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Guide - How to choose the correct transducer

Oppdatert: 24. feb. 2022

Understanding how an echo sounder works, and thus also choosing the correct transducer for the purpose you need, can be difficult for many. This is not so strange, there is a lot to choose from, and many factors come into play. In this article, I have received help from Morten Blix and Rolf Fossumstuen, two very talented guys on this topic. Morten has had marine electronics as his main focus since he started Ramotech in 2015, now he works as a sales manager at Norbåt AS, dealer for Nimbus and Axopar who also use Simrad in their boats. Rolf has almost 30 years of experience as a user and seller of maritime electronics, both leisure and commercial. Rolf has previously worked for Raymarine but is now employed by Navico.


The purpose of this article is to go through the most common transducers used in Norway. We will focus on purpose of use, power, frequencies, cone angles, depth and how deep you can see fish. This article is a follow-up article to the previously published article "Guide - Simrad chartplotter/sonar". What most people who contact me ask is; how deep does the transducer range and how deep can I see fish? There is no simple answer to that question, but on a general basis we can say that most transducers (with some exceptions) see bottom down to 300m and fish down to 100m. Then there will be many things that affect how a transducer will perform in each case.

We start by taking a general look at the most important factors that define a transducer and its area of use.

The illustrations shows usage areas for transducers.


The power of a transducer is measured in w (watts) or kw (kilowatts). Rolf Fossumstuen has a metaphor he uses when he explains how the effect affects the transducer.

- Power can be compared to the length of a string. If you have a higher frequency or a wider cone, it will be used up faster!


The frequency has a direct impact on how deep you can reach with your transducer. In addition, the frequency also determines how much detail you see on the screen. High frequency gives lower range but more detail, low frequency gives more range but less detail. If you want a high frequency but still reach deep, you must increase the effect on the transducer. If we take Rolf's comparison as our starting point, the example below shows how the effect is distributed over the different frequencies. We see that with high frequency, it uses more string (power) than with a low frequency, which in turn means that you reach deeper with a low frequency when the power is equal.

The illustration shows how frequency effects range if the cone angle and power are the same.

Cone angle

The cone angle can best be compared to the light from a flashlight and is given in degrees. A wide cone shows you more of what is under the boat, but gives you a poor description of bottom structures. A narrow cone angle will give you a better description of the bottom structures, but you will see a smaller area under the boat. Here it is also important to understand that what you see on the screen is a two-dimensional reproduction of what the echo sounder receives. This means that the bottom line is drawn as a composite image showing the total of the deepest and shallowest part of the echo. If the bottom is rocky, you will lose details on the bottom if you have too wide cone. If you are looking for fish near the bottom with a wide cone, you will get a "blind zone" where you will not be able to see fish that are close to the bottom where there is a rocky bottom. On the other hand, you will see more fish swimming upwards in the water column with a wide cone than with a narrow cone. If you do pelagic fishing, it can be an advantage to have a wide cone to see as much as possible under the boat, but if you are looking for fish that are close to the bottom, it is an advantage to have a narrow cone. I have tried to illustrate this in the picture below here.

The illustrations illustrats how a wide cone creates "blind spots".

If we summarize these three factors then we can say that it is the combination of power, frequency and cone angle that determines how the transducer behaves. If you have the same effect and cone width, then it will be the frequency that determines how deep you reach. If you want to reach deeper with a high frequency, you must increase the effect (or the length of the string if you want).

Navico transducers

We start with a review of Navico's own transducers. I have asked Morten Blix to give an assessment of the transducers that he himself has tested. Morten focuses on deep-sea fishing, so it is natural that his comments are aimed at use for that purpose.

Standard HST-WSBL 83/200khz

This is the option for you who are only looking for a transducer for standard use, you are most interested in being able to read the depth and see fish in the water column under your boat. This transducer is suitable for fresh water and coastal fishing.

Standard HST-WSBL 50/200khz and 83/200khz

Power: 600W

Frequency: 83kw/200kw (medium and high chirp)

Cone angles: 22 degrees at 200khz and 52 degrees at 83khz

Depth range stated by Navico: 300m

Locates fish down to: approx. 100m

HDI 50/200/455/800khz and 83/200/455/800khz

Quite similar to the same application as HST-WSBL but also has Downscan, but not Sidescan. HDI 83/200/455 / 800khz has a wider cone than the 50 / 200khz version and is suitable for freshwater and coastal fishing, while HDI 50/200/455 / 800khz is suitable for deep sea fishing, but can also be used for freshwater fishing and coastal fishing. In addition, there is an HDI LH version (low and high chirp) and this can really be recommended for deep sea fishing, the best variant of the three.

HDI 50/200/455/800khz and 83/200/455/800khz

Power: 600W

Frequency: 50khz/200khz and 455/800khz, 83khz/200khz and 455/800khz LH (low/high chirp and 455/800khz

Cone angles: 50/200khz=12 degrees at 200khz and 29 degrees at 50khz. 83/200khz=22 degrees at 200khz and 52 degrees at 83khz.

Depth range stated by Navico: 900m(!)

Locates fish down to: approx. 100m

Morten's comment:

The best budget version from Navico for deep sea fishing in my opinion. It provides surprisingly good images and separations. I have also had good results even in deeper water. Big plus for the Fish Reval feature on my part.

TotalScan 83/200/455/800khz

This was the predessor of Active Imaging 3-1. Like the latter, it gives you both 2D sonar, downscan and sidescan in the same transducer. However, the performance is not as good as its successor. The transducer is suitable for fresh water and coastal fishing.

TotalScan 83/200/455/800khz.

Power: 600W

Frequency: Medium chirp og high chirp

Cone angles: 22 at high chirp, 52 at medium chirp

Depth range stated by Navico: 305m (chirp), 92m (downscan), 92m (sidescan)

Morten's comment:

Better suited in fresh water than for deep sea fishing in Norway if we look at the 2D part in my opinion. Absolutely great for learning the echo and the scanning part is good.

Active Imaging 3-1 83/200/455/800khz

This is the solution for you who want both 2D, Downscan and Sidescan without having to mount several different transducers on the boat. The transducer is suitable for fresh water and coastal fishing.

Active Imaging 3-1 83/200/455/800khz.

Power: 600W

Frequency: High og medium chirp

Cone angles: 22 at high chirp, 52 at medium chirp

Depth range stated by Navico: 45m ved 800khz, 90m ved 455khz

Locates fish down to: approx. 100m

Active Imaging 2-1 455/800khz

Same as Active Imaging 3-1, but this one only has downscan and sidescan. This is the solution for you who want a separate dedicated 2D transducer. Airmar TM150M is a good choice together with Acitve Imaging 2-1. The transducer is suitable for fresh water and coastal fishing.

Active Imaging 2-1 455/800khz.

Power: 600W

Frequency: 455khz og 800khz

Cone angles:

Depth range stated by Navico: 45m at 800khz, 90m at 455khz

Structurescan 3D 455khz

Dedicated transducer for Downscan, Sidescan and Structurescan 3D. Quite similar to the image from Active Imaging on Downscan and Sidescan, but operates only at 455khz frequency and has significantly better range. The transducer is suitable for fresh water and coastal fishing.

Structurescan 3D 455khz

Power: 300W

Frequency: 455khz

Cone angles: Almost 180 degrees for sidescan

Depth range stated by Navico: 100m depth and 200m to each side

Transducers from Airmar

Here we take a look at the transducers that are produced by Airmar, the ones we believe are most relevant here in Norway. We include the stated data from Airmar's website and also let Morten Blixt comment on the transducers he has tested himself. Note that Airmar's stated depth on the various transducers is very moderate, in reality several of these transducers will read the bottom much deeper than what Airmar itself states.

Airmar names its transducers in a specific way that makes it possible to understand what kind of transducer it is based on the name. The first part of the name indicates what kind of mounting the transducer is made for, the middle part contains the name/number of the transducer itself while the last part says what kind of frequency range the transducer operates in and whether it is a transducer that operates with extra wide cone.

TM=Transom Mount

B=Bronze (thru hull)

SS=Stainless Steel (thru hull)

L= Low chirp frequency range

M=Medium chirp frequency range

H=High chirp frequency range

W=Wide (refers to cone angle)


TM275LHW - TM=Transom Mount , 275=name/number for transducer, LH=Low and High (Low and high chirp) W=Wide.

It is worth noting that the same transducer is often found in several different mounting options. In addition, there are often several transducers who use one or more identical elements, despite different names/numbers. This means that the performance of these will be identical when using this element.

P66, B60, P79, B45

These are very popular entry-level transducers from Airmar that have been on the market for years. Suitable for fresh water and coastal fishing. The transducer do not have chirp, but operate at 50/200khz. The transducer is suitable for deep-sea fishing, coastal fishing and fresh water.

Airmar P66.

Power: 600w

Frequency: 50/200khz

Cone angles: 12 grader ved 200khz og 45 grader ved 50khz

Depth range stated by Airmar: 353m at 50khz and 206m at 200khz

Locates fish down to: approx. 100m

Morten's comment:

Probably very similar to Navico's variant (50/200khz HDI), but my opinion is that this is outdated and the Navico variant has chirp wich gives better pictures. The world has moved on.

TM150M, B150M and SS150M

This is definitely a favorite in the trolling community. The transducer provides a very good target separation (ie shows individual fish in a shoal) and is very suitable for pelagic fishing in fresh water and for coastal fishing.

Airmar TM150M.

Power: 300W

Frequency: 95-155khz (medium chirp)

Cone angles: 17-26 degrees (depending on choice of frequency)

Depth range stated by Airmar: 183m

Locates fish down to: approx. 100m

Morten's comment:

This one is good. Suitable for sport fishing and recreational fishing. In northern Norway, it finds cod in all depths at which it is fished. The limitation is only effect, but for people who want to get into real chirp with a limited budget, this does not fail. Even though the cone angle is wide, it is great for halibut fishing. As a halibut fisherman, I am most concerned about whether the halibut comes up to the bait when we use the echo sounder while fishing, and this one does the trick. My experience is that it gives so much for the money that you can recommend it every day for varied fishing between 0-100m, even though I myself have used it for deeper fishing. I have registered a bottom of 550m in Skjerstadfjorden with this, I have registered fish at 120-130m, but the area of use is not here. Otherwise, it has been full of praise also in the trolling community, and with good reason. But we must not forget that it is an affordable thoroughbred CHIRP with weak effect, so there are limitations. For deep fishing, this falls short.

B75H and SS75H

This transducer has a relatively narrow cone and is suitable for those who fish primarily in shallower waters (eg down to 120m) and want a transucer that provides very good images of bottom structure.

Airmar B75H.

Power: 300W

Frequency: 130-210khz (high chirp)

Cone angles: 9-15 degrees (depending on choice of frequency)

Depth range stated by Airmar: 214m

Morten's comment:

A slightly forgotten transducer in Norway, for much of the deep sea fishing that takes place at 5-100m depth, this is a transducer I want to highlight. The cone angle is perfect for details towards the bottom and the separation is beautiful. A recommendation for cod, halibut and coalfish fishing. If you have e.g. a TM150/B150M that has a wider cone angle and you want to upgrade your two channel echosounder, I'm sure this gives the most for your money if you fish mostly at depths 5-100m.

B75M and SS75M

This transducer has many similarities to the TM150M, but runs at 600w instead of 300w, which gives it more power and better performance than the TM150M. Suitable for coastal fishing and fresh water.

Airmar B75M.

Power: 600W

Frequency: 80-130khz (medium chirp)

Cone angles: 16-24 degrees (depends on choice of frequency)

Depth reange stated by Airmar: 274m

Morten's comment:

If you like the TM150M/B150M but have a little more money to spend, then this is the way to go. Here, the biggest difference will be between 50-110 meters against the little brother (TM150M). It has more muscle.

B175H and SS175H

Now we are talking about powerful transducers that have 1kwh effect. This transducer has a very narrow cone, which makes it well suited for seeing bottom structures and looking for fish near the bottom. Suitable for deep sea fishing, but can also be used for coastal fishing and fresh water.

Airmar B175H.

Power: 1kw

Frequency: 130-210khz

Cone angles: 6-10 degrees (depending on choice of requency)

Depth range stated by Airmar: 304m

Morten's comment:

Great for fishing near the bottom and where bottom structure is important. Works optimally down to about 200m. A little too narrow for e.g. drift fishing in my opinion, but definitely a score if you are looking for bottom structure and fish that are close to the bottom.

B175L and SS175L

This is a powerful transducer that with low chirp is well suited for deep sea fishing. However, it has a relatively wide cone, so if you fish mostly for fish that are close to the bottom or want to see the bottom structure, you should consider a transducer with a narrower cone.

Airmar B175M.

Power: 1kw

Frequency: 40-60khz

Cone angles: 21-32 degrees (depending on choice of frequency)

Depth range stated by Airmar: 762m

Morten's comment:

A necessity if the depths pass 200m, and you are looking for fish at these depths. It can in many cases be a good compromise for a multi-use transducer due to the wide cone.

TM185M, B175M and B285M

This transducer runs in the medium chirp frequency range and can be a good compromise for people who want a powerful transducer with high sensitivity. Probably best suited for pelagic fishing, i.e. to look for fish that swim pelagic. Suitable for freshwater and coastal fishing, but can also work for deep sea fishing down to a depth of 450-500m.


Power: 1kw

Frequency: 85-135khz

Cone angles: 11-16 degrees (depending on choice of frequency)

Depth range stated by Airmar: 457m

Morten's comment:

My safest choice for deep sea fishing. The cone makes it easier to find fish closer to the bottom but at the same time is wide enough tell a little about the quantities of fish. I have drawn fish at over 200 meters deep with this. When searching for fish you can use this down to about 200-220 meters, for bottom detections this stops at 500 meters ish. Personally, I think it gives much better details and separations than Low 1kw down to 150 meters, but after here it short against Low.

TM185HW and B175HW

This is the king of seas for transducers who are suitable for trolling and pelagic fishing, for most people. High power, high sensitivity and a cone angle that is well suited for looking for fish up in the water column. Suitable both in fresh water, for coastal fishing and for pelagic deep sea fishing.


Power: 1kw

Frequency: 85-135khz

Cone angles: 11-16 degrees (depending on choice of frequency)

Depth range stated by Airmar: 457m

Morten's comment:

Superb transducer that are mainly used for pelagic fishing. It separates well and draws beautiful arches. The sensitivity is excellent, the clarity you can get in the picture is impressive. In cod fishing in the winter, where much of the fish swims pelagically, and there are small amounts in layers, it is 100% reliable. Can also be used for halibut if the your interest is pelagic fishing and halibut fishing.

TM260 and B260

If you do deep drop fishing in deep water near the bottom, it is hard not to mention. It is still sold, but if you are looking for a transducer in this price segment now, you should also look at the successor, TM265LH or TM265M before you decide. Suitable for deep-sea fishing, especially if you fish near the bottom due to a relatively narrow cone, but can also be used in freshwater and for coastal fishing.


Power: 1kw

Frequency: 50/200khz

Cone angles: 6 degrees at 200khz, 19 degrees at 50khz

Depth stated by Airmar: 294m at 200khz, 800m at 50khz

Locates fish down to: approx. 500m using 50khz under optimal conditions.

Morten's comment:

This is really good and now replaced by a CHIRP variant. You get the best of both worlds is my opinion. At 200khz, I have experienced that it detects and separates fish down to 150-160 meters, that is good utilization of the narrow cone.


A good alternative if you go deep sea fishing in slightly shallower waters or do pelagic fishing or trolling in the sea.


Power: 1kw

Frequency: 50/200khz

Cone angles: 6 degrees at 200khz, 19 degrees at 50khz

Depth range stated by Airmar: 294m ved 200khz, 800m ved 50khz

Locates fish down to: approx. 150m during optimal conditions


This transducer has the same usage areas as TM260, but with chirp you have several options to fine-tune the frequency to what you are looking for. The very best choice for deep sea fishing if you fish mostly close to the bottom. Provides good reproduction of bottom structure and fish that are close to the bottom. Personally, I use low chirp when I fish in deep water, but when I fish shallower than 200m I go over to high chirp to be able to look for bottom structures and fish near the bottom. If you have an echo sounder that supports the display of 2 different frequencies at the same time, I recommend running both high and low chirp in the same screen layout.


Power: 1kw

Frequency: 50/200khz

Cone angles: 6 degrees at 200khz, 19 degrees at 50khz

Depth range stated by Airmar: 294m at 200khz, 800m at 50khz

Locates fish down to: approx. 500m using low chirp during optimal conditions. Locates fish down to approx. 200m using high chirp during optimal conditions.

TM275LHW / B275LHW

A very good transducer for pelagic deep sea fishing, perhaps the best you get for this purpose. However, I would not recommend it for deep sea fishermen who are looking for fish near the bottom and for bottom structures as the cone is too wide for this purpose.


Power: 1kw

Frequency: 46-65khz (low chirp) and 150-250khz (high chirp)

Cone angles: 16-25 degrees (low chirp) og 25 degrees (high chirp)

Depth range stated by Airmar: 914m

Locates fish down to: approx. 450m during optimal conditions

Morten's comment:

The low element has what is needed at greater depths. Detecting fish down to 250-300m in my experience. Combined with the clear and detailed high element that provides good opportunities to search for fish pelagically, it suits both leisure and professional users. To make the most of this I would have had two echo sounders or an S5100 to be able to chirp both independently.


If you want more from your transducer than just seeing how deep it is under the boat, you should think carefully before you shop. Are you going to fish in freshwater or saltwater, over shallow water or over deep water? Are you going to find fish that swim pelagically (freely in the water column) or fish that are close to the bottom? Is it important to see the bottom structure? These are questions you should ask yourself before buying a transducer.

Also remember that the ultimate all-round transducer suitable for all purposes does not exist. Choosing a transducer is always a compromise. This is the reason why some anglers choose to mount both 2 and 3 transducers on their boat. However, such a setup is very expensive and not something I would recommend if you are just a regular recreational fisherman. After all, it is not the transducer who catches the fish, it is you who do it. Experience, good maps, current conditions etc. are all factors that are decisive when it comes to successful fishing, an echo sounder is after all just an aid and not a decisive factor. It is worth keeping in mind when you decide whether to go for a transducer for NOK 2,500 or a donor for NOK 15,000!

I hope you found this review helpful! The content is based partly on own experiences, partly on input from Rolf and Morten and partly on data from Navico and Airmar's websites.

PS: If you want to make a comparison between different transducers, Simrad has a nice site for this purpose. You can find it by clicking here.

Best regards, Atle

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1 Comment

Hello. Great summary.

which transducer do you recommend when fishing for only snapper at depths up to 25m?

what Are your reasons for this choice?


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