Re: FOR snapperbait, Furuno manual is missing pages
Sure, I'll give it a shot for you. Its all pretty easy actually so we'll just go though it all. This is going to take a while to type so there may be other responses that cover this that pop up before I'm done so there may be duplicate information - sorry about that.<br /><br />Start with gain, just to get it out of the way. All of our recreational fish finder's put out all the power they are capable of all the time. That would be fine except that in shallow water or water with a lot of debris submerged there is an overload of information comming back in the form of return echos. What the gain does is turn down the sensivitity of the reveiver side of the fish finder. Now the way they are set up its a little bit backwards. What it means to turn up the gain is actually to reduce the level of signal reduction - a bouble negative. Think of it this way; do you remember the days when the old folks used to wear hearing aids with a wire to a small amplifier usually carried in a shirt pocket? Well, with the old hearing aids when the user wanted to hear faint sounds they turned up the receiver. It didn't make the speaker speak any louder, it just turned up the amplifier's ability to use what was comming in.<br /><br />OK, how they work and the importance of range scales. This one is very important and not well understood from what I've seen,<br /><br />All of our fish finders work the same way. A power signal is generated in the display unit. That signal is sent to the transducer. The transucer pings (clicks) as a result of the power surge. The sound waver from the ping travels through the water at 4,500 feet per second. Sound strikes whatever and bounces back as an echo. The echo returns to the transducer where its remaining sound energy is converted back to electricity. That electricity is wired back to the display unit. The display unit interprets the returing signal for strength and how long it took from the outgoing surge to the return echo. The length of time determins the depth, the strength of the return determins how the echo will be displayed.<br /><br />At the display unit incomming signals are analized for strength and time in transit. More than one echo may result from any outgoing signal, all are analized and displayed. One vertical column of pixels (little dots in a matrix on the screen) will be displayed with echos noted at appropriate indicated depths and strengths (done by use of color or tone). This process is repeated many times and as each new set of information is processed by the display unit it is exhibited on the screen and the one that had been there is moved one column to the left. So in time a picture marches across the screen. That's it in a nutshell.<br /><br />So, what is range and what's it got to do with anything, you might reasonably ask. OK, here goes.<br /><br />One of the great limiting problems with any fish finder is that its transducer can not do two things at once. That is to say it can not talke and listen at the same time, it can not be pinging and waiting for a return echo at once. So, that's one thing. So that tells us that a display unit's software must decide how frequently to put out sound pulses and what the duration of each sould pulse must be. Because it takes sound longer to reach the bottom and return an echo in deep water than it does in shallow water some things should be clear. If the fish finder thinks its in deep water it will have to slow down the number of pings it can make in a minute and each one it makes need to be of a little bit longer duration. In shallow water it can get away with quick little pings shot out in rapid succession, but in deeper water it has to slow way down to give time for the sound to get to the bottom and the echo to get back. Make sense?<br /><br />The thing is that for a fish finder to really perform well it has to have the ability to vary its pulse rate and pulse duration - and to some extent or another all of our machines have that ability.<br /><br />Now, the faster a machine can shoot the more detailed the picture can be. But if its too fast the return echos from one pulse may be returning at the time the machine is alredy fireing for a later cycle. That Won't work. The opposite won't work either, where the machine is shooting long duration pings on long intervals. In any case to work properly, or at all really, the machine has to have some idea how deep the water its in is. That's what range scales are for.<br /><br />Range scales define the maximum depth that will be surveyed on the screen, and that is what the user sees. What the user doesn't see is that the depth range that is selected also determines the Pulse Repititon Rate and the Pulse duration. For high quality fishfinders the maximum you can expect on the repititon rate is about 1,500 pulses per minute. The duration will vary but from about 0.15 to about 3.5 ms. A fish finder that is not in the proper range will only be able to make sense out of signals that are within the range that the machine is set on. <br /><br />Most machines these days have an Automatic feature. What this feature does is find the working range scale and stick with it until it looses a return echo. After that it just goes and searches though the available range scales until it hears a return.<br /><br />So one of the tasks for the new owner, if his machine allows for user defined range scales, is to figure out how he or she wants the display to look and when to make the switch between ranges and how that will effect use. Almost no one really gives this much thought but if you do it will do wonders to enhance your enjoyment of your machine. I'll let others tell you about how to pick what to set, or at least what sorts of things to pay attention to.<br /><br />Thom
Good Job ThomWV...<br /><br />Weird.. Gain and range show up in the directions for me..
