RG58 co-axial cable

Ian_Edwards

Ian_Edwards

Well-Known Member
Joined
9 Feb 2002
Messages
2,222
Location
Aberdeen Scotland
Visit site
Hi,

I need to replace the VHF cable to the mast head, so I need about 25m of 50 ohm co-axial cable ( the standard length supplied is 20m, which isn't quite long enough and would mean a joint inside the mast where it is inaccessibly, unless the mast is un-stepped)

The current cable, supplied with the Hawk VHF antenna is quite thin, much smaller than the standard VHF cable I'm use to, which seems to be about 5mm in diameter.

I've tried to identify the cable, but the Hawk website just says RG58, so there must be some additional identifiers to specify the cable.

Does anyone out there know the correct term for "thin RG58"?
 
Ian_Edwards said:
Hi,

I need to replace the VHF cable to the mast head, so I need about 25m of 50 ohm co-axial cable ( the standard length supplied is 20m, which isn't quite long enough and would mean a joint inside the mast where it is inaccessibly, unless the mast is un-stepped)

The current cable, supplied with the Hawk VHF antenna is quite thin, much smaller than the standard VHF cable I'm use to, which seems to be about 5mm in diameter.

I've tried to identify the cable, but the Hawk website just says RG58, so there must be some additional identifiers to specify the cable.

Does anyone out there know the correct term for "thin RG58"?
Click to expand...

It could be any 50 ohm impedance cable. Thicker cables have less loss, generally speaking.
 
Yes, that's true, but the connector on the Hawk VHF antenna is designed for the thinner cable, its got "O" rings and sleeves, which are specific to the cable diameter. So I'm looking to match the cable supplied with the Hawk.
 
Ian_Edwards said:
Hi,

I need to replace the VHF cable to the mast head, so I need about 25m of 50 ohm co-axial cable ( the standard length supplied is 20m, which isn't quite long enough and would mean a joint inside the mast where it is inaccessibly, unless the mast is un-stepped)

The current cable, supplied with the Hawk VHF antenna is quite thin, much smaller than the standard VHF cable I'm use to, which seems to be about 5mm in diameter.

I've tried to identify the cable, but the Hawk website just says RG58, so there must be some additional identifiers to specify the cable.

Does anyone out there know the correct term for "thin RG58"?
Click to expand...

RG58 OD is 0.195 inches, = 4.9mm, as you say. So what is the diameter of the current cable? RG178 is common, see Farnell for instance, but it has a higher attanuation. Its OD is around 2.2mm.

On second thoughts, RG 174 is also plausible, OD 2.8mm. It's stoked by Maplins for instance.
 
Last edited:
Are you saying that the cable you have now is even thinner than RG58? I'm not sure why they would do that. For optimum performance I think VHF usually uses RG8 which is significantly thicker than RG58. You can get 50 ohm cable in very tiny diameters but that is generally only used inside equipment.
 
RG58 is the most common on boats - it is easier to route through than the very thick (and stiff) lower loss alternatives and the cable runs on most pleasure boats are sufficiently short that the looses will not be significant.

There certainly are thinner 50ohm cables around - RG174 and 178 are candidates and can be bought from Maplins. The losses will be higher - but probably still acceptable on a small boat with cable runs of perhaps 10m. Your bigger problem is going to be connectors. You certainly will not find PL259 plugs over the counter anywhere designed to take it, so you find yourself either having to bodge some kind of a join together, or resort to a daisy chain of adaptors - not good for physical strength of connection and will introduce its own losses.
 
maby said:
RG58 is the most common on boats - it is easier to route through than the very thick (and stiff) lower loss alternatives and the cable runs on most pleasure boats are sufficiently short that the looses will not be significant.
Click to expand...

I'm pretty sure mine is RG8-X which is a slightly thinner version of RG8.
 
maby said:
The losses will be higher - but probably still acceptable on a small boat with cable runs of perhaps 10m.
Click to expand...

The OP has more than twice that.

Personally I would never go searching for thinner VHF cable. The thicker the better (assuming equal quality, braid coverage, etc). The downlead in my mast is about 10mm, converting to 5mm for the short run across the deckhead from mast foot to radio.

Only downside is picking up French chatter in the Solent :D

Pete
 
CreakyDecks said:
I'm pretty sure mine is RG8-X which is a slightly thinner version of RG8.
Click to expand...

Hmmm, that's interesting - I have to admit to not having actually read the lettering printed down the side of the cable and assuming RG58 across the board - RG8X is extremely similar in dimensions but slightly lower loss - certainly will not perform any words than RG58U!

RG8X is quite a lot thinner than RG8 - you would not want to be trying to mouse full size RG8 through difficult spaces!
 
RG58 is nominal 6mm, actual about 5mm. Loses around 5dB per 100' at 150 MHz.
RG8X is nominal 7mm, actual about 6.25mm. Loses around 3.7 dB per 100' at 150 MHz
RG8 is nominal 10mm, actual about 9.5mm. Loses around 2.5 dB per 100' at 150 MHz.

3dB loss is a halving of the signal strength.
 
Ian_Edwards said:
Hi,

I need to replace the VHF cable to the mast head, so I need about 25m of 50 ohm co-axial cable ( the standard length supplied is 20m, which isn't quite long enough and would mean a joint inside the mast where it is inaccessibly, unless the mast is un-stepped)

The current cable, supplied with the Hawk VHF antenna is quite thin, much smaller than the standard VHF cable I'm use to, which seems to be about 5mm in diameter.

I've tried to identify the cable, but the Hawk website just says RG58, so there must be some additional identifiers to specify the cable.

Does anyone out there know the correct term for "thin RG58"?
Click to expand...

Suggest you contact Salty John of this parish, although by the time I have written this he will probably have responded........


and on cue!
 
Salty John said:
RG58 is nominal 6mm, actual about 5mm. Loses around 5dB per 100' at 150 MHz.
RG8X is nominal 7mm, actual about 6.25mm. Loses around 3.7 dB per 100' at 150 MHz
RG8 is nominal 10mm, actual about 9.5mm. Loses around 2.5 dB per 100' at 150 MHz.

3dB loss is a halving of the signal strength.
Click to expand...

Quite true - as I said before, depends on the size of the boat - 100' is a long cable by the standard of most boats.

Also depends on the accessibility of the cable ducting - we took delivery of our boat with a VHF antenna installed at the mast head but no radio fitted - I was surprised to find that the cable terminated at the base of the mast - mousing RG58 through was hard enough - I would not have wanted to try to get RG8 through. I must admit to not having inspected closely the cable installed at the mast base, but it certainly appeared to be RG58 - certainly not RG8.
 
maby said:
Quite true - as I said before, depends on the size of the boat - 100' is a long cable by the standard of most boats.
Click to expand...

100' is almost exactly 30 metres. The OP is looking for 25m of cable. So it's not in a completely different league.

Pete
 
An interesting fact about RG58 is that it isn't recognised by the ISAF for offshore racing. They allow RG8X up to 50' cable length, thereafter RG8U and so on.
Off topic, but the ISAF regs are quite an interesting read, giving what I think is good guidance if you are considering systems for an offshore boat:
http://www.sailing.org/tools/documents/OSR2012Parts1to605012012-[11791].pdf
 
Last edited:
As Salty John says, the ISAF regulations are worth a read even if they just confirm that the commonly used cables are rather lossy over more than say fifteen metres.
Since they just specify loss and not exact cable types, I went for Aircell 7 as sold off the shelf by Nevada Radio when we needed to comply... It is just over 7mm outside diameter, lighter than 10mm cable yet has a similar loss to those much thicker cables.
 
Good cable. The only problem is I've never been able to find it with tinned braid and centre conductor. Some people won't accept anything less for marine work.
 
Indeed, but how many chandleries sell tinned co-ax with their aerials.
As a replacement to the standard supplied cable that comes with most boaty aerials, and at the same cost per meter it was a no-brainer at least for me.
Radio hams seem to use it outdoors with waterproof connectors with no worries.
 
Martin_J said:
Indeed, but how many chandleries sell tinned co-ax with their aerials.
As a replacement to the standard supplied cable that comes with most boaty aerials, and at the same cost per meter it was a no-brainer at least for me.
Radio hams seem to use it outdoors with waterproof connectors with no worries.
Click to expand...

Radio hams love to get by on virtually no power at all! I'm still telling everyone that will listen about the time that I had a conversation with a DX expedition on one of the remote Scottish islands while standing on the beach near Bordeaux using a hand held transceiver running 2w into a rubber-duck antenna. That was SSB on 6m during a good spor opening.
 
prv said:
So all the more important that their aerials are up to snuff?

Pete
Click to expand...

Well, in my case it is almost always a "piece of wet string" - with a total property that fits into a cube about 20m on a side, it's simply impossible for any of my cables to be very long! :( It is amazing how far you can get on virtually no radiated power!
 
You must log in or register to reply here.

Share this page

Top