Identifying VHF antenna cable type

[MattS]

Removing headlining on (relatively) new boat to inspect mast cabling has revealed a VHF connector looking a bit worst for wear.

On the assumption that this might be having a material impact on signal strength / quality, I intend to snip these grotty connectors off and replace with new PL259 / SO239 connectors. The cable itself doesn't seem to have any identifying marks.

Is there any other way of identifying which type of VHF antenna cable has been used, so that I can ensure I buy the correct PL259 / SO239 versions?

 

[Roberto]

Check also you have a sufficient available loose length of cable, if oxydation has grown inside the cable the braid will be blackened, if it s made by very thin filaments you might have to cut away a good length before finding relatively cleaner copper for new connectors.

 

[AntarcticPilot]

Those are BNC connectors, and I would replace them like for like or upgrade to TNC connectors. BNC connectors provide very good coupling. TNC connectors are the same principle but use a screw coupling rather than the bayonet fitting, providing a stronger mechanical connection. TNC and BNC connectors are standard connectors in the RF world. I'd regard the PL259 type as a downgrade.

 

[Bilgediver]

Removing headlining on (relatively) new boat to inspect mast cabling has revealed a VHF connector looking a bit worst for wear.

On the assumption that this might be having a material impact on signal strength / quality, I intend to snip these grotty connectors off and replace with new PL259 / SO239 connectors. The cable itself doesn't seem to have any identifying marks.

Is there any other way of identifying which type of VHF antenna cable has been used, so that I can ensure I buy the correct PL259 / SO239 versions?


View attachment 192472

If the cable where your hand is goes to the mast/antenna then that corrosion etc on the connector suggests water penetrative at the top of the mast . This will have degraded the cable and it should be replaced.

The antenna cable is 50 ohm cable and not the similar 75 ohm used on TV 's

 

[MattS]

Check also you have a sufficient available loose length of cable, if oxydation has grown inside the cable the braid will be blackened, if it s made by very thin filaments you might have to cut away a good length before finding relatively cleaner copper for new connectors.

Thanks @Roberto - I'll do that before I start cutting anything, as I do think there's a risk that I'm a bit short on free cable. In which case I'd probably be safer to not cut anything until I can run new cable.

Those are BNC connectors, and I would replace them like for like or upgrade to TNC connectors. BNC connectors provide very good coupling. TNC connectors are the same principle but use a screw coupling rather than the bayonet fitting, providing a stronger mechanical connection. TNC and BNC connectors are standard connectors in the RF world. I'd regard the PL259 type as a downgrade.

I didn't realise this @AntarcticPilot - I'd just always thought the PL259s were the industry standard for use on board! Didn't realise they were inferior to BNC / TNC. Chandleries etc. don't seem to stock BNC / TNC as readily!

If the cable where your hand is goes to the mast/antenna then that corrosion etc on the connector suggests water penetrative at the top of the mast . This will have degraded the cable and it should be replaced.

The antenna cable is 50 ohm cable and not the similar 75 ohm used on TV 's

Thanks @Bilgediver - I did wonder if it might be a sign of water ingress through the deck, but I can't see any evidence that water is getting in through the cable gland. Possibly historical damage before it was made watertight. Unfortunately the mast isn't due to come down any time soon, so I don't know how practical it would be to run replacement cable unless someone is confident that they can pull the cable through by climbing the mast.

On cable type - I was trying to work out if it was RG58 or RG8, as they seem to require different versions of the connectors. It doesn't seem overly thick, so I'm guessing it's RG58...

 

[oldgit]

50p worth.
RG 58 thin cable. 50 ohms.
RG 8 thick cable. 50 ohms..
On the marine frequencies we operate on ie. 156.00 mhz over the likely length of cable involved the signal loss between RG 58 and RG8 might be measurable with a posh power meter of some description, in the real world not much difference.
Agree about the possibility on all the cable between the top of the mast and the plugs in the picture being corroded.
Cable insulation must be cut back until bright shiny(ish) braid can be found, if you are lucky only an inch or two, more than a foot or two and likely the entire length is full of water and in extreme cases a mushy mess.
Plugs .
BNC , "N" etc. plugs are wonderful pieces of kit but absolute fiends to fit and must be crimped or soldered. PITA even for those with 40 years of fitting and the patience of a saint.
Pl 259 are perfectly adequate and simple to fit especially in confined spaces.Whatever you use, solder them
Cable.
Buy from the chandler if you must ...but there is decent quality PL259s and RG58 out there at fraction of the cost , simply the more braid the better, most likely to be found at sensible prices from amateur radio shops.
Best Quality Radio Spares or Farnell etc.
You do not need Gold plated plugsand in the name of heaven NO 75 ohm TV Co-ax plugs.
Seen much hairer messes than that, you might get away with undoing those plugs and a good soaking of proprietary switch cleaner such as Servisol
( Not WD40 ), make and break that joint a few times to clean the surfaces.
A pedant might check with a SWR meter, the Practical Boat Owner would call up the local VTS and ask if they can hear you.
Job done.

 

[Boathook]

Thanks @Roberto - I'll do that before I start cutting anything, as I do think there's a risk that I'm a bit short on free cable. In which case I'd probably be safer to not cut anything until I can run new cable.


I didn't realise this @AntarcticPilot - I'd just always thought the PL259s were the industry standard for use on board! Didn't realise they were inferior to BNC / TNC. Chandleries etc. don't seem to stock BNC / TNC as readily!


Thanks @Bilgediver - I did wonder if it might be a sign of water ingress through the deck, but I can't see any evidence that water is getting in through the cable gland. Possibly historical damage before it was made watertight. Unfortunately the mast isn't due to come down any time soon, so I don't know how practical it would be to run replacement cable unless someone is confident that they can pull the cable through by climbing the mast.

On cable type - I was trying to work out if it was RG58 or RG8, as they seem to require different versions of the connectors. It doesn't seem overly thick, so I'm guessing it's RG58...

I've found it easier to run new cables with the mast down. Splice the new cable to the old one and pull the old one out drawing in the new one. 2 people doing the job means one pulls and the other pushes plus guiding the new cable in.

 

[MattS]

50p worth.
RG 58 thin cable. 50 ohms.
RG 8 thick cable. 50 ohms..
On the marine frequencies we operate on ie. 156.00 mhz over the likely length of cable involved the signal loss between RG 58 and RG8 might be measurable with a posh power meter of some description, in the real world not much difference.
Agree about the possibility on all the cable between the top of the mast and the plugs in the picture being corroded.
Cable insulation must be cut back until bright shiny(ish) braid can be found, if you are lucky only an inch or two, more than a foot or two and likely the entire length is full of water and in extreme cases a mushy mess.
Plugs .
BNC , "N" etc. plugs are wonderful pieces of kit but absolute fiends to fit and must be crimped or soldered. PITA even for those with 40 years of fitting and the patience of a saint.
Pl 259 are perfectly adequate and simple to fit especially in confined spaces.Whatever you use, solder them
Cable.
Buy from the chandler if you must ...but there is decent quality PL259s and RG58 out there at fraction of the cost , simply the more braid the better, most likely to be found at sensible prices from amateur radio shops.
Best Quality Radio Spares or Farnell etc.
You do not need Gold plated plugsand in the name of heaven NO 75 ohm TV Co-ax plugs.
Seen much hairer messes than that, you might get away with undoing those plugs and a good soaking of proprietary switch cleaner such as Servisol
( Not WD40 ), make and break that joint a few times to clean the surfaces.
A pedant might check with a SWR meter, the Practical Boat Owner would call up the local VTS and ask if they can hear you.
Job done.

Thanks @oldgit - very helpful advice. I'll definitely give the switch cleaner a go to start with, just to see what happens.

I do have a Moonraker SWR meter (one of these Moonraker SWR-270 - Dual Band SWR/Power Meter) so if I get hold of appropriate converter I can certainly give it a test - and as you say I should do that first before touching anything!

Useful context around RG58 vs RG8 and also around the connectors - certainly I have fitted PL259s before so am reasonably confident I can do a half decent job. And genuinely didn't realise I don't really need gold - thought that was the 'gold standard'!

I'm expecting a poor VSWR result, because my AIS transceiver has been complaining of high VSWR for a while, even when I connect directly to the antenna rather than going through my Quark Active VHF splitter.

 

[wonkywinch]

A pedant might check with a SWR meter, the Practical Boat Owner would call up the local VTS and ask if they can hear you.
Job done.

You're better off calling a more distant NCI station as VTS are not really there to provide radio checks for all and sundry.

A local call doesn't prove much at all if there are weaknesses in the system. Someone had wired by VHF antenna cable using F connectors (satellite TV) at the bottom of the mast inside the saloon ceiling. I had lots of problems transmitting AIS, received traffic only within 2-3 miles and the VHF appeared to work perfectly normally.

Only when I changed the connector did it all burst into life properly. If I ever need to do radio checks, it is to a more distant NCI, not a local channel.

You need to understand the weaknesses of FM transmission and the clever circuitry inc squelch, in a modern receiver to realise that even a piece of wet string would make a reasonable antenna if only transmitting a mile or so.

 

[Roberto]

I'm expecting a poor VSWR result, because my AIS transceiver

If it is for a masthead AIS antenna, in particular if a 2W power txr, you might consider using a low loss cable. There are cables with very low losses which are as thin and manageable as the RG58 you most certainly have (RG8 a different beast). For 25w VHF antennas on average size mast is more debatable, but for just 2W trying and reduce the loss (via better cable, connectors etc) is more relevant or your antenna will be left radiating a tiny fraction of W.

 

[MattS]

You're better off calling a more distant NCI station as VTS are not really there to provide radio checks for all and sundry.

A local call doesn't prove much at all if there are weaknesses in the system. Someone had wired by VHF antenna cable using F connectors (satellite TV) at the bottom of the mast inside the saloon ceiling. I had lots of problems transmitting AIS, received traffic only within 2-3 miles and the VHF appeared to work perfectly normally.

Only when I changed the connector did it all burst into life properly. If I ever need to do radio checks, it is to a more distant NCI, not a local channel.

You need to understand the weaknesses of FM transmission and the clever circuitry inc squelch, in a modern receiver to realise that even a piece of wet string would make a reasonable antenna if only transmitting a mile or so.

I took the sentiment of @oldgit's message, but yes I do avoid using VTS for radio checks, and regularly use NCI stations. With a family member who is an NCI volunteer, I think they quite like receiving a call now and then! So I generally do a radio and AIS check whenever I'm passing a new NCI station - it's interesting to see how their visibility of you varies (which I'm sure might be to do with the kit their side sometimes as well!).

If it is for a masthead AIS antenna, in particular if a 2W power txr, you might consider using a low loss cable. There are cables with very low losses which are as thin and manageable as the RG58 you most certainly have (RG8 a different beast). For 25w VHF antennas on average size mast is more debatable, but for just 2W trying and reduce the loss (via better cable, connectors etc) is more relevant or your antenna will be left radiating a tiny fraction of W.

Understood. My AIS is 5W, but I'm guessing your principle still stands. I do have a Glomex stubby AIS-tuned antenna which I could fit to pullpit for my AIS transceiver, and I have to say am now tempted to prioritise that job if only to have some kind of backup antenna, having seen the potential state of my masthead...

 

[oldgit]

Our VTS antenna is 12 miles away at Sheerness, a hill or two in between, the actual VTS office however is in Liverpool.
At low tide we are lucky to hear them, let along give them a call.

 

[MattS]

Our VTS antenna is 12 miles away at Sheerness, a hill or two in between, the actual VTS office however is in Liverpool.
At low tide we are lucky to hear them, let along give them a call.

Very true for us on the Medway - and no NCI station within reasonable reach until you're right out in the estuary.

Whitstable NCI is actually the only station I've never been able to raise, even from off the Whitstable coast!

 

[st599]

A PL259 is a shielded banana plug with a +/- 20 ohm manufacturing tolerance.

Deserve to be left in the 1940s where they belong.

 

[William_H]

A PL259 is a shielded banana plug with a +/- 20 ohm manufacturing tolerance.

Deserve to be left in the 1940s where they belong.

Except all the radios for boats I have seen require PL259 to attach antenna cable to radio. Yes BNC far better for joining cables. I must fitted hundreds of BNC connectors in my work on aircaft. One real trap is that the centre cable can shrink pulling the pin back so looks fine but does not make contact. Always check male connector with finger nail. Centre pin should be level with case. ie you can feel it with finger nail. ol'will

 

[oldgit]

"A PL259 is a shielded banana plug with a +/- 20 ohm manufacturing tolerance."
"Deserve to be left in the 1940s where they belong."

Have you mentioned this to ICOM, all their VHF Marine equipment has a SO259 along with their VHF Amateur radio stuff.

 

[ProDave]

One real trap is that the centre cable can shrink pulling the pin back so looks fine but does not make contact. Always check male connector with finger nail. Centre pin should be level with case. ie you can feel it with finger nail. ol'will

There are many different makes and designs of BNC plug. Some of the better ones have the pin captive between 2 plastic parts that form the insulation, so that problem will not occur. That is the sort I use whenever I have a choice.

To the OP, before you tear it all apart, have you uncoupled your plug and socket to look inside at the mating surfaces. It is entirely possible all is clean and dry inside and your plugs have just got wet on the outside somehow.

All the good connectors like BNC, TNC, N etc all have rubber seals on the mating faces so they are at least splash proof, something which a PL259 / SO239 will never be.

 

[MattS]

To the OP, before you tear it all apart, have you uncoupled your plug and socket to look inside at the mating surfaces. It is entirely possible all is clean and dry inside and your plugs have just got wet on the outside somehow.

So I had a go a this today. The mating surfaces didn't look anywhere near as bad as the outside of the connectors, so I was hopeful.

I had a go at cleaning the connectors up a bit with WD40, which was working quite well. But in the process, must have tugged a little hard and the BNC connector just came away - revealing that the core and braid were very badly corroded. The core connection must have only been hanging on with a few strands.



I cut back a bit to see how far the corrosion went, and unfortunately it does look like it goes a way back. The braid feels very brittle.

There's very little of the actual antenna cable left below deck now, so although i might be able to get a PL259 on what's left of the braid it won't be an amazing connection. There's a real chance that as soon as I attempt to screw up a connector onto the braid, it will just disintegrate.

I suspect the proper solution is replacing the cable to the top of the mast unfortunately - something I'm hoping can be done with a mast climb by a professional.

The only other option I can think of is to see what the cable is like above deck, and possibly put a join in above deck to get me through the season.

 

[MattS]

Seen much hairer messes than that, you might get away with undoing those plugs and a good soaking of proprietary switch cleaner such as Servisol
( Not WD40 ), make and break that joint a few times to clean the surfaces

Reading back through the thread have now seen that @oldgit said not WD40 and I misread. B***er it.

 

[oldgit]

A temp/perm solution.
Check braid condition just below deck level.
If manky its a new cable run.
If OK, mebbe a deck fitting will solve the problem for now or forever depending on your keeness.

This is obviously PL but other plugs are used.
Ps.....Every joint made loses you a bit of RF output at the aerial.