BNC connector for RG400

kbehrent · #1 07-08-2012, 06:17 PM

I'm installing a GA 56 GPS antenna and a UAT antenna that both use a BNC type connector. I'm using RG400 coax.

I happend to have a couple of Amphenol 31-320-RFX and was planning on using them. However, when I checked the Amphenol assembly doc, I see that RG400 is not listed for this connector, but is listed for 31-326-RFX. Will the 31-320-RFX still work?

These connectors are left overs from my avionics install I got from Stein and I'm pretty sure I used the 31-320-RFX on all my other antennas which also used RG400.

Captain Avgas · #2 07-08-2012, 07:19 PM

Quote:

Originally Posted by kbehrent

I'm installing a GA 56 GPS antenna and a UAT antenna that both use a BNC type connector. I'm using RG400 coax.

I happend to have a couple of Amphenol 31-320-RFX and was planning on using them. However, when I checked the Amphenol assembly doc, I see that RG400 is not listed for this connector, but is listed for 31-326-RFX. Will the 31-320-RFX still work?

These connectors are left overs from my avionics install I got from Stein and I'm pretty sure I used the 31-320-RFX on all my other antennas which also used RG400.

The 31-320-RFX connectors are for the RG 58 coax. Their pin cavities are too small for the larger diameter wire core of the RG400.

You can use the 31-320-RFX with the RG400 if you thin out the wire core but that is a messy and second rate solution. I'm not sure why Stein supplies 31-320-RFX with RG400.

The correct Amphenol crimp plug for the RG400 is either the 31-326-RFX or 36875. See here for Amphenol BNC plug specifications.

http://datasheet.seekic.com/PdfFile/...-432102068.pdf

kbehrent · #3 07-08-2012, 08:25 PM

Bob,

Thanks for the response, although that was definitely not what I wanted to hear.

I'm running against a tight deadline and I don't have time to reorder from Stein unless I overnight them and with my current run of luck I'll get the same ones. My local options are pretty slim, but I will give them a shot. If they have them, I'm going to buy a lotto ticket immediately!

rocketbob · #4 07-08-2012, 09:28 PM

31-320-RFX work fine with RG-400. They are the connectors Stein sells. I've crimped roughly 100 of these connectors on RG-400 and have never had a problem inserting the conductor. Much of it has to do with your stripping and trimming techniques...no thinning of the center conductor required.

Ironflight · #5 07-08-2012, 09:59 PM

I agree with Bob - I've used Stein's connectors with RG400 and had no issues. If you really want the 326's, check Mouser - I have found all sorts of weird stuff for really good prices with quick delivery.

Snowflake · #6 07-09-2012, 07:25 AM

I haven't checked to see if they carry this specific part, but Digikey has a lot of these parts too, and guarantees 9 or 10am delivery if you order by 4pm.

Neal@F14 · #7 07-09-2012, 07:46 AM

As mentioned above, I too have had no problems getting the BNC connectors from Stein to fit on RG-400 coax. I've installed many of them on RG-400 and they fit just fine, no need to cut any strands of the center conductor. The RV-8 in my avatar is full of RG-400, and BNC fittings all purchased from Stein.

Captain Avgas · #8 07-09-2012, 08:32 AM

I have both the 31-320-RFX plugs and the 31-326-RFX plugs (and have used them both). The 31-320-RFX plugs are specifically designed to make installation easier on RG-400 coax and they are what Amphenol recommends.

The 31-326-RFX plugs are different from the 31-320-RFX plugs in the following two key areas. Firstly they have a larger, deeper countersink in the entrance to the pin to allow for easier insertion of the multifilament RG-400 core (the RG-58 core is solid). Secondly they have a larger diameter hole in the plug itself to allow for easier insertion of the insulated core.

The BNC plug is not an easy termination for first timers and yet they require a relatively high level of installation quality control to avoid glitchy transmission faults (that can be a pain in the rear to locate down the track).

31-320-RFX plugs can be made to work with RG-400 coax with a bit of time and practice but they are not "ideal" and the average RV builder who is producing only a few terminations will find it significantly easier to achieve a good result by using the correct plug.

aerhed · #9 07-09-2012, 09:08 AM

Quote:

Firstly they have a larger, deeper countersink in the entrance to the pin to allow for easier insertion of the multifilament RG-400 core (the RG-58 core is solid)

Bad info here. The standard GA coax for decades was RG58C/U. It has a stranded core and still works just fine for most antennas. Especially with the short runs we have in little planes. RG58/U (no letter C) is solid core. I call it TV cable.

Captain Avgas · #10 07-09-2012, 10:25 AM

Quote:

Originally Posted by aerhed

Bad info here. The standard GA coax for decades was RG58C/U. It has a stranded core and still works just fine for most antennas. Especially with the short runs we have in little planes. RG58/U (no letter C) is solid core. I call it TV cable.

I do not use RG-58 coax so I was not aware that the aircraft version was specifically stranded. Thanks for that information. In checking the actual specifications for coax I note that the stranded RG-58AU conductor has a nominal diameter of 0.94mm while the nominal diameter for the RG-400 is 1.0mm. That may explain why the RG-400 is more difficult to insert into the BNC 31-320-RFX pin.

My best guess here is that due to variations in batch manufacture of the coax and BNC pins some builders will find that their RG-400 conductive core will fit into the 31-320-RFX pins...and others will struggle a bit. To my mind it just seems to make sense to buy the right plugs in the first place and be guaranteed of a good fit of all the wires into the pin every time.