Waterproof connector for coax cable

DoubleEnder

DoubleEnder

Well-Known Member
Joined
27 Apr 2002
Messages
1,559
Location
N Hemisphere
Visit site
I have a hollow, spruce mast, which is 50 feet long. The VHF antenna cable is routed internally. It mostly goes through the hollow centre but is routed in at the points where the mast is blocked for the spreaders. The cable has been tested end to end , and it is intact and undamaged.

However, the very top end of the cable has suffered damage and there is now only a very short length emerging from the mast, maybe 2 inches. I am looking for the best and tidiest way to make a really waterproof connection between this and the length of cable that is attached to the antenna itself. Ideally this connection should be ‘undoable’ but if I could be very certain about its integrity I would accept a permanent join.

To complicate things further, the standing rigging (shrouds, backstay, jumpers and diamonds) is attached by dropping spliced wire eyes over the top of the mast. This means that the wire stays form a very acute angle with the mast and there is limited room for any fitting, between the wood and the wire.

It would be mind bendingly expensive to replace the cable in the mast, just to get another foot of length at the top, so that isn’t an option. And I will not lead the antenna cable up the backstay! So it’s a join at the top, or recommendations for a very good hand held VHF.

One idea would be to use standard fittings to make the join (ideally made of solid gold hehe) , then slide the whole thing into a piece of hose, which I could fill with Sikaflex. But that‘s sh1t or bust approach, which I’d prefer to avoid.

Any good ideas?
thank you
 
Last edited:
If the top of the cable has been damaged, I would suspect the rest of the cable might have corroded/oxidised braid. This can increase the loss dramatically.
Unless you can test it for loss, it is suspect and should be scrapped.
There are plenty of 'waterproof' coax connectors, the key thing you need up the mast is a connector which does up with spanners, a 'clamp type', which seals the connector to the cable. It has to fit the diameter of the cable in question. A TNC connector, or rather mating pair of, might be a reasonable choice being smaller than N type and more robust than SMA, but more waterproof than BNC. I would go for a known make like Suhner, Radiall, Amp (TE).
TNC Connectors | RS Components

Is there an 'RGnnn' marking on the cable?
 
And also cover the connector with self amalgamating tape and it will be totally waterproof, but the best method, as mentioned would be to replace the whole cable.
 
PetiteFleur said:
And also cover the connector with self amalgamating tape and it will be totally waterproof, but the best method, as mentioned would be to replace the whole cable.
Click to expand...
It would quite literally be cheaper for me to buy a sat phone and a couple of years’ data than to replace the cable In the mast. And the cable has been tested, by a professional marine electronics engineer. It is fine, undamaged, not in need of replacement. I just have a very limited amount with with which to make a connection at the top of the mast.
 
gdallas said:
It would quite literally be cheaper for me to buy a sat phone and a couple of years’ data than to replace the cable In the mast. And the cable has been tested, by a professional marine electronics engineer. It is fine, undamaged, not in need of replacement. I just have a very limited amount with with which to make a connection at the top of the mast.
Click to expand...
How did he test it?
It can measure fine with an ohmmeter but be completely useless at VHF.
 
You could try a Shakespeare Solderless Joiner because it doesn't require soldering (I'm assuming the mast is up) and it will fit RG58 and RG8X. You would need to then wrap the join in non-adhesive silicone compression tape.
 
lw395 said:
How did he test it?
It can measure fine with an ohmmeter but be completely useless at VHF.
Click to expand...
tested for impedance and for continuity. The problem is mechanical damage at the top, leaving just a short piece for connection. but I’m interested to know more about how it could be useless for VHF if the cable’s integrity has been checked. What could cause that?
 
not sure how it could have been tested for RF without connection on end, would need either tuned antenna or dummy load connected, as lw395 said normally electrical checks don’t mean a lot other than showing a break or a short
 
  • Like
Reactions: G12
gdallas said:
tested for impedance and for continuity. The problem is mechanical damage at the top, leaving just a short piece for connection. but I’m interested to know more about how it could be useless for VHF if the cable’s integrity has been checked. What could cause that?
Click to expand...
At high frequency, current mostly flows in the surface of a conductor, the skin effect.
At VHF the majority of the current is in the top few microns.
If that surface is corroded, it's resistive and losses can be enormous.
In my old job, I've seen cables fail to meet spec simply because they were made with coax that had been in a factory with the ends not sealed for a while.
Outdoors I regard coax as a service item.
 
gdallas said:
...One idea would be to use standard fittings to make the join (ideally made of solid gold hehe) , then slide the whole thing into a piece of hose, which I could fill with Sikaflex.
Click to expand...

I’d just go with this personally. I wouldn’t trust self amalgamating tape as much as a decent sealant to fend off the elements.
 
I'd assume that there's enough excess in place to to solder an extension piece on? This done properly with self-amalg and heatshrink would allow you enough slack to not have a sh1t or bust option that you have now.
This company sell RG58 by the meter, and would appear to be reasonably priced, unless I've missed something in your post.
 
I'd be thinking of other places to locate an antenna, even just as a backup.
Ultimately in time the cable will need replacement regardless of the situation at the top of the mast.
Despite the tortuous route, can the existing cable be eased up the mast with slack from below? Better to have a join there.
 
Out of interest, what diameter is the current cable? If it's RG213 and about 10mm in diameter then you can get good quality 7mm cable that has even less loss than the 213 which might make it cheaper to replace as it'd be easier to pull through.

As others have said, you can't just test a cable with a normal meter - well you can continuity check it but that's all. You need to put a dummy load on it and shove some RF in the end...
I've replaced one cable that tested fine for continuity but was completely buggered as far as radio goes and it doesn't take much moisture at all to create a rather large loss/impedance changes.
 
Oh and Self amalgamating tape is fine with two caveats. It has to be done properly in the first place and you need to protect it from UV with a good quality PVC tape such as 3M Scotch 88. If you're able to source some then 3M ScotchKote (electrical sealant) is the icing on the cake to make sure the PVC tape doesn't unwrap in the wind which invariably it does a bit after a while. I also recommend the 3M self amalgamating tape over other cheap brands. I use a large amount of self amalg at work doing antenna connections in some of the most horrendously exposed places you could imagine. A well made and PROTECTED connection will last years.
No connection to 3M, their stuff just works that's all.
 
A point that doesn't seem to have been mentioned - ISTR that there are systems around where the total length of the cable matters. I think this is rare nowadays, but on some older systems the cable length was figured into the timing calculations, so changing it could seriously affect the display. It's unlikely with a modern system.

Just to reiterate a point others have made - a bad join in a co-axial cable can attenuate the signal enormously - more than 50%. Even a good join will result in some attenuation and is to be avoided if at all possible. Joins should certainly use good quality connectors designed for the diameter and impedance rating of the cable; a chocolate block won't cut the mustard! And I'd echo the suggestion of G12 that replacing the cable may be preferable in the long run; corrosion in coaxial cable will certainly spread along the cable very rapidly.
 
Replacing the cable is really not an option. It would mean a huge amount of work and it is not going to happen. It’s a 50 Foot spruce mast that is hollow in sections, where the cable is led internally, but at the spreaders it is blocked solid, so the cable emerges and is then routed in..... to change it would mean stripping all the mast fittings, routing out the old cable, reapplying 14 coats of varnish. Not an option, and in any case.....

The existing cable really is fine! It has been properly tested, I am confident of that. The engineer is trying to come up with a connector that will fit in the limited space, but I thought I’d ask on here in case someone had a suggestion. I know the cable won’t last for ever but it is good for now.

the radio is a one year old SH, nothing unusual.

I think we will Just go with a good quality standard connection and protect it with G12’s recommended brand of tapes and sealant. Thank you everyone for the input,
 
lw395 said:
At high frequency, current mostly flows in the surface of a conductor, the skin effect.
At VHF the majority of the current is in the top few microns.
If that surface is corroded, it's resistive and losses can be enormous.
In my old job, I've seen cables fail to meet spec simply because they were made with coax that had been in a factory with the ends not sealed for a while.
Outdoors I regard coax as a service item.
Click to expand...
Interesting and maybe a bit worrying. Thank you. I am just not prepared to replace the cable right now, so let’s see how it goes. But worth bearing in mind. Maybe I need an alternative. In the future. Thanks
 
You must log in or register to reply here.

Other threads that may be of interest

stav
Active antenna AAX5 is it just a vhf antenna?
Replies
3
Views
176
stav
stav

Share this page

Top