Transducer installation question.

[dingbat]

The problem with an in-hull is two fold. Your loosing power thru absorption and introducing a frequency switch.

3db is typical used to calculate the peak response plateau. On a low "Q" transducer you could have a max. sensitivity window of plus or minus 2 kHz.

The frequency shift of a signal passing thru a hull is well documented http://www.airmartechnology.com/uploads/installguide/In Hull Frequency Shift.pdf

 

[alldodge]

My first impression was the OP (Bluedart) was discussing the installation of a depth sounder and locations. In the first or subsequent posting by BD I saw nothing where maximum accuracy was requested. If the signal is attenuated a bit, the cone is not straight down, or some effect changes a reading slightly doesn't appear to be an issue (correct if wrong). If a reading is off a reading at 300 plus at 40mph may not be an issue, so long as it can read below 50ft at 40 mph.

 

[bruceb58]

My first impression was the OP (Bluedart) was discussing the installation of a depth sounder and locations. In the first or subsequent posting by BD I saw nothing where maximum accuracy was requested.

He asked for it in the first post.

From the experiences of those reading which is the easiest install for a semi handy chap along with greatest accuracy?

 

[dingbat]

If the signal is attenuated a bit, the cone is not straight down, or some effect changes a reading slightly doesn't appear to be an issue (correct if wrong). If a reading is off a reading at 300 plus at 40mph may not be an issue, so long as it can read below 50ft at 40

The attenuation of the signal will have no effect on the accuracy although you'll loose a couple feet off max. depth from the power loss

 

[alldodge]

He asked for it in the first post.

I am so sorry Bruce and sorry that I wasn't paying enough attention, my deepest apologies to you sir

 

[bruceb58]

I am so sorry Bruce and sorry that I wasn't paying enough attention, my deepest apologies to you sir

That's ok...we are all used to it.

 

[Texasmark]

You might want to look up what CHIRP means.

Best place to mount is on the transom.

It means compressing a variety of frequencies in time such that their peaks occur at the same instant, maximizing the amplitude of the combined energy. Each element of a target reflects a different frequency differently. By changing frequencies across the target you maximize the response of each peculiarity of the target. Something you use in periscope detection with something like a folded tape meandering line to do the pulse compression or in todays world a digital harmonic filter.

So are you going to tell me that current day depth finders chirp their carrier frequencies?

 

[bruceb58]

So are you going to tell me that current day depth finders chirp their carrier frequencies?

Yes they do. And some expensive ones are doing spread spectrum so in those its a coded chirp with phase shifts with a correlator at the receiver. Simple sonar chirps are just doing a pulse with a frequency sweep within or between pulses.

It means compressing a variety of frequencies in time such that their peaks occur at the same instant, maximizing the amplitude of the combined energy.

That kinda describes what is done in the receiver of spread spectrum radar/sonar. That is the result of the correlation.

 

[dingbat]

http://www.airmartechnology.com/uploads/Brochures/CHIRP_Presentation_2015.pdf

 

[Texasmark]

Well it's just not fair. Today's technology just doesn't respect the pioneers of most everything, like our ancestors crossing this great country. Having worked my ass off in a trade with what we had at our disposal....designs limited by available components mostly. I am glad I retired 10 years ago. Todays madness is just out of my league. Problems most people using all this stuff today have no earthly idea as to what it took to get it to what they have today. But so what! A friend's son is getting a laptop for Christmas. He's 3!

 

[bruceb58]

I was designing digital pulse compression radar receivers back in 1986. Hardly new technology.

 

[Swoosh3]

I'm going the previously suggested route myself. pick a location on the starboard side of the transom, not too close to the prop
and clear of any trailer rollers. Drill two slightly oversized holes only part way in, not through transom, fill with 5200 and let set.

Drill the correct size holes for your mounting screws out of the 5200. Goop up back of a small piece of Starboard and attach
to transom.
Follow install directions that came with your electronics from there.

Personally the science behind how my electronics work matters not to me....only that they do.

I'll add..I am in awe of the people that thought,designed and executed building such things, thank you.

 

[BlueDart]

Thanks to all and must admit that information provided was at times more technical than a "non techie" like me to fully comprehend.
I'm very impressed with this forum as it provides new boaters and even veteran boaters looking for advice to get just that ... good advice.
Thanks to all.
My comfort level is to go with a transom plate glued in place with a transit mounted transducer depth finder.
It appears from my research and the many comments here that this should give me reasonable accuracy with minimal installation challenges.
Note that it is fully acknowledged that having a depth finder does not guarantee against running aground ... one must still run a boat responsibly.
Stay dry and those of us living in the north will anxiously await spring so we can get out on the water.

 

[Texasmark]

I was designing digital pulse compression radar receivers back in 1986. Hardly new technology.

Yeah but you didn't have an ipad to do your calculations and depth finders were analog time domain devices........ Hmmmm '86 not long after the HP 45 replaced the K&E Deci-Lon slide rule and the card reader became a thing of the past thanks to the digital computer.

 

[bruceb58]

Yeah but you didn't have an ipad to do your calculations and depth finders were analog time domain devices.

Believe it or not, we actually had PCs back then and everything was digitized in the radar receiver after everything was mixed down. Not sure I have ever seen anyone use an iPad to do engineering calculations

A/D convertors that we used were $2k at the time and we used 4 of them so they were too pricey to go into consumer electronics. Military sonar was using pulse compression tech back then as well.