Topic: HB Greg, sonar cycles, pixels, chart and boat speed

[promapper]

Greg

I started a new topic here as i thought I was getting off topic in another thread.

Can you describe what a 'transmit/receive cycle' consists of?

Also, how does this cycle relate to the pixel rows or columns being displayed?  And how does chart speed or boat speed relate to the cycles?  I assume the cycles are somewhat consistent in time???

I also note a lot of posts say the best detail is with a boat speed of from 2 to 4 mph.  Is that just because of the motors in use?  It is easy if running a trolling motor to match a boat and chart speed of 1 which I would think would give you the best resolution or have you reach a point of diminishing return meaning the detail is only as good as the least of all the variables?

Greg G

Thanks

[Humminbird_Greg]

Greg,
When the unit transmits, it does not transmit just one cycle of sonar energy; it transmits a burst of sonar energy than it listens.  Depending on how deep the water is will depend on how long this burst of energy is.  How often it has to update the display will help determine how many of these transmit/receive cycles it can perform.  That is why the most detailed images come from a slower moving boat.

The best detail will come at slower boat speeds due to the limitations of how often the unit can transmit/receive.  There are some on this board who get very good detail from a boat moving at less than 1 mph and many more that get good detail up to almost 10 mph (this is usually more dependent on transducer installation and how the water flows off the boat hull).  The detail will be only as good as the least of the variables which could include the display you are viewing them on (and in my case: the strength of my bifocals!).

[rnvinc]

Well...I learn something every day....

It was much easier to explain when I thought it was 1 sound pulse "ping" per cycle...

Now I get to explain it as a "burst" of sound energy....(that does sound cooler...lol...)

Rickie

[promapper]

Good info.  Thanks!

[Humminbird_Greg]

Well...I learn something every day....

It was much easier to explain when I thought it was 1 sound pulse "ping" per cycle...

Now I get to explain it as a "burst" of sound energy....(that does sound cooler...lol...)

Rickie

I dunno, I think that “ping” sounds pretty cool…
[Hunt for Red October] Captain Ramius: Give me a ping, Vasili. One ping only, please

[rnvinc]

Here is a what I hope to be a "reasonable" explaination of this "burst of energy" that Greg speaks of..(and of which I, and others, have always blanket labeled the "ping"...)

Copied from an interesting read at thehulltruth forums in a thread discussion about CHIRP technology....(this is a long and growing read...and mostly over my head...but it has tidbits of info that really help understand "pulse lengths" and their effects on resolution of the sonar image..)
http://www.thehulltruth.com/marine-electronics-forum/506221-chirp-sounders-fish-finder-explained.html

Quote: Recall that traditional sounders send a single tone pulse (usually 50 or 200 KHz) and listen for the return signal. The length of the pulse determines the resolution of the system looking down. Hence, the smaller the pulse, the better or finer our ability to separate targets (e.g. fish). On the other hand, the pulse also determines the power injected into water. So the longer the pulse the better. As an example, if I have a 1 millisecond pulse (1/1000 sec) and I have 500 watts in my sounder, the actual net power in the water is 0.5 watts. If I keep the transmission power fixed, then my only option for more power to combat losses due to depth, is to increase the pulse length. But if I did that, I would lose resolution. Clearly then there is conflict in traditional sounders between wanting to have enough power to get a reasonable signal back and wanting it to be short enough to tell objects apart.

Rickie

[promapper]

Thanks Rickie.  A good explanation.  I don't suppose multi beam has any relationship to this forum as I believe it is low frequency and limited to high resolution data for bathymetry.  It is a neat system though.

[Philip Brown]

Thanks Rickie.  A good explanation.  I don't suppose multi beam has any relationship to this forum as I believe it is low frequency and limited to high resolution data for bathymetry.  It is a neat system though.

So.... 7 years later, I chime in to say that this is really cool!!!   It also provides some context as to why Humminbird now offers CHIRP, and how and why CHIRP can give you the best of both worlds, at least to some extent!