VHF Antenna/coax routing

[goose327]

Thanks guys. I used to play with CBs, so I know a little. The Shakespear antenna has RG58 already hooked up(PL259 is with it but not connected). The coax isn't long enough for a masthead install, so I need to lengthen it. I really don't want to use a union(259-259 w/ 2 female ended union). Is there a better way to make the wire longer? Or is this as question for a VHF radio forum,,,LOL.
I picked up 30' of 1/2 PVC for condiut. I'm going to leave a "pull string" in it in case I decide I need another wire at a later time.

[btrayfors]

goose,

Replace the RG58 with RG8X or RG213 if you possibly can. All of it. There should be a way to replace the existing coax at the antenna base. Check it out.

RG58 has very high loss at VHF frequencies...not good for a long run. RG8X is much better, and is only a tiny bit heavier/thicker than RG58. RG213 is same size as RG8, but has better properties. There are other coax types available with even less loss, but they're exotic and quite pricey.

Bill
WA6CCA

[goose327]

I have a couple hundred feet of RG8 on an old spool. I don't see anyway to change it out though. I may have to go with a different one. Damn shame a CB antenna won't work, I've got dozens of'em.
While were on it. What is the ideal length for the coax? I know for 27Mhz any derivitive of 18 worked great, SWRs were spot on every time. Is there a set number like that for VHF?

[k1vsk]

The length of coax should be the length required to go from the transceiver to the antenna. It's a CB myth that there is some magic length of feedline. The myth derives from the fact that an electrical half-wavelength resonates thereby producing the appearance of an impedence match at the transceiver but that is useless if the antenna mismatch is significant. If the antenna is mis-matched, no length of coax will change it and the signal will be poor.

As someone already said, use RG8X or preferably 213 in one continuous length and make sure the antenna is resonant for marine VHF frequencies and the PL259s on each end are soldered, not crimped on.

[sailingdog]

Someone should mention that you want marine-grade coax cable, which is tinned...and use adhesive-lined heat shrink to cover all the connections.

[captchetco]

In 1996, I added a new vhf cable up the 54' mast of my boat, before heading to Mexico. Since I do not have internal halyards, that was not a problem, I simply dropped a weighted line down from the top, and pulled the cable up from the bottom. To secure it, I picked up the cable through the motoring light opening, a deck level wire outlet, a spreader opening, and through one or maybe two holes from which I had removed the machine screw holding the schaffer sail track to the mast. the support medium was Nylon "Mule Tape", which I supported in different creative ways throu the holes. Some of the details of this, I don't remember, but I do recall trapping the tape under the gasquet under the motoring light at the bottom. On the mast track hole(or possibly two), I melted the tape into the flathead screw recess, and screwed in a smaller flathead self tapping sheetmetal screw. Very Rube Goldberg overall. This is generally regarded as not sufficient support, but it has worked fine for over 10 years and at least 10,000 miles at sea.