Topic: Leak between channels on helix 10 g2n

[sjefsrafsern]

Hi, we have notice something that look like a leak between the si and DI channels on the new helix 10 mega. The image below show a pipeline with floaters at the surface on the right Si with a reflection/leak in the DI image. Have anybody had similar experiences? If so did you manage to get rid of it or do we need a software fix to get rid of ghost echoes?
Best regards
Stig

[Rickard]

Hi Stig,

I'm not an owner of a Helix or any other "true" DI/SI capable unit, but I think I understand why this happens. It's not about a leak between channels, it's simply what happens when an object (the pipeline) is located where the DI and SI beams cover the same region in the water. All SI transducers I have used cover a wide angle from the surface to straight down towards the seafloor. An SI transducer is directed towards the seafloor, but it must have some width which means there must be a region that is covered by the DI beam and the SI beams. Thus, an object may well appear in the DI and SI views at the same time.

Rickard

[sjefsrafsern]

Hi Rikard and thanks for Your reply. im am aware of this effect and we use this to decide where the Fish is in the water column. sadly this is not the case in this image as the pipeline were foating on the surface as they were going to do maintenance work on it. and there is no way the 75 degree angeled di beam could Reach that, or at least it should not do that. so im still thinking it is a ghost from the si beam or some hole in the software. but maybe you have could share some Insight or therories on that?
best regards
Stig

[Rickard]

Sorry, I didn't read your post carefully... I thought the floaters and pipeline were suspended at some depth. Still, I suspect my explanation may hold. In theory, all transducers with a flat sound window transmits in 180 degrees, but with very low intensity close the extremes. A very reflective object may send back sound that can be received and displayed even if the object is located much farther from the central beam axis than the beam angle specified for the transducer. One must also consider refraction due to temperature differences. Cold surface water and warmer water below sometimes bends the beam alot. I remember one morning when I planned for using SI. All that was shown in the display was a few meters with seafloor, the rest was waves as they appear from below! I then realized the surface water had been cooled down during the night while the water a few meters down still was warm. Of course this is not the only possible explanation for your observation.

Kind regards, Rickard
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[sjefsrafsern]

Intersting, ive never seen anything like that i think. Ad long as the contitions (waves and rain, i wish we had 455khz 130° for those conditions) alow me to use the 455khz i have never experenced that i could not see my planerboards when i make a turn. But ive never really cared to look at the bottom/sea bed as suspending fish trout (and sometimes salmon in lake vaneren) is my primary target. And for this purpose the 455khz is outstanding and probably the best tool ever. But that was aturn outside the track, but you do actually believe that the weak "side" returns of the di craystal is causing this rather than the element picking up a ghost for si at the same frequensy? Either way, i would like it removed. It kind of bugs my brain when the combination of different channels and math cant help me narrow down where the fish is located, it kind of brings up some trust issues between me and the helix... :-)
So would you have some thoughts on how to filter them out? Is this even possible, and in just about how many cases of hundred will this happen?
Best regards
Stig

[Bob B]

Rickard is much more knowledgeable than me on this subject, but I know the transducer all have side lobes that extend beyond the advertised beam angle.

[rnvinc]

Did you try the 800kHz sweep frequency  ...?? (Or 800kHz fixed frequency  ...??)

It is supposedly narrower than the 455kHz and may not pick up these fringe echoes in the DI beam  ...

Rickie

[sjefsrafsern]

Hi guys. No we did not try the 800khz, but even if that did remove these echoes it could just be because it did not pick up the 455 khz because it was set to read 800khz or is that wrong? If we are going to test that theory we will have to find some other test subject as the pipeline has been lowered back to the seabed now. And id prefer to find a filter solution to the 455khz problem as that frequensy is far superior to both 800khz and mega at theese depths and in open water. :-)
Best regards
Stig

[Rickard]

Hi, Rickie's idea reminds me of a problem with the "L-brands" first models with SI and DI. DI and SI were synchronized at the same frequency. This means the channels were transmitting and receiving at the same time resulting in various irritating phenomena in the images. If HB's DI/SI models do the same it is wise using different frequencies for DI and SI. Then there should be no risk for interference at the transducer level. With synchronized channels and the same frequency some returns from the SI direction (from the pipeline) may sneak in via the DI elements when the channels are in (synchronized) receive mode.The SI beam will actually act like a very strong sidelobe in the DI channels beam pattern. So, do we know if these units have synchronized DI/SI channels?

Rickard

[sjefsrafsern]

Yes it is this i was thinking about(but may not have explained good enough, as my english language skills arent really excelent...) :-) and that is why i thougt there would be some sort of software filter to remove those signals/ghosts from the si. :-)
Stig

[sjefsrafsern]

But if this is the case, i think Hb should work on a new software fix pretty soon with dfferent transmitt cycles.
I love this unit, but i think this is kind of important to work out. :-) as stated abowe the 455 is far superior to 800 and mega as they tend to phase out over deep water and will not show "weak" returns like fish in theese conditions. Due to theromclines, and currents (i think).The fish is the first thing that dissapears from the screen, examples on that is that i got some antifouling paint on the ducer once. Everything seemed fine exept alle the fish were missing, one of my friends has alternator noise from his suzuki df 140, bottom returns and everything looks nice, exept for the little most important thing, the fish only appear on screen when the motor is turned off(theese examples even phased out fish fron the 455khz). And the 455 is really the only option for us. :-)
Stig

[rnvinc]

As this floating object was a unique situation of where it was and why it was there  ... Is this ghost echo scenario going to be a frequent issue in the waters you fish ...??

Are there hard objects at the surface other than this pipeline creating ghost echoes in DI  ...??

I can't imagine fish on the surface creating a hard enough return to ever create these ghost echoes in DI  ...

Rickie

[rnvinc]

So, do we know if these units have synchronized DI/SI channels?

Rickard

We know the core numbered series SI units and HELIX G1 SI units capable of the "Jigging Mode" mode feature are alternating ping sequence  ...

Jigging Mode -  is a selection in the 2D Sonar Express Menu.  It allows the user to select the sonar ping pattern for use while vertical jigging.  When turned ON the ping pattern will be:  200 kHz, Left SI Beam, Right SI Beam, 83 kHz, repeat.  With this mode turned OFF the ping pattern will be:  200 kHz, Left SI Beam, Right SI Beam, 83 kHz, Left SI Beam, Right SI Beam, repeat.    Basically this feature prioritizes the 2D beam over the SI beam.

We have no confirmation of transmit cycle of the MEGA units (or ONIX/SOLIX units that also incorporate a DI piezo in the SI Xducer)  ...

Rickie

[sjefsrafsern]

Well that is really a part of the question (about the fish)? I guess we can try it out and try to trigger the same reflection /ghost with our planerboards. But that will have to wait for three weeks, when we having a brake from fishing tournaments. :-)
Stig

[Rickard]

 Rickie, very interesting info on ping patterns. This confirms the channels operate separately when transmitting which can eliminate inter-channel interference at that moment, but do they also sample incoming echoes in a way that isolates the channels from each other? I doubt they can. In receive mode all channels must wait for echoes from the moment the ping cycle ends which means a channel may pick up a signal sent from another channel. Sampling may occur in separate time slots for each channel, but signals transmitted by other channels may well interfere at the transducer surface on their way back and a channel can pick up something that was sent with another channel.
 
 What can be done with chirp to eliminate this problem? Suppose different channels using the same central frequency are given unique chirp profiles, would'nt that present a way to filter out unwanted signals? Is this used in the new chirp models?
 
 Rickard
 

[rnvinc]

Rickie, very interesting info on ping patterns. This confirms the channels operate separately when transmitting which can eliminate inter-channel interference at that moment, but do they also sample incoming echoes in a way that isolates the channels from each other? I doubt they can. In receive mode all channels must wait for echoes from the moment the ping cycle ends which means a channel may pick up a signal sent from another channel. Sampling may occur in separate time slots for each channel, but signals transmitted by other channels may well interfere at the transducer surface on their way back and a channel can pick up something that was sent with another channel.
 
 What can be done with chirp to eliminate this problem? Suppose different channels using the same central frequency are given unique chirp profiles, would'nt that present a way to filter out unwanted signals? Is this used in the new chirp models?
 
 Rickard
 

We just don't know yet Rickard (and maybe never)  ... HB only released the ping cycle scenario for the older core series SI units with the addition of the "Jigging Mode" feature around version 7.460  ...

There's quite a history on factors leading up to the release of the Jigging Mode feature (and the reasoning for it)  ... and I feel that HB would never have disclosed the ping cycle of their units at all if it were not for those factors leading up to Jigging Mode release  ...

I do have confirmation that the dedicated DI core units also use an alternating ping sequence (in an email from a HB CRC reply) that was offered to me during the same discussion time frame of Jigging Mode release  ...

I have requested info of ping cycle for MEGA, ONIX, and SOLIX xducers that have 2d/dedicated DI/SI piezoes in the same xducer housing  ... but I haven't received an answer  ...

Rickie

[rnvinc]

Well that is really a part of the question (about the fish)? I guess we can try it out and try to trigger the same reflection /ghost with our planerboards. But that will have to wait for three weeks, when we having a brake from fishing tournaments. :-)
Stig

It would be interesting to see your results  ...

I would guess that "normal" situations would be rare that there would ever be a hard target scenario (at the surface) similar to your floating cable scenario  ...

Planer boards may be such a small target that the ghost echo in DI may be difficult to pick out (as compared to your long floating cable target)  ...

Maybe a floating wave break or string of large buoys may create the ghost echoes noticeable in DI  ...

My ONIX also has a dedicated DI piezo in the same housing as SI  ... I will have to see if I can replicate your scenario of ghost echoes in the DI view from hard targets floating on the surface  ...

Rickie

[sjefsrafsern]

Hi again guys, we didnt really have to try to recreate this scenario.  here is a image showing our side paravanes in bot right si and di. Theese are the small planerboards/paravanes that you attach to your fishing line (supra cruz medium).
Stig

[Rickard]

Stig, Your new image is puzzling. The SI view (the right window) shows nothing in the left channel. Did you move along a very steep shore, that could explain the image? But there should at least be some trace of the seafloor close to 25 m (or feet?) even in the left channel. Something seems weird here.

Rickard

[Whistler]

I think this is caused by a bug in the previous software (pre 1.4) version.  When either DI or SI enhancement  is turned on (i.e. sharpness set to any value other than off).  If you disable the SI or DI enhance option or upgrade to version 1.4, this software bug should go away. 

I saw the same behavior in my Helix 12 SI G2N.  An upgrade to firware 1.4 corrected the problem.

[sjefsrafsern]

Hi again guys, our norwegian lakes are wery deep even close to shore. This together with our changing temperatures -30°c during winter to +30°c during summer(on good days)). Along with a lot of windy days, this give us a lot of underwater currents. So the right si and di show a underwater current that we are fishing along, as the fish tend to stick close to those (you can see some of them in di). :-)   sometimes they are strong like this, at other times they are smaller and weaker and will turn out in the si image the same way it diaplays the propeller trail from a passing boat. :-)
Stig

[sjefsrafsern]

Whisteler, tgis unit has the latest software. But it does have the sharpness set to low in both si and di as tha is an awsome feature for fishfinding. :-)
Stig

[Whistler]

Try turning the sharpness "off" and see if this doesn't go away.  In my case, the SI/DI view where the SI only shows the right side, definitely goes away.  The sharpness setting may be your issue.

[sjefsrafsern]

Whistler, there is no problem with the left si. Read my last post it is an underwater current that is on our right side. That displays on the right si and di. Turning off sharpness does nothing to prevent this, we tweak an turn theese units all the time to get optimal prefaormance in different conditions. :-)
Stig

[sjefsrafsern]

And whistler, turning off sharpness is no solution it will only hide the problem. Turn up you sens a tad, or turn the sharpness back on an the problem is back. I use this unit to find fish and track their movments in the water column, and to do that you need to be able to use high sens and low sharpness...
Stig

[Whistler]

Stig - I'm not making any excuses for Humminbird's lack of software QC.  In fact, if you look at some of my posts you'll see that I'm pretty frustrated by them as well.  My post was only intended to provide you with a work around to the problem you are having.  Whether or not you take advantage of that work around is totally up to you.