[Paddlewise] [Fwd: telescoping whip..VHF]

I hope this is of some help as I shared this discussion with a friend
who
happens to be in the communications industry and accordingly his
thoughts are as follows.

Regards,

Philip

attached mail follows:

Interesting posts. I agree with them. NiTi wire is probably a good idea.

RADIO 101:

1) A rubber ducky antenna will typically cover only half as far as a quarter-wavelength antenna. That's because rubber duckies, while convenient, are short. Generally, the longer the antenna, the better the coverage (assuming the antenna is properly trimmed to length).

2) Doubling the antenna height doubles your coverage (on water, at least). 

Sitting in a kayak with a handy-talky against your mouth would put the antenna, say, three feet above the water. Doubling the antenna height to six feet would double the coverage distance. Doubling again to twelve feet would double the distance again (which would be quadruple the distance possible while sitting).

3) To double your coverage, you have to quadruple your power. Thus, increasing power is usually the most "expensive" parameter, especially if you are running on batteries.

4) Another way to increase range is to use a directional antenna. On a kayak, this would be physically difficult, due to the amount of hardware needed, though it might be feasible to build a small antenna that could probably double one's range over the quarter-wave case. A small antenna could be made of PVC pipe and assembled in a few minutes in an emergency (assuming the emergency allowed for it!)

5) Other factors include keeping the antenna out of the ocean (!) and keeping it more or less upright.

These can be combined, and their benefits are additive. For example, a doubling in coverage could each be had from using a quarter-wave antenna instead of a rubber duck, another doubling could be had from going to a small (five-element) directional antenna, and another doubling could be had from raising the antenna to six feet above the water. Three doublings equals eight times the coverage distance from using only a rubber ducky.

In conclusion, increasing coverage is most easily accomplished by 
a) keeping the antenna up and in the clear, 
b) next by abandoning the rubber ducky and going to a quarter-wave antenna, 
c) and finally, by raising the antenna. 
A six-foot piece of PVC tubing (or mounting to the baidarka sail mast!) would seem feasible.

+++++++++++++++++++++++++++++++++
KEN        You are today where your thoughts 
                have brought you; you will be tomorrow 
                where your thoughts take you.
                                            ~ James Allen ~


-----Original Message-----
From:	MarcJensen [SMTP:marcjensen_at_earthlink.net]
Sent:	Thursday, March 05, 1998 8:02 AM
To:	PaddleWise_at_lists.intelenet.net
Subject:	Re: [Paddlewise] telescoping  whip..VHF


> A telescoping whip isn't necessairly going to provide a 
> noticible improvement over a rubber duckie. You'd have to 
> set the length using an SWR meter and then it will only be 
> marginally better then a 1/4 wave RD and probably no where 
> as good as a 5/8 duckie.
> 
> BTW, I have talked to Europe using 0.5 watts... but the 
> antenna was 66 feet wide and 88 feet long...

I have access to NiTi super elastic wire (the metal used in the fancy
eye glass frames).  I could make an antenna that would stand up 3 to
4' in length but fold up to a little ball.  You could even wrap it
around the VHF unit.  The question I have is what length would you
make the antenna?  I could potentially make two or three of these
to try out if anyone is interested.  I would need to make the O.D.
more conductive but I have several way of doing that.

Marc.




"If the Women don't find you handsome, they should at least find you 
handy!"
Red Green

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