Topic: Does SI Range Affect Ping Rate?

[Bob B]

I am trying to understand how the SI range setting affects the unit.  I know objects will appear larger when the range is reduced, but wondering if other things might be affected by reducing the setting.

To put it another way, is the range setting simply a "zoom" function or does the range setting actually let the unit scan faster and therefore allow more hits and clearer images?

[RGecy]

Bob,

you are absolutely correct. The ping rate is affected by the  SI range as well as the 2d depth.

I'm on the road right now but will post more on this later. Maybe chuck or 1 of the guys can add some more information to this. 

robert

[Bob B]

Thanks Robert,
I apprciated the feedback.  It helps a lot when trying to operate the unit to understand what is actually being affected.
I am not in a rush, but would  appreciate as much insight as you or others can provide about this.

I am already encouraged that the si scan rate increases as the range decreases.

[RGecy]

Bob,

I understand there has been some discussion on this topic and thought I would answer your question here.  The ping rate is definitely affected by SI and 2d depth.  If the SI range is set to max and 2d is very shallow (say 10') the unit still has to listen long enough to allow the SI signal to return, so the SI is range is affecting ping rate.  An to the contrary, if the 2d depth is very deep, lets say 300', the unit will have to listen a little longer to hear the 2d return.  Of course we see a significant slow down in the unit when it loses bottom signal on the 2d return.  What happens is, when the loses bottom signal it adjust the ping rate to listen longer, thinking it may be in deeper water and the ping rate drops to maybe 1 a second or even less, until the unit gets a solid return.  Then it adjust the ping rate back to the correct depth.

This has all been verified by examining the recording files.  The ping rate for 2d and SI are matched at all times, regardless of which depth or range is changed.

There is an adjustment of the ping rate that was in earlier software versions that would slow the rate down, but this affected both 2d and SI.  It was put there as a way to reduce file size on the recordings.  But as cards got bigger, it really doesn't make any sense to not record the pings at the max.

Hope that makes sense.

Robert

[newkid4si]

I copied/pasted part of an old post that may have interesting info on this.

       Topic: 798 quality scan...  (Read 186 times)

 xSilmarilSx

Unit(s): HB 798ci SI HD - HB 778c Quad Beam
Software: 6.250 - 5.320
Accessories: TG W, NMEA Cable, Ethernet

798 quality scan...

« on: May 06, 2012, 12:26:10 PM »

I just got my first day on the water with a 798HD.

Now, I have questions for the seasoned guys here..
From what I have deduced, quality wise, you have a couple of choices to make a good recording.
You have to choose a speed ans chart speed that match closely. This is the easy part.
But next you must choose the width you want to scan and the depth you will be scanning.

The big problem is that the width and depth will change the unit ping rate and the speed the
screen update.
So, for example, with a speed of 5 mph and a chart speed of 5 (which people here seem to agree)
will produce different results in 5 ft or 50 ft of depth, and 50-200ft of width.

So, the deeper you get, and the farther you want to scan, the slower the boat need to be to
produce the maximum number of pings par distance travelled.

I checked quickly, and to achieve a ping of around 100ms ( 10x a second) you must scan at no
farther than 75 feet each side, in max 50ft of depth.

With a little math here, if we choose the above setting of 10x pings par second and want to resolve
a image with a resolution of 1 in par ping, we must travel a max 10" per second. (10 pings of 1" each)

10 in/s is 0.56 mph

At 5 mph scan speed, you can't resolve detail smaller that 10" in scan resolution.
Chart speed have no effect on ping speed as I can see.

I will check next on the beam width to see what are the resolution the 455 kHz beam can theoretically
achieve.

What are your thoughts on this one?
Any tips on resolving the max detail on side imaging?
 xSilmarilSx


Re: 798 quality scan...

« Reply #1 on: May 06, 2012, 12:41:32 PM »

Ok, so with a little research, I found that the 455 kHz SI transducer should obtain a beam width around
1.7°.

With a little math, we can obtain that on a 75ft wide scan (each side, 150ft total), the maximum resolution the beam can achieve, is around 2-1/4"

So at 2.25" per pings, with a speed of 10 pings per second. For maximum image quality we need a speed of 22.5" per second.

Which translate to 1.3 mph.

Beam resolution:

50 ft = 1.5"
75 ft = 2.25"
100 ft = 3"
150 ft = 4.5"
200 ft = 6"


I will investigate the ping rate of each side range to check the best speed for each scan width.
 xSilmarilSx

Re: 798 quality scan...

« Reply #2 on: May 06, 2012, 07:46:34 PM »

I have found the data on the ping rate of the unit.

50ft scan = 85ms avg
75ft scan = 105ms avg
100ft = 125ms avg
150ft = 165ms avg
200ft = 206ms avg

With the remaining data posted above, the best theoretical speed for optimum image quality is:

50ft = 1.0mph
75ft = 1.27mph
100ft = 1.36mph
150ft = 1.53mph
200ft = 1.7mph

With a speed between 1 and 2 mph will produce maximum image quality for almost every settings.
 xSilmarilSx


Re: 798 quality scan...

« Reply #6 on: Today at 01:37:57 PM »

Since we have no replies here, I will add some more information that I have found analyzing the HB data.

Everyone can agree that HB use the 200 kHz signal to derive the depth.
And with the depth data, HB adjust the ping rate of the 2D AND SI beams.

So, to collect the maximum data per unit of length, you need 2 things: fast Ping rate and slow speed.

With the above calculation we can find the best speed for the best imaging.
Now, with my researches, I discovered that the Ping rate and depth calculation form HB can greatly
improved with a little setting in the unit.

From a decision from HB engineers, the ping rate is set to 4 to 7 times the depth found by the unit.
This process enable the unit to have data well below the real bottom and provide a clean image in the
case the screen changes ranges. If you check a Lowrance/Garmin video, when the unit change depth, you will seen a blank screen in a section when the unit changes range.

The problem with the HB setting, is that the ping rate is greatly reduce because the unit must wait to receive data from 7 times the real bottom.

Here are the data I collected.

depth = ping depth
10ft = 75ft
20ft = 75ft
30ft = 90ft
40ft = 140ft
70ft = 230ft
100ft = 380ft

So if you are standing in 100ft of water, the unit slow down to wait for signal coming back from 380ft of water.


Now, the simple way of bypassing this "semi-problem" is to set the MAX DEPTH RANGE in the unit to a range just over the depth of the lake you plan of fishing/mapping.

So in a 100 ft lake, just set the MAX range to 130-150ft.
You will see a boost in speed from the Live view, screen refresh, Si refresh just by doing this simple change in your settings.

You can even try this in simulation mode!

                           Mike

[RGecy]

Not sure I completely agree with all statements in Mike post you copied.  Setting MAX DEPTH will certainly help with the issue of losing 2d bottom reading and causing the unit to listen longer, but what if you are scanning SI at 240' with MAX DEPTH set to 150'.  The unit is going to take the higher of the two and use that as its baseline for the ping.

As for 4-7 times depth I would have to do some checking with some math.  I can see where this would occur at shallow depths, but mainly because you really don't need to ping THAT fast.  The electronics do have some limitations as to how much data it can process.  So in return, the unit just listens longer.  I will take an educated guess and say as you go to greater depths, this multiple is actually reduced.

As for Bob B's question on weather 2d and SI affect ping rate, I think that we can conclusively show that both have some determining factor in the rate at which the unit pings!

[Bob B]

Thanks Robert....I think this is starting to make sense.

I think the reason some thought the SI range didn't affect the ping rate was that the history on the SI screen seems to adjust instantly when the range is changed.....That seems to show that the unit was processing data wider than the range was set to.
It may be that this phenomena would vary depending on the water depth.

[Bob B]

I also found the discussion about adjusting the boat speed based on the ping rate to get the best images.

Adjusting the scroll speed based on the boat speed would be the other variable to consider there.

Seems like ping rate, boat speed and scroll speed would all play together in creating the best image.

[Humminbird_Greg]

Hey guys, I checked with an Engineer on this just to make doubly sure:
"If 2D is pinging deeper than SI Range, SI will ping at the same depth as 2D.
If 2D is pinging shallower than SI Range, SI will ping at the set SI Range."
So it looks like the SI Range could affect the ping rate, depending on what the water depth is.

[LittleGazoo]

Hey guys, I checked with an Engineer on this just to make doubly sure:
"If 2D is pinging deeper than SI Range, SI will ping at the same depth as 2D.
If 2D is pinging shallower than SI Range, SI will ping at the set SI Range."
So it looks like the SI Range could affect the ping rate, depending on what the water depth is.

Not to nitpick, but:

On the water, wouldn't 2D ALWAYS be pinging shallower, otherwise all SI would be is the water-column?
Operation standard is to set SI three times depth?

So SI Range controls the ping-rate.  Or am I not seeing something?

[ezfishn]

Greg,
Referring to your statement "If 2D is pinging deeper than SI Range, SI will ping at the same depth as 2D".   Confusing to me...are you actually saying depth or that it will ping at same rate?  Also, suggested to me and mentioned in above post, was changing Max Depth setting to affect ping rate in order to reduce crosstalk between two units. 

[Humminbird_Greg]

LG,
“On the water, wouldn't 2D ALWAYS be pinging shallower, otherwise all SI would be is the water-column?”
No, someone could have their SI Range set to less than the water depth.

“Operation standard is to set SI three times depth?”
2x to 3x the water depth is a recommended starting setting for the SI Range, but once you develop a better understanding of the Si sonar you should change it to better fit your needs.

“So SI Range controls the ping-rate. Or am I not seeing something?”
The SI Range can control the ping rate but so can the water depth.

[Humminbird_Greg]

Greg,
Referring to your statement "If 2D is pinging deeper than SI Range, SI will ping at the same depth as 2D".   Confusing to me...are you actually saying depth or that it will ping at same rate?  Also, suggested to me and mentioned in above post, was changing Max Depth setting to affect ping rate in order to reduce crosstalk between two units. 

ezfishn,
I think that he really meant water depth instead of rate.  I copied what was sent to me as sometimes my fingers type something I did not intend them to and I don’t always catch it before posting.  So copy and paste was faster and more accurate than typing for me.

Changing the Max Depth menu setting could help but only if the two transducers were farther apart than the water depth.  I don’t see how it could help if both were on the same boat.

[Bob B]

If bottom signal is lost by the 200Khz transducer, the unit will wait longer to see if it gets a bottom return.
I think the intent of setting the max depth is to keep the ping rate from slowing way down if the bottom signal is lost.

[RGecy]

Greg,

Thanks for confirming this with engineering!   

Robert

[ezfishn]

ezfishn,
I think that he really meant water depth instead of rate.  I copied what was sent to me as sometimes my fingers type something I did not intend them to and I don’t always catch it before posting.  So copy and paste was faster and more accurate than typing for me.

Changing the Max Depth menu setting could help but only if the two transducers were farther apart than the water depth.  I don’t see how it could help if both were on the same boat.

Thanks Greg....guess I'm being dense....that sometimes comes with older age too....LOL  Don't know how you can stop the actual ping in terms of water depth.  Isn't it really what min/max settings allow you to view on the screen.  Sound keeps on going unless it dissipates or cannot be detected. 

[Humminbird_Greg]

You don’t stop the actual ping (transmit pulse), you just stop listening after a certain period of time.  Remember that sonar is time based, so if you don’t listen long enough to hear a sonar return from 200 feet away you will never hear it (and it won’t be shown on the display).

[ezfishn]

You don’t stop the actual ping (transmit pulse), you just stop listening after a certain period of time.  Remember that sonar is time based, so if you don’t listen long enough to hear a sonar return from 200 feet away you will never hear it (and it won’t be shown on the display).

Thanks Greg...I should have known that...just a simple matter of timing the receiver on/off.