Author Topic: Using two humminbird SI units at the same time  (Read 6409 times)

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Offline doddauto

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Using two humminbird SI units at the same time
« on: January 23, 2011, 11:10:53 AM »
I am new to this so please bear with my ignorance. I have a 998c SI mounted on the console with  the transducer mounted on the transom. I just purchased a 798Ci SI that I plan to install on the bow of the boat. Boat is a 21 foot Stratus. I plan on installing a transducer on the bottom of trolling motor for the 798Ci SI. Will I be able to use both units at the same time? Will I have to turn off one of the units because of interference due to both transducers working at the same time? If I understand it rite I cant hook both units to one transducer and use both at the same time? Thanks for any help given


Wayne P.

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Re: Using two humminbird SI units at the same time
« Reply #1 on: January 23, 2011, 12:05:05 PM »
Anytime you have two units with the same cone shaped 2D frequencies operating at the same time in the same area, you can get cross talk. The brand makes no difference, mixed or the same and not necesssarily on the same boat.
With the SI beams, you rarely will be overlapping the beams between units so that is not an issue.

Your issue may well be trolling motor RF interference on the 798.
« Last Edit: January 23, 2011, 12:07:17 PM by Wayne P. »

Offline sonar2000

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Re: Using two humminbird SI units at the same time
« Reply #2 on: January 23, 2011, 05:23:24 PM »
We have experienced display differences when in the proximity of another HB boat transducer. Not on a defined occurance but random.  It does happen.
As long as every thing is normal then it is ok, but if, for example, you are on a search then you dont need any external influence on your received signals. So simply asking the other boast to turn off usually is accepted because of the understanding of the mission need.
I am not a fishing tournment person so dont know how this would be viewed for those guys..
We have seen other brand 200 freq  destroy our 200 returns more so than the 455 or 800...
Chuck

Offline Humminbird_Greg

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Re: Using two humminbird SI units at the same time
« Reply #3 on: January 25, 2011, 08:40:42 AM »
Anytime you have two sonar units that use the same frequency on a boat and their sonar beams overlap; there is the chance that you will see sonar-to-sonar interference.  There are a lot of factors that go into whether this will happen, whether your sonar unit may be able to automatically filter them out or if you can manually filter them out.  I have seen where 20 foot bass boats with bow and transom mounted sonar have interference and yet our test boats with two transducers mounted side-by-side show no interference.  If you do this (and many do) just turn on and up the Noise Filter menu on the unit that is showing the sonar interference.  Not a 100% fix but it helps many times.  Further things to try would be to manually set the lower depth range (Lower Range menu) to a setting that is different than the other units automatic lower depth range setting.

Usually any sonar-to-sonar interference is seen on the 200kHz and 83kHz 2D sonar beams due to their conical shape and the way the beam spreads out.  Most do not understand that a 20 degree sonar beam reflects back towards the surface at that same 20 degrees, so in a water depth of 20 feet that 20 degree sonar beam may be covering 7 feet of the bottom but it covers 14 feet of the water surface (bottom composition and shape will affect this width as well).

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com


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