While working Hurricane Debby at the Franklin County EOC this past week, I had a chance to talk with a deer hunter who's been bootlegging on the 2m ham band with his buddies. Mostly, he was amazed that I could talk from Apalachicola to people in Pine Log and Alligator Point, 28 and 39 miles away respectively, when the best they could get was about 5 miles truck-to-truck. I told him about the repeater in Carrabelle, said the deer hunters were welcome to use it, but they'd have to license up first, and that it would give them complete coverage of Tate's Hell Swamp and most of Franklin County for that matter. And we both agreed that that last part, licensing up, would be a sticking point. (it's pretty easy though, here's how)
Then I started thinking, they ought to be using CB. Is CB all that bad? With FM mode now allowed on CB, would that help? Well, let's use the Egli model and find out. First, solve this equation for d, the useable transmission distance for some given minimum reception level – use 2.87x10^-13 watts for PR, 3 dBi gain and 8' height on both antennas, and plug in 27 MHz & 4 watts for CB. Try it for both AM and FM modes (adjust the net gain down by -13 dB for AM here, using results from this paper). Then repeat again for 2m ham, at 145 MHz & 50 watts on FM mode. (Don't forget the unit conversions. We want miles for deer hunting, we're not playing some damn metric soccer game here.) Got all that? Want to do the math or just cut to the chase? Right, I thought so. Here's what we get:
CB, AM: 2.4 miles
CB, FM: 5.0 miles <-- winner
VHF, FM: 4.1 miles
Those numbers look about right. Things will vary a lot, but it's a starting point. We can tweak up the VHF to 65 and 80 watts, two other common maximum powers. That only gets us out to 4.4 and 4.6 miles. That's not nothing, but not all that much either. CB on FM still beats it out by a noticeable margin. Why? 2m ham has a 5x shorter wavelength than 11m CB. More wavelengths to cover the same distance, more loss. It's just that simple. I can see why deer hunters shifted to VHF years ago though. It just about doubled their range over old-school AM CB, quadrupled their coverage. Great. The shift to FM CB changes all that. Times change, technology changes; adapt or get fossilized.
Now look at the costs. A basic AM/FM CB at this site is $54. A similarly basic Yaesu 2m FM at this other site is $180. Antennas for the same quality are about the same price, so that's a wash.
OK, the bottom line is CB has 20% better range for 1/3rd the cash. And FM-capable CB radios can do AM as well, so you can still talk to friends who haven't upgraded. Lots of advantages there.
I think I'll be buying a new CB soon.
ps 8/12: A friend asked today about how MURS (FM, 2 watts, 151 MHz) or GMRS (FM, 50 watts, 465 MHz) would perform in truck-to-truck: 1.8 and 2.3 miles, respectively. CB FM still wins by a wide margin.
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