CHIRP Systems

Sonar reaches a whole new level.

March 30, 2011

CHIRP is the new sonar technology recently released to consumers by marine electronics gurus Garmin and Simrad. Its complete name is compressed high-intensity radar pulse, and while the technology has been around some decades in military and commercial applications, these two players are the first to bring boaters the ultimate coolness of sonar clarity.

CHIRP makes reading sonar signals on a chart plotter amazingly simple by using a technology that is really not so simple. Essentially, CHIRP replaces a single-frequency ping with a pulse that crosses from low to high frequencies. Think of the chirp a bird makes. It starts on a high or low note and ends on the opposite end of the frequency scale to make a pleasing noise. It is essentially a myriad of pings fired in a single burst. Thanks to the computing capabilities within the black box, these new sonars separate these frequencies, measure their distinctive returns, weigh the timing of the returns and their volume or amplitude and use the information to plot a high-resolution image of the bottom and targets in between.

Ok, that’s a mouthful, but their benefits were easy to define in our recent tests. It’s like the difference between watching standard-resolution television on a circa-1980 TV and watching high-definition TV on a 50-inch 1080p screen. Remarkable.


While capabilities and features of these CHIRP systems vary, one commonality among CHIRP sonars is specialized transducers developed by Airmar. Choices of Airmar transducers are slightly different in frequency ranges but comparable in their ability to transmit and receive a powerful, clear signal throughout the water column. Without them, CHIRP’s black-box modules are mute and blind.

Simrad BSM-2 Broadband Sounder Module
Suggested Retail Price: $2,495
Airmar Transducer: $1,795 to $2,995

Our perfectly calm Simrad test day proved ideal for showcasing the company’s CHIRP sonar capabilities to the max. We scanned various wrecks and breaks from 40 to 500 feet and were impressed by the degree of detail.


-We saw that target resolution was consistently detailed from shallow to very deep water and easily maintained a solid bottom return at depths of 1,000 feet. A trademark advantage to CHIRP is its ability to plot depths to 10,000 feet.

-Simrad offers various color palettes to suit light conditions and personal taste. We found some targets were more clearly distinguishable with different palettes.

-Our test unit allowed us to scroll back the chart plotter and “mark” a spot with the cursor to register that waypoint on the GPS chart plotter.


-It allowed us to set a custom zoom window as small as five feet and showed remarkable zoom detail in that window at 500 feet.

-Access to menus and functions was more complex than on the touch-screen Garmin unit we tested, but Simrad recently announced the addition of touch-screen capability on its latest units to be released later this summer.

-Airmar offers two transducers with two nonadjustable frequency bands each: CHIRP no. 1 — 130 to 210 kHz or 40 to 60 kHz for shallower ranges, and CHIRP no. 2 — 40 to 60 kHz or 25 to 45 kHz for deeper ranges.


Garmin GSD-26 Sounder Module
Suggested Retail Price: $2,000
Airmar Transducers: $1,795 to $2,995

Test conditions for the Garmin CHIRP unit were not so favorable. Three- to four-foot rollers meant our boat rocked heavily, and with that, the signal oscillated back and forth, weakening the ability of the unit to paint the photo-like images of which it is capable.

-Target resolution (for fish and baitfish) and distinction were comparable to those of the Simrad unit, and we were able to see individual baitfish in schools.

-Touch-screen operation made it easy to manage the system, shortening the learning curve from that of the Simrad unit.

-Garmin allows users to customize CHIRP frequencies within the transducer’s frequency range, 25 kHz to 210 kHz, and to adjust transmit power from 300 watts to 3 kW to help better define desired targets.

-We did not find the broad selection of color palettes on the Garmin unit that we had enjoyed on the Simrad, but we did find ample clarity on the palette available.

-Garmin lacks the scroll-back function we enjoyed on Simrad, but we understand that function may be added by the time you read this.

What Is CHIRP?
The first consumer sonars came from Lowrance, more than 50 years ago.

These sonars transmitted a ping that could be heard by the human ear as a “click.” They measured the time it took the ping echo to return to the transducer and measured its volume, called amplitude, to determine the target depth. It took a long ping to penetrate water to the target. The longer the ping, the more targets blended together. For 5o years, sonar-interpreting capabilities improved with software and LCD screens, but the single-frequency ping remained as its weak link.

A CHIRP signal crosses from high to low frequencies in an elongated pulse and penetrates the water better. Next, sophisticated “black box” software distinguishes the returns of varying frequencies, their timing and volume in a complex but instantaneous calculation that allows the device to plot a much-higher-resolution image of targets on the screen instead of one faceless blob.


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