How Chirp Sonar (Fishfinder) works?

How Chirp Sonar (Fishfinder) works?

Or actually how I think it works. So Chirp sends a pulse or multiple at multiple frequencies and different angles and then reads and processes it. A non-Chirp, regular sonar has fixed frequencies. Simrad for example supports 455Khz and 800Khz in Chirp mode and the standard 50kHz/200kHz i normal mode.

An Airmar B765LH uses the low frequency 40 to 75 kHz and high frequency 130 to 210 kHz at angle of 32° to 21° for the low range and 9° to 15°.

The more narrow the angle the more detailed is the response just like the zoom on you camera. If then angle is wide means you can cover more area below your boat.

Narrow angle on High Frequency
Wide angle on High Frequency and Narrow angle on Low Frequency

The higher the frequency the more resolutions you get and the smaller fish echos are received back. Lower frequencies on the other have a wider beam, which means it can find larger fish over a larger area below the boat - but it will miss smaller fish.

The different sonar characteristics can be used to create sonar 3D maps and each manufacturer seems to have a "unique" marketing name to these products. Garmin makes ClearVu, LiveVu, RealVu, DownVu and LiveScope under the Panaoptix brandname. Raymarine does DownVision, SideVision and new RealVision and just as Garmin, they have trademarked these names. Simrad has TotalScan, StructureScan 3D and wait for it... StructureScan HD and Active Imaging 3-in-1 as well as SideScan and DownScan. Simrad and Lowrance share brandnames.

Either way, there are hundreds of chart plotters on the market and the main manufactures have done all in their power to confuse the users and squeeze every penny of every available market segment. Apparently they are doing the same with sonars.

I have two Pizza places where I live, one that has had 120 different pizzas in their menu for the past 10 years. Another place  has 9 pizzas at any given time and they rotate 3 of their pizzas every month. I have never order more then 2-3 kinds of pizzas in the first place, the second place I've tried most of their pizzas and they get bulk of my business.

The reasons are "I trust them to pick the right stuff for me" and focus their effort on quality ingredients and the making process. The 120 pizza place tries to get every penny, but having poor quality ingredients due to stocking a lot of different ingredients for long time and choosing the cheapest stuff and low price.

They need to feed their kids, so they don't care much for what I feed myself or my kids with. Just think for a second, why is Marine Chart Plotter theft still an issue in 2020? Because it makes the manufactures a ton of money - insurance money!

The idea is to figure out how the chirp technology actually works and what is the output from the chart plotter/sonar unit to the transducer. Then do a prototype of 600W, 1kW 2kW configurable Chirp unit and test them in field. Transducers should be stock, like Aimar B765 or B744.

Aimars explanation of sonars: