Author Topic: 998c SI and 958c HD DI frequency differences  (Read 2506 times)

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Offline jimmythegreek

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  • Unit(s): 998c SI, 958cHD DI, 596HD, 595cGPS, 565
998c SI and 958c HD DI frequency differences
« on: August 12, 2013, 01:12:19 PM »
THis is a advanced question, but here goes.  I have a 998c SI from last year bought new, its on my boat on transom w the SI transducer.  Works great just some things I noticed the other day.  I got a new 958C HD DI for the bow in april.  I run it thru the terrova80 using US2, I dont use DI w this unit.  The 958 shows WAY better 2D sonar than the 998, its very sensitive even when turned down, I have the ducer option set to US2.  I tried swapping the 998 to the bow for a bit, and set the unit to US2 as well to see the difference.  Now the 998 still shows the same pictures, just not as detailed and strong.  When I go over a bait ball its just that, a bunch of dots like a normal bait ball.  When they come by the 958, I can see the bait ball and even see fish arches in/around the bait ball.  Even if I turn up the 998 and adjust to the max I still dont get the detailed returns like the 958 up front.  All software is up to date.  Im thinkin I have marrower beams up front or higher frequency and thats why returns are better?  Im very experienced w these units, Im in advanced mode and know how to adjust for surface clutter, sensitiviey, chart speed, etc.  After doing some reading I see the 958c HD that has DI has a diff dualbeam frequency than usual, the refular dual beams are all 20/60 but the DI units are 200/455 w 16/25 beams.  For testing purposes I turned on FishID and I am getting blue AND orange symbols, so the US2 is displaying 2 beams it seems, but minn kotas site says the US2 is capable of 20/60 only.  Can anybody tell me what frequency I am seeing up front w this 958.  2D sonar is so good Im thinking of selling the 998c SI and getting an 1158c HD DI as I dont use sidescan as much as i thought.  THanks in advance Im stumped on this one

Offline Humminbird_Greg

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Re: 998c SI and 958c HD DI frequency differences
« Reply #1 on: August 20, 2013, 03:10:52 PM »
I would check the software version on the 958c DI unit.  The current available version is 6.680 and I thought that they got rid of the US2 menu option in it.  So I donít know of you want to change the software or not.

With the unit set to the US2 option it should be transmitting and receiving at the same 200kHz and 83kHz as the standard DualBeam units do (and the Si units do).  From your testing there must be some difference in each unitís circuitry and/or software to explain the differences you are seeing or there may be something wrong with the 2D sonar in your 998c Si unit.  Only way to know for sure would be to test another 998c Si unit (or a 898c Si unit) and see what the results are.
Greg Walters at Humminbird

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