Garmin Fishfinder 250 Owner's Manual

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Garmin Fishfinder 250 Owner's Manual Manual pdf 32 page image

24On the Water Transducer CoverageThe area covered by the transmitted sound waves is determined by the cone angle of the transducerand the water depth. Cone angles may vary between different types of transducers. For example, a 50kHzfrequency may provide a “wide” 40° cone angle, with a coverage width that is approximately 2/3 of the waterdepth. As shown in the diagram on the left, the 40° cone angle (50kHz frequency) approximately covers thearea of a 20 foot diameter circle at a 30 foot depth. A 200kHz frequency may provide a “narrow” 10° coneangle, with a coverage width that is approximately 2/10 of the water depth. As shown, the 10° cone angle(200kHz frequency) approximately covers the area of a 6 foot diameter circle at a 30 foot depth.When using the Fishfinder 250/250C in ‘Dual’ frequency mode, the unit alternately transmits 50kHzand 200kHz signals and combines the information. The ‘Dual’ frequency capability of the Fishfinder 250/250C allows the user to have a large coverage area and still retain good bottom resolution. When in ‘Dual’frequency mode the unit uses the narrow cone angle (200kHz) to display detailed bottom information,keeping “Dead Zones” to a minimum, and the wide cone angle (50kHz) for the large coverage area.Fish returns from the wide and narrow beams appear differently on the display. The wide beam tends toshow longer fish returns than the narrow beam, as shown in the diagram below.Wide Cone AngleTransducer Coverage200kHz - 10˚ Cone Angle72" coverage at 30'50kHz - 40˚ Cone Angle20' coverage at 30'Narrow Cone Angle