Correct spec VHF cable and how to join ?

[st599]

I also avoided a splitter but put my stubby Ais ntenna at the mast head and it gets very far off targets... My rational is that solo off shore I want as much notice as possible....

I have a second vhf on a pole at the Stern and another vhf at the mast head which is currently not working.

One of my winter jobs is to fit a new Metz antenna and some superflex 7 at the masthead.

I then intend to use a second vhf in the cockpit connected to the Stern antenna for use in the unlikely event that I need to speak to anyone.

Whilst the masthead will allow me hear forecasts and further off stations below decks...

I might have an issue with feedback if I try to transmit whilst the other is switched on and I'd be slow to transmit at full power through an antenna that is only a foot or so from my Ais antenna...but this will just require switching off the Ais momentarily..

If you put two antennas at the masthead, they will affect each other and may cause worse performance in some directions.

 

[pandos]

If you put two antennas at the masthead, they will affect each other and may cause worse performance in some directions.

I have heard that, but if you look at many trawlers you will see antennas stuck everywhere often almost on to each other.

I can't see the stubby causing too much of an issue with the whip, but I'll but I'll keep it in mind.

 

[theoptimist]

Ideally your new coax cable would be stranded tinned core with a tinned shield, but unfortunately since the retirement of Salty John this is not possible, especially in obtaining good quality branded RG8x, but is still possible for RG58 (which you don't want anyway). My personally suggestion would be a compromise, Times LMR 240 which would be similar to RG8x or Times LMR 400 being similarly to RG213. The benefit here is these cables are made for outside installation, stranded copper core (the compromise) and a tinned shield. Various types of LMR 400 are available, as in standard, ultraflexible, DB (watertight jacket) etc etc. Look them up and see what you think. The LMR 400 would be the better quality but may prove to be difficult to install due to space.

 

[Wing Mark]

Cables like Times LMR get their low loss from having a solid copper core and an aluminium foil conductor inside the braided screen. Tinning is a bit crap at VHF.
This means these cables depend on being assembled properly with the right connectors.

To get the last 0.1 dB from cables like this, you have to start with a sealed cable and put the connectors on in a clean lab. Once you buy a cut length from a Ham Shop and they send it by post, all that's right out the window.

The big picture is that a new, properly installed generic coax which has never got damp might have an extra dB of loss compared with the optimum cable, but a lot of yachts probably have 20dB or more loss, because their coax cables have got damp and the conductors have oxidised. You probably won't even notice 20dB most of the time, radio works with path losses something like 150dB.

 

[st599]

Cables like Times LMR get their low loss from having a solid copper core and an aluminium foil conductor inside the braided screen. Tinning is a bit crap at VHF.
This means these cables depend on being assembled properly with the right connectors.

To get the last 0.1 dB from cables like this, you have to start with a sealed cable and put the connectors on in a clean lab. Once you buy a cut length from a Ham Shop and they send it by post, all that's right out the window.

The big picture is that a new, properly installed generic coax which has never got damp might have an extra dB of loss compared with the optimum cable, but a lot of yachts probably have 20dB or more loss, because their coax cables have got damp and the conductors have oxidised. You probably won't even notice 20dB most of the time, radio works with path losses something like 150dB.

You may not notice it in ideal conditions, but if I'm trying to use the radio in an emergency at a long range, I'd still like any extra that I can get as it may put me above the noise floor.

My one wish is that the manufacturers would move to BNC or TNC - I could route that through the mast and deck gland and make the length up at work properly having dried the cable as best as possible.

 

[Wing Mark]

You may not notice it in ideal conditions, but if I'm trying to use the radio in an emergency at a long range, I'd still like any extra that I can get as it may put me above the noise floor.

My one wish is that the manufacturers would move to BNC or TNC - I could route that through the mast and deck gland and make the length up at work properly having dried the cable as best as possible.

I expect that the radios are tested for type approval etc with an adaptor to some other connector series.
It would be interesting to measure the loss of say PL259 > cable vs Pl259 > TNC > cable.

It's easy to want the best of fractions of a dB and forget there's a fat tolerance on things like the radio's power output (etc) in the first place.

 

[theoptimist]

For clarification purposes, Times LMR 400 comes in a range of specifications, the standard yes being solid core. LMR 400 UL being stranded, hence the reason why it is important for a person to do their own research to decipher which suits their needs. The jacket or outer casing is very important, many allude to any old cable will do. A cable with a PVC jacket found on a majority of cables is less than ideal and better suited to indoors, much preferred is a TPE or PE etc outer coating. I said the cable was suitable but a compromise, hence the inner is not tinned but the sheath is, tinned has its place in the marine salt water environment purely and simply as it prevents oxidation! The tinning of the outer sheath does not inhibit the performance of the cable in any way evident form the specification sheet, and compared to RG213 coax. Personally I would buy a branded cable with a decent outer jacket at the right price over some unbranded cheap rubbish from you all know where.
If it's possible to find a branded RG8x cable with a decent outer jacket and your run is shorter than 20 meters, or can find branded Belden RG213 for instance, go for it, however good quality coax cable suitable for the marine environment in the UK certainly does not seem easily accessible.

 

[Wing Mark]

...., tinned has its place in the marine salt water environment purely and simply as it prevents oxidation! The tinning of the outer sheath does not inhibit the performance of the cable in any way evident form the specification sheet,....

If any slat water even gets to look at the braid, it's Game Over, the foil and braid will disintegrate due to the electrochemical difference between tin, copper and aluminium.
The reason the tinning of the braid does not affect the loss is because the RF current doesn't really flow in the braid, it flows in the aluminium foil.

Even quality cables like this claim something like a 10 year life outdoors, so people who think of taking the mast down once a decade should probably think about a new cable.