Choosing A Frequency - Raymarine L470 Instruction Manual

Choosing a Frequency

We said that the FishFinder uses sound waves to "see" through the water
under the boat. The "frequency" is a measure of how fast the sound
waves change or "vibrate." The FishFinder uses sound waves with two
different frequencies – 50 kHz and 200 kHz. Raymarine uses these two
frequencies because each is better for a particular purpose:
50 kHz frequency
• Scans a wide area
• Penetrates water well, good for deep water
200 kHz frequency
• Scans a narrower area, but produces a more detailed view
• Good for seeing fish near the bottom or fish close together
• Better for use in very shallow water
"Dual" frequency (both 50 kHz and 200 kHz at once)
• Has the advantages of both frequencies
• Good depth penetration
• Good detail in display
• Using the "Dual 50 kHz" setting, the display is produced using the
signal from the 50 kHz beam, with additional information from the 200
kHz beam.
• Using the "Dual 200 kHz" setting, the display is produced using the
signal from the 200 kHz beam, with additional information from the 50
kHz beam.
If you are using one of the dual frequency settings, you can get some
useful information from the fish symbols. If the fish is spotted by the
narrow 200 kHz beam, the fish symbol will be black or filled-in. If a fish is
detected by the wide 50 kHz beam, the symbol will be hollow.
When the unit is first turned on, it is set to use the Auto frequency feature.
When set this way, the unit begins by using the 200 kHz frequency. If the
bottom depth increases to more than 250 feet (or 50 fathoms or 80 meters),
the unit will automatically switch to the 50 kHz frequency. If the unit cannot
find the bottom, it will try both the 200 kHz and the 50 kHz frequencies.
The unit will then use the frequency which finds the bottom first.
Operating Instructions
37