Re: [Paddlewise] Boosting handheld VHF range

At 05:47 PM 1/21/99 -0500, Kenneth Cooperstein wrote:
>I have an Apelco 510 5w. handheld VHF radio that I use on my sailboat.
>No one can hear me even 3 miles away unless I climb onto my cabintop.
>
>I can boost the range by using a 4' base-loaded s.s. whip antenna (3 db)
>at the masthead, which is the standard solution.  However, the folks at
>Raytheon told me that I would do almost as well by just mounting the
>whip on the rail, because that would get me almost to the limit of what
>5w will do with a 3db antenna.  Although Raytheon wouldn't quantify the
>range, they felt that it would at least triple -- going from the rubber
>ducky in the cockpit to the whip on the rail.
>
>I am considering bringing the whip antenna along on a paddle, in the
>belief that if I need greater range, switching to the whip (handheld or
>on a stick) will greatly increase my range.  Anyone know if this will
>work?
>
>Ken Cooperstein

Hi Ken et al!
Yes, you can use your whip from your boat, however, I do not believe that
would help all that much. The real problem lies in the fact that normally
VHF radio signals only travel in a straight line, much like a flashlight
beam. When you are sitting in a kayak with your nose only a couple of feet
above the water your horizon is quite close, probably only a mile or so.
Even less if you are in the trough of a wave. When you mount your antenna
at the masthead of a sail boat, you have effectively increased the horizon
the antenna can see. I hope no one minds, but I have included a couple of
small attachments to illustrate this. If you refer to figure 1, I have
sketched this, greatly exaggerating the curvature for the purposes of
illustration. (please, I know my artwork sucks . . .)
Anyway, what you really need is a way to get your antenna up in the air a
bit. I will present a method to make a very simple antenna and antenna mast
that will allow you to elevate your radiation point an arbitrary distance
above the waves (~18 ft in my illustration).
Refer to figure 1 again. Visit your local electronics junkyard (or Radio
Shack if nothing else), and find a ~25ft length of RG48 or preferably RG174
(thinner and more flexible) 50ohm coaxial cable with a connector on one end
that matches the one on your radio (BNC is common). Carefully strip back
about 18in of the outer jacket, and double the braided shield back over
itself to expose 17.75in of the inner conductor. Wrap a bit of electrical
tape around it to hold things in place. Visit a kite store or the like and
get 6 pieces of fiberglass tubing 36 inch long by 1/2in OD (figure 2). Size
is not real critical, consider your requirements for stowing it on your
boat. Also get a length of the next larger size to make coupling ferrules.
The OD if the smaller tubing should be a snug fit into the ID of the
ferrule. Cut an appropriate number of ferrules with a very fine hacksaw,
and superglue a ferrule onto one end of the 36in lengths. 6 of these as I
have illustrated, fitted together, will be about 18ft long, and stiff
enough that you can hold it straight up without excessive flex. Obviously,
change any dimension to suit. Next, slide the prepared end of your coax
into the tubing as illustrated in figure 2, and use epoxy or something in
the uphill end to hold it in place. You should then be able to separate the
sections starting from the top, and fold the entire thing up like a tent
pole. The 17.75in antenna length should be OK for a 160MHz marine radio,
but if you wish, you can use the following procedure to tune it before you
permanently fix the upper end in place. Have a friend with another radio
drive off down the beach until you can barely hear each others signals.
Slide the braid back or forward to change the length of exposed center
conductor in ~1/4in increments until you find the point where you have the
best signal. (do this with the cable inside of the tubing) Your bud might
have to move further away as you tune the antenna; you want to just be able
to copy each other. Admittedly, this is a rather low tech approach, but I'm
sure you will find it a vast improvement over the ol' ducky!
Feel free to contact me if you need more info! ByeBye! Steve J. KG0MB

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