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Axiom 9 showing double depth
08-07-19, 05:49 PM (This post was last modified: 08-15-19 11:19 PM by Tom - Raymarine - Moderator.)
Post: #1
Axiom 9 showing double depth
Yesterday while using my Axiom 9 it intermittently started showing a 'reflected' bottom with double depth. We could reboot and it would then show correct depth. Today, it's always showing that reflected bottom and double depth. Re Rebooting doesn't correct the problem. Am I doing something wrong? Any advice on correcting the issue would be appreciated.
Thank you. jc
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08-15-19, 11:28 PM
Post: #2
RE: Axiom 9 showing double depth
Hello jc,

No, there's nothing you're doing wrong, it's just a result of the fact that the Axiom is sensitive enough to pick up the 'second-echo'. This is most common with a fairly flat, firm (e.g. sandy) bottom and calm conditions, when the sound energy from the transducer reflects off the bottom, up and back off the flat water surface and vessel hull, back down to the bottom and finally to the transducer after a double trip. It's a well-known sounder phenomenon. The second echo is strong enough sometimes that the sounder can think that it's the real bottom and the first return is a mid-water bait school or thermocline, and that sounds like it's what's happening in your system sometimes.

You can hide it if you wish by manually ranging to a slightly shallower depth. Note that if you do this you may still pick up a faint 'ghost' of this second echo as 'second echo interference' in between the real bottom trace and the surface, depending on the relative timings of the pings (ping-rate limit setting, true water depth, current range scale.) If this happens, you can reduce or remove the second-echo interference by turning on the interference rejection (IR) and 2E-IR in the sounder's setup menu, and/or by reducing the Ping Rate Limit.


Raymarine since 1999.
Interests: Diagnosis of problems in sonar/fishfinders, NMEA2000, ethernet comms, autopilots, thermal cameras
Location: Sydney, Australia.

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