Tidal Fish Forum banner
1 - 12 of 12 Posts

·
Registered
Joined
·
4,576 Posts
Discussion Starter · #1 ·
CHIRP Fish Finders Are Here
March 29, 2011
By Glenn Law
"Chirp" is not the sound of the robins coming back north for the spring. But it does herald the arrival of a new era in fish-finding sonar. CHIRP (compressed high-intensity radar pulse), which we've discussed in this space before as the fish finder of the future, is here.

CHIRP technology is quite simply a modulated pulse broadcast by the transducer. Instead of firing a 50 kHz or 200 kHz pulse beneath the boat to bounce off things and return at the same frequency, CHIRP technology modulates the pulse so the ping sent by the transducer sweeps across a range of frequencies, say 28 kHz to 60 kHz, or 130 kHz to 210 kHz, or 42 kHz to 65 kHz. The advantages are revolutionizing fish-finding sonar.

New View
The return or bounce-back off a target reflects the frequency at which the target was struck, so even two targets close together are going to return the ping at different frequencies. The result is improved separation and detail, far in excess of what is available with traditional single-frequency sonar - the familiar 50 kHz for deep water and 200 kHz for shallow water.
At the same time the frequency modulates, the width of the signal cone changes. Airmar's Mark Reedenauer explains: "Make a V with your index and middle fingers and lay it on your desk. Now move your fingers in and out, changing the distance between your fingertips. That's how the cone angle expands to cover more bottom with the modulation in frequency."
For the coming season, two companies are ready to put CHIRP on the helm of your fishing boat. Simrad broke the news late last summer in Seattle at the National Marine Electronics Association show, but it hadn't had any units on the water yet. Now it has.
Garmin got its first CHIRP units on the water in mid-January and went to market with the product in February at the Miami International Boat Show. Down the road: Geonav has announced it will release CHIRP sonar; Furuno has the technology but has not yet packaged it for recreational anglers; and Raymarine states emphatically that "Raymarine will be releasing some very innovative sonar products that incorporate CHIRP technology before the end of the year." So all the cool kids are doing it, and the language of fish-finding sonar, and anglers' expectations of it, are going through a big change.

Go Deep
This revolution has been driven by transducers developed by Airmar. That company's transducer line for CHIRP sonar includes a low-frequency transceiver that operates at 25 kHz to 45 kHz and 40 kHz to 60 kHz; the high-frequency transceiver supports 40 kHz to 60 kHz, and 130 kHz to 210 kHz, among others. These ranges are basically expansions of the familiar 50 kHz and 200 kHz options.
"The [CHIRP] technology, methodology and signal processing and mechanics are now possible because we have the transducers," says Don Korte, senior engineer for Simrad. "A couple of years ago we couldn't do CHIRP. We didn't have the sensors."
Simrad's BSM-2 ($2,495) delivers as much as five times greater target resolution over conventional sounders and, Simrad claims, offers bottom readings beyond 10,000 feet. It's not that anyone has that much line on their reels, but as Korte explains, "If you are able to see bottom at 10,000 feet, imagine how well you'll see things much shallower, at fishable depths."
An adjunct to the impressive resolution is the lack of noise or interference in the return image. This is due partially to the modulated frequency of the pulse but is also augmented by the low power requirements of the transducers. "We don't need that much power. These depths are all reached at 250 watts," says Korte.

Big Guns
Garmin's flagship product is the GSD26, a black-box sonar that retails for $2,000. Garmin's name for its version of CHIRP is Spread-Spectrum technology. "We're able to afford the sport fisher better target separation and resolution at extraordinary depths while allowing them to dial into specific frequencies to target certain species of sport fish," says Garmin's Greg DeVries.
"This is our SS broadband fish finder," he says. "The GSD26 will be manually tunable from 25 kHz to 210 kHz, creating a modulated pulse across the whole range of frequencies for superb resolution and target return." With traditional fish-finding sonar, says DeVries, when you see the bottom in deep water, you often don't see what is in the water column above it. With a modulated pulse, you get both: a good view of the bottom and an accurate look at everything between it and your boat.
Garmin's range is transducer-dependent, defined by frequencies in Airmar's new transducers. The GSD26 is not a plug-and-play unit. All connections are bare wire, so installation is a little more than a morning project in the driveway. "This is the 'big guns' product that serious anglers have been asking for," says DeVries. "When your black-box finder costs more than your plotter, it's a whole different ballgame."
Upgrading to CHIRP capability can be an easy transition with both Simrad and Garmin equipment. Both manufacturers have made convenient allowances for new sounders to function with existing fixed-frequency transducers, those you are currently using. Adapters allow the transducers already installed to remain functional, albeit at a fixed frequency, until you are ready for a haul-out - or ready to write the check - to upgrade to modulated-frequency transducers
 

·
Registered
Joined
·
2,937 Posts
I have heard about Furuno's new unit being able to identify, by species, what you are seeing below. Is this part of the CHIRP technology?
 

·
Registered
Joined
·
636 Posts
Chirp technology has been around for years. To ever reach the mass recreational market, the cost would have to come way down.
With the current Simrad BSM-2, or the future Garmin black box, plus the AIRMAR transducers, the cost is way, way up.
At least for my recreational boating and fishing, this is how I feel.

Would not mean much in the Chesapeake Bay area anyway, where 100' is deep and 30'
to 60' in the norm.
 

·
Registered
Joined
·
4,576 Posts
Discussion Starter · #5 ·
According to Garmin's website, the GSD 26 is indeed plug-and-play via the Garmin Marine Network.
Its plug and play to the MFD. The connections to the transducer are via screw terminals, not connector.
Would not mean much in the Chesapeake Bay area anyway, where 100' is deep and 30' to 60' in the norm.
Depth has little to do with it. It's all about the sensitivity of the unit. You can't see what the unit is unable to detect. You will see a considerable performance gain in even 2 foot of water.
I have heard about Furuno's new unit being able to identify, by species, what you are seeing below. Is this part of the CHIRP technology?
Don,
The Furuno "CHIRP" unit is not due for release until sometime later this year.
No problem determining what species with Furuno's existing technology. The new stuff will be unreal.
 

·
Registered
Joined
·
801 Posts
Not saying you can or can't discern which species appears under/near a transducer here, but how (exactly) can one 'know' the ID. Might be wrong here, but my understanding has been that the echoes we detect via sonar come principally from the swim bladder of the fish, since the air/gases inside are of a significantly different density than water (unlike say, fish flesh). I suppose that there might be some echoes off of vertebrae and skull bone also.

Now, all we have to display really is return signal strength, right? But how can you discern a weak echo of a big fish that happens to be only briefly overlapped by the 'margins' of the theoretical cone(s) from say, a smaller fish right in the cross-hairs and suspended directly under the path of the transducer? The first spends less time being sonified, and the second more time, and so on a scrolling screen the second might appear to be both 'longer' and 'stronger' even though its a relative 'dink'.

I suppose that the swim bladder of a truly big fish would return separable echoes from both the top and the bottom of the swim bladder (it being physically bigger than the swim bladder on a rather small fish), and therefore return a 'taller' signal to a scrolling screen, but then I have to think there would be a significant scaling issue when over any significant depth of the water column (maybe zooming in on the zone in question overcomes this?)). But other than this "tallness" of the return signal (and perhaps just an educated guess about which few species might be found over a particular bottom somewhere) its not clear to me how it is possible to discern either fish size or its actual ID (say, discerning a speck from a striper of the same size at the same depth), or whatever.

Not claiming any expertise in this area... this is just an open question/topic I'd like to have a better understanding of. Does anyone here really know at a technical level, as opposed to just passing along second-hand interpretations/rumors of the capabilities of these new (or old) units? Not doubting that improvements in performance are possible, but one expects all measure of hype from manufacturers and sales reps with every hot new breakthrough too.
 

·
Registered
Joined
·
4,576 Posts
Discussion Starter · #7 ·
Not saying you can or can't discern which species appears under/near a transducer here, but how (exactly) can one 'know' the ID. Might be wrong here, but my understanding has been that the echoes we detect via sonar come principally from the swim bladder of the fish, since the air/gases inside are of a significantly different density than water (unlike say, fish flesh). I suppose that there might be some echoes off of vertebrae and skull bone also.

Now, all we have to display really is return signal strength, right? But how can you discern a weak echo of a big fish that happens to be only briefly overlapped by the 'margins' of the theoretical cone(s) from say, a smaller fish right in the cross-hairs and suspended directly under the path of the transducer? The first spends less time being sonified, and the second more time, and so on a scrolling screen the second might appear to be both 'longer' and 'stronger' even though its a relative 'dink'.

I suppose that the swim bladder of a truly big fish would return separable echoes from both the top and the bottom of the swim bladder (it being physically bigger than the swim bladder on a rather small fish), and therefore return a 'taller' signal to a scrolling screen, but then I have to think there would be a significant scaling issue when over any significant depth of the water column (maybe zooming in on the zone in question overcomes this?)). But other than this "tallness" of the return signal (and perhaps just an educated guess about which few species might be found over a particular bottom somewhere) its not clear to me how it is possible to discern either fish size or its actual ID (say, discerning a speck from a striper of the same size at the same depth), or whatever.

Not claiming any expertise in this area... this is just an open question/topic I'd like to have a better understanding of. Does anyone here really know at a technical level, as opposed to just passing along second-hand interpretations/rumors of the capabilities of these new (or old) units? Not doubting that improvements in performance are possible, but one expects all measure of hype from manufacturers and sales reps with every hot new breakthrough too.
The bottom doesn't have an air bladder. Either does a tuna yet both are detected by sonar

Sonar reflects off different densities at different strength and frequencies. The harder the surface the more energy it reflects. This is why you can tell the difference between mud, sand and rocky bottoms.

Same holds true for fish. It's very easy to tell the difference between a bluefish and striper. A bluefish are not as dense and shows up with a greenish / blue color rather the red/ black a big striper returns. Croakers shown up as red sticks. Spot and perch show up green / light blue, with a greenish haze around them. The green haze around them is the disturbed water from their fins. Over time you learn to associate the various returns with the fish that return them.

The easiest way to increase any fish finder is to install a better quality transducer. Something as simple as changing from a stock transducer to a high performance transducer will increase performance substantially.
 

·
Registered
Joined
·
801 Posts
Thank you, Seahunter. I understood that various bottom types could be discerned, and that anything with a density much different that water (like bone) would differentially return a sonar signal (even sunken leaves in the fall, or SAV for that matter). But my experience is both dated AND limited to flashers and LCD units in freshwater only. With this more basic equipment, one suspended fish looks just like the next, except perhaps for the "height" and length (really duration in the 'beam').

That's great to know that contemporary units can offer the user so much more info... maybe one day they'll come out with a unit which displays the one's actually willing to bite as blinking targets versus the others that have one of those non-smoking type, circle/slash symbols put around 'em (just kidding now)!?!

Not that I need or could afford one, but what model fishfinder do you refer to that can present fish targets in so many colors - just curious to look up same on the web here. Appreciate the tip on swapping out a stock for a high performance transducer... also didn't know that was possible/compatible. Seek and ye shall find...

I knew that fish like darters (strongly benthic oriented) lacked swim bladders of course, but never considered that there might also be pelagic species like tuna that ALSO lacked them... very interesting. Do tuna ever stop swimming, or enjoy neutral buoyancy by some other means, allowing them to rest in place like an ordinary suspended fish can (to 'sleep' or whatever)? How about sharks?
 

·
Registered
Joined
·
4,576 Posts
Discussion Starter · #9 ·
I ran Sitex sounder for a while then switched over to Furuno with an Airmar B164 transducer. I had no problem identifying species with either unit.

Lots of technical information on transducer performance and selection:

http://airmartechnology.com/uploads/Brochures/BB_Transducers_BR_rC_lr.pdf
http://www.airmartechnology.com/uploads/installguide/Theory_of_ Operations.pdf
http://www.airmartechnology.com/uploads/brochures/AIRMAR Transducer Guide 2009.pdf
http://www.airmartechnology.com/uploads/brochures/xducer_specifications_pc_rA_lr.pdf
 

·
Registered
Joined
·
10 Posts
I ran Sitex sounder for a while then switched over to Furuno with an Airmar B164 transducer. I had no problem identifying species with either unit.

Lots of technical information on transducer performance and selection:

http://airmartechnology.com/uploads/Brochures/BB_Transducers_BR_rC_lr.pdf
http://www.airmartechnology.com/uploads/installguide/Theory_of_ Operations.pdf
http://www.airmartechnology.com/uploads/brochures/AIRMAR Transducer Guide 2009.pdf
http://www.airmartechnology.com/uploads/brochures/xducer_specifications_pc_rA_lr.pdf
Hi, being a novice angler, that's a lot of useful information shared by you, I really appreciate it, and keep updating us with more of such useful information. Regards
 
1 - 12 of 12 Posts
Top