Re: Try cell/ VHF Radios

Posted by Laszlo on Nov 22, 2006

Line of sight and 2 miles is a bit of a simplification.

First, that's based only on the handheld's antenna being 28 inches above water. It does not take into account that the receiving antenna is probably substantially higher (on a land-based tower, on a larger vessel, etc.) Every time the antenna height is doubled, the range increases by a factor of 1.4. So if the Coast Guard has a 100 foot tower on a 100 foot clff, you'll be able to communicate with them from a little over 18 miles away.

Second, no radio is limited to true line of sight. The all have reflective and diffractive propagation modes, too. Cell phones, which operate in the high UHF/low microwave spectrum, actually have more restricted range than VHF radios since their propagation more closely resembles true line of sight. The only reason they have such large areas of coverage is because of all the cell phone repeater towers scattered every few miles over the landscape.

Which brings up the third point - cellphones only work when you're within range of a cell tower. If the local towers are arranged to favor a populated area, instead of the empty water where you're paddling, you won't be able to get through. Maritime VHF antenna installations, like the Coast Guard, are designed to cover the water so they're more likely to hear you than the cell towers which are aimed at the cities.

VHF handhelds also have larger battery packs than cells. That means that they can either broadcast the same amount of power longer, or they can broadcast a more powerful signal, albeit for a shorter period of time. That extra power can be used to take advantage of some of the non-line-of-sight propagation modes mentioned in point 2 to extend the communications range, especially over water.

Finally, that fishing vessel that's looking as if it's on a collision course - what's the captain's phone number? Uh-huh. Chances are, though, that he's listening on VHF 16.

So if you're operating in an urban water setting, cell phones will probably work fine. But if you're going a ways offshore, or need to talk directly to other vessels, a VHF will be better.


PS - HF radios on kayaks could be fun, but the antenna installation could be a real problem.

In Response to: Re: Try cell/ VHF Radios by Darryl on Nov 21, 2006


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