What Does Sonar Frequency Really Mean to Your Fish Catches

Sonar Fequency What does it mean to you


Fall 2019

page 64

200 kHz are like a semi-automatic rifle that steadily fires the same bullet. CHIRP is like a machine-gun that fires bursts of multiple frequencies all at once, and then listens for all the returns.

3D JACKPLATE This is an image of my Lowrance 3D StructureScan

transducer mounted on my jackplate with

a TransducerShieldandSaver.com mount.

The lower frequencies in a CHIRP burst provide the

benefit of range, while the higher frequencies provide

superior clarity and target separation. CHIRP is best

known for a sonar display with very little clutter or


Most Lowrance transducers are capable of CHIRPing,

and the software on HDS, Elite Ti, and other units allows

the user to select different CHIRP ranges for optimal clarity

in different water conditions. For those who want to get

even higher performance (at a higher cost), you can buy

transducers built specifically for CHIRP, like the Airmar


High Chirp

This is the most frequently used CHIRP setting because

it has fantastic target separation. Bass that hug the bottom

or structure can be seen with Hight CHIRP where ordinarily

they would not be distinguishable.

The exact frequencies used in High CHIRP vary, but it is

typically around 130 kHz -210 kHz.

Medium Chirp

Medium CHIRP is sometimes better if you wish to cover large areas for schooling fish and want to find them quickly.


The frequency range is usually 85 kHz -135 kHz, which

Lowrance’s various StructureScan transducers

makes bigger fish arches and provides wider coverage. It

typically use 455 kHz and 800 kHz. StructureScan is

does not do as well with separating individual fish close to

Lowrance’s term for both SideScan, and DownScan. Unlike

the bottom or objects.

sonar, these frequencies are transmitted in a thin slice.

Low Chirp

SideScan sends the slice 600-feet side-to-side out of the

Primarily used in deep applications beyond 300-feet

transducer, and DownScan sends the slice directly below

deep, and is usually operating in the 42 kHz -65 kHz range. the boat.


in concept to

a CAT Scan,



the high


signal in a

narrow slice,

and as the




each slice of


is stitched

together to

draw a highly



Instead of

blobs, images


CRANE BOOM 33 - Notice the 2D Sonar image on the bottom right panel. You can clearly see there is some type of cover sitting on the bottom, but 200kHz at that depth doesn’t show enough detail to know what the object is. Note how the 800 kHz image on the DownScan Image (upper Right) and the SideScan image on the upper left clearly show this is a crane boom that fell into the lake and stuck in the bottom.

exactly as they are. A tree shows the trunk and