VHF Aerial wire

[Daydream believer]

My VHF has not been a problem since new in 2003. However, I have 2 friends whose VHFs have failed to perform as expected, due to gradual deterioration of the cable in the mast. My mast is currently down for new rigging & hopefully will not be dropped for another 5 years for a mid term rig survey.
From experience of such things, how long do forumites normally get out of their VHF wire & do they recommend a change after 20 years? Would it be wise to change it now, or should it be OK to leave well & good alone? The wire drops through the deck via a hawse pipe & the joint plug is above the cabin headlining in the dry. So there is no issue there.
I do not run AIS through it, as that is on a pushpit aerial.

 

[Birdseye]

The common problem with aerial coax is that water weeps in between the inner and outer insulation at the mast top which alters the impedance of the cable. I have had it get to the point where a patch of water appeared in the cabin below the aerial / vhf set connection!

Take your opportunity to change the cable whilst the mast is down and to ensure the connection to the aerial at the mast top is as watertight as you can make it.

 

[LadyInBed]

My coax is 20+ years old. I replaced the antenna about 15 years ago using an inline coax connector sealed in self-amalgamating tape and arranged the connector to be at the top of a loop of coax so any water runs away from the connector.
Still working well todate, Tx range is what I would expect.
In my experience, it's the connector's / termination that causes problems unless the coax has a wear point.

 

[Stingo]

My coax was perfect until a bolt of lightning ruined both it and a clean pair of grundies. Does that help your query?

 

[oldgit]

If you do replace the RG58 buy the best you can find/afford.
At one time all their was on the market was the decent stuff usually sourced from RS.
Top quality external sleeving and a very tight heavy braid sometimes silver plated.

At some point the race to the bottom started, awful thin sleeving which became brittle on exposure to the elements and the density and thickness of the strands in the braid becoming vanishingly small.
Amazed that any of the signal got from one end of the cable to the other.
The importers/ sellers did not feel the least guilty in selling this junk as meeting some long ignored military spec.
The longer the run the greater the losses.
If the connection between the antenna and the extention cable going down the mast is not ultra moisture proof ,preferably with self amalgamating tape , water will get in and by way of gravity/capillary action could end up in extreme cases actually inside your marine radio.
It can reduce the braid to a watery brown goo which makes real mess of the PCB.

 

[st599]

If you do replace the RG58 buy the best you can find/afford.
At one time all their was on the market was the decent stuff usually sourced from RS.
Top quality external sleeving and a very tight heavy braid sometimes silver plated.

At some point the race to the bottom started, awful thin sleeving which became brittle on exposure to the elements and the density and thickness of the strands in the braid becoming vanishingly small.
Amazed that any of the signal got from one end of the cable to the other.
The importers/ sellers did not feel the least guilty in selling this junk as meeting some long ignored military spec.
The longer the run the greater the losses.
If the connection between the antenna and the extention cable going down the mast is not ultra moisture proof ,preferably with self amalgamating tape , water will get in and by way of gravity/capillary action could end up in extreme cases actually inside your marine radio.
It can reduce the braid to a watery brown goo which makes real mess of the PCB.

Also, if you're re-running the co-ax, then you need to pay attention to minimum radii - it should be on the cable data sheet.
(The signal passes along the cable as an electric field between the core and outer, the impedance of which is dependent on the gap between the two)

 

[Daydream believer]

Also, if you're re-running the co-ax, then you need to pay attention to minimum radii - it should be on the cable data sheet.
(The signal passes along the cable as an electric field between the core and outer, the impedance of which is dependent on the gap between the two)

I am limited to the radius formed between the exit at the mast & the "U" bend, or hawse pipe,that the cable goes through down through the deck & into the area in the space above the headlining.
I know that when I installed my Raymarine seatalk kit the instructions for the wiring were quite specific on large radii that I could never achieve. But it still works- fortunately.
Any idea what sort of radius a VHF cable needs to be? What would be the outcome when I can only get about 40mm rad? My system works OK at present.

 

[MoodySabre]

I had to replace my aerial and it was done by Banaby whilst in the water. Boat alongside the dock and him on a bit of yard plant and me pulling the cable through.
I‘d do it now and it’ll see you out!

 

[Daydream believer]

I‘d do it now and it’ll see you out!

Oh ! Thanks Roger

 

[st599]

I am limited to the radius formed between the exit at the mast & the "U" bend, or hawse pipe,that the cable goes through down through the deck & into the area in the space above the headlining.
I know that when I installed my Raymarine seatalk kit the instructions for the wiring were quite specific on large radii that I could never achieve. But it still works- fortunately.
Any idea what sort of radius a VHF cable needs to be? What would be the outcome when I can only get about 40mm rad? My system works OK at present.

RG58 is 50mm. If you bend it more than that, the impedance changes, you get a mismatch and some of the power is reflected back the way it came.

You can normally get better quality cable, cheaper from a Ham radio supplier. For a 20m mast using RG58, you're losing more than half the 25W radio output power between the radio and the antenna. Spend a bit more and you'll get that down nearer to a quarter.

 

[MoodySabre]

Oh ! Thanks Roger

Ever the optimist Sam. Hoping for another 20 years sailing. ?

 

[samfieldhouse]

I’ve just replaced mine with Glomex RG8X.
I’m really confused as to why new aerials often come with around 20m of RG58 coax - all the literature I’ve read says RG58 shouldn’t be used on runs over 10m and the instructions for my VHF say not to use RG58 for runs of more than 7m.