Dual Frequency For Complete Coverage

Most non-commercial fish finders are high frequency models that operate at around 200 KHZ. The primary advantage of high frequency is in the definition or precision of read-outs, which identify individual fish and structure.

The problem is that high frequency sound waves degrade in saltwater and deep water through energy absorption. Also, cone angles on high frequency units tend to be narrow and more focused, reducing the viewing area under the vessel especially in shallow water.

The answer to the above problem is a dual frequency fish finder. Dual frequency operation allows two frequencies and two cone angles on the same system. 50 KHZ and 200 KHZ are commonly used low and high frequencies. In this way, fishermen can view closer objects in high detail while also viewing farther objects in low detail.

Consider how interesting signals could be observed from a distance on low frequency and then observed more accurately on high frequency once the boat has moved over the objects.

Variations on the dual frequency idea include using multiple cone angles as in the case of 3D fish finders, or user adjustable frequencies. Side view fish finder capability is generally found in high-end commercial fishing boats, which detect targets without being directly above them.

Quite simply instead of generating a single cone in one frequency, the transducer generates two cones in two different frequencies. The inner cone with the smaller cone angle operates at high frequency and is better for fine detail. The outer cone operates at low frequency and is better for wider distances. Fish detected by the outer cone may be displayed as hollow, lighter, or different color images, depending on the model.

Dual frequency depth finders, although expensive, are favored by boat fishermen who claim that they see fish they would previously have missed. They also enjoy the flexibility of freshwater and saltwater functionality.

According to Lowrance® LCX104C user manuals 80% of fishing needs can be meet by a 200 KHZ unit using a 12-degree cone angle (beam). The other 20% of usage is in saltwater from 300 – 500 feet or more, and by downrigger users who want to know where their baits are located. Presumably, because it is the Lowrance default angle, the optimal cone angle is 20 degrees on single frequency 200 KHZ units.