WORK-IN-PROGRESS
Introduction
We are often asked why a fishfinder/sounder/sonar might be producing a poor-quality image, or not achieving the depth performance that the owner expects. It might be that the sounder or transducer are faulty but usually they're not, and simply replacing hardware like-with-like usually won't fix the problem (unless the cause is incorrect setup on the sounder being replaced.) Here are some of the potential problems, causes and solutions distilled from more than a dozen years of successfully diagnosing these problems.
First steps
First of all, we need to ask a couple of simple questions about the problem:
What a sounder needs in order to perform well - some background
All sounders, of whatever brand, require as large as possible a difference in the signal level (voltage on the transducer cable) and the background noise level. Every electronic system contains noise (unwanted randomly fluctuating voltages in parts of the circuit) to some degree, and both the sea and boats are relatively noisy places so there will always be a background noise level: the sounder needs to be able to clearly hear the echoes from fish and the bottom above this noise. If you imagine the amount of energy contained in a sound echo coming back from a single fish 100m down, or the bottom 500m or more down, and then picture that echo moving the transducer element and that movement then inducing a voltage onto the signal cable, I think that gives a bit of an idea of the low level of the electrical signals on the transducer cables, which can be less than 0.00001V. It doesn't take a lot of either sound or electrical noise to start to cause problems.
The larger the difference in signal level between the wanted echoes and the noise (what's known as the signal-to-noise ratio, SNR), the better the sounder image.
A low SNR will always lead to a poor image:
When a sounder isn't performing to the level it was designed to, then, the cause is either lower than normal signal level or higher than normal noise. Because what matters for the sounder is SNR rather than simply overall signal level, low signal and high noise have exactly the same effect. It's like trying to have a conversation in a busy bar or a good party: it can be hard for your to hear what your mate (or date) is saying clearly even when they're yelling. By repetition the general idea of what they're saying might come across (the bottom echo), but the fine details (fish) is lost in the noise.
Do you have low signal or high noise?
At the start of this guide we advised always using Auto sensitivity for normal use on any modern sounder. This is because our automatic sensitivity algorithms do a great job, in normal conditions, of adjusting to changing conditions from one moment to the next in order to give a clear, clean, easy-to-read picture. The problem with this is that this constant auto adjustment masks the actual signal levels, so if you get a poor result (a cluttered image with a weak bottom mark for example) then you can't see whether that's because the signal level is low (causing the system to increase the Gain in order to still show a weak bottom echo, and also inadvertently show background noise as well) or because the background noise is high (causing the system to drop the Gain in order to try to keep the noise off the screen, and inadvertently hiding all but the strongest bottom echo at the same time.)
What we need to do instead is use all-Manual setup.
Before we start: you should never do this for normal day-to-day use (unless you are an expert charter skipper who spends 200+ days a year on the water), but it's the only way to see for sure whether the cause of your problem is low signal level or high noise.
Here are recommended levels for diagnosing problems in all current (late 2019) sounder models. If you have something older, see the appendix at the bottom for the right settings for your system). XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.
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Introduction
We are often asked why a fishfinder/sounder/sonar might be producing a poor-quality image, or not achieving the depth performance that the owner expects. It might be that the sounder or transducer are faulty but usually they're not, and simply replacing hardware like-with-like usually won't fix the problem (unless the cause is incorrect setup on the sounder being replaced.) Here are some of the potential problems, causes and solutions distilled from more than a dozen years of successfully diagnosing these problems.
First steps
First of all, we need to ask a couple of simple questions about the problem:
- Does the problem still happen when the sounder is in its default/auto setup?
Try doing a sounder reset through the display's menu, going to Sensitivity Settings and All to Auto, and making sure that Range is on Auto too. How does that change things? A lot of the time image problems are just setup so going back to defaults is a good sanity check.
If the sounder is constantly cycling through a range of depth scales which are significantly different from the current water depth then it's in bottom search mode, where it's looking at various ranges to reacquire the bottom lock in Auto Range:
- Is the sounder operating within its expected capabilities (range)?
Not all sounders and transducers are equal. Some are aimed at high detail in shallow water, some at value-for-money, and some at offshore performance. Do you have the right system for the depth of water you want to fish in? The below gives example absolute maximum depths for some Raymarine sounder technology types, and you can find transducer-specific information by searching for your transducer type on Airmar's cross-reference, clicking through the Description column to the product page and then opening the transducer's Brochure link (Airmar make most of the transducers we use). I would suggest halving these numbers for depths where you'll get a nice image for fishing as opposed to just seeing a thin bottom trace:
If you're getting nowhere close to the expected level of performance for the sounder and transducer that you have, read on.
What a sounder needs in order to perform well - some background
All sounders, of whatever brand, require as large as possible a difference in the signal level (voltage on the transducer cable) and the background noise level. Every electronic system contains noise (unwanted randomly fluctuating voltages in parts of the circuit) to some degree, and both the sea and boats are relatively noisy places so there will always be a background noise level: the sounder needs to be able to clearly hear the echoes from fish and the bottom above this noise. If you imagine the amount of energy contained in a sound echo coming back from a single fish 100m down, or the bottom 500m or more down, and then picture that echo moving the transducer element and that movement then inducing a voltage onto the signal cable, I think that gives a bit of an idea of the low level of the electrical signals on the transducer cables, which can be less than 0.00001V. It doesn't take a lot of either sound or electrical noise to start to cause problems.
The larger the difference in signal level between the wanted echoes and the noise (what's known as the signal-to-noise ratio, SNR), the better the sounder image.
A low SNR will always lead to a poor image:
- smaller/weaker targets being missed
- excessive clutter in the water column
- failure to track the bottom in deeper water (when the signal levels are lower)
- failure to track the bottom at higher speeds (when the noise levels are higher)
- ...
When a sounder isn't performing to the level it was designed to, then, the cause is either lower than normal signal level or higher than normal noise. Because what matters for the sounder is SNR rather than simply overall signal level, low signal and high noise have exactly the same effect. It's like trying to have a conversation in a busy bar or a good party: it can be hard for your to hear what your mate (or date) is saying clearly even when they're yelling. By repetition the general idea of what they're saying might come across (the bottom echo), but the fine details (fish) is lost in the noise.
Do you have low signal or high noise?
At the start of this guide we advised always using Auto sensitivity for normal use on any modern sounder. This is because our automatic sensitivity algorithms do a great job, in normal conditions, of adjusting to changing conditions from one moment to the next in order to give a clear, clean, easy-to-read picture. The problem with this is that this constant auto adjustment masks the actual signal levels, so if you get a poor result (a cluttered image with a weak bottom mark for example) then you can't see whether that's because the signal level is low (causing the system to increase the Gain in order to still show a weak bottom echo, and also inadvertently show background noise as well) or because the background noise is high (causing the system to drop the Gain in order to try to keep the noise off the screen, and inadvertently hiding all but the strongest bottom echo at the same time.)
What we need to do instead is use all-Manual setup.
Before we start: you should never do this for normal day-to-day use (unless you are an expert charter skipper who spends 200+ days a year on the water), but it's the only way to see for sure whether the cause of your problem is low signal level or high noise.
Here are recommended levels for diagnosing problems in all current (late 2019) sounder models. If you have something older, see the appendix at the bottom for the right settings for your system). XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.
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From the Home screen:
- First, please set up a sounder page with at least two sounder channels displayed (for example, if you have a CP470, a two-way split with both Low Chirp and High Chirp at the same time would be great. If you have an RV system, Sonar and Downvision would be good. The idea is to compare the results from the two channels (frequencies.)
From your newly-configured fishfinder page, Menu > Settings > Page settings > Edit data overlays - Please set up overlays for SOG, Vessel Position and Depth (so that we can see how fast you were going and from a chart, what the correct depth ought to have been compared to what the system is measuring)
In Adjust Sensitivity, please set exactly the same Sensitivity and display configuration on each sounder channel, as below: - Gain: Manual, 65% (if you only see -50% to +50% you're still in Auto, make sure you untick the Auto box at the bottom of the gain slider)
- Intensity (Contrast, Colour Gain): Manual, 15% (again, make sure you're not still in Auto)
- Surface Filter (Noise Filter, TVG): Manual, 0%
In Menu > Settings > Sonar Display: - A-Scope: Right
- Bottom Lock: Off
- White Line: Off
- Bottom Fill: Off
- Colour Threshold: 100%
In Menu > Settings > Sounder > Ping Control: - Power Mode: 100%
If you have the right Sensitivity setup then your sounder picture ought to look something roughly like this:
Once you have the system set up correctly, it's time to go for a run and take some screenshots.. Please take lots of images on the water, ideally in the conditions you normally use it. If the sounder normally works ok when going slowly and the problem only occurs when going faster, please take images at a range of speeds from idle/engine-off up to normal cruising speed. Please use exactly the same setup (above) throughout so that we can directly compare images.
Common causes of poor performance
Whats_wrong_with_Classic_White.png (Size: 221.18 KB / Downloads: 3)
Depth_range_comparison-2018.png (Size: 193.38 KB / Downloads: 3)
IMG_1970-cropped.jpg (Size: 158.31 KB / Downloads: 3)
Auto-In_hull_through_cored_hull-scaled.jpg (Size: 156.53 KB / Downloads: 4)