Using Split Frequency ?

Discussion in 'Fishing Electronics Review' started by Floyd, Jan 5, 2007.

  1. Floyd

    Floyd New Member

    Messages:
    14
    State:
    Indiana
    I was fishing the river with a friend and he was using split frequency and the 200 was showing better detail and marking some fish.understanding that the 50 has a wider cone it will show fish beyond the 200 makes me ask why the 50 was marking "fish" with less structure and bottom detail within the same cone range. the 200 would show what appears to be structure when the 50 would show fish.the settings could be the same or have its own and it made no difference.could this be a false reading on the unit itself or will the 50 just give a better reading without greater detail ??
     
  2. special liberty

    special liberty New Member

    Messages:
    295
    State:
    Maryland
    The 200 Hz is designed for shallower water, i.e. less than 50 fathoms/300 feet. The 50 Hz function is for deeper waters, i.e. offshore. The higher the frequency the more detail a return it will provide although it's detection ranges will be considerably shorter. At higher freq's a signal suffers more propogation loss through spreading, scattering and attenuation loss. Due to these losses most sonar systems are designed with narrower transmit beam widths to focus that energy into a narrower beam to minimize propogation loss and increase the effective range. In water less than 300 feet I would recommend using soley the 200Hz function; the 50 Hz signal will lack the resolution you need and any detailed returns such as fish arcs are highly suspect.
     

  3. ryang

    ryang Well-Known Member

    Messages:
    5,289
    State:
    Blacklick, Ohio
    Name:
    Gary
    Great reply Tawn and very easy to understand (at least for me)
     
  4. bigun12

    bigun12 New Member

    Messages:
    35
    State:
    Texas
    Thanks! That clears up a lot for me but I still have a couple of questions on this subject and since I have always been told that Master Chief's know most everything :big_smile: you seem like the one to ask!

    I just purchased a humminbird 787C2 with one of these dual frequency transducers used on the sonar side. They sell this as a method of covering more bottom area with a single pass (wider beam covers more bottom). With this unit one can use either the 200hz beam, the 50hz beam, or both of them togther. My idea is to use them both together when searching for structure in new areas and then use the high frequency to really nail things down. I will always be fishing in fresh water that is less than 50' deep. Am I "all wet"?

    Secondly, the unit I am replacing (Humminbird TRCid-1) uses a 455hz transducer which, according to the excellent explanation you gave earlier ought to be even better for the relatively shallow waters I fish. The problem is this old technology unit doesn't display things very well (dots for fish etc.) but does a GREAT job of locating structure although one must first learn what they are looking at.

    The question is if higher hz is better in shallow waters why has humminbird, and every one else in so far as I can determine, gone away from 455hz for everything but their very high definition, and very expensive, side scanning units?
     
  5. special liberty

    special liberty New Member

    Messages:
    295
    State:
    Maryland
    I don't know everything - just ask the guys that work for me!!:lol:

    My recommendation is to toy with it and see how the dual freq mode works for you. The 50kHz will give ya a wide footprint and off the top of my head I don't see why it wouldn't work in conjunction with the 200kHz transmission. As I said before, just don't expect the resolution from the lower freq.

    I have no idea why they would discontinue a 450kHz transducer. It would provide much more detail but the trade off would be in the water depth in which you could successfully use it. Higher freq's attenuate much more rapidly than LF transmissions - so the higher the freq the less range you have and moving the transducer closer to the bottom isn't an option in our case. It may have to do with production costs or they are simply falling in with other manufactures in which 200kHz is an industry standard.
     
  6. bigun12

    bigun12 New Member

    Messages:
    35
    State:
    Texas
    LOL! LONG ago I heard another Master Chief say:

    "No I don't know everything but I sure as hell know the fellow who does!"