Lowrance CHIRP -
2014 Oct 12
The ‘buzz’ word in sonar these days is CHIRP (Compressed High Intensity Radiated Pulse) technology. At first I had no interest in it as I am a shallow water (8ft-300ft) inland / coastal angler, and I was under the impression that CHIRP is for 1000ft plus users only.
Then all of a sudden people started talking about ‘CHIRP Lite’, which is essentially the name given to a low power affordable shallow water fishfinder. The unit that made me reach for my wallet was the launch of the Lowrance Elite-7 CHIRP. I had a pretty realistic expectation of the unit as the release video by Lowrance was not that impressive, but I am a ‘sonar addict’ so I had to try it for myself.
My first time out did not impress me at all as I could see no improvement whatsoever over the standard 200/83kHz while trolling (3mph). Then I found a brushpile with fish on it and sat above it while dropshotting to it. The Medium CHIRP gave a much cleaner water column without having to turn the sensitivity down. This meant that I could track my lure and the fish a lot better than traditional 200/83kHz. This statement has previously earned me comments such as “this is an inexperienced CHIRP user”, which I cannot deny, but those were my honest findings and I still stick by my statement months later.
After several months of using the Elite-7 CHIRP and continually tweaking the settings, I still could not get a better result and could not understand why. Then one day while playing with the unit on simulation using a few recordings I took previously I found something very strange … a major loss in history resolution as one changes from 200kHz / 83kHz / High CHIRP / Medium CHIRP.
So I went out and logged an area using the four frequencies over a course of the exact distance in meters. Take note that I was idling along the exact course at the exact same speed for all four passes. The most shocking is how slow the Medium CHIRP scrolls when compared to the 200kHz, and the result – nearly 50% loss in history resolution. (p/m = pixels per meter)
This is the same thing that happened to StructureScan with the LSS-2 and Touch, we lost history resolution, giving the appearance of being compressed from left to right. Both these screenshots below were at dead idle – 3mph with the SideScan range set to 60ft, and yes, the waypoints were purged and all trails were deleted. These are all things that contribute to loss in history resolution in case you were wondering what I’m going on about.
I was very interested to see if the SonarHub with the Airmar TM150 would do the same thing with regard to history resolution, and it does – exactly the same as the Elite-7 CHIRP. Putting what we know about history resolution aside, I spent the day yesterday on Inanda Dam taking screenshots in a number of different depths and speeds to illustrate what one can typically expect from an HDS9 Touch with SonarHub (latest software V1.26) and a TM150 CHIRP transducer when fishing inland waters for freshwater species -
Range - 60 to 80ft
Speed – 4.8kph
1 – Standing timber
2 – Rising bubbles
3 – Fish
Range – 50 to 60ft
Speed – Stationary
This is a big tree on a very steep ledge that keeps repeating itself as the back of the boat moves with the breeze while the bow is on spotlock with the iPilot trolling motor.
Fish can clearly be seen swimming in and around the timber. These fish are typically very hard to see using 83kHz as the timber dominates the display, and when using 200kHz, the cone is so small that the fish don’t stay in the coverage area long enough in order to track them properly. This to me is a great advantage, and should not be disregarded.
Here is another typical stationary situation where I have stitched 3 screenshots together so you can see more history as the boat sways over the standing timber in shallower water this time.
So if you are fishing similar waters to what I do, and are using either a HDS7 or 9 Touch and are considering adding the SonarHub and TM150 transducer, these are the kind of realistic images you can expect.