Expected Resistance of VHF Cable?

[Refueler]

My Icom AIS has a diagnostic that includes antenna. If you have a set with similar facilities swop the antenna leads to check the VHF antenna - assuming of course that you have sufficient slack in the antenna leads to allow them to be easily exchanged.

Post #9 ......

The main item to make sure is that antenna is direct connected to VHF and not through any splitter .... splitters cause diagnostic to fail.

 

[Ian_Rob]

I hope the weather is kind to you and you sort your problems out easil

I hope the weather is kind to you and you sort your problems out easily.

Thanks very much indeed. We are next but one to launch at or about 10.30. Not too bad so far but we need to get the boat out to our swinging mooring and dinghy back before it gets too bad.

 

[samfieldhouse]

The cable supplied with the Hawk Aerial - RG58 C/U.

The VHFs I've installed recently from Standard Horizon and Garmin, in their instructions state that the maximum run of RG58 is 8 meters. On my 28ft boat the run from VHF to mast head was around 18m.
It would seem that RG58 will do, but that RG8x is better.

 

[Refueler]

The VHFs I've installed recently from Standard Horizon and Garmin, in their instructions state that the maximum run of RG58 is 8 meters. On my 28ft boat the run from VHF to mast head was around 18m.
It would seem that RG58 will do, but that RG8x is better.

There's actually a Recc'd table of lengths online for VHF cables and the losses incurred etc. Google picks it up easy.

But at end of day - many people use 58 and survive .... usually because its easier to work with ..

 

[samfieldhouse]

But at end of day - many people use 58 and survive .... usually because its easier to work with ..

Oddly, I chose RG8x because it was easier to work with - Glomex's system has small diameter pre attached terminals so the routing holes are nice and small and there's a stronger connection at the mast head.

 

[Refueler]

Oddly, I chose RG8x because it was easier to work with - Glomex's system has small diameter pre attached terminals so the routing holes are nice and small and there's a stronger connection at the mast head.

Maybe I have wrong way round .... I know that the 3 recc'd cable types get harder/ stiffer and slightly larger diameter each step up ...

 

[st599]

Maybe I have wrong way round .... I know that the 3 recc'd cable types get harder/ stiffer and slightly larger diameter each step up ...

Not sure a hawk can use a different type of cable, it's got a centre pin that pushes in to the centre conductor as you wind in a plastic nut. Works well, once.

 

[Martin_J]

The VHFs I've installed recently from Standard Horizon and Garmin, in their instructions state that the maximum run of RG58 is 8 meters. On my 28ft boat the run from VHF to mast head was around 18m.
It would seem that RG58 will do, but that RG8x is better.

After you've got to about 8m length, you've probably lost about 30% of your signal strength. By the time you get to 12m of RG58 you could be closer to 45% loss..

So it's not a hard cut off at 8m, just a diminishing signal strength.

I know you're not racing, but it can be nice to be guided by the Offshore Special Regulations, which specifies a co-axial feeder with no more than 40% power loss to be used, so it's likely neither of those cable types would meet their requirement (unless you have a very short mast).

 

[st599]

After you've got to about 8m length, you've probably lost about 30% of your signal strength. By the time you get to 12m of RG58 you could be closer to 45% loss..

So it's not a hard cut off at 8m, just a diminishing signal strength.

I know you're not racing, but it can be nice to be guided by the Offshore Special Regulations, which specifies a co-axial feeder with no more than 40% power loss to be used, so it's likely neither of those cable types would meet their requirement (unless you have a very short mast).

Does that feeder loss include the connector? Even expensive co-ax and 2 PL 259s could easily be over that.

 

[Martin_J]

It was a very approximate guestimate and totally off the top of my head.. (or whatever the saying is)..

And yes, of course connectors will introduce loss and so will bends if they're too tight a radius, as will moisture.

A good quality co-ax feeder will of course be much less lossy than those numbers, even over much longer distance... but you're unlikely to get one of these much better cables from a UK chandlery.

It was just to give an idea that whatever comes packaged with most of these masthead antennas is more lossy than you really want.. as seen by the earlier post that suggested no more than an 8 metre feed to the antenna was recommended by the manufacturer.

 

[john_morris_uk]

After you've got to about 8m length, you've probably lost about 30% of your signal strength. By the time you get to 12m of RG58 you could be closer to 45% loss..

Uhh…. RG58 has a loss of 4.9 db per 100ft at 100 MHz so your guess is out by a considerable margin. 3db is 50%.

 

[littledancersadhu]

Have you fitted cheap led lights from china, anywhere on your boat lately? My freind did this and he could not transmit on his vhf ,but he could recieve transmitions, He took out all the cheap leds,and the problem was gone,

 

[fredrussell]

Have you fitted cheap led lights from china, anywhere on your boat lately? My freind did this and he could not transmit on his vhf ,but he could recieve transmitions, He took out all the cheap leds,and the problem was gone,

Hmm. Having fitted loads of cheap led lights to my boat recently, your post worries me! I think I’d better do a transmission test next time I’m down the boat.

 

[Plum]

Have you fitted cheap led lights from china, anywhere on your boat lately? My freind did this and he could not transmit on his vhf ,but he could recieve transmitions, He took out all the cheap leds,and the problem was gone,

Yes, and some 12v phone chargers can upset the VHF radio too. A helpful person at Standard Horizon told me this and was the cause of the problem I had.

 

[Alicatt]

Yes, and some 12v phone chargers can upset the VHF radio too. A helpful person at Standard Horizon told me this and was the cause of the problem I had.

Many plug in chargers, both 12V and mains, are a big source of electrical noise across many frequency bands, and those network over mains wiring can totally blank out the receiver with broad spectrum noise.
As a ham radio operator when I powered up my receiver in our last house here the amount of RFI from wall-warts and powerline network devices had the Signal meter pegged against the stop.

 

[littledancersadhu]

Hmm. Having fitted loads of cheap led lights to my boat recently, your post worries me! I think I’d better do a transmission test next time I’m down the boat.

I definately would test your vhf! better to know, 1 way or the other!