Dual Frequency vs Dual beam transducers

[janz]

A lot of eye opening good reading here. Maybe I should tell you what i want to do, I am pretty sure it should work but only time will tell. After purchasing a larger boat it came with a sitex Koden color FF with the thru hull 132KHz transducer (works very well) the rest of the fishfinders, fly bridge and transom, were junk so they were tossed. I added my LCX 104 C Lowrance to the helm but use it only for GPS (love the big size and color and accuracy). So Now I have a 7" HDS Lowrance 50/200 that I will put up on the fly bridge so I can have a FF up there if I want to operate the boat from up there. I also want to place another FF at the transom of the boat so I can keep track of whats going on from back there while working the rods and downriggers so I am looking at the 83/200 dual beam. If I am running all at once, the Koden at 132KHz, the Lowrance at 50KHz and the soon to be transom FF at 83KHz, they should all get along without interfering with each other right??? I am planning on mounting another transducer for the 104C at the helm but leaving the sonar in the off selection so it won't produce a signal as I will only use this for a backup for the helm if the Koden ever craps out. This is the reason I was looking closely at the 83/200 units so I could run the transom FF at the 83KHz setting. So when I saw that the 83KHz only comes in the dual beam it had me thinking that if the unit mixes the 2 freq 83/200 that it would interfere with the other (flybridge) FF. A lot to digest here but I would like to try to get it right the first time as the boat would need to be hauled out of the water to change out transducers. I would like to complete this once its out of storage and before it gets launched back into the water.

BTW thanks to all who have participated in this thread. Bigger boat=bigger problems.

[janz]

Clark mine show up pretty good with the 50KHz but if I get going to fast or currents pushing the weights or even to deep it will loose them. Sometimes even to deep (to much downrigger cable out) the blow back will take the weights out of the "seeing" cone. I also found it helpful to tilt the transducer towards the back of the boat so it helps to put the weights in the "seeing cone". Tilting the transducer back will have a negative affect while going fast (more than 10mph) or up on plane.

[Matthew]

A lot of eye opening good reading here. Maybe I should tell you what i want to do, I am pretty sure it should work but only time will tell. After purchasing a larger boat it came with a sitex Koden color FF with the thru hull 132KHz transducer (works very well) the rest of the fishfinders, fly bridge and transom, were junk so they were tossed. I added my LCX 104 C Lowrance to the helm but use it only for GPS (love the big size and color and accuracy). So Now I have a 7" HDS Lowrance 50/200 that I will put up on the fly bridge so I can have a FF up there if I want to operate the boat from up there. I also want to place another FF at the transom of the boat so I can keep track of whats going on from back there while working the rods and downriggers so I am looking at the 83/200 dual beam. If I am running all at once, the Koden at 132KHz, the Lowrance at 50KHz and the soon to be transom FF at 83KHz, they should all get along without interfering with each other right??? I am planning on mounting another transducer for the 104C at the helm but leaving the sonar in the off selection so it won't produce a signal as I will only use this for a backup for the helm if the Koden ever craps out. This is the reason I was looking closely at the 83/200 units so I could run the transom FF at the 83KHz setting. So when I saw that the 83KHz only comes in the dual beam it had me thinking that if the unit mixes the 2 freq 83/200 that it would interfere with the other (flybridge) FF. A lot to digest here but I would like to try to get it right the first time as the boat would need to be hauled out of the water to change out transducers. I would like to complete this once its out of storage and before it gets launched back into the water.

BTW thanks to all who have participated in this thread. Bigger boat=bigger problems.

I'll make an attempt at this.

It sounds like there are 4 frequencies in question. 200khz, 132khz, 83khz and 50khz. Most sonar units do not have superhet transceivers so it is doubtful any mixing would happen. Frequencies do produce harmonics and generally the harmonics are double or half the frequency, for example 50khz would have a harmonic at 100khz and 25khz and the harmonic would cause interference. The frequencies in question look good as far as interference is concerned if the sonar element produces just one frequency. Most times a ceramic element will have more then one frequency as stray frequencies are present and this is where the crap shoot lays. The company that makes the transducer generally will use the strongest frequency for the sonar unit, for example a ceramic element has a weak frequency of 75khz, 112khz, 192khz but a very strong 132 frequency. In this case the sonar element would be used for the 132 frequency sonar units.

The only way you are going to find out is to hook them all up and point the transducers at the same object from the same direction, for the purpose of testing harmonic interference this does not have to be completed in the water.

[janz]

Thanks Mathew that was how I was understanding the whole picture and the reason for my choice of freq. It was just the "Dual beam" moniker that threw me for a loop. Crap shoot is right, it might work just great and then again worse that could happen is I won't be able to run (activate sonar) on a combination of fish finders while the transom FF is on.

[spoonfed-1]

Clarke the answere to your question is yes I can mark my weights on the 50 at all depths. The deepest I've run them is about 200 feet. The signal was weaker down there and just showed as a faint line on the screen but I could see them. As the cone angle travels deeper, the coverage area increases which probably compensated for the additional blowback. As a side note I run a thru hull airmar. The thru hull made a huge difference over the transome mount with my Furuno.

Glen