CHIRP – The Future Of Sounders?

Depth sounders, aka fish finders, have evolved rapidly in recent years. In only a few decades we’ve gone from the lo-tech paper sounders of the 1970s and ‘80s to modern digital units with massive full colour hi-res screens. Who would have thought as little as five years ago that futuristic sounding technology like side and down scanning, not to mention touch screens and full integration with engines and other electronic devices such as GPS and radar, would be widely available to small boat anglers? Hell, even kayaks are being fitted with full-on sounder/GPS units these days! It is amazing stuff but the developments in sounder technology are continuing and if what I’ve seen lately is anything to go by the best is yet to come.

For the past few months Fisho has been testing out the newest and possibly most exciting development in depth sounder technology we’ve yet come across. It’s known as CHIRP and it promises to radically change how we view and use sounders.
Simrad, a big player in high end marine electronics industry, is leading the way with the development of CHIRP in the recreational market. CHIRP has been used in the military and commercial arenas for some years but in recent times has been adapted by Simrad and a couple of other marine electronics companies for use by sportfishing vessels.

I’ve been using a state-of-the-art Simrad NSE 8 in the Fisho Bar Crusher for the past few years. Linked in with Simrad’s BSM-1 sounder module and a standard 600W Skimmer transducer, the NSE is without doubt the best and most effective sounder I’ve ever used. It boasts fantastic clarity and is relatively easy to use, allowing for precise adjustments to get the best possible screen display.

Earlier this year Simrad released its BSM-2 broadband transducer module, which offers vastly improved “signal detection and post detection digital processing” via CHIRP technology.

The guys at Simrad were pretty keen to get me to see how this actually works in fishing situations so we installed the BSM-2 and a new Airmar CHIRP transducer on the Crusher and I’ve been playing around with it in both deep and shallow water over the past few months or so.

South Coast-based marine electronics specialist Matt Adamson, from Emjay Communications, has assisted greatly with fine-tuning the unit and adjusting the transducer for maximum performance. We still have a bit of work to do to in this regard but initial results reveal that Simrad’s CHIRP technology promises a quantum leap in overall sounder performance.

Matt and I are planning a full rundown of CHIRP and how it will improve your ability to find fish in the February issue of Fisho. In the meantime, here’s a sneak peek of what it is and what it can do. Bear in mind that I’ve tried to explain this without bamboozling you (or me!) with techno-jargon. There’s a hell of a lot more to be revealed as to how exactly this all works but unless you’ve got a degree in astrophysics you’ll be like me and just look sort of mildly retarded when some tech-head starts rabbiting on about “range resolutions”, “band widths” and “Frequency Sweeping Pulse Compressions” … Most of us don’t need to know this stuff but the basics as will be explained below will definitely help you comprehend how cool CHIRP is and how useful it will be to fishos.

Anyway, as it stands now, sounders use a single “ping” at a single frequency (usually either 50 or 200KHz). This “ping” travels down through the water and the sounder translates the return signal and uses the data to reveal water depth and the presence of fish. The problem with a single “ping” at a given frequency is that it doesn’t offer much discrimination between fish close to the bottom or grouped together. Also, the use of a single frequency, say, 200KHz, means that the signal basically runs out of puff once it gets to a certain depth.

Equipped with the BSM-1 module, my Simrad NSE8 sounded bottom in about 130 fathoms before losing signal. That’s fantastic performance for a 600 Watt transducer and I’d doubtless get much better results if I used a much more powerful 1000 Watt transducer – but CHIRP takes things to a whole new level.

Very basically speaking, CHIRP works by “sweeping” a range of frequencies through the signal being sent down into the water and then deciphering the return info to give much more defined displays. For example, current broadband sounders can differentiate between objects about 360mm apart. So if two fish are a foot or two away from each other, the sounder should be able to pick them up as two separate signals. The CHIRP-enabled sounder can differentiate between fish 40mm apart – that’s five times better than the currently class leading technology. This is unheard of sensitivity! And I’m talking about this sort of reading being achieved in hundreds of metres of water, not just in shallow stuff.

The other really cool thing that CHIRP does by sending multiple frequencies down the water column is that it enables longer transmissions (ie, more intense pulses) without losing resolution. To reach the sort of depths CHIRP can, a traditional sounder would have to send really long signals, which would result in it being unable to differentiate between targets, thus reducing its efficiency in regards to actually finding fish.

Testing Simrad has done indicates that the BSM-2 unit can reach 10,000 feet, which is about 1700 fathoms or more than 3,300m. Matt and I easily reached 650 fathoms (3900 feet or 1300m) using only 250 Watts of power during a recent offshore expedition in the Fisho Bar Crusher. That’s about six times deeper than with the previous BSM-1 module. And we haven’t even learnt to properly fine-tune the unit yet… Imagine the potential for finding mid water bait schools or even tuna and marlin with this sort of hi-res depth capacity.

The first of the accompanying screenshots shows the bottom clearly being displayed in 658 fathoms. The second shot displays a school of bait sounding under the boat in 29.5 fathoms and the third shot shows individual slimy mackerel being sounded out at my local bait grounds in just under 10 fathoms. These shots clearly show the CHIRP readings work in shallow and deep-water situations. Check out the differentiation between fish hanging just off the bottom in the bait ground shot – it’s pretty amazing stuff. Imagine it being used in a snag sounding out bass, bream or barra, or finding jewies or snapper on an offshore reef? Lots of potential …

Stay tuned for the February issue where, all going to plan, we should be able to present a really detailed and informative article on what CHIRP is and what it can do to help you catch more fish. This technology is only very new at present and it’s not cheap. But in saying that colour screens were bloody expensive when they first appeared and now they’re a dime a dozen. My prediction is that CHIRP will soon become a viable option for all sportfishing boats, big or small. Regardless, it is very interesting stuff so make sure you stay tuned to Fisho and for more details.

Meanwhile, if you want to find out more about Simrad’s CHIRP technology, go to or call Matt at Emjay Communications on 0413 808 507.




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