Toronto Fishing Forum

看了一下介绍， 好像有1 个 波段 或者2个波段 ， 另外覆盖角度也有区别， 有些只有10-30 度， 是不是太小/窄了？

Most sonar units today operate at 83 kHz - 200 kHz (kilohertz) and there are advantages to each frequency, but for almost all freshwater applications and most saltwater applications, 192 or 200 kHz is the best choice. It gives the best detail, works best in shallow water and at speed, and typically shows less "noise" and undesired echoes. Target definition is also better with these higher frequencies. This is the ability to display two fish as two separate echoes instead of one "blob" on the screen.

There are some applications where a 83 kHz frequency is best. Typically, a 83 kHz sonar (under the same conditions and power) can penetrate water to deeper depths than higher frequencies. This is due to water's natural ability to absorb sound waves. The rate of absorption is greater for higher frequency sound than it is for lower frequencies. Therefore, you'll generally find 83 kHz used in deeper saltwater applications. Also, 50 kHz transducers typically have wider coverage angles than 192 or 200 kHz transducers. This characteristic makes them useful in tracking multiple downriggers. Thus, even when these downriggers are in relatively shallow depths,83 kHz is preferred by many fishermen. In summary, the differences between these frequencies are:

192 or 200 kHz

* Shallower depths
* Narrow cone angle
* Better definition and
target separation
* Less noise susceptibility


83 kHz
* Deeper depths
* Wide cone angle
* Less definition and
target separation
* More noise susceptibility

When operating a SONAR in water with a depth of only 20-feet, the portion of the bottom being scanned is typically rather small. SONAR transducers are specified with a particular cone angle, which is an expression of the sensitivity of the transducer with respect to signals arriving off-axis. While usually not explicitly stated, the angle measurement probably refers to an off-axis orientation at which the sensitivity decreases below a particular threshold. The threshold is generally not stated, either. We can assume the decrease in sensitivity must be fairly significant, at least enough to reduce detection of echoes below the point of usability.
A LOWRANCE 200-kHz SKIMMER transducer for an HDS unit with an 83 and 200-kHz rating is specified to have a cone angle of 120-degrees in the 83-kHz mode. This is by far the widest cone angle rating that I can recall for a SONAR transducer.

If operating in 20-feet of water, a transducer with a cone angle of 120-degrees would cover a width of the bottom of about

2 x 20-feet x tan60 = 68-feet

In contrast, if using the high frequency transducer, the cone angle will be much smaller, perhaps no more than 30-degrees. In 20-feet of water the depth of the bottom covered is only

2 x 20-feet x tan30 = 23-feet

好贴！学习了。

物理专业的人，对此的认识是显而易见的。要是有变频的就好了。。。。。。。

元帅学问就是大.码这么多字,辛苦了.哈哈,看错了不是元帅.元帅大作,何时问世?