Here's some information that was really interesting about Humminbird Sonar Technology...

Digital Sonar - An Explanation

Sonar by its very nature uses an "analog" sound wave that is transmitted into the water by the fishfinder transmitter. These sound waves travel into the water on a carrier frequency such as 200kHz. These sound waves echo off the bottom, fish, and structure creating many varying sonar echoes that return back to the receiver on the analog frequency. This analog signal is then converted to digital within the fishfinder by virtually all marine electronics companies - the differences lie in what point within the sonar system the conversion takes place. Those promoting "digital" sonar convert these analog signals to digital within a sonar receiver itself. Humminbird converts analog signals using the analog to digital capability of the on-board microprocessor. Therefore, Humminbird offers digital technology, however the conversion from analog to digital just occurs differently that what is being promoted by others. It is interesting to note that Humminbird has been converting analog to digital in this manner since 1989.

Infinite Variable Bandwidths

Further benefits of units marketed as "digital" sonar include technology such as adaptive transmitters, and "virtually" infinite variable bandwidths. It is important for the consumer to know that these benefits are not limited to the methodology of the so called "digital" sonar products. If fact these and other techniques are central to Humminbird's Professional Grade Sonar. Humminbird transmitter design offers adaptive technology that modulates power and pulse width based on conditions.

Additionally, our receiver offers variable bandwidth and wide 90db dynamic range to hear both high and low intensity signals simultaneously. Another key benefit touted by marketers of "digital" sonar is the use of filtering algorithms in their design to remove unwanted noise and clutter. The use of filtering techniques produces results counter to the desires of all anglers, since these "intelligent" algorithms actually remove information that is important to the angler - such as detail in structure and fish. This is clearly evident when comparing on-water sonar images from the "digital" products to the same structure when viewed by a Humminbird product.

Guess Humminbird has been Digital...long before Digital was a cool buzz word...And Broad Range of Listening to Sonar Returns.