Saturday, 2 May 2015



This article is to talk about Transducers and all that makes them work, including frequency settings on sonar and structure scan, cone angles on the transducer beams and the all new latest Chirp.
To understand how a transducer works firstly is paramount, then you can start to understand how cone angles work to determine what frequency you should be running for your style of fishing.


To understand how a transducer works I wanna firstly explain how a transducer transmits a sound wave beam known as a "Cone Angle". this is like a V shaped fan that shoots sound waves to targets and returns back to the transducer like a ricochet. The reflected signal is received by the transducer and is sent to the sounder unit to be processed into a more likely recognizable object on the screen. The signal that is sent out from the transducer varies in frequency, this frequency is set by you in the units settings. The most common sonar frequency settings are 50 kHz, 83 kHz and 200 kHz and more high definition Structure Scan frequencies can run larger amounts like 455 kHz and 800 kHz, but ill go into that in more detail below. 

Transducer beaming a cone angle

A cone angle or beam angle determines the coverage of an area under your boat from the transducer, the larger/wider the cone angle is the greater the area of coverage. Cone angles vary in difference between each manufacturer, but generally a 200 kHz transducer will have somewhere in between a 12-20 degree cone angle, and a 50 kHz transducer will have anywhere between a 30-40 degree  cone angle. 

Explaining how different frequencies have different cone angles

This may be hard to process so try and think of the cone angle as an adjustable torch light, when the light is expanded out it illuminates a wider area than what it would if it was a narrower light beam when adjusted. But when the light source is wider may light up a bigger area but the area isn't as defined or as lightened as it would if the light beam was narrowed. So what I'm trying to explain is, If the wider the cone angle is selected for example the 83 kHz frequency the more area it will cover and identify fish and structure. But it wont necessarily be as clear. But if the cone angle was say 200 kHz which is a larger beam it wont cover as much area but the sonar beams will be more accurate in returning the image back to the transducer therefore give a more detailed image on your sonar chart screen. I will cover frequency selections in moire detail below.


SONAR FREQUENCIES 200, 83 and 50 kHz 

Most sonar units that are sold on the market for general sonar fishing operate a frequency of 200 kHz, some models use 50 kHz and 83 kHz, and some have the capabilities to have a split screen and have 200 kHz on one screen and say 83 or 50 kHz on the other screen so you have a wider cone angle and a narrower angle on the other side to cover both aspects of water coverage. As i mentioned your typical higher frequenies like a 200 kHz setting will excel in showing minute details of the underwater world, but will have a smaller area it will cover as opposed to the 83 kHz or 50 kHz frequency, it will have a larger area covered but in less detail.

Larger cone angles have less detail, Smaller cone angles have more detail
The menu is in the top right corner of HDS models to change frequencies

In shallower water usually I fish for Bass in the summer months in water up to 20 meteres and generally set my frequency on 200 kHz as I'm after a smaller area of coverage cause the water depths are shallower and I'm after more detail cause im generally looking for that structure that the Bass hide in. If I was fishing a deeper style of fishing like reefs I would set my frequency cone angle to 83 kHz as im after that larger cone to cover more area of the waters depths as the 83 kHz frequency setting (or 50 kHz if you dont have a transducer with 50kHz) has a greater depth penetration for deeper water applications but will return less definition in image quality on the sonar screen.

Display of how fish look as they enter and leave the cone angle


A Structure Scan transducer frequency works nearly exactly the same as a standard sonar frequency using con angkles. But a side scan sends the waves outwards and down which is explained in a section of these articles when Structure Scan is explained in detail. so basically a frequency of 455 kHz cone angle will be a larger cone and cover a greater area of  underwater, but will return back to the sonar chart in less definition. An 800 kHz frequency will send out a smaller cone angle covering less area of coverage but will give a more detailed image displayed on screen.

A diagram explaining exactly how beam cone angles on a transducer work
The menu is in the top right corner of HDS models to change frequencies on Structure Scan

Structure Scan frequencies are far bigger cone angles than the standard sonar imagery that was explained aboive. it is created to show 3D images of fish suspending or structure laying in the water column. These frequencies when used with side scanning cause make spotting fish or finding structure of up to 600 feet (183 metres) either side of the boat. Makes it ideal for those anglers that find it c=ritical in fisding either structure on the banks edge or below the boat in order to find fish hiding and habitats.

This is the top and front view of different cone angles for different frequencies

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