When you’re in the market for a fish finder, you’re also in the market for transducers, and to find a good transducer you’re going to need to understand a little bit about a transducer’s cone angle.
You might think that the wider the transducer cone angle the more you’re going to see, which is sometimes maybe the case, but it depends on what you’re looking for with your fishfinder.
Join me as we take a look at transducer cone angles so you can find the right sonar unit for your fishing needs.
What is a transducer’s cone angle?
The cone angle on fish finder transducers, also known as a beam angle, determines how wide a beam of sound/radio waves are shot out into the water column towards the sea, river, or lake bottom.
A wider, bigger beam angle of sound waves will give you coverage of a larger area to see in an image on your display.
For example, a sonar unit using 200 kHz sound waves frequencies might have a narrow-angle beam of 12° with limited coverage area or a wide 20° beam with more coverage area for seeing more fish.
How much area does a transducer cover?
Is there a way of measuring cone angle diameter? Measuring the diameter of a transducer is easy to calculate using this simple formula, 1feet of coverage for every 3 feet of depth with a 20° cone and thus about half for a 10-degree cone.
This means that in shallow water, say 9 feet, you will see a much smaller area of the bottom, around 3 feet of the lake for example, while in deep water, like 60 feet, your coverage will be a lot larger at 20 feet.
Actual Vs.Specified Cone Angle
In all the diagrams you see of transducers and their cone angle you generally see a conical shape of coverage and this instance is described as the industry standard specific cone angle.
The shape of the beam starts at a point and then opens up from a narrow diameter to a large circle of coverage on the bottom.
The actual cone or beam angle of transducers has a different shape, the difference being that the actual beam angle opens up into more of a circle or ring shape with side lobes on the edge where sound waves also travel.
The side lobes protrude out the outer edge a few feet in each direction making the diameter much larger than specified.
Whether you can see anything within the extra edge range depends on how well the target reflects the sound wave frequencies back.
When you’re fishing, you can use this to your advantage by keeping an eye out for anything that arrives into the side of the image on the screen as this will be a sure sign of a group of baitfish moving in the direction of the boat a few feet under the surface.
How are transducer cone angles measured?
Manufacturers measure their cone angles by measuring the power level from the center of the transducer out into the cone until it hits the half power point, which gives them their angle.
The center of the circle is the most powerful part of the sonar beam, and the manufacturers only count the sonar down to half-power within their cone calculations.
This is because any sound wave frequencies without enough power behind it may struggle to scan effectively and pick up an object, structure, target, or the fish you want to see while you’re fishing.
This also explains why there is a difference between the actual and specified angle we discussed above, as manufacturers don’t count anything past half power.
A Chart Of Transducer Cone Angles
|Coverage (ft)||Angle °|
The table above shows the coverage you will get from different angles at different depths but this only applies when your gain is set to the maximum. When it isn’t, you won’t pick up all the details within the specific areas.
When your gain is too high you will see too much detail and not be able to decipher fish from debris as they will merge in the detail. You have to play a balance between gain, readable images, and full coverage to get the image you want.
Which cone angle to use on your fish finder?
The larger the cone the more coverage you’re going to get of the lake or sea bottom and therefore the more you might see on your display, at every depth. However, wider angles mean less detail in a shallower depth, so it depends on where you’re fishing.
If you’re fishing in the sea looking for a big structure like seamounts and canyons in a depth of up to 3000 feet, then larger beams will help you find these.
If you’re fishing in a bass lake with a max depth of 20 feet, smaller beams will help you find a smaller object like a brush pile, a location fish like bass love to hang out in.
What angle should my transducer be at?
Your transducer needs to sit parallel to the surface of the water so the signal of sonar sound waves is projected straight down instead of off to one side.
Depending on where you mount the unit, you may need to adjust the angle.
For transom mount transducers, having it level with the water’s surface is easy as the unit will sit out the back of your boat and it just needs to be parallel to work. If mounting it inside your boat hull, you’ll need to adjust for the V to ensure the sonar goes straight down and not to one side.
Is there a dead zone with the sonar beam?
Yes, there is a dead zone in every sonar beam that can hide fish from you and this is due to the sonar marking the bottom at the nearest point it sees. So if you’re fishing over a ledge, you could only see the shallowest depth of the ledge which the sonar has marked as the bottom depth.
When this happens, the deep side of the ledge becomes invisible to you and you will not see a fish or target that might be holding there. However, if the boat is moving, it should become visible eventually as the bottom will be remarked at the shallowest depth it finds.
The larger the sonar beam, the bigger the dead zone too, so this is something to be aware of when selecting a transducer or while fishing.
How do power & gain affect the cone angle?
Every transducer is powered at a certain level and this doesn’t change, it pumps out a sonar frequency with the same signal power regardless of the cone angle.
This means that a narrower beam will appear to have more power as the power isn’t diluted into a wider area, so narrower beams have an advantage over wider ones in deeper water and vice versa in shallower depths.
Take a look at how adjusting the gain affects what you see in the video below…
Upping the gain on your display only ups the signal frequency received when sonar waves are picked up post reflection. Increasing the gain lets you see more details in the sonar image while you’re fishing, but it can also take things too far and merge things such as fish and seaweed, giving you a poor target separation.
What is the cone angle for a side imaging transducer?
It’s the exact same for a normal transducer and depends on the transducer you buy. Most side imaging units send out sonar frequency waves at a 30-degree angle to see what’s on the side, the cone however is dependent on the manufacturer and will be measured in the same way I described above.
When should I use different cone angles on a tri beam transducer?
The answer to this is, whenever you like. If you have a tri-beam unit, you can see a separate sonar picture for every beam, and if you’re covering a lot of ground to find fish, then you might want to see the sonar signal for every beam so you don’t miss anything.
Driving around with a down beam and two side beams gives you a much more detailed picture of what is around you in the water than the single circle of a down beam.
Thanks for reading my article, I hope you found it useful and now know enough to select the right transducer cone angle for your fishing needs. Please share the article with your friends in the fishing community as we all need a bit of help when it comes to the complexities of cone angles.
- Sonar Diagram (1) Sonar and transducer basics. (n.d.). Lowrance USA. https://www.lowrance.com/sonar-basics/
- Beam Angle (2) Sonar and transducer basics. (n.d.). Lowrance USA. https://www.lowrance.com/sonar-basics/