The Cat-and-Mouse Game

September 21, 2007
The Standard Horizon Spectrum VHF uses DSC to communicate information – including your position – to other radios, but only the ones you choose.

In the mid-1960s I crossed the Gulf Stream to the Bahamas for the first time aboard my father’s 21-foot, aluminum Dura-Craft. We ran from Miami to Bimini, a trip that people now make regularly on day trips just to eat lunch. Back then, though, it was a big deal, or at least it seemed like one to a wide-eyed eight-year-old.

We had spent the better part of the previous winter soldering wires together in the evenings as we assembled our new HeathKit radio direction finder (RDF), which had come in the mail. Some of you may not be familiar with a RDF. It was a manually tuned receiver that homed in on radio transmission towers or beacons and “pointed” the way to them via a large, rotating antenna on top of the unit. By knowing the frequency of a radio beacon at your destination (which were widely published at the time), you could follow the signal to its source. The RDF sounded like a magical device to me, as Dad explained how it would guide us safely across the great blue ocean and lead us to an island that was only seven miles long.

Our day of departure dawned flat-calm, and we headed out from the Matheson Hammock Park boat ramp into the great unknown. Not long after we entered the Stream, the RDF began emitting a long beep followed by three short beeps, a Morse Code “B”, the signal transmitted by the radio beacon on Bimini. We followed that magic B right into Alice Town Harbor.


Pointing the Way

What does this have to do with the cat-and-mouse fishing game? Not long after the introduction of the RDF came an important modification of this technology, the automatic direction finder, or ADF. An ADF automatically homes in on a radio signal, alerting you to the direction from which it emanated. The original ADFs operated on the same frequencies as the RDFs, namely the low-frequency beacon band (most coastal beacons, like the one in Bimini, operated on this band) and the AM radio broadcast band. But subsequent ADFs were designed to operate on the very-high-frequency (VHF) spectrum.

That’s where our story about fishing stealth begins. Now fishermen had the ability to determine from which direction a VHF radio transmission came. If somebody called someone on the VHF to say the fishing was hot, you could get a bearing on him, even if he wasn’t talking to you. Then it was a matter of running along that bearing line until you saw where the fisherman was holed up.

On the downside, ADF posed a real problem on those occasions when you wanted to alert a friend or two to some hot fishing, but didn’t want the entire fleet showing up. To throw off these would-be hole-stealers, anglers came up with “secret” VHF channels to switch to, and even then they invented codes to make transmissions short, difficult to decipher and difficult to track. For example, if someone said he was fishing “two miles south of the rock,” he may have really been telling his buddies he was four miles north of it instead.


Then along came radars that could be interfaced with loran or GPS to reveal the position of a target. SI-TEX dubbed this system “Position Pick-Off,” and that’s precisely what it lets you do. When a correctly equipped and interfaced radar shows a target on-screen, you can move the radar’s cursor to the target and the target’s latitude and longitude will appear. Many a favorite bottom-fishing hole has been lost to this technology, and it’s almost impossible to defend against since the boat with the radar may not even be within sight! It’s especially potent when coupled with an ADF. A boat equipped with both technologies can lock onto a radio signal with the ADF, then follow the EBL (electronic bearing line) with the radar to pinpoint the location of the transmitting vessel.

High-Tech Protection

Two new technologies have helped blunt some of this covert action, however. The development of VHF radios with scramblers has allowed people with identical radios to communicate in a secure mode. The downside is that you and your buddies have to buy the same radios and exchange scrambling codes, and we all know how hard it can be to get fishermen to agree on anything. Cell phones also provide secure communication, but if you’re very far from land they offer spotty coverage at best, especially since the full-power bag phone seems to be going the way of the dinosaur.

Now there’s a new way to let friends know where you are without alerting the rest of the world. We’ve written quite a bit about DSC (Digital Selective Calling) technology in VHF radios in past columns, with all of its inherent safety advantages, and the communications possibilities being brought together by MariTEL. But here’s a new wrinkle to the DSC story.


Standard Horizon recently introduced several new products that integrate to make advanced communications between fishermen possible. Like all DSC-equipped VHFs, Standard’s Spectrum radio receives DSC transmissions on VHF channel 70, now a designated DSC channel. But the Spectrum will also export non-emergency DSC information to other Spectrum radios when asked to.

It works like this: Say you and your fishing buddy both have a Spectrum VHF interfaced with a GPS receiver, and your buddy wants to know where you are. He can tell his VHF to “ask” your Spectrum where it is, a process Standard calls Digital Polling. It shows up on your VHF as a Position Request Display. Like cell phones, both radios will have a proprietary code programmed into them. You can then punch a key and your VHF will send your lat/lon position to your friend’s VHF. It’s all digital and encoded so only he can get it.

WAAS Plotters

But that’s not all. Standard Horizon just came out with three new chart plotters as well: the CP150, the CP160 and the CP170C. All three come with built-in WAAS satellite-based differential receivers, but the big news is that when someone sends his position to you through a Spectrum radio that’s interfaced with one of these plotters, the position automatically shows up on the plotter screen. The plotter immediately zooms out to the appropriate scale so that both your vessel and your friend’s vessel are shown on screen. And with the touch of a button you can plot a course directly to him.


You can program the plotter with the numeric codes from each of your friends’ Spectrum radios and attach an alphanumeric name to it, just like a cell phone. When one of them queries your radio for your position, his alphanumeric ID pops up on screen and lets you know who’s looking for you. The Spectrum works in manual or automatic mode. In manual, the radio beeps when someone queries it and you must either manually send back your position or exit, thereby not sending it. Or you can set it to automatic and the radio will automatically send your position out when asked to. If an emergency distress call comes in, the plotter will automatically show the position of the vessel in distress as a circle with a “D” in it so you can render assistance.

Think of the possibilities for a tournament team. When combined with other stealth technologies like the cell phone, it makes for a seamless and very private exchange of information. And even if you’re not the hard-core tournament type, it will still be invaluable. Doesn’t it always seem like your friends radio you at the worst possible time to see what you’re catching, right when the bite is on? Then you have to either drop what you’re doing to talk to them or ignore them. With this new system, a very brief radio conversation will alert them to the action and they can find you on their own. You can go back to fishing, and the guys with ADFs will have missed the whole thing.

On increasingly crowded waters, a little stealth can be a good thing. Unfortunately, we can’t do much about the radar pick-off thing until someone invents some type of radar-confusing chaff device for boats, or a titanium hull material that absorbs radar waves. The invisible boat? Don’t laugh – it could happen!

For more information on Standard’s new Spectrum radios, call (562) 404-2700 or visit


More Gear