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why dual frequency feature?

Old 07-22-2004, 03:44 PM
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Default why dual frequency feature?

I am wondering why a dual frequency feature on a depth finder? Under what conditions would this feature be helpful? Also does anyone know the best viewable screen out there and is it a good idea to have a combo depth/fish/temp/speed/gps model or should these be separate units? Got a lot to catch up on with all this new techology. I appreciate any help.
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Old 07-22-2004, 03:54 PM
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Default RE: why dual frequency feature?

I have the combo Lowrance LCX 15MT and love it. The dual freq's are to match with the water depth, 200 for "shallow" water and the 50 for "deeper" water. Best I remember the break of depths is about 200 feet, and saltwater does have a bearing on which freq works better......
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Old 07-22-2004, 04:06 PM
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Thanks, Bailey's Boat...I will check out that model. And muchas gracias for the info on 'dual frequency'...amazing how simple things are after being explained. Your forum name...odd coincidence...my neighbor is another 'Bailey' and we fish in his boat a lot...a 26' Striper WA. Thanks again for clearing away some cobwebs.
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Old 07-22-2004, 04:14 PM
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Default RE: why dual frequency feature?

about $700 and shipping?
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Old 07-22-2004, 04:21 PM
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Default RE: why dual frequency feature?

I bought mine when they had just hit the market and were going in the 900 range, with transducer and GPS antenna. They seem to have come down in price a little, unless the 'ducer and antenna are seperate now???????



The "Bailey" name is actually my Chocolate Lab's name, she's my main girl.......
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Old 07-22-2004, 05:23 PM
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Default RE: why dual frequency feature?

The operation of the fish finder really does vary a lot depending on which frequency you are using. Almost all the fish finders made today are dual frequency anyway, but it wasn't that way not all that long ago. At any rate sound waves of high frequency attenuate rapidly in water and so the 200 kHz side is really not going to be able to shoot into particularly deep water. Normally its range would be limited to something around 300 feet or so with the power found in most bottom machines found on small boats. The thing about the high frequency side is that the area that is covered by the outgoing beam is at a fairly narrow angle, usually (depending on the transducer itself) somewhere around 10 degrees if the norm for what is called the 'cone angle'. With a beam that narrow you cover a relatively small patch of bottom but you can do it with great clarity.

In order to penetrate to deeper water you have to go to a lower frequency. That is what the 50 kHz side of the transducer is for. Because the lower frequency sound attenuates at a lower rate you can shoot much deeper, and in fact will only be limited by the fish finder's power output and the sensitivity of the transducer. Of course there is a price to pay and that price is in what you might want to think of as the resolution of the picture. The cone angle is much wider on the 50 kHz side, usually somewhere around 45 degrees, and so a much larger area is available for sampling. Of course there is nothing to stop you from using the 50 kHz side in shallower water just to have that wider view.

50 and 200 kHz are the norms for the frequency but there are some companys that use some off frequencys. One thing that passes a lot of folks by is that importance of picking the right transducer. There are three mounting styles for the things, transom mount, thru-hull, and in-hull but what a lot of folks don't understand is that generally they all use the same transducer element no matter which mounting style you pick, if you go with the standard transducer. They all use a single element for both frequencys, its just potted in a different style. There are some speciality transducers out there that can greatly improve the performance of your fish finder, but they ain't cheap.

Thom
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Old 07-22-2004, 07:16 PM
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Default RE: why dual frequency feature?

not to counter anything Thom, but just a record.

I have a LCX-104C and use a B256 thru hull with it (personally it blows away my old furuno 600 ). It uses 500 watts for 200Khz, and 1000 watts for 50Khz.

I can see to 1000 - 1300 feet in 200Khz, and easily see 2500' with the 50Khz.
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Old 07-22-2004, 08:57 PM
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Default RE: why dual frequency feature?

I had very bad luck with the Lowrance LCX 15MT. Factory said they fixed it twice. I bought another transducer on their suggestion, and it still wouldn't go past 280 feet. Bought the cheapy Garmin240Blue, 900' feet at 1-40 mph, first trip out.
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Old 07-22-2004, 09:58 PM
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Default RE: why dual frequency feature?

2150' at 35 mph. Lets see your garmin do that. Heck lets see that garmin record it so you can prove it.


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