VHF Antenna Cable

[Spirit of Glenans]

I've just discovered that my VHF antenna cable is damaged where it emerges from the base of the mast. Can I just replace the cable or is it normally integral with the antenna so that the whole assembly has to be replaced ? If the former, what type of co-ax cable should be used?
Thanks in anticipation.

 

[john_morris_uk]

It depends on the make of the antenna as to whether its 'integral'. I've never seen a cable that can't be disconnected and replaced although some people seem to struggle with fitting the end connectors properly. (They need soldering and doing neatly to work best.)

A good quality 50 ohm impedance coax with tinned copper is the way ahead. You can get all sorts of coax, but the best ones cost more as they have more copper in them and that does make a difference. You can get away with untinned, but I don't scrimp when I replace ours and use the best stuff.

Something like: http://www.amazon.co.uk/Ancor-Electrical-Premium-Coaxial-100-Feet/dp/B000NUX61W perhaps?

 

[Salty John]

As above, some antennas have a factory crimped connection, some a proprietary connection and some a PL259 plug onto an SO239 socket.

For cable runs over about 6m (20') and less than 20m I recommend RG8X cable - it's a 7 mm cable. If you have a longer run you can go to RG8U or RG213 but they are 9 mm cables and more difficult to handle. The smallest size cable, for runs under about 6m, is RG58, a 6 mm cable. (I've given the nominal diameters for the popular cable sizes, actual diameters vary slightly depending on the thickness of the outer sleeve). You should choose tinned copper, as said above, to avoid corrosion.

I have a commercial interest, we sell vhf antennas and cable.

 

[nigelmercier]

I've just discovered that my VHF antenna cable is damaged where it emerges from the base of the mast...

Do you have enough slack to install a pair of connectors?

 

[David2452]

If you need to splice it I can recommend these, I have recently taken to using them largely due to the bulk of other joining methods and their speed and simplicity of use on site.

 

[oldbilbo]

If you need to splice it I can recommend these, I have recently taken to using them largely due to the bulk of other joining methods and their speed and simplicity of use on site.

View attachment 42960

David,

I'd like to use some of those you've illustrated. Could you kindly advise what and where from? If yourself, so much the better....

 

[William_H]

Just to explain Salty Johns suggestions. Coaxial cable has quite a dramatic loss at VHF frequencies. Coax cable is described by its attenuation in decibels per 100ft or similar.
Essentially the bigger physically the cable size the less loss. The loss is a function of wire resistance and loss through the insulation.
The loss from a small RG 58 coax in a 40 ft mast can approach loss of half of the transmit power. Strangely losing half the power does not make a hugely noticeable difference because the effect is logrythmic however at extreme range obviously every bit helps. So the low loss and or really fat cable should be used on bigger boats. some smaller cables have quite reasonably low loss. But ultimately the haevier cable will withstand corrosion etc longer than this stuff. good luck olewill

 

[David2452]

David,

I'd like to use some of those you've illustrated. Could you kindly advise what and where from? If yourself, so much the better....

Shakespeare gold RG58 centre pin splice, Cactus Nav but I can do cheaper.

 

[Spirit of Glenans]

If you need to splice it I can recommend these, I have recently taken to using them largely due to the bulk of other joining methods and their speed and simplicity of use on site.

View attachment 42960

Do I need a ratchet crimper to attach these?

 

[Spirit of Glenans]

Do you have enough slack to install a pair of connectors?

Nigel's suggestion is the blindingly obvious solution, cutting out a large amount of work and expense. I have some slack at the top of the mast which I can pull down to make the splice. My mast is down at the moment so this will be very easy to do.
Sorry about the delay in getting back to my thread and thanks to all for your contributions.

 

[David2452]

Do I need a ratchet crimper to attach these?

No, just cut the coax square, push it in so the centre pin contacts the centre conductor then squash the four "lobes" with pliers and tighten the collars with pliers so the pins on those pierce the braid, job done. Also if required, they are small enough so 3:1 heat shrink will shrink down well enough to seal on the coax unlike a barrel and plugs where even 4:1 is difficult to seal due to the coax v plug dia. All in all a very elegant solution and relatively inexpensive, in fact quite a bit cheaper than two similar quality plugs and a barrel connector.