Offered by a host of marine electronics brands, chirp systems operate in much the same way as old-school fish finders but transmit a wide band of frequencies at once versus a single frequency with a traditional system. Then digital signal processing analyzes the chirp returns to paint color images of the underwater world that are very well-defined. There’s also less screen clutter than with fish finders of the past. A wide range of frequency bands, measured in kilohertz, are available for chirp systems. Generally speaking, the greater the water depth, the lower the frequency band is needed, though there are other factors such as power to consider. All things being equal, a high-frequency band of say 150 to 250 kHz, for instance, is good for depths to about 600 feet, while a low-frequency band of 28 to 40 kHz may be needed to read at extreme depths of 3,000 feet or more. Medium-frequency bands of around 85 to 165 kHz provide a compromise for both shallow and deep waters.