Making Sense of Sensitivity
| Cheston Hammonds is a pro-staff member of
Lowrance Electronics from Louisville, KY. Recently, he
has provided demonstrations at regional boating and
outdoor shows; and frequently conducts GPS/depthfinder
seminars. A native of Hopkinsville, he considers Kentucky
and Barkley lakes home. Currently, Cheston competes in
the Fishers of Men National Tournament Trail, a Christian
oriented bass fishing organization. Making Sense of Sensitivity I can still remember a summer day back in the early 1970's when my father came home with a nearly brand new Ray Jefferson depth finder. We couldn't wait until the next Saturday to take it to the lake on our 14ft Starcraft aluminum V-bottom boat. Daylight came on Saturday to find us sitting in the middle of Barkley Lake turning the sensitivity up and down watching the wide "bottom" line appear and disappear. Little did we know that we were witnessing only the tip of the iceberg of what was to come in boating electronics. For the next twenty plus years, depthfinders continued to evolve with more power, more detail, more knobs and buttons, and bigger screens. Unfortunately, the skill level of many, if not most, fisherman lagged behind the capabilities of their equipment. To get the most out of a unit required studying and practicing the function and purpose of sensitivity, noise rejection, screen contrasts, chart speed,depth scale, and zoom; not to mention the period of replacing paper, styluses, belts, etc., etc., etc. And, that took away from valuable and never-enough fishing time. Those dedicated few who did learn the ropes enjoyed an untapped wealth of crappie, bass, walleye, lake trout, and many others. But, like too many others, most of us conceded to seeing the bottom, a few creek channels, and not much else. We didn't really "see" what we were seeing. To understand what a depth finder is seeing requires a basic understanding of what a unit is doing. And that begins with sensitivity. To understand sensitivity requires a joint discussion regarding transducers. While one brand of depthfinder may advertise a 38 degree transducer, or 40 degree, or 60 degree, that number is relative to the brand of unit and sensitivity settings. In other words, take it with a grain of salt (there are of course specific narrow cone transducers for exceptionally deep and/or commercial applications generally 8 to 18 degrees; not relative to this discussion). For example, a particular unit may come with a 60 degree cone transducer. That means 60 degrees at the maximum sensitivity setting in optimum water clarity. Think of a transducer as a flashlight hanging from the ceiling projecting light to the floor. The beam leaves the flashlight at a very wide degree of angle and shines in a circle on the floor. Some of the light shines on a chair, a table, toys on the floor, etc. It is easy to see that the light near the edge of the circle is not as bright as the light in the center of the circle. At least one company rates its cone angle at a ring within the circle where 50% of the sound returns. In our illustration, as we look away from the center of our circle of light it gets dimmer and dimmer until we reach a point where the light is only half as bright. That inner circle of brighter light would illustrate the cone rating of our flashlight. At the sensitivity setting used in our illustration above, any sound returning below 50% is filtered out and does not show on the depthfinder screen. When the sensitivity level is raised, weaker sounds outside the original coverage area (below 50%) are progressively accepted by the unit and shows on the screen. Also, as the sensitivity level is raised, weaker or smaller return signals within the original coverage area appear on the screen. This is why higher sensitivity settings show more fish and also more debris or clutter (take 2 aspirin and continue to the next paragraph). So, which setting is the right setting? That depends. It depends on the power and quality of the unit. It greatly depends on the clarity of the water. And, it depends on the depth. The power and quality of the unit establishes how strong the signal can be and how well it can accurately filter out unwanted noise. Water clarity makes a big difference in sensitivity. Very clear water allows for a moderate sensitivity setting while still detecting even a minor thermocline (yes, a correctly installed and adjusted unit can show a minor temperature changes). Conversely, dirty water requires a higher sensitivity setting to target detail and increases the irritating clutter. Targeting deep water structure generally requires greater sensitivity, especially in stained or dirty water. Salt and brackish water also requires a comparatively higher sensitivity setting (aspirin starting to take effect). While this analysis may seem confusing, the concept is simple. As a unit's sensitivity is elevated, a broader area and smaller details show on the screen. But, with a broader and stronger view comes more clutter and debris. The clearer the water, the less sensitivity needed to get accurate details. Until the last few years, getting quality detail from a depthfinder required a lot of manual tweaking and retweaking. Frankly, today's super powered, multifiltered, units can often be very effective in the "full-auto" mode. And in many models, the sensitivity can be adjusted without taking the unit out of auto mode. Still, it's critical to know what the unit is doing and why. Then, you can make it work for you. The results are more fish and less aspirin. And that makes sense. visit our website at http://www.blessingsinstone.com Your Christian source for inscribed tile and stone decor and gifts. |
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