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Old 05-26-2012, 05:28 PM   #1
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Default Fish finder frequencies

I'm a bit confused about my fishfinder. It is a dual transducer 50/200 hz. I am never sure which frequency to use when. I fish shallow water for stripers and mackeral and deeper water for cod and haddock. My understanding is that the 200 hz frequency has a narrower cone in that it shows a small area of the bottom but with better detail. The 50hz has a wider beam so shows a larger area. Ironically the 50hz has better penetration into deep water. My question is this. In shallow water I want the 50hz to cover a larger area of bottom. In deeper water (275-300 feet) I want the 200 hz so as not to show too much area. The area covered is greater with increasing depth. I have use the 200hz (i like the pictures better) in shallows and can get a school of mackeral right under my lines. Am I missing anything here? Are there any books on using fishfinders?

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Old 05-26-2012, 08:00 PM   #2
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In sonar the higher the frequency the shorter the pulse length and also the finer the detail.
But because of the shorter length at 200 kHz you also do not have enough energy available to have great depth penetration.
That is why at 200 kHz you have narrow cone widths...a narrow cone at the higher frequencies allows good to moderate depth penetration while still getting excellent detail.
Most 200 kHz units can get 500' to 700' depths.

The lower frequencies have a much longer pulse lengths and thus have far more energy available for greater depth penetration.
But being a longer pulse length also limits the sensitivity to smaller targets but allows wider cone angles because of the the greater energy in the longe pulses.
Many 50 kHZ units can penetrate down to 2500' .

Most sonars have the capability of showing dual screen viewing...both 200 and 50 kHz.
That way the uses can compare the two returns and thus getter a greater amount of information on the same screen.





Last edited by semperfifishing; 05-26-2012 at 08:58 PM.
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Old 05-27-2012, 05:26 AM   #3
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Thank you,
I have an old Raymarine C70. The screen is so small that when I split it the size is too small. I usually split between the chart plotter and the fish finder. It is a lot of fun watching a school of mackeral come by and letting the crew know where to cast. I just haven't had much luck spotting cod on the bottom. I look for depth of around 250 feet and drop lines. Last season at our last drop I did see bottom detail and was able to drift over cod and haddock. Your help is great as usual. Do you have a website where you sell equpt.
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Old 05-27-2012, 06:29 AM   #4
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Quote:
Originally Posted by fmrsailr View Post
Thank you,
I have an old Raymarine C70. T. I just haven't had much luck spotting cod on the bottom. I look for depth of around 250 feet and drop lines. Last season at our last drop I did see bottom detail and was able to drift over cod and haddock. Your help is great as usual.
Do you have a website where you sell equpt.
Feel free to call me direct. I am available 7days.

If you have the stock Garmin transducer you might get a far better return to upgrade your transducer.
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Old 05-27-2012, 06:34 AM   #5
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Quote:
Originally Posted by fmrsailr View Post
Thank you,
I did see bottom detail and was able to drift over cod and haddock. Your help is great as usual.
Do you have a website where you sell equpt.
If you are still using a stock single element Garmin transducer it may help to upgrade your transducer.
Feel free to call me direct. I am available 7days .



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Old 05-27-2012, 06:02 PM   #6
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I have a dual frequency Raymarine transducer. I may be selling my boat this year's end so don't want to do any upgrades now but if I get my next boat next year I want to have a separate unit for the fish finder and the GPS/radar. I don't think i am going to go CHIRP unless prices really come down. Right now I can't do both frequencies at once. For 300 feet water which frequency do you suggest? I have been only using the 200 Hz since the cone size is a reasonable area.
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Old 05-27-2012, 06:10 PM   #7
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Right ....no sense spending money on a boat you will not bee keeping very long.

You can just stay on the 200 kHz side a good deal but switch over to the 50 kHz side every so often..that way you get the best of both worlds.
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Old 05-28-2012, 11:08 AM   #8
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General rule of thumb for most is 200 hz up to 200 feet and 50 hz after that. Targets on 50 hz will show up much larger and thicker. 200 hz is more focused and will show better resolution, but as semperfi said it lacks the power to go deeper
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