VHF Cable replacement

[lustyd]

Hi all, I need to replace the cable on my mast top aerial. I'm happy that I can do the connections OK but have 2 easy questions (hopefully).

1. RG58 cable seems to be cheaper from Maplin, I assume this is OK?

2. Does anyone have a solution to stop the cables dinging inside the mast?

Thanks all
Dave

 

[guernseyman]

2. Does anyone have a solution to stop the cables dinging inside the mast?

Water pipe insulation.

 

[dmmbruce]

Check with your vhf manual, supplier, or any installer what cable should be used.

I am fairly sure that it is NOT RG58. We used to make that and it was specifically for TV use, not for anything else. There are lots of other co-axial specs and I have long since forgotten which is which.

Mike

 

[lustyd]

Check with your vhf manual, supplier, or any installer what cable should be used.

I am fairly sure that it is NOT RG58. We used to make that and it was specifically for TV use, not for anything else. There are lots of other co-axial specs and I have long since forgotten which is which.

Mike

The aerial comes with 20m of this so I know that it's the right stuff

 

[Salty John]

RG58 is 50 ohm 5mm cable that is ok for vhf. Unfortunately it has high transmission losses - around 5 dB per 100 feet of cable run, but it is cheap.

This level of attenuation is not acceptable in my view. The transmission loss over 20m is 2dB. (3dB loss is a halving of the signal power). The various offshore racing institutions specify that the vhf antenna cable loss be no more than 40%. To achieve this you need low loss RG8X (6.4mm) cable up to 20m or so and RG8U (9.5mm) thereafter.

I realise that some manufacturers fit 18m and even 20m lengths of RG58 coax to their antennas; this doesn't mean it's right, just cheap. They used to only fit 5m lengths of RG58 but in recent years this has increased. If you have an antenna with 20m of RG58 fitted it will work, but give you less range than using the more appropriate cable. I'd suggest you don't make the situation worse by adding even more RG58 cable - try to use the 20m and even shorten it if you can.

 

[lustyd]

Thanks John, I don't plan to add extra cable I plan to replace what's there and was going to use RG58 because that's what comes with the aerial when new. I'll look into the other cable you mention, it's only a 6m length so cost difference shouldn't break the bank.
Cheers
Dave

 

[Salty John]

Oh, to stop the cable dinging in the mast: Obviously a conduit is the best way but if it isn't already built into the mast profile fitting one can be challenging, but I've seen it done a few times. It's the only way to avoid clashes with internal halyards.

Otherwise you can use the cable-tie method which involves fitting three cable ties so the 'legs' radiate out from the cable - like a Mercedes Benze badge. Do this every 4 or five feet. The tails of the cable ties prevent the cable hitting the mast wall.

 

[vyv_cox]

2. Does anyone have a solution to stop the cables dinging inside the mast?

Cable ties every couple of feet, tightened to grip on the cable and each oriented at 120 degrees from the previous one. With the tails left on. Assuming you don't have to feed the cable through a very small hole.

 

[lustyd]

Thanks guys, cable ties seem like a perfect solution.

Do you have any links to info about the different cable types? I'd like to read up a bit myself before making the decision.
Thanks
Dave

 

[lustyd]

Never mind, just found that Some bloke on the internet has a nicely written PDF

 

[aluijten]

Thanks guys, cable ties seem like a perfect solution.

Do you have any links to info about the different cable types? I'd like to read up a bit myself before making the decision.
Thanks
Dave

I found this page some time ago. Regrettably it's in Dutch, but the graph tells you something about different cable qualities ("loss" = "verlies" or "verliezen" in Dutch).
I've once used the CELF400 quality, but you almost need a bending tool to get it around a curve. But it works very well

http://www.antennekabel.nl/antenne-kabel-1.htm

 

[AOWYN]

RG58 vs RG8X

Just an extra comment re using RG8X, it is a much higher spec product, but it requires a different size spacer for the PL259 plug than that used with RG58. From memory the 8X requires a 7mm spacer while RG58 uses a 6mm spacer. As the plug connections are usually the biggest source of signal loss getting them right is important and 7mm PL259's are not so readily available.

 

[Salty John]

That's correct, make sure you get the appropriate adapter sleeve for your PL259's. Normally a PL259 will have an inlet that suits 9.5mm RG8U and RG213 and you then fit an adapter sleeve for RG8X or RG58 as required.
You can also get 'one size' PL259's for each specific cable size.
I like the adapter sleeve because it very effectively traps the braid in the PL259 body - you don't need to solder the braid, just the centre pin. This makes it less likely you will damage the dielectric (between centre conductor and braid) by overheating.

 

[pmagowan]

I have to say I got all my stuff from Salty when replacing the aerial and coax a year ago and got really good info from his site. There is some good self amalgamating tape for all the joins. I went for the better cable as I felt this is a very important piece of kit. Works really well, excellent range. I fitted some conduit in the mast but it was tricky and I had the mast down at the time. Required poking a stick in openings to hold the conduit to the side, drilling and then riveting. Fiddly and a pain in the ...