Scan depth
the
maximum depth at which the sonar locator (see "Type") is able to operate effectively — in other words, how deep underwater the device is able to "see".
It is worth choosing an echo sounder according to this parameter, taking into account the actual depths at which it is planned to be used. Of course, this does not place a certain margin, but within reasonable limits (15-20%, less). For example, it hardly makes sense to specially take a model with a scanning depth of 200 m for a lake with pits of 30-40 m — such devices are expensive, while there will simply be nowhere to realize their full potential, and a powerful signal can also scare away the fish. But for marine or oceanic applications, a depth of a kilometer or more may be required; the most advanced echo sounders are quite capable of providing it.
Radiation frequency
The frequency(s) of radiation at which the device with the echo sounder function is capable of operating (see "Type").
The higher the frequency, the better the resolution and noise immunity of the device, the better it is suitable for working at high speeds, but the range and coverage suffer. Low-frequency (up to 200 kHz) sensors, on the contrary, "reach" deep and cover a wide angle, but are sensitive to interference and do not work well with fine terrain details and small objects. Accordingly, the first option is considered optimal for shallow depths and high-precision topographic measurements, while the second option is for deep water bodies, as well as for searching for fish and other tasks that require wide coverage.
Models with several radiation beams (see “Number of radiation beams”) often provide different frequencies for individual beams, which allows you to combine the advantages of different options in one device and compensate for their disadvantages.
Total radiation angle
The angle covered during operation by the transducer of the echo sounder (or an instrument with such a function, see "Type").
Technically, the
wider the angle, the better the echo sounder is suitable for finding fish and other underwater objects, because. a large coverage area reduces the likelihood of missing prey. On the other hand, to accurately determine the depth, the beam must be as narrow as possible. This is due to the fact that the depth is determined by the maximum protruding point that fell under the beam; thus, if the size of the hole at the bottom is smaller than the spot from the beam, the device simply will not notice this hole. The smaller the angle (and, accordingly, the projection of the beam onto the bottom) — the less likely this phenomenon is.
However, it should be taken into account that all of the above is unambiguously true only for single-beam echo sounders (see "Number of radiation beams"). But multibeam models, usually, combine beams of different widths, thus compensating for the shortcomings of narrow and wide angles. In them, the total radiation angle describes only the dimensions of the space covered by the device.
CHIRP Technology
Sonar support
for CHIRP technology.
The meaning of this technology is to use the echo sounder at the same time several frequencies. In other words, each pulse consists of several signals, each at its own frequency. According to the creators, this allows you to improve image quality, increase detail (including at great depth and high speed) and at the same time reduce the level of noise and other interference on the screen compared to single-frequency sonars. However, models with CHIRP are noticeably more expensive.
Side scan
Availability of the
side scan function in the echo sounder.
Devices with this feature are able to "see" the bottom and underwater objects not only directly under the vessel, but also on the sides of it. Note that different models can differ markedly in the angle of coverage of the side space. However, the side scan anyway expands the capabilities of the echo sounder and provides additional features compared to the usual bottom one.
Bottom scan
Echosounder support for special
bottom scanning technologies.
"Viewing" the space under the bottom of the boat is a classic sonar mode and is supported by all models by definition. However, in normal mode, the sound beam propagates in the form of a cone, and the area of the bottom that falls under the beam has the shape of a circle. This degrades the accuracy and does not allow you to achieve a detailed image. Thus, many echo sounder manufacturers have developed special technologies to improve the performance of the instrument; Lowrance has DSI, Hummingbird has DI, Garmin has DownVü. The nuances of these technologies may differ, but the basic principle of operation is the same: the echo sounder beam narrows and goes not in a cone, but in a strip. Due to this, the resolution of the device is significantly increased; at shallow depths, such an echo sounder can “draw” even individual stalks of algae, making it possible to distinguish underwater thickets from schools of fish. Some models combine a narrow beam with a classic cone to further expand detection capabilities. However, such devices are expensive.
Number of routes
The maximum number of tracks that can be stored in the chartplotter's memory at one time.
If you have to regularly travel on fixed routes, it is much more convenient to memorize these routes once and then select the desired option than to reprogram the navigator each time. Modern devices can store several tens or even hundreds of routes; the larger this number, the less often you have to free up memory for new routes.
