Humminbird sidescan sounders

ronje
Jedi Seadog
Jedi Seadog
Posts: 2077
Joined: Sat Feb 14, 2009 5:23 pm
Contact:

Re: Humminbird sidescan sounders

Post by ronje » Thu Jul 11, 2019 9:43 am

Here's a screenshot of the o/b leg effect.
Sidescan 1.PNG
I picked a non-descript bottom with similar ground each side of boat.

The bottom half of the image shows the screen with the leg raised back and up from the transducer line which is mounted on the starboard side.

The leg gearbox etc isn't in line with the transducer. Its further back from the transom than the transducer but still interferes due to beam "leakage" at close range.

Port side image a bit darker. Note the bottom line where the beam meets the bottom on the left and compare it with where the beam meets the bottom on the right. Change line is less distinct on the left. Right is pretty clearly defined for a mud/sand bottom. Bit more bottom detail on the RHS.

Lesson 1 is that o/b leg still has an effect despite being raised.

The top half of the image shows when the leg is lowered. Bottom detail to left is nearly gone. It'd take a pretty strong return to been seen easily.

In addition, the bottom/beam line is practically non-existent.


Note also that there is no discernible image change on the RHS no matter where leg is.
You do not have the required permissions to view the files attached to this post.


Regards
Ronje

Ocean Storm Fishing Tackle
al57
Seadog
Seadog
Posts: 236
Joined: Tue Jul 31, 2018 11:41 am
Location: hervey bay qld

Re: Humminbird sidescan sounders

Post by al57 » Thu Jul 11, 2019 10:23 am

after this dicussion i will have to do some research on my lowrance hds 9 gen 2 ,didnt realise there was that much interference with the leg

ronje
Jedi Seadog
Jedi Seadog
Posts: 2077
Joined: Sat Feb 14, 2009 5:23 pm
Contact:

Re: Humminbird sidescan sounders

Post by ronje » Thu Jul 11, 2019 6:26 pm

I'll be interested, Al.
Regards
Ronje

NinjaFish
Jedi Seadog
Jedi Seadog
Posts: 614
Joined: Sun Aug 27, 2017 8:20 am
Location: Darwin

Re: Humminbird sidescan sounders

Post by NinjaFish » Thu Jul 11, 2019 8:28 pm

I’m wondering if it could be prop wash ?

I’m reading this with interest but same as FlickIn, I have no issue with my Lowrance units but, there’s so much to consider in the mounting of transducers. I haven’t used a Hummingbird for 20 years though and maybe they’re more sensitive than a Lowrance nowadays?

Silly question... could you have it mounted too far out causing shadow?

ronje
Jedi Seadog
Jedi Seadog
Posts: 2077
Joined: Sat Feb 14, 2009 5:23 pm
Contact:

Re: Humminbird sidescan sounders

Post by ronje » Fri Jul 12, 2019 6:35 am

Not prop wash. Effect remains with motor off and gliding through water.

I believe that the problem is really this.

Beamwidths of transducers are not cut and dried. A beamwidth of 20 degrees is not simply 20 degrees. The 20 degrees comes from measured points across the beam where the power level transmission drops to half power in that direction. That's 3 decibels (-3 db) in technical talk.

So while half the transmitted power goes out within that 20 degrees, half of it also goes out in wider angles than the 20 degrees. They're called lobes.

Here's a simple diagram of a transducer beam.
Beamwidth.png
Note the lobes outside the "specified cone".

A signal reflected from an object to the port side but very close to the transducer will hit the transducer as a return at a reduced level even though its outside the "specified cone" angle.

The strong unwanted return from very close by can mask a return from an object within the "specified cone" but much further away . In this case the masking shows up as per the image I put up yesterday.

Lifting the motor so the prop is clear of the water solves the problem but then you can't move around to search for fish unless you have an electric (very slow esp in adverse run).

Interestingly, Humminbird use one tenth power level points of a beam to measure their beamwidth angles. -10db points.

Therefore Humminbird's beamwidths will seem to be wider than others but they're not in reality. Its just a marketing ploy as there are no standard beamwidth measuring standards with the sounder industry. Most use -3db points and H'Bird use -10 db points (but they tell you that and 99% of the buyers wouldn't know what that meant.)

Clear as mud?
You do not have the required permissions to view the files attached to this post.
Regards
Ronje

User avatar
Sullo
Seadog
Seadog
Posts: 336
Joined: Tue Dec 11, 2012 4:51 pm

Re: Humminbird sidescan sounders

Post by Sullo » Fri Jul 12, 2019 1:57 pm

Side scam is only a 1-2mm slice x 180deg,not really a cone.

ronje
Jedi Seadog
Jedi Seadog
Posts: 2077
Joined: Sat Feb 14, 2009 5:23 pm
Contact:

Re: Humminbird sidescan sounders

Post by ronje » Fri Jul 12, 2019 6:55 pm

Who told you that?
Regards
Ronje

User avatar
Sullo
Seadog
Seadog
Posts: 336
Joined: Tue Dec 11, 2012 4:51 pm

Re: Humminbird sidescan sounders

Post by Sullo » Fri Jul 12, 2019 7:11 pm

UNDERSTAND THE BEAM
Humminbird® Side Imaging® Sonar uses a razor thin beam to take a “sonar snapshot” of the area up to 240 ft. to the left and right of your location.

ronje
Jedi Seadog
Jedi Seadog
Posts: 2077
Joined: Sat Feb 14, 2009 5:23 pm
Contact:

Re: Humminbird sidescan sounders

Post by ronje » Fri Jul 12, 2019 7:16 pm

Did you take "razor thin" to mean 1-2mm?
Regards
Ronje

User avatar
Sullo
Seadog
Seadog
Posts: 336
Joined: Tue Dec 11, 2012 4:51 pm

Re: Humminbird sidescan sounders

Post by Sullo » Fri Jul 12, 2019 7:52 pm

Just what i always thought it was, and what humminbird says it is

Is it a cone or oval beam?

ronje
Jedi Seadog
Jedi Seadog
Posts: 2077
Joined: Sat Feb 14, 2009 5:23 pm
Contact:

Re: Humminbird sidescan sounders

Post by ronje » Sat Jul 13, 2019 5:43 am

When viewed from above, Its an elongated beam like a oval shape stretched out to make it thinner but longer.

Probably a better way to describe it is the term "fan shaped".

Its actually a 3 dimensional shape. The terms "cone" and "oval" only refer to the 2 dimensional shapes and then only to the main 3 D pattern.

ALL beam patterns have "lobes" that fire off in different directions.

To look at beam patterns from transducers (or radio antennas), you need to see what's called a polar diagram which shows both a horizontal view and a vertical view of a single pattern.

I'll put one up on here so u can see what I'm talking about.

"Razor thin" is one of those of those marketing descriptions I was talking about
Regards
Ronje

al57
Seadog
Seadog
Posts: 236
Joined: Tue Jul 31, 2018 11:41 am
Location: hervey bay qld

Re: Humminbird sidescan sounders

Post by al57 » Sat Jul 13, 2019 9:01 am

out yesterday in the salt .fished 3 mtrs of water mostly ,when motor was down there was a thin line right in centre of sounder with the normal pics both side ,i did notice the side where beam was interupted with leg that it was a lot fuzzier but still showed structure.i lifted the motor fully and the thin blue line dissappered and fuzziness went .the prob with that is my main reason for side image is in the fresh after barra and lifting the leg totally it destroys the steering when moving along the edges just to make the picture clearer .i will have to do a few tests next trip out to dam .i really dont want to put another big transducer on the other side though ,as people with lowrance sounders know the transducers are enormous

ronje
Jedi Seadog
Jedi Seadog
Posts: 2077
Joined: Sat Feb 14, 2009 5:23 pm
Contact:

Re: Humminbird sidescan sounders

Post by ronje » Sat Jul 13, 2019 9:55 am

Did you get any screenshots, Al?
Regards
Ronje

ronje
Jedi Seadog
Jedi Seadog
Posts: 2077
Joined: Sat Feb 14, 2009 5:23 pm
Contact:

Re: Humminbird sidescan sounders

Post by ronje » Sat Jul 13, 2019 12:10 pm

Sullo

The sounder manufacturers don't like showing their transducer polar diagrams to their competitors so are reluctant to publish them.

However, here's one showing a horizontal pattern. Imagine a boat heading towards the 0 degrees up the page and you're looking from above.

To create a narrow beam the piezo-electric crystals/ceramics are "stacked" both electrically and physically to shape the beam pattern. A narrow fan shaped beam means lots of stacking so the transducers have to be bigger. The pattern is also dependent on the frequency.
polarPattern.jpg
]

Imagine the pattern each side is a sausage balloon. To make narrower, put a flat surface plate on it and press. You'll see that it'll get narrower/flatter and that the compression makes bits of the balloon bulge out at different places mainly at the centre like the diagram does. See the lobes. Flatten it more and you'll get more lobes developing close to the transducer as well as the beam being squeezed out longer.

And its from those lobes at the transducer where the o/b motor leg gets hit by the lobes at very close range, reflections occur and interference develops.

Here's another image showing the 2 different types of pattern imaging but its not in scientific polar diagram. The bottom part of the image shows the simple side-scan pattern (but doesn't show the lobes that actually exist)
polarPattern.jpg
The last diagram shows how "thin" Humminbird's description actually is. If the beam had a width of 2 degrees (which it hasn't), the diagram shows how wide the beam actually is. 340mm @ 10 m and less coming in closer to the transducer. A transducer that only has 1-2 degrees of beamwidth would be one towed underwater and 2-3 metres long to accommodate the "stacking" required to get very narrow beams.
Sidescan.jpg
Still trying to come to terms with the new attachment arrangements. Bit jumbled up. Sorry
You do not have the required permissions to view the files attached to this post.
Regards
Ronje

al57
Seadog
Seadog
Posts: 236
Joined: Tue Jul 31, 2018 11:41 am
Location: hervey bay qld

Re: Humminbird sidescan sounders

Post by al57 » Sun Jul 14, 2019 8:12 am

soory didnt get any ,i will get a few once out again

Post Reply

Return to “Electronics”