Both list different connectors for the two different cable types. I'll just order some and be done with it. Only reason I really didn't want to order anyway is I didn't have a crimp tool but I'll get one of those too.

Again, I appreciate all the help always available here.
 
Importance of the correct BNC Connector

BNC RF connectors are readily available in several levels of quality with the less expensive using brass as a center pin. Brass has a tendency to corrode causing poor system performance and are easily mistaken for the higher quality gold plated pins.

Years ago some of the early ARC radio equipment that came standard equipment on Cessna used brass pins in the electrical connections and were very troublesome, interestingly it was not uncommon for some pilots to carry a very long screwdriver to release the unit and reseat into the rack after approach lost the transponder reply.

Electrical applications that demand high reliability and performance only use gold or silver plated connections, a simple check of the mfg's data sheet will confirm makeup of the connector and could save hours of troubleshooting in the future.
 
Center conductor dia.

RG58U-0.032"BC; RG58AU-0.0355" 19/0.0011"TC; RG58BU-0.032"BC; RG58CU-0.0355" 19/0.0071"TC; RG400-0.0385" 19/0.0077" SC.
BC=bare copper; TC=tinned copper; SC=silver covered copper.
Please don't use cheapy connectors or cable in an aircraft! Why spend big buck$ on avionics and then connect them with someone's throw-off products! Remember, a chain is only as good as its weakest link, and that should apply to everything you build or put on your plane!
 
As always Paul is correct, do not use RG58 connectors with RG400. The proper connector is the Amp 31-320-RFX.
 
Other end

Garage Guy said:
Actually, the data sheet for Amphenol (not AMP) 31-320-RFX http://www.amphenolrf.com/pdf/108.pdf lists it as a RG-58 connector.

The 31-326 or 31-326-RFX is the one listed for RG-142/400.

That said, the 31-320-RFX does seem to work fine with RG-400.

--Paul
Click to expand...

Not being an electrical person, I always hate sorting through the Mouser catalog. So, what is the "other end," needed to complete the connection? Also, is there a female bulkhead version that is compatible.

Thanks in advance.
 
RV7Guy said:
Not being an electrical person, I always hate sorting through the Mouser catalog.
Click to expand...

HA! As an electrical person, sometimes that's 99% of the work!

Go on mouser and do a search for "BNC panel". That will get you a reasonable selection of BNC style panel-mount connectors.

From there it would be a good idea to filter by RF Series = BNC and Impedance = 50 Ohms.

Is Mouser# 523-112272 like what you're looking for?
 
Stein has great BNC connectors at only $1.50 each. But you do need a good crimper for them. He's got a $30 ratcheting crimper that works great. You have to buy a BNC crimp die for another $12 but you can also get a die for standard electrical connectors for the same cost to interchange. He's also got the special BNC screw on fittings required for some GPS antennas and 90 degree BNC fittings.
 
mcattell said:
Stein has great BNC connectors at only $1.50 each. But you do need a good crimper for them. He's got a $30 ratcheting crimper that works great. You have to buy a BNC crimp die for another $12 but you can also get a die for standard electrical connectors for the same cost to interchange. He's also got the special BNC screw on fittings required for some GPS antennas and 90 degree BNC fittings.
Click to expand...

The threaded connector is actually called a "TNC" (Threaded Neill-Concelman) connector. Becker's compact transponders also use this style connector too.

BTW, I've been putting BNC connectors of all styles (twist-on, crimp and soldered) and sizes of coax for more than a couple decades, and have found the absolute best way to terminate a coax end is with a good crimped-on Amphenol connector. It's also the quickest way to make a factory-quality connection if you've got the right tools. The cheap BNC crimper & die from Stein Air works just fine, I use one myself all the time. A dedicated 2-blade coax stripper cailbrated for RG-400 is nice to have also, but not really necessary. A razor knife works just fine as long as you're careful with your measuring and cutting. BTW, the $1.50 crimp-on male BNC connectors that Stein sells work perfectly fine on RG-400. That's where I buy my connectors, coax and tefzel wire anymore.
 
I used a three-blade stripper for the RG-400. It's just so much easier -- at least for me -- then trying to strip with a knife or non-precise way although I recognize it can be done. The one I bought from Home Depot -- for RG58 - didn't work, but I found one online. As with everything else, I got spooked with the idea that anything less than perfect here would result in noise etc.

Plus I like buying tools. ;)
 
Amphenol BNC connectors

Here's some info I've put together on Amphenol double crimp male BNC connectors for RG-58 and RG-400 coaxial cable.

The connectors come in 3 grades: commercial, industrial, and military. Amphenol literature says:

Military grade connectors are produced in accordance with MIL-C-39012. Industrial grade connectors provide comparable performance and generally feature nickel-plated brass bodies, teflon insulators, and gold-plated contacts. Commercial grade are low-cost connectors typically utilizing die-cast and molded components.​

So far as I can tell, all three grades in the series listed below have gold plated center pins. Commercial grade insulating plastic is rated to 85C; industrial and military use teflon rated to 125C. Commercial and industrial connector bodies are nickel plated; military is silver plated. All these connectors use the same size crimping dies.

Here are the Amphenol part numbers, grade, and unit cost in USD from mouser.com as of July 15 2010:

For RG-58:

031-320-RFX / commercial / $1.44
031-320 / industrial / $4.60
031-4320 / military / $5.67


For RG-400:

031-326-RFX / commercial / $3.84
031-326 / industrial / $5.36
031-4427 / military / $7.09


--Paul
 
If you want the absolute best coax and connectors for your equipment, then Andrew FSJ1-50A semi-rigid cable has the lowest loss and immeasurable leakage. It is about the same weight and size as RG58U, can be bent into a 1" radius, and Andrew supplies all of the connectors available for it, C, TNC, BNC, UHF, etc., and with some suppliers is the same or cheaper than RG400. I used this for X-band on a radar simulator I designed and I had it obtained for our test lab, and it was the best phase-and-amplitude-stable for use in calibrating our test equipment. I recommended this coax to a friend of mine with Orbital, who did a comparison of its attenuation with the other cables, and found that it was the only one of the 1/4" cables that could meet the FAA signal specs for the transponder Tx-Rx with a short cable run. His indisputable analysis was posted on a canard forum; look it up. When the fit hits the shan, and signals are marginal due to static and rain, wouldn't you want to have a signal that's above the noise, rather than buried in it? That's why, for attenuation as with drag, you want to have least amount of it. Again, if you're going to spend thou$and$ or ten$-of-thou$and$ on your avionics, shouldn't you at least get the best cabling even if it costs you $25 or $50 more?
 
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