37KHz from Black Box

[mfeinstein]

Hey Dave, watching so many of your videos I know you worked for a long time with sonar buoys and other seismography related equipment for the navy, right?

With all the lastest news of the missing malasian flight, I keep hearing that the pinger inside the Black (orange) Box, sends a signal of 37KHz when it's under water...the thing that gets my curiosity is why 37KHz? Is it a "magic" number? Does signals in this frequency go further in the ocean? Does anyone has a knowledge why they chose this particular frequency as a standard?

Thanks!

[T3sl4co1l]

About 37kHz exactly, I don't know, but extremely low frequencies do propagate further in water.  Military submarine channels go all the way down to 50-90Hz I think.  Think of it this way: salt water is a conductor, and therefore exhibits skin effect; high frequencies are absorbed easily, or bounce right off altogether.

Tim

[mfeinstein]

About 37kHz exactly, I don't know, but extremely low frequencies do propagate further in water.  Military submarine channels go all the way down to 50-90Hz I think.  Think of it this way: salt water is a conductor, and therefore exhibits skin effect; high frequencies are absorbed easily, or bounce right off altogether.

Tim

Yes, that's exacly my point! I know as low frequency as you get, the further you can go...so why 37KHz? I think it's quite ""high frequency"" for this kind of application, isnt it?

[pickle9000]

Have a look here, bottom of the page.

https://www.eevblog.com/forum/chat/twenty-passengers-on-missing-flight-370-worked-for-freescale-semiconductors/360/

[Fsck]

I'd guess it's a frequency selected to not interfere or affect the ecosystem otherwise the tree huggers would be on a rampage, not used for long range deep sea communications to avoid interference and low enough to not get screwed by the physics of communication through the ocean.

[bench_knob]

Hey Dave, watching so many of your videos I know you worked for a long time with sonar buoys and other seismography related equipment for the navy, right?

With all the lastest news of the missing malasian flight, I keep hearing that the pinger inside the Black (orange) Box, sends a signal of 37KHz when it's under water...the thing that gets my curiosity is why 37KHz? Is it a "magic" number? Does signals in this frequency go further in the ocean? Does anyone has a knowledge why they chose this particular frequency as a standard?

Thanks!

www.radiantpowercorp.com/dk-series-underwater-locator-beacons.aspx

www.radiantpowercorp.com/dk-180-airframe-locator-beacon.aspx

[pickle9000]

The frequency and repetition rate was selected because it's not naturally occurring and therefore easier to find.

[mfeinstein]

Have a look here, bottom of the page.

https://www.eevblog.com/forum/chat/twenty-passengers-on-missing-flight-370-worked-for-freescale-semiconductors/360/

Which part? I dont see any part where someone explain why they picked this particular frequency for this purpose...

[mfeinstein]

I'd guess it's a frequency selected to not interfere or affect the ecosystem otherwise the tree huggers would be on a rampage, not used for long range deep sea communications to avoid interference and low enough to not get screwed by the physics of communication through the ocean.

Well it could be...I mean it could be 1000 things and people could especulate about it in here for ages but if someone knows for sure, it will be nice to share

[mfeinstein]

Hey Dave, watching so many of your videos I know you worked for a long time with sonar buoys and other seismography related equipment for the navy, right?

With all the lastest news of the missing malasian flight, I keep hearing that the pinger inside the Black (orange) Box, sends a signal of 37KHz when it's under water...the thing that gets my curiosity is why 37KHz? Is it a "magic" number? Does signals in this frequency go further in the ocean? Does anyone has a knowledge why they chose this particular frequency as a standard?

Thanks!

www.radiantpowercorp.com/dk-series-underwater-locator-beacons.aspx

www.radiantpowercorp.com/dk-180-airframe-locator-beacon.aspx

Thanks for sharing the specifications, but I dont see where it says WHY they chose this particular frequency, and not like 100Hz or 20KHz or 40KHz or 30KHz or even 35Khz or even 37KHz, but 37,5KHz :0 it sounds too magical for me...maybe they flip a coin, but i rather ask then speculate

[Wytnucls]

37.5kz is not the best frequency. There is a push to change that to a lower frequency to increase the detection range.

Today, aircraft are equipped with Flight Recorders with Underwater Locator
Beacon (ULB). The range of the current used Flight Recorder ULB’s is limited
due to the used frequency of 37.5 kHz.
An initiative has been founded to investigate in Wreckage Localization
Technology where among other things, a Low Frequency ULB transmitting on a
frequency between 8 to 9 kHz was proposed.
In 2012 SAE Aerospace has published an Aerospace Standard (AS6254) to
cover the Minimum Performance Standard for Low Frequency Underwater
Locating Devices (LF-ULB) transmitting on a frequency of 8.8 kHz ±1 kHz.
ICAO published its annex 6 amendment 36 (Nov 2012), stating that a LF-ULB
shall be installed on all aircraft with a maximum take-off mass of over 27,000 kg,
operating over water at particular distances to land suitable for making an
emergency landing.
This ICAO requirement is currently in the process to become national rules by
local Airworthiness Authorities.

[zapta]

IIRC Sonar range goes down by the square of the frequency but lower frequencies require larger hydrophones so it's a balance act.

[vk6zgo]

Hey Dave, watching so many of your videos I know you worked for a long time with sonar buoys and other seismography related equipment for the navy, right?

With all the lastest news of the missing malasian flight, I keep hearing that the pinger inside the Black (orange) Box, sends a signal of 37KHz when it's under water...the thing that gets my curiosity is why 37KHz? Is it a "magic" number? Does signals in this frequency go further in the ocean? Does anyone has a knowledge why they chose this particular frequency as a standard?

Thanks!

www.radiantpowercorp.com/dk-series-underwater-locator-beacons.aspx

www.radiantpowercorp.com/dk-180-airframe-locator-beacon.aspx

Thanks for sharing the specifications, but I dont see where it says WHY they chose this particular frequency, and not like 100Hz or 20KHz or 40KHz or 30KHz or even 35Khz or even 37KHz, but 37,5KHz :0 it sounds too magical for me...maybe they flip a coin, but i rather ask then speculate

It is probably a convenient division of  a standard crystal frequency.
If it comes to it,why are receiver I.Fs the weird frequencies they are?

[mfeinstein]

37.5kz is not the best frequency. There is a push to change that to a lower frequency to increase the detection range.

Today, aircraft are equipped with Flight Recorders with Underwater Locator
Beacon (ULB). The range of the current used Flight Recorder ULB’s is limited
due to the used frequency of 37.5 kHz.
An initiative has been founded to investigate in Wreckage Localization
Technology where among other things, a Low Frequency ULB transmitting on a
frequency between 8 to 9 kHz was proposed.
In 2012 SAE Aerospace has published an Aerospace Standard (AS6254) to
cover the Minimum Performance Standard for Low Frequency Underwater
Locating Devices (LF-ULB) transmitting on a frequency of 8.8 kHz ±1 kHz.
ICAO published its annex 6 amendment 36 (Nov 2012), stating that a LF-ULB
shall be installed on all aircraft with a maximum take-off mass of over 27,000 kg,
operating over water at particular distances to land suitable for making an
emergency landing.
This ICAO requirement is currently in the process to become national rules by
local Airworthiness Authorities.

That makes lots more of sense! It's still a frequency that doesnt require big hydrophones, but still can cover a lot more space...

[Wytnucls]

It may be in addition to the current system.
It is also important to use a frequency free from interference from other transmitters.

[zapta]

... a Low Frequency ULB transmitting on a
frequency between 8 to 9 kHz was proposed. ...

IIRC this is, the standard frequency for underwater voice commutation, 8.75 SSB or something like that. Used by submarines, divers, etc.

[VK5RC]

Don't you get better direction finding (phase difference between 2 separated mikes) at higher frequencies,  note the range went only to 3.6km in specs,  it's in close to 4.5km of water depth.

[dannyf]

The frequency and repetition rate was selected because it's not naturally occurring and therefore easier to find.

Bingo!

[David Hess]

It is probably a convenient division of  a standard crystal frequency.
If it comes to it,why are receiver I.Fs the weird frequencies they are?

Receiver IF frequencies are chosen to place their image and fundamental frequencies out of the way.

[MartinX]

37kHz is convenient because it is easy to make a reasonably cheap and small piezo electric transducer using existing technology from depth sounders and sonar, I wonder what they will use if they change to 8kHz it seems a bit low but maybe there is no problem, I am only speculating.

[mfeinstein]

I was expecting to hear from Dave by now... I dont see him replying much in the blog... I wonder what is he up to nowdays....

[Zero999]

It may be in addition to the current system.
It is also important to use a frequency free from interference from other transmitters.

About 37kHz exactly, I don't know, but extremely low frequencies do propagate further in water.  Military submarine channels go all the way down to 50-90Hz I think.  Think of it this way: salt water is a conductor, and therefore exhibits skin effect; high frequencies are absorbed easily, or bounce right off altogether.

Tim

There seems to be a lot of confusion here. It has nothing to do with the conductivity of the water or the electromagnetic spectrum. The black box produces an acoustic signal, i.e. sound, not an electromagnetic wave. Lower frequency sound travels further than higher frequencies but larger transducers are required and it's probably less easy to locate the signal.

[Wytnucls]

Doh, of course, forgot it was an acoustic signal.
Is it not a possibility electromagnetic signals could interfere with the ship's detection equipment though?
I suppose the shielding is pretty good inside a big ship, but perhaps not so much on a Chinese inflatable.

[dexters_lab]

I was expecting to hear from Dave by now... I dont see him replying much in the blog... I wonder what is he up to nowdays....

up to his eyes in uCurrents?

[dexters_lab]

ultrasonic bath cleaners work around this frequency too... must be more to it than random choice