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Raymarine CHIRP Fishfinder screen shot.

Is CHIRP just another way of showing the same old picture on your fishfinder or do you gather lots of worthwhile information from this state-of-the-art technology? I was really impressed when I played with a new Garmin GSD26 off of Pompano Beach, and I'm looking forward to investigating Raymarine's new CP450C Clear Pulseā„¢ CHIRP Sonar introduced at the Miami Boat Show. It's easy to see that finders using this new technology are far better than anything previously available.

With this new technology you will be able to target a big kingfish feeding in the middle of a school of bait, and you can operate these new sounders at a higher boat speed.

If you are ready to get one, you should know that in many cases the new sounder black boxes can be fitted to most existing networks, but you will need a new transducer installed at the same time. The new transducer designs are radically different inside and they are the key ingredient that enables the CHIRP software to work.

The transducers are available for nearly every type of boat installation from transom-mount to in-hull, shoot thru-hull and up to big thru-hulls with fairing blocks. CHIRP is not just for big sportfishing boats or for commercial seiners, they are the ticket for any sport fishing application and work equally well in any depth of water. CHIRP works deep without an expensive, high-powered black box. Of course, because CHIRP is new, the price has some premium built in to cover all the product development, but it's still very reasonable and a worthwhile addition for any SKA boat.

You can find these CHIRP black boxes for less than a couple thousand dollars, and the new transducer could range from a couple hundred for a transom-mount up to thousands for a big multi-frequency thru-hull with a tank. Hauling your boat and installing the new transducer is a variable, to put it gently.

What you get for your money is amazing detail and resolution, even at fairly high boat speeds. This sort of detail became available when fishfinders went from analog to digital a few years ago, but now the ability to pick out game fish in a school of bait is improved. Also, fish at the bottom appear quite separate from the bottom, not just as a definite bump on the bottom like you got with the transition to digital sounders.

We have known for a while that certain fish return an echo at a certain frequency, and some at other frequencies. Up till now, fishfinders did the best they could but there was only a single frequency or maybe two fixed frequencies. The frequency was usually selected by the depth of water or one that worked best for a specific application.

You know about the common 200 kHz and 50 kHz transducers. Resolution is better at 200 kHz, but 50 kHz reached into deeper water past 500 or 600 feet. Now CHIRP puts out a swept range of frequencies. Then the computer processor picks out the fish with an identity based on the certain frequency that they return to the transducer, as opposed to other fish, or a wreck or bottom or interference. You find big and small fish in shallow or deep water with the same detail.

It's not just the range of frequencies, but the advanced processors that pick out the images from all the variations of return echoes that are imprinted in a pattern.

It takes a bunch of crystal elements inside the CHIRP transducer to provide the required range of frequencies, and by good luck, that also allows Airmar, who builds transducers for almost all fishfinders, to better focus the energy downward than if there was only a single element.

These are not dilithium crystals, and they have no magical curative power like the crystals you hang from your rearview mirror, but they sure do find fish. The fact that crystals are molded into the bottom face of the transducer is why we ask you not to bang or scrape the bottom of the transducer when you're cleaning your boat.

With CHIRP, you also get accuracy down to as far as 10,000 feet, without the powerful burst of sound needed with the former technology. However, CHIRP doesn't get rid of all the fishfinder's current drain on the battery, like it does in new CHIRP radars, because the pulse is relatively long at that lower power compared to previous fishfinder pings, which are short and powerful. We're speaking of milliseconds here, a little longer than a bird's chirp. The total amount of energy in one CHIRP pulse is ten to 50 times the total energy of a traditional fishfinder, if that helps you imagine the increase in "data" that can be in the return echo.

If you can imagine that we can tell different fish apart by the subtle differences in reflected frequencies, imagine the difference in the returned echo of the bottom or reef or wreck, compared to a fish on the bottom. CHIRP can tell a lot by digitally analyzing these frequencies as well as strength of echoes. You get a good picture of fish near the bottom, and you get a better feel for whether the bottom is hard, soft or seaweed.

Thru-hull or transom mounting options.

Now we get to higher boat speeds. By using frequency discrimination as well as strength in the digital screen "clean-up" the new CHIRP sounder can do a better job of getting rid of noise, "snow," bubbles and the other problems of running fast.

I'm a geeky kind of guy, so I am itching to tell you the details of the theory and the technology involved, but I'll fight that urge. Let's just sum it up by saying that CHIRP takes advantage of the way that different fish reflect different frequencies of sonar, and so they can be displayed on a screen as different if you can use a range of frequencies through a transducer. Airmar has developed a transducer that can do this and it is their research and technology that enables any fishfinder manufacturer who uses Airmar to build a CHIRP sounder.

WHAT'S IN A NAME

Between trade names and people who don't like acronyms, there are a few terms being kicked around for this new technology. Some are calling it Broadband but in the marine business we all think of Broadband as a name for high speed data downloads from satellites to boats and ships. In fact, the frequency bandwidth in the CHIRP pulse is narrow compared to Internet bandwidth, but very wide for a depth transducer. For instance in a sweep from 42 to 65 kHz or from 135 to 210 kHz in transducer output, the range is closer to what you would hear in a bird's warble, and so I think CHIRP is a good name. CHIRP also stands for Compressed High Intensity Radar Pulse.

With both the Raymarine and Garmin CHIRP sounders, you are able to vary the pulse frequency for various depths and/or kinds of fish. For kingfish, your settings would be near the higher end since they are found in shallower water for the most part.

Some are calling CHIRP by the name Spread Spectrum, but that is a technology developed for military radios a while ago, which is now used for cordless phones in your house and some satellite phones. It hops from one frequency to another, and isn't the sort of a sweep or brushed frequency range like in a CHIRP fishfinder. Spread Spectrum is hard for an enemy to monitor and also reduces interference with satellites and other radios, but it really doesn't describe what a CHIRP radar or fishfinder does. The sophisticated processor in the new sounders does borrow from Spread Spectrum, though.

Can CHIRP be called Frequency Modulation? You think of FM as being the car or HiFi radio that got rid of static in old AM radios. In fact, the return CHIRP echo is modulated onto the frequencies that are transmitted, but they are digitally processed using pattern matching or pulse compression circuitry. I guess you should be aware of all the trade names for CHIRP that will be kicked around as every brand comes out with their version of these great sounders.

Whatever the marketing people may call it, I am truly impressed with this new way of finding fish with a piece of electronic gear. If you get a chance to try it, you will be amazed, too.

Raymarine's CP450C Clear Pulse CHIRP Sonar Module





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