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Transducer frequency and cone angle ?



I have a technical question I hope someone can help me with.
I have a 17.7 foot tiller boat with a Fishmark 320 in the back. My bow mount graph need replacement. I just got the Spring Cabelas catalog and they are showing all the new electronics. Now I know why stores are selling the Fishmark 320s for $169, they added new models and upgraded the pixel counts again.

My questions are: If I buy another Graph with a 200 kHz frequency and a 20 degree transducer, how deep will I be able to fish without getting interference between both units when they are on. Does the interference start when the cone angles overlap or is there some other factor that causes the interference?

I busted out the protractor and assuming the transducers are about 16 feet apart, it seems that the cone angles won't overlap until I start fishing water deeper that I normally fish while using the bow mount trolling motor.

Thanks for any feedback.

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In 60 ft. of water the diameter of the cone in ft. equals the degrees. Each time you halve the depth you halve the diameter of the cone. 30 ft. water=10 ft. cone. 15 ft. water=5 ft. cone.
In theory you will not overlap in anything less than about 40 ft of water. However in real life you will be dealing with uneven bottom conditions which will reflect the signal at odd angles. grin.gif

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  • 'we have more fun' FishingMN Creators

Say you have a 20 degree cone angle. In 20 feet of water the cone angle will cover 7 ft on the bottom. The return echo will however will bounce all over. So the question would be what sounders are compatibly with the Fishmark 320. I don't have one so i couldn't tell you. I can tell you I've run different brand sounders with same 200 kHz frequency and had no interference what so ever.

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