DIY VHF areial

[abdiel]

Hi there everyone, I would like to know if it is possible to construct your own VHF aerial for use at sea. I have looked at alot of web sites on diy aerials but they dont look anything like the straight up and down types on other boats.
Thanks, David

 

[damo]

You can make an antenna from wire or cable, the main criterion being its length. IIRC it should be 19"/480mm long

 

[VicS]

You could but a serios mismatch might damage your radio or at the very least result in very poor performance.

The design below (click the pic to enlarge) was published in PBO Dec !979 which could be used in an emergency.

If you want decent performance without risking your radio buy a proper one and for emegencies buy an emergency one. No sense in having several hunderd quids worth of radio and scrimping on a few tens of quids worth of aerial.

 

[damo]

Just looked it up (Calder):

"A serviceable emergency antenna can be made from any 19" length of wire...
The range will be limited...
Care must be taken not to short this antenna to the outside of the the terminal socket...
The radio should be used only on low power and as little as possible since lengthy transmissions could eventually do damage."

Nuff said

Thanks for that pic

 

[William_H]

I use a homemade antenna on my boat as the main antenna with great success. It is mounted in a piece of plasic conduit clamped to a vertical on the pushpit. It s VSWR is good and performance seems fine.
A little like the described antenna I exposed 17.3 inches of the centre of a coax cable long enough to go to the radio. I cut the braid off but got a similar length of braid from a larger coax RG8U and fed this over the end of the coax so it sits from the end of the original braid down the cable toward the radio by 17.3 inches the braid of the original coax and the additional braid are twisted and soldered in 4 different spots. The additional braid can be covered and clamped in place by shrink heat plastic tubing.
So it is similar to that described above except the second arm of the dipole antenna folds back over the feed cable. This makes it very convenient for pushing up a tube and more suitable for vertical polarisation. (which you need) The braid coming down the cable should be well clear of metal parts as the braid is part of the antenna.

The beauty of VicS antenna is that you make it in an emergency by wrecking/using the existing cable. All you need is a knife and ruler.

Those who suggest that the radio will be destroyed are perhaps exagerating the danger which is much worse if the proper antenna falls off or the cable fails. ie it happens often with seldom destroyed radios. good luck olewill