Sounder Module Introduction
Sounder Modules are the component in a modular marine electronics network between the depth transducer and the vessel’s displays. They power and control the transducer and feed bottom profile data to the network. The displays can then present the bottom profile, the type of bottom, and the fish in the water column beneath the boat. They are indispensable for fishermen and are used by boaters to monitor the depth and bottom conditions.
Integrated Fishfinder vs. Sounder Module
Integrated Fishfinders are historically more common than Sounder Modules attached to displays. But the Sounder Module offers some advantages:
- Power. Sounder Modules are available with higher power than most integrated Fishfinders.
- Flexibility. You can select a Sounder module with the power you need, and large displays that fit your boat.
- Lower Noise. Since the Sounder Module can be mounted away from your other electronics, it is less susceptible to noise pickup.
How Do Sounder Modules Work?
The Sounder Module sends a high frequency signal to a transducer mounted on your boat. Each pulse sent to the transducer is called a “Ping”. Think of the Sounder Module as a radio and the transducer as a speaker. The transducer can be mounted on the boat’s transom, through the hull, or bonded to the inside of the hull.
This Ping is broadcast by the transducer and travels through the water. It is reflected off the bottom or anything in its path and travels back to the transducer. The transducer, after transmitting the pulse, listens for this tiny signal to return. In other words, the speaker is now a microphone. The received signal is sent back to the processing unit. Since the Sounder Module knows when the ping was sent, when the echo was received, and the speed of sound through water, it can calculate the depth. By analyzing the returned signal it can also display any fish or other items in the water column between the transducer and the bottom.
The display is independent of the sounder module, but must be compatible. Although most marine networks are based on Ethernet, they are actually proprietary. You cannot attach a Sounder Module from one vendor to another vendor’s network or Display.
Since the Sounder Module is separate from the display it can be mounted in a convenient location isolated from noise, and be as large as necessary for the power it supplies. You can also choose the Module appropriate for your needs. A modular network provides flexibility and a path for expansion.
The Sounder Module’s output power determines how deep you can read, assuming all else is equal. Remember that the transducer changes from transmitting a high power pulse to receiving a very small signal. So the Sounder Modules internal noise level is critical to preserving this signal. In other words, a well-designed, low-power Sounder Module can read deeper and detect more fish than a poorly designed, high power Sounder Module. Since the Module is independent of the display it can be mounted away from noise sources.
Manufacturers use different methods and units to report output power. Some use Watts RMS, others Watts Peak–to-Peak. Since the actual depth you can read depends upon the quality of the water beneath the boat, your transducer, and your installation, manufacturers do not quote the maximum depth their Sounder Modules can read.
The Sounder Modules ability to ping at many times per second will affect the apparent resolution. A low ping rate can be an indication of a low-cost design.
More About Transducers
Transducers are designed to work at different frequencies. Generally, higher frequencies are used in shallower water, and lower frequencies in deeper water. When you review the Sounder Module data, you will see that they support 200 kHz for shallow water and 50 kHz, 38 kHz or 28 kHz for deep water. Lower frequency transducers cost more than higher frequency transducers.
The transducer design also yields the beam angle. The wider the beam angle, the greater the amount of water covered by each ping. Greater beam angle lets you search more area for fish but also means lower resolution of the bottom profile directly beneath the boat. Higher resolution (lower beam angle) transducers are generally used in shallow water, and greater coverage (wide beam angle) transducers are generally used in deeper water.
As mentioned, transducers can be mounted in several ways-
Attaching the transducer directly to your boat’s transom is the most common method of mounting smaller transducers. Transom mount transducers can combine depth, speed and temperature sensors.
There is a wide variety of high quality, high performance, and high power through-hull transducers available, but they require that you drill a hole in your hull. If you are not comfortable doing this, get professional installation assistance. Through-hull transducers can combine depth, speed and temperature sensors.
Similar to through-hull, there is a wide variety of high quality, high performance, high power through in-hull transducers available. They don’t require a hole in your hull, but power is lost when the pulse travels through the hull. You must choose the in-hull location very carefully to minimize this loss. Again, if you are not comfortable doing this, get professional help. In-hull transducers can combine depth and temperature sensors, but not speed. Since many boaters obtain the speed reading from GPS anyway, this is usually not a concern.
Transducers come with very detailed installation instructions. Be careful to follow these directions carefully during the installation.
Transducers cannot read through air bubbles, so any turbulence caused by irregularities on the boat’s hull will adversely affect your Sounder Module’s performance. Keep the transducer away from the props, not behind any through-hull fittings or behind any steps in the hull. If you find that your Sounder Module works well when the boat is not moving but does not work well when underway, the installation is suspect.
Choosing Your Sounder Module
If you are simply cruising, and not looking for fish, any Sounder Module that can work at the depths you cruise should work well. Check the Comparison Guide carefully, pick one that has the features you need, install it and the transducer carefully, and enjoy.
If you will be fishing, check the specs for model that has the features that are important to you. Chose a model that supports the frequencies appropriate to your needs and that has a suitable transducer available.
Many features are available on Sounder Modules. Not all of them will be important to you. Most boaters simply use the automatic mode on their Sounder Module and are completely happy. Others want more sophisticated control. These features include:
- Depth Range Settings: automatically adjusts the range to the maximum depth being read
- Frequencies: automatically adjusts transducer frequency for optimum depth results
- Power: automatically adjusts the Sounder Module’s Gain
- Color Gain: adjusts the displayed colors to indicate depth
- Zoom: magnifies the bottom detail
- A-Scope: shows the detail directly beneath the boat
- Bottom Lock: shows the data from the bottom up
- Scroll Speed: adjusts the rate the data scrolls across the Sounder Module display
- Alarms: for Shallow Water, Deep Water, Fish detected, and Temperature
- TVG (Time Variable Gain) or STC (Sensitivity Time Control): adjust the gain for the water depth
- Interference Rejection: minimizes interference from other Sounder Modules or noise sources
- Target Depth ID: shows the individual fish’s depth
- Metric / US Measurements: the ability to display depth in feet or meters
- Depth Offset: adjusts for the distance below water of your transducer