1 M or m â prefix designating a number in thousands (not to be confused with SI prefix M for mega-or m for milli).
There are two types commonly referred to as: 'Shallow' and 'Deep' water. The differences are not only in the Frequency but also in the Beam Width and they are as follows: 'Shallow' water HST-WSBL 106-72 Transducer will operate on 2 frequencies on the HDS models: 200 (20Â°) & 83KHz (60Â°). 'Deep' water HST-DFSBL 106-77 Transducer will operate on 2 frequencies on the HDS models: 200KHz (12Â°) & 50KHz (35Â°).
The cutoff frequency of Earth's planet-sized natural waveguide is around 3 kHz -- that's the frequency where half a wavelength will fit between our planet's surface and the bottom of the ionosphere. Waves with frequencies above the cutoff can travel through the waveguide, but lower frequency waves cannot.