# Sonar 50kHz vs. 200kHz



## Danno

My Lowrance LMS 525 has two settingfor the transducer, 50 and 200 kHz. If I am reading it correctly the 200 kHz setting is best for coastal waters (shallow) and the 50 kHz is better for the off shore deeper waters.

Do I understand this correctly, I am having a hard time getting the past the bigger number being better for the deep stuff. Or does it have something to do with wave lenghts and other stuff that I don't need to know about.


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## Matt Mcleod

I put mine on 200 all the time. 200 is a narrower beam as far as I understand andis better in deeper water.


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## RiverGulfFshr

The 200 khz. is used for shallower water applications usually less than 100'. The 50 khzis used for deeper water. The single on the 50 side is not as detailed in water less than 50' as where the 200 gives great detail from 0-100'. The 50 gives the best detail from 100'-what ever the watts of your transducer will allow. They also say the 50 is more of a saltwater application. I always keep mine on 200 but I only have a flats boat so I only fish bay's and rivers. I hope that helps.


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## AUradar

> *Danno (7/14/2008)*, I am having a hard time getting the past the bigger number being better for the deep stuff. Or does it have something to do with wave lenghts and other stuff that I don't need to know about.


used to build digital RXers for radars, don't know much about sonars. But, the bigger the frequency the smaller the wave length. So the 200KHz has a 1/4 wavelength of the 50KHz.

Different wavelengths travel differently through mediums. Maybe an issue there as well.

Sorry I didn't add much, just wanted to post something to make me look smart. Did it work?


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## Deeplines

Hope this site helps you a little.

http://www.fishfinder-store.com/howfifiwo.html

It mostly has to do with the cone of the RX/TX, power and freq. 

Sonar in laymans terms: (It's like AUradar said) (Radar and Sonar is basically the same)

Higher the freq the more detail

Smaller the cone the more energy is TX in this area

More power the further it will go with the same results

If you can use dual freq just use that and problems solved.


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## 60hertz

It has to with the permeability of the medium in which you are transmitting through and the wavelength of the transmitted signal.

A longer wavelength will travel farther through a dense medium - in this case water - than one with a shorter wavelength. Remember, frequency and wavelength are inversely proportional and are proportional to c, the speed of light.

Frequency = c / Wavelength.

Therefore, a smaller frequency will have a larger wavelength.

So I still have not explained permeability - the higher the permeability the less dense the material. Obviously, air is more permeable than water. So, electromagnetic waves will travel farther in air than in water. This relationship is also reversely proportional.

Think about light/color you see when diving- the first colors to go are the higher frequency (shorter wavelengths)ones (purples, greens, blues, etc...) and then as you dive deeper the yellows and reds finally go before you're totally in the dark.

Colors are nothing more that electromagnetic waves that we "see" with our eyes. The same principle is going on with your transducers on your fishfinders.

Hope this helps.


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## Matt Mcleod

> *RiverGulfFshr (7/14/2008)*The 200 khz. is used for shallower water applications usually less than 100'.


I am curious about this idea that the 200 khz is used for shallow water. I have used tried them both bottom fishing out to 700' of water and the 50 just doesn't work near as well in any depth, but particularly deep water. The return is very slow and it makes the scroll speed crawl. Just not very effective in my experience.


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## RiverGulfFshr

> *Matt Mcleod (7/14/2008)*
> 
> 
> 
> *RiverGulfFshr (7/14/2008)*The 200 khz. is used for shallower water applications usually less than 100'.
> 
> 
> 
> I am curious about this idea that the 200 khz is used for shallow water. I have used tried them both bottom fishing out to 700' of water and the 50 just doesn't work near as well in any depth, but particularly deep water. The return is very slow and it makes the scroll speed crawl. Just not very effective in my experience.
Click to expand...

Accoding to Lowrance, on the website, the 50 khz is for deep saltwater fishing. They say that 50 khz doesnt detail as well in water less than 30' as does the 200. I even read it again after reading your post. I strictly use 200 on my Lowrance but I am never in water over 80'. I guess it might just come down to what ya like.


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## AUradar

some more useless information.

Cone (sonar) = beam width (radar) = field of view (camera)

bascially, the energy leaves the device and fillsthe surface of acone. If you look at that plane of energy at any distance from the source than it would be a portion of a sphere from that source. The energy level is constant, but as it gets further away the surface area gets larger so the energy is dispersed more. The equation for the surface area of a sphere is 4 pi R^2 where R is the radius, or in this case the distance from the target to you. So if youincrease the targetdistanceby 2, then the power reaching the target is reduced by 4. BTW, that 2 in dB is equal to 3 dB, or half power. Thats why you get a half power reduction as you double your distance. Probably heard that with sound speakers.

According to that link above, the 50KHz have a wider cone angle. That should be better for shallow water. The reason is the beam doesn't have time to expand much when going down. For deeper waters you would want a narrower beam so that by the time it reaches the bottom the actual width would be the same as the wide beam in shallow water. Does that make since?

wide beam

/ \
/ \
/\
---------------

narrow beam

/ \
/ \
/ \
/ \
/\
---------------

so you have the same beam width at the bottom even though you have different depths with differernt starting beam widths


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## AUradar

i'm pretty sure its the cone width you want to think about, not hte freq. The freq probably selects the cone width.

Wider cone width will do better for shallow water

Narrow cone width for deeper water


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## AUradar

> *60hertz (7/14/2008)*
> 
> A longer wavelength will travel farther through a dense medium - in this case water - than one with a shorter wavelength. Remember, frequency and wavelength are inversely proportional and are proportional to c, the speed of light.
> 
> Frequency = c / Wavelength.
> 
> Therefore, a smaller frequency will have a larger wavelength..


sonar uses speed of sound as the reference point, notc (speed of light). Other than that the comparisions is the same


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## 60hertz

> *AUradar (7/14/2008)*
> 
> 
> 
> *60hertz (7/14/2008)*
> 
> A longer wavelength will travel farther through a dense medium - in this case water - than one with a shorter wavelength. Remember, frequency and wavelength are inversely proportional and are proportional to c, the speed of light.
> 
> Frequency = c / Wavelength.
> 
> Therefore, a smaller frequency will have a larger wavelength..
> 
> 
> 
> sonar uses speed of sound as the reference point, notc (speed of light). Other than that the comparisions is the same
Click to expand...

OOPS! My bad - thanks. But, like you said whether it is speed of light or speed of sound the comparisons are the same. Thanks for catching my mistake...


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## msagro1

what about the watts? is that more power for a better picture??? what about machines that say upto 1000 watts rms or some machines that say 8000 watts rms...... any breakdown in relation to the 50/200 would help.


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## spiderjohn

The question was about which to use (50 or 200 kHz) for deep water. Answer is 50 kHz. 

It is equivalent to a tweeter and a bass in a stereo system. Which do you hear from the punk's carin the neighborhood coming down the street first. The bass. Why? The longer wavelengths (lower frequency like 50 < 200) are able to better pass thru "stuff". In our case the stuff is water. As for power, the higher the power, the further and better your signal will travel thru the "stuff". "RMS" simply means root mean square and is a fancy electrical engineering term referring to a way to measure power in a waveform. Not all signals are the same waveform so you must define how you are calculating the power in the wave. It's been a while but I recall that a sine wave rms is found by multiplying the peak measurement by square root of 2. Just electrical engineering jibberish mostly.

For deep water you use the 50 kHz frequency for its ability to travel through the water a greater distance without being dispersed (unreadable to receiver) and get the highest power transmitter you can buy.

In the animal world, they found that elephants use such low level frequencies that our ears can't hear them but other elephants miles away could. In contrast, porpoise use a higher frequency that only goes a short distance but that is all they are looking for - what is right in from of them.


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## eddy2419

Unless you need to see bottom in over 600' water the 200 is all you need. I have a 50/200 and have used the 50 side for about 1 minute. When trolling off shore I only look at maybe 150' of water for bait. I thought I needed the 50 side when I bought. A single 200 from Eagle/Lowrance is about $100 cheaper.


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## Captain Rog'

There are more questions than answers. Chancers are your machine will perform better on 200. These cheep transducers have a narrower cone angle and more elements in that band width. While 50 may penitrate deeper it may have a 40 degree or bigger cone angle and very few elements in the transducer. A good deep water transducer for a Raymarine or Furuno will bee around 850.00. A top of the line transducer for deep water will run you 3500.00 , another 2000.00 for the sounding unit and a decient display is another 4,500.00. Lowrance is a freshwater company tring to break into the saltwater market. You may be getting all your machine can produce.


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## X-Shark

> These cheep transducers have a narrower cone angle and more elements in that band width.




Actually that is backwards. The cheaper ones up to about 600watts have single elements.



The higher end units have many elements.



I'll use the one I have as a example. Airmar B-260. [It's the same for the M-260.]



It has 1 Large element for the 200hz and 6deg cone angle. That is a very narrow cone angle.



The 50hz has 7 elements and a 19deg cone angle. That is why I run mine in 50hz ALL the time. I want the wider cone angle .



Airmar has since come out with a SS270. It is the same physical size as the B-260, but a wider cone angle on both 200 & 50hz. [They are both a 25deg cone angle.]





http://www.airmartechnology.com/uploads/brochures/B260.pdf



Airmar's transom mount lower end units have a single element for both 200 & 50hz

The P-58 for example has a cone angle of 11deg in 200hz. and 45deg in 50hz. Their P-66 is the same.



This is typical of what you would get with the FF unit that has the X-ducer included.

That is the lower end stuff, but it works for a lot of people.



A B-260 is aprox $700. The fairing block is a MONSTER! It's another $250 to $300.



If you want to flush mount a B-260 with the outside of the hull like I did, figure $1K for labor and the fairing block will not be used.

























Here's the box I built and the hole I cut thru the bottom of the hull.














A big hole like that. I ain't scared.


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## Hydro Therapy 2

Good info.


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## rauber

some charter captains explained it to me like this: they are using the 200 even in deeper water when they cruise around or troll- it covers much more water. when they get near a spot they want to fish they switch to 50 lto have the echo closer to the boat. they all say with 50 spots are much easier to find because more or less you have the object right under the boat vs a bigger circle around you.



fergie


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