Someone explain this please

[LWinches]

It doesn't seem to matter which brand of electronics is being discussed, the theory and manuals talk about how the lower frequencies penetrate deep water better than higher frequencies. Some emphasize the low frequencies like 50 khz and 83 khz for salt water and for use in really deep waters.

So why is it that my experience seems exactly the opposite. Regardless of brand, 50 Khz and 83 Khz do not seem to show fish well at all below 50 feet, 60 feet for certain. The 200 Khz shows fish very well at 60 feet and below.

Many units provide a side by side split screen with one frequency show on the left and the other on the right, so it makes for easy comparison and I'm sure that many of you have done this same thing. I'm also confident that several of you on this board will know the answer. Please enlighten me.

Thanks.
L.Winchester

[VernH]

It doesn't seem to matter which brand of electronics is being discussed, the theory and manuals talk about how the lower frequencies penetrate deep water better than higher frequencies. Some emphasize the low frequencies like 50 khz and 83 khz for salt water and for use in really deep waters.

So why is it that my experience seems exactly the opposite. Regardless of brand, 50 Khz and 83 Khz do not seem to show fish well at all below 50 feet, 60 feet for certain. The 200 Khz shows fish very well at 60 feet and below.

Many units provide a side by side split screen with one frequency show on the left and the other on the right, so it makes for easy comparison and I'm sure that many of you have done this same thing. I'm also confident that several of you on this board will know the answer. Please enlighten me.

Thanks.
L.Winchester

Your definition of "deep" water may be on the shallow side. Here's a`section from a Lowrance Manual (.pdf file from their website).

The default frequency is 200 kHz, which is best for use in shallow water
(about 300 feet or less). This frequency is the best choice for about 80
percent of the fresh and salt water sport fishing applications. When you
get into very deep salt water, 300 to 500 feet or deeper, the 50 kHz
frequency is the best choice.
The 200 kHz transducer will give you better detail and definition, but
less depth penetration. The 50 kHz transducer will give you greater
depth penetration, but a little less detail and less definition.

Are you saying that you don't get better displays with the higher frequencies deeper than 60 ft? I guess I can read your post a couple of ways. By "below", do you mean shallower? (Ya gotta remember that there are lots of us who rarely fish for 'eyes in water deeper than 40 ft.)

None of the tranducers mounted on my boat currently show fish at any depth. Our water will still be hard for about another 2-4 weeks.....:boohoo:

Vern

[LWinches]

Thanks Vern.

Yes, my definition of deep water is on the shallow side. Until 4-5 years ago, on the lake I fish, people talked about walleye going deep, meaning 50-60 feet deep. Fishing most of the time, it was hard for me to quit fishing for walleye when everybody else dld. I fished a whole summer when I was the only person on the lake still jigging for walleye. I followed them as they went deeper, 70,80,90,100. Year before last they went to 150. Last year they stopped at 120. Now, on this lake deep means 100 or deeper. I'm using the term as it applies to where the walley are.

Second, I use my electronics as a fish finder, not as a depth finder. I am looking for fish with the electronics. Yes there is a correlation between good structure and finding fish but you can fish good structure all day and come up empty. That's why I was disappointed in the Genetron. Some have said that it would show you fish on the bottom. That was and still is the hole in my electronics performance, all of them. The primary reason I purchased the Genetron was to try to fill that hole. While it is an outstanding unit, superior in many ways, it does not show fish on the bottom. I don't think there is a unit out there that will show fish on the bottom once you pass 50 feet deep.

It does me no good whatsoever that a particular frequency (50, 83 Khz) will penetrate 1000 feet of water to show me the bottom. I'm not trying to catch the bottom. What is meaningful for me is the depth that it will show me a sonar return of a fish 16 inches long and what depth it is at. I also need for it to show me my jig.

We only have a short period of time, now-springtime, when our walleye are shallower than 50 feet. The rest of the time they are from 60-150 feet.

Vern, I probably couldn't catch a fish in your water. My most difficult fishing is when fish are 40 feet or less. They are more spooky. They do not like to be under the boat and they are much more particular of what they will bite. Dread the thought, I would probably have to start trolling.

[tzonetom]

Have you tried a flasher type?

[Wall@y@]

According to the information in Cabela' catalog for the HDS transcucers, the 83/200 kHz transducer is recommended to be used in shallow water less than 900 ft. The 50/200 khz transducer is recommended for depths below 900 feet. Now I know that walleyes don't get down that deep but like you I have jig fished for walleye at depths greater than 60 feet many times and caught them in 100 feet. As far as I can tell the 83 khz transducer is recommended for searching for suspended fish because is has a much wider beam than the 200 or the 50 khz transducer. The 50 khz has a very narrow beam but tremendous power to get down in that really deep water. I'm no expert on this but from what I have read on the different transducers this is what Lowrance is saying about their transducers. Please set me straight if I'm wrong.

[LWinches]

tzonetom,

Yes, I have a flasher and it's okay. Throws my poor little mind in a circle. I prefer the real time sonar window on the Humminbird. It has a wide setting and my mind works better looking at a top down representation of the water column.

wall@y@,

I tried an HDS with the 83/200 transducer. Nice unit. Good color, sunlight viewable, very clean screen. I think you reversed the wide/narrow pairing on the frequencies. The 83 or 50 lower frequencies are wider cones and suggested for deep water use. the 200 Khz has a 20 degree cone and is recommended for general use. The problem I have with the lower frequences (all brands) is that I cannot get them to show a sonar return of a fish 60 feet or deeper. They show the bottom well, and occasionally a fish. When you use a split display with the low frequency on one side and the 200 on the other side what I'm saying is that any fish that shows in the 200 narrow cone should also show in the low frequency wide cone. Generally they do not unless I am in shallow water.

Thanks to both of you for your comments and assistance.
L.Winchester

[tzonetom]

No problem,

It took me a while to get used to a flasher too. But once I did it is pretty cool.

[Wall@y@]

The information I gave you came from the information that Cabela's is giving about the 83/200 khz transducer. I rechecked to make sure I didn't make a mistake when I typed my message to you. If I'm not correct then Cabela's information is wrong. Sorry about that.

tzonetom,

Yes, I have a flasher and it's okay. Throws my poor little mind in a circle. I prefer the real time sonar window on the Humminbird. It has a wide setting and my mind works better looking at a top down representation of the water column.

wall@y@,

I tried an HDS with the 83/200 transducer. Nice unit. Good color, sunlight viewable, very clean screen. I think you reversed the wide/narrow pairing on the frequencies. The 83 or 50 lower frequencies are wider cones and suggested for deep water use. the 200 Khz has a 20 degree cone and is recommended for general use. The problem I have with the lower frequences (all brands) is that I cannot get them to show a sonar return of a fish 60 feet or deeper. They show the bottom well, and occasionally a fish. When you use a split display with the low frequency on one side and the 200 on the other side what I'm saying is that any fish that shows in the 200 narrow cone should also show in the low frequency wide cone. Generally they do not unless I am in shallow water. The 107 Khz of the Vexilar doesn't have this problem, neither does the 120 Khz of the Genetron.

Thanks to both of you for your comments and assistance.
L.Winchester

[Wade@JollyAnnMarine]

Here's some information that was published by Lowrance some time ago...

-----------------------------------------

There are advantages to each frequency, but for almost all fresh water applications and most salt water applications, 200 kHz is the best choice. It gives the best detail, works best in shallow water and at speed, and typically shows less "noise" and undesired echos. Target definition is also better with 200 kHz. This is the ability to display two fish as two separate echos instead of one "blob" on the screen.

There are some applications where a 50 kHz frequency is best. Typically, a 50 kHz sonar (under the same conditions and power) can penetrate water to deeper depths than higher frequencies. This is due to water's natural ability to absorb sound waves. The rate of absorption is greater for higher frequency sound that it is for lower frequencies. Therefore, you'll generally find 50 kHz used in deeper salt water applications. Also, 50 kHz transducers typically have wider angles of coverage than 200 kHz transducers. This characteristic makes them useful in tracking multiple downriggers. Thus, even when these downriggers are in relatively shallow depths, 50 kHz is preferred by many fishermen.

50khz:

deeper depths (very deep)
wide cone angle
less definition and target separation
more noise susceptibility

The type of water you're using the sonar in affects its operation to a large degree. Sound waves travel easily in a clear fresh water environment, such as most inland lakes.

In salt water however, sound is absorbed and reflected by suspended material in the water. Higher frequencies are most susceptible to this scattering of sound waves and can't penetrate salt water nearly as well as lower frequencies. Part of the problem with salt water is that it's a very dynamic environment - the oceans of the world. Wind and currents constantly mix the water. Wave action creates and mixes air bubbles into the water near the surface which scatters the sonar signal. Micro-organisms, such as algae and plankton scatter and absorb the sonar signal. Minerals and salts suspended in the water do the same thing. Fresh water also has wind, currents, and micro-organisms living in it that affect the sonar's signal - but not nearly as severe as salt water.

Mud, sand, and vegetation on the bottom absorb and scatter the sonar signal, reducing the strength of the return echo. Rock, shale, coral and other hard objects reflect the sonar signal easily. You can see the difference on your sonar's screen. A soft bottom, such as mud, shows as a thin line across the screen. A hard bottom, such as rock, shows a wide line on the sonar's screen.

------------------------------------------

Since this was written, Lowrance has introduced the 83/200khz ducer option. The 83khz option has a wider beam than the 200khz, so it will cover more area beneath your boat, but it is also more susceptible to "noise" and the returns will not be as well defined as the 200khz option. For walleye fishermen looking to read bottom content and "find fish" in what we consider "deep" water, the 200khz option is best. The 50khz option is generally reserved for saltwater, or tracking downriggers. I hope this helps.

[LWinches]

Thanks Wade. I see what you are saying. Greater penetration in deep water is a completely different characteristic than definition and target separation. Of course when I have the dual screen with the low frequency on one side and the 200 on the other side I don't know how big the fish is. I just notice that the 200 shows it and the 50 or 83 does not. While the low frequency will show the downrigger ball quite well because of its size and huge change in density is very useful for those trolling it's not of much use for me.

Thanks again for the excellent explanation.
L.Winchester