BNC plugs

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sailorbaz

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I have just put my boat back in the water after a refit which included getting rid of a VHF whip aerial on the rear quarter and replacing it with a masthead antenna - it's a Shakespeare with the curly bit in the middle. I bought 50 ft of RG8x, as recommended on here, from the USA as it's not available in Oz. It came with a PL259 plug on each end. I connected one to the radio, cut the cable and soldered it to a female BNC socket on a bulkhead. I connected the other plug to the aerial and ran the cable inside the mast, through a deck gland and then attached a male BNC plug. IMO it's the weak link in the system - you leave a short piece of the multi-strand central conductor sticking out, kind of wrap the outer braid round the insulation and just screw it into the plug. I suspect the plug is made for the kind of co-ax with a solid copper core. Having said all that I did a radio check and it's loud and clear!
I can't help feeling that the cable might come out of the plug at some point and I've read of dire warnings that transistors etc could blow.
Does anyone know if a better BNC plug exists?
By the way a PL259 won't go through the hole for the deck gland when I need to take the mast down.
Sailorbaz
 
sailorbaz said:
I have just put my boat back in the water after a refit which included getting rid of a VHF whip aerial on the rear quarter and replacing it with a masthead antenna - it's a Shakespeare with the curly bit in the middle. I bought 50 ft of RG8x, as recommended on here, from the USA as it's not available in Oz. It came with a PL259 plug on each end. I connected one to the radio, cut the cable and soldered it to a female BNC socket on a bulkhead. I connected the other plug to the aerial and ran the cable inside the mast, through a deck gland and then attached a male BNC plug. IMO it's the weak link in the system - you leave a short piece of the multi-strand central conductor sticking out, kind of wrap the outer braid round the insulation and just screw it into the plug. I suspect the plug is made for the kind of co-ax with a solid copper core. Having said all that I did a radio check and it's loud and clear!
I can't help feeling that the cable might come out of the plug at some point and I've read of dire warnings that transistors etc could blow.
Does anyone know if a better BNC plug exists?
By the way a PL259 won't go through the hole for the deck gland when I need to take the mast down.
Sailorbaz
Click to expand...
On both my Benes the cable is cut to go thru the gland then a 259 plug is soldered on, the bit going to the radio has a plug and straight connector on. easy peasy. If you want to disconnect just unscrew the connector and desolder
Stu
 
My Bnc plugs have a small central pin into which you solder the conducting wire. The pin is quite small and easily lost and I wonder if you have got the complete unit?
The outer wire is clamped in when the end ferrule is screwed in, so I don't understand why you are concerned about the wire pulling out.
 
Thanks for the replies. I got the BNC plug from a local electronics shop - Jaycar. They said it was a 50 ohm plug.
There is no clamp for the outer it just screws in as tight as you can get it by hand. Looking inside the plug the contact for the conductor seems to be a narrow slot - I think a solid copper core would push through it, but I fear the multi strand may be just squashed against it.
I don't have a VSWR meter and don't know how to use one!
Sailorbaz
 
I would disagree with Nigelmercier about BNC being only good for a few insertions. I have never seen one fail from overuse. I think the OP has bought a screw type Tv aerail connector where indeed the wire centre is the pin. As said a BNC has the pin soldered or in some cases crimped onto the centre conductor.
The final test for a terminated BNC connector (male) is that you should be just able to feel the needle point of the pin with your finger nail. ie it should be just level with the end of the barrel tha tmakes the shield connection. The protrusion distance of the pin depends on the length of centre and insulation extending out of the shield. Use a small hot soldering iron and don't put too much solder onto the pin and through the tiny hole in the side. it is a good idea to tin the centre conductor first. The pin must fit into the hole so no build up of solder on the outside. I have done many in my working life but it did take a while to get the hang of it so may be buy a spare connector so you can start witha new pin if you mess up. However you can use an old pin especially if you have a tiny drill bit to drill solder out of old pin. good luck olewill
 
William_H said:
I would disagree with Nigelmercier about BNC being only good for a few insertions... I think the OP has bought a screw type Tv aerail connector where indeed the wire centre is the pin...
Click to expand...
When I worked at the BBC, the manufacturer of our oscilloscopes (Tetronix) suggested no more than 50 insertions on the BNC socket. They all had permanent adaptors plugged in.

I agree about the connector, it sounds more like an F-plug.
 
Like anything, you get what you pay for. There are some poor BNCs around that can corrode easily & also have poor mechanical strength.

I've never seen a BNC where the cable inner is used as the pin. There's always a pin that is soldered or crimped to the cable inner. Beware of 75ohm connectors too. They must be 50ohm for VHF radios.

BNCs rely on pressure squeezing the screen & outer sheath for strain relief. So they must be assembled correctly.

There are various types of coax, some of which are slightly bigger. So make sure that you get the right plug for the cable. A bigger plug will fit the smaller cable but the plug will short or fall off.

The main things to beware of when assembling are:

1. The pin sits correctly inside the connector. If you cut the inner too long, then it can cause the screen to short to the inner. If you cut the inner too short then the pin won't sit far enough out & may not make contact.
2. Make sure you cut the screen correctly. Some plugs ply on the screen folding back around some compression ring inside. Without that, the plug can fall off. If you cut the screen too long, then It can cause shorts.

So whichever plug you get, try to get assembly instructions too. Assemble with care & you'll have a system that works fine.
 
wooslehunter said:
Like anything, you get what you pay for. There are some poor BNCs around that can corrode easily & also have poor mechanical strength.

I've never seen a BNC where the cable inner is used as the pin. There's always a pin that is soldered or crimped to the cable inner. Beware of 75ohm connectors too. They must be 50ohm for VHF radios.

BNCs rely on pressure squeezing the screen & outer sheath for strain relief. So they must be assembled correctly.

There are various types of coax, some of which are slightly bigger. So make sure that you get the right plug for the cable. A bigger plug will fit the smaller cable but the plug will short or fall off.

The main things to beware of when assembling are:

1. The pin sits correctly inside the connector. If you cut the inner too long, then it can cause the screen to short to the inner. If you cut the inner too short then the pin won't sit far enough out & may not make contact.
2. Make sure you cut the screen correctly. Some plugs ply on the screen folding back around some compression ring inside. Without that, the plug can fall off. If you cut the screen too long, then It can cause shorts.

So whichever plug you get, try to get assembly instructions too. Assemble with care & you'll have a system that works fine.
Click to expand...

I agree (and also disagree with Nigel). When I worked at the Royal Radar Establishment, nearly all of the lab equipment used BNC or N connectors. I have never heard of a maximum number of connect-unconnect useage for them! Certainly not a figure of fifty which some bits of kit would have got through in a few weeks. There are lots of different quality of connectors in manufacture though, and we only used top quality silver plated ones.

Anyway if what Nigel said was true, on a boat, even if you plugged and unplugged once a year at lay up and launch that would be fifty years of boating...!
 
Last edited:
BNC connectors have a life of between 50 and 1000 matings, typically. The BNC was designed for lab work where a quick connect/disconnect regime was required, but have become more widely used.

They 'leak' a bit at the higher frequencies (Above 4GHz) but are fine for vhf levels. Biggest drawback is, as noted above, their fiddly assembly and also their non positive connection -TNC is better from this point of view.
 
There are a vast number of BNC connectors.
The twist-on one the OP mentions sounds like a type intended for old-style computer networking.
You need to get one that matches the cable size.
Reputable brands include Suhner, Vitelec, Radiall, Amp....

There are crimp and clamp variants.
I think most will need the centre pin soldered.
A properly assembled BNC clamp plug is waterproof, which extends cable life.

The 'mating' life of 50 cycles would probably be for a tightly spec'd connector intended for either certain measuring instruments or high power.
For our kind of use, they will be perfectly good unless corroded.

Lots of data in the catalogues such rswww.com, farnell etc.
 
Salty John said:
BNC connectors have a life of between 50 and 1000 matings, typically...
Click to expand...

Thank you.

Of course at the BBC they had to go by the worst-case scenario, as given by the manufacturer of the (very, very, expensive) oscilloscopes. Did I mention I broke one once, it was certainly more than a year of my salary.
 
Last edited:
Thanks for all the replies/comments. I have ordered a silver plated set from indexmarine. The instructions for fitting in post#5 are clear. The plug/socket on my boat are on a bulkhead inside so not exposed. They will only be undone once a year when I drop the mast. The boat is an Aussie built Catalina 25 with a swing keel and was sold as a trailer sailer but I keep it in the water as I don't have a trailer!
The PL259 plug on the masthead antenna is weather proofed with self amalgamating tape.
Sailorbaz
 
It seems to be difficult to buy solder on fittings on the high street now.

In my local maritime city I could find screw on or crimp on but none of the real things. In the end I found some old stock in a chandlers 60 miles away.
 
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