User manual LOWRANCE 1240A

[. . . ] Using a 3 3/8" hole saw, drill the display mounting hole. The display's bezel will overlap the hole by 5/16", hiding minor chipping which may occur when drilling the hole in fiberglass. Now drill the hole for the control. MAKE CERTAIN THAT ALL HOLES ARE DRILLED PERPENDICULAR TO THE MOUNTING SURFACE AND NOT AT AN ANGLE. A "U" bracket is supplied to hold the sonar to the dash. Place it over the studs on the back of the unit and secure it using the nylon wing nuts provided. [. . . ] If it does, the present water depth is the depth shown plus 100 feet. If the signal travels around the dial two times, the water depth is the depth shown plus 200 feet. SENSITIVITY Vary the sensitivity by rotating the small knob. It works similarly to the volume control on a radio. Turned fully counterclockwise, it's at minimum and the only signal that will appear on the dial, (unless it's in extremely shallow water) will be the constant surface signal at "0". Turning the knob clockwise will increase the receiver sensitivity and weaker echoes from deeper water shows on the dial. For example, if you are in 10 feet of water and the sensitivity control is at minimum, you will see only the "0" signal. As you turn up the sensitivity, a signal appears at 10 feet on the dial. As it's turned up more, this signal will get wider and other smaller signals from fish (if present) appear between 0 and 10 feet. The bottom signal gets wider because you are seeing more bottom area. Remember that the true depth is always the shallowest edge of the bottom signal, NOT the middle. As you turn the sensitivity up more, another signal appears at 20 feet on the dial, double the depth of the first signal. It's caused by the sound waves hitting bottom, bouncing back, hitting the surface of the water and then bouncing down to the bottom and back again. These signals have travelled double the actual depth. Always set the sensitivity to return a steady bottom signal, regardless of depth. To show fish, adjust the sensitivity to show a second bottom signal, when possible. SUPPRESSION Use suppression to reduce or eliminate false flashes on the dial caused by electrical interference or cavitation on the transducer. With the small knob pushed in, suppression is at minimum. This is the normal position for trolling as it gives the highest resolution (ability of the sonar to separate targets such as fish that are close together or near the bottom). To switch to high suppression, pull out the small knob. The knob in the "pulled-out" position gives the best interference rejection which is usually required when operating at speed. Because of the type of suppression circuity used by Lowrance, the unit's sensitivity is not affected. [. . . ] If you're in the United States and you have questions, please contact the Factory Customer Service Department using our toll-free number listed below. You must send the unit to the factory for warranty service or repair. Please call the factory before sending the unit. You will be asked for your unit's serial number. [. . . ]