Adrian
Member
Can any one give me the name/spec for VHF cable? im sure my friendly neighbour electrical supplier will get some for me but i don’t know what to ask for!
Thanks
Thanks
VHF Cable
- Thread starter Adrian
- Start date
sr04
New member
Your antennas coax lead-in cable should be as short as possible and as large as diameter as you can afford to fit. On average, 50 feet of RG-58 coax have about 3 dB loss, 50 feet of RG-8X coax will have about 2 dB loss, and 50 feet of RG-213 (RG-8U) will have about 1 dB loss. They are all 50 ohms impedence as opposed to TV coax which is 72 ohms.
fluffc
Member
Adrian,
The cable you need is RG58. This is quite satisfactory on most yachts.
Of course, if you want to guild the lily, you could get RG-8X, RG-213, or some other such low loss cable.
Just make sure all your terminations are well made, and the aerial is in good order.
The cable you need is RG58. This is quite satisfactory on most yachts.
Of course, if you want to guild the lily, you could get RG-8X, RG-213, or some other such low loss cable.
Just make sure all your terminations are well made, and the aerial is in good order.
TradewindSailor
Active member
When you fit your coax make sure it's waterproof at the aerial ... and you form a drip loop before your radio and cut the outer insulation at the bottom of the drip loop to let any water out. It is amazing how much condensation can get in a coax wire .... and the last thing you want is to direct water to the back of your VHF.
Adrian
Member
AIDY
Active member
that's a big boat you have if you require a reel of 100 metres /forums/images/graemlins/grin.gif
Salty John
Active member
As sr04 says. If you want the absolute best use RG213 (same size as RG8U but higher spec, more difficult to attach connectors), next down is RG8U. RG8X (sometimes called mini 8) is a good compromise giving flexibility, relatively low weight and good performance. RG58 is typically for interconnecting pieces of equipment adjacent to each other although you find it factory crimped to some aerials. Look for tinned copper and better than 95% braid coverage. A uv resistant cover is advantageous if there are longish runs outside. The dielectric, the bit between the centre and the braid, should not be foam for marine applications because it can wick water into the cable from the ends.
If you intend to do any offshore racing you need at least RG8X to achieve the required performance under the rules of a couple of the big governing bodies.
If you intend to do any offshore racing you need at least RG8X to achieve the required performance under the rules of a couple of the big governing bodies.
JonBrooks
New member
Whilst RG213 has he best spec it is not the easiest to lay in.
it is much thicker than the RG58 and can be a real pig to get round bends and up masts etc.
Most marine antenna come supplied with RG58 these days.
it is much thicker than the RG58 and can be a real pig to get round bends and up masts etc.
Most marine antenna come supplied with RG58 these days.
searover
New member
The cables the easy bit its the radar i cant get to match my ploter John cp1000 now thats a real shame...
emnick
Member
Is it possible to keep a SWR meter permantly attached to the VHF, I am not sure that our Simrad DSC is always transmitting at full power. and we may be Tx off the mast, is there a way of testing the cable to the whip?
whipper_snapper
New member
It is certainly possible. But it is almost never done on a normal marine VHF because, as you are always transmitting on virtually the same frequency, the SWR should not change unless your setup changes. Most people just do an occasional check - leaving a meter permanently attached increases complexity and the chance of problems.
brianrunyard
New member
Surely as VHF range is basically line of sight and limited by the curvature of the earth and height of the antenna, the extra loss with RG58 isn't going to make much difference.
JonBrooks
New member
[ QUOTE ]
Surely as VHF range is basically line of sight and limited by the curvature of the earth and height of the antenna, the extra loss with RG58 isn't going to make much difference.
[/ QUOTE ]
In simple terms yes but power will and does effect your range.
On 25w you message will go a lot further than at 10 or 5.
If power did not have an effect then a 5w hand held connected to your mast head antenna would be as good as your 25w fixed unit. We all know in practicce it is not.
So by keeping the loss down you will increase your range.
3dB loss is half power!
Some people do keep a VSWR meter in line but once again this will cause loss.
The only realy way to test the cable is to have the VSWR meter at the bottom of the antenna you can then compare the reading from the back of the set to the antenna end. In practice this is not wasy to do.
If you suspect the cable or antenna, if it were me, I would change them.
Cheers
Surely as VHF range is basically line of sight and limited by the curvature of the earth and height of the antenna, the extra loss with RG58 isn't going to make much difference.
[/ QUOTE ]
In simple terms yes but power will and does effect your range.
On 25w you message will go a lot further than at 10 or 5.
If power did not have an effect then a 5w hand held connected to your mast head antenna would be as good as your 25w fixed unit. We all know in practicce it is not.
So by keeping the loss down you will increase your range.
3dB loss is half power!
Some people do keep a VSWR meter in line but once again this will cause loss.
The only realy way to test the cable is to have the VSWR meter at the bottom of the antenna you can then compare the reading from the back of the set to the antenna end. In practice this is not wasy to do.
If you suspect the cable or antenna, if it were me, I would change them.
Cheers
Salty John
Active member
To some extent, but power is a factor as Jon says. With a reasonable quality RG58 on a 50' run and 25w in, the power out of the cable is about 13 watts, and for RG8X it's about 16 watts. That may or may not be critical but it's a substantial loss just for the wire. The connections and the antenna could further sap the Effective Radiated Power (ERP), which is what it's all about.
The International Sailing Federation requires less than a 40% coax cable loss for offshore racing, so the RG8X would comply and the RG58 wouldn't.
I think you also need to consider the mechanical integrity of the cable when making a selection - braid coverage, tinned copper, uv resistance - and also the quality of connectors and the susceptibility to corrosion.
No point having a superb radio if you can't maximise it's performance. All IMHO as usual.
The International Sailing Federation requires less than a 40% coax cable loss for offshore racing, so the RG8X would comply and the RG58 wouldn't.
I think you also need to consider the mechanical integrity of the cable when making a selection - braid coverage, tinned copper, uv resistance - and also the quality of connectors and the susceptibility to corrosion.
No point having a superb radio if you can't maximise it's performance. All IMHO as usual.