Surface water temp: ..... Yes.

Speed/distance log: ....... Optional (requires optional speed sensor).

NOTICE!

The storage temperature range for your unit is from -4 degrees to +167 degrees Fahrenheit (-20 degrees to +75 degrees Celsius). Ex- tended storage in temperatures higher or lower than specified will damage the liquid crystal display in your unit. This type of damage is not covered by the warranty. For more information contact the factory's Customer Service Department. The phone numbers are listed on the last page.

How Sonar Works

Sonar has been around since the 1940s, so if you already know how it works, skip ahead to the next segment on the typographical conventions used in this manual. But, if you have never owned a sonar fish finder, this segment will explain the under water basics.

Sonar is an abbreviation for SOund NAvigation and Ranging, a tech- nology developed during World War II for tracking enemy submarines. A sonar consists of a transmitter, transducer, receiver and display. In simple terms, here's how it finds the bottom and the fish:

The transmitter emits an electrical impulse which the transducer con- verts into a sound wave and sends into the water. The sound frequency can't be heard by humans or fish. The sound wave strikes an object (fish, structure, bottom) and bounces back to the transducer which con- verts the sound back into an electrical signal.

The receiver amplifies this return signal, or echo, and sends it to the display where an image of the object appears on the scrolling sonar chart. The sonar's microprocessor calculates the time lapse between the transmitted signal and echo return to determine the distance to the object. The whole process repeats itself several times each second.

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Eagle Electronics 640c manual How Sonar Works
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640c specifications

Eagle Electronics has made a significant mark in the world of marine electronics with its innovative and reliable products, notably the Eagle Electronics 640C, 640cDF, and the 640c models. These devices are designed for anglers and navigators who seek advanced functionality combined with user-friendly operation.

The Eagle Electronics 640C is a high-performance fish finder that is primarily admired for its vibrant display and precise mapping capabilities. Equipped with a 640x480 pixel, full-color LCD screen, it provides crystal-clear visibility even in bright sunlight. This device uses advanced sonar technology to offer detailed underwater images, allowing users to locate fish with remarkable accuracy. The high-resolution graphics enhance the experience while providing an intuitive interface for easy navigation through its various features.

The 640cDF, a variant of the 640C, elevates the standard fish finder experience by incorporating dual-frequency sonar capabilities. This model operates on both 200 kHz and 83 kHz frequencies, allowing users to switch between narrow and wide beams based on their fishing needs. The dual-frequency technology provides a more comprehensive view of the underwater environment, making it easier to identify different types of fish and underwater structures. Additionally, the 640cDF boasts temperature sensing capabilities, giving anglers valuable data regarding water conditions that can influence fish behavior.

All models in the Eagle 640 series feature built-in GPS navigation. The integrated GPS provides a reliable mapping system that allows users to mark waypoints and create routes, significantly improving navigation efficiency. This technology is vital for those who engage in long-distance fishing trips or travel in unfamiliar waters. The GPS functionality, combined with the sonar capabilities, makes these devices essential tools for successful fishing excursions.

Furthermore, the Eagle 640 series devices come equipped with customizable display options, allowing users to tailor the information presented based on their preferences. The intuitive menu system simplifies the navigation of the device's various features, empowering users to quickly access critical data without unnecessary complications.

In summary, the Eagle Electronics 640C, 640cDF, and the 640c represent a blend of cutting-edge technology and user-centric design in the marine electronics space. With features such as high-resolution displays, dual-frequency sonar, built-in GPS navigation, and customizable settings, these devices enhance the fishing experience, making them invaluable assets for anglers and navigators alike.
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