VHF antenna wire length

[WaterWitch2]

I installed my 8ft VHF antenna on the boat and only need about 9ft of coax. It has 15ft attached. Can I cut off extra or should I just coil up extra 6ft of coax up under dash?

 

[TBarCYa]

Re: VHF antenna wire length

Don't coil the extra. It creates an electronic 'choke' and will have adverse affects on the amount of power that makes it to the antenna.

I have shortened my feed line and my 15 year old radio still seems to get out pretty good. It will not damage the radio or antenna but feed line length does have an effect on the tune of the antenna. Most marine VHF antennae seem to be very well tuned from the factory to be tolerant to having the feed line shortened.

 

[miswirvin]

Re: VHF antenna wire length

yes you can shorten the wire up to three feet. so your nine feet with be fine. Just make sure you do a good job in sodering the pl259 con.

 

[jrenard]

Re: VHF antenna wire length

I would second that on the soldering job. You can lose up to 6 dB of signal strength with a poor solder joint. If you have access to an SWR meter, you can place it inline to measure the reflected transmit power and tune your antenna accordingly. You measuer forward power, then reverse (reflected) power. You may wish to take the measurement before and after your cut and solder to have a baseline of the ratio.

 

[jurgenscraft]

Re: VHF antenna wire length

Hello all
There seems to be quite a few radio hams arourd giving good advice on this forum, yes once the swr has been tested then all should be just fine and dandy.
kind regards William Wright ZS6WC / MM

 

[QuadManiac]

Re: VHF antenna wire length

Don't need to shorten it, but dont coil it. Just wrap it back and forth over a foot or two, changing the direction of wrap at each end (like folding it) so as NOT to create a coil. Zip tie the wraps in place.

Coiling into a helix can add inductance to the coax, changing its frequency response; wrapping back and forth will not. Keep your bend diameter at the end of wraps to at least 3 inches or you may squeeze the coax a bit, slightly changing its impedence.

I've spent many years performing scientific experiments on the water. If I had to cut an RF co-ax to install the same system on a different boat, then I'd have to replace it on the next boat that required a longer install... wrapping works just fine.

Good Luck!