How DEMON works ?

Dr.Sid · 11-30-06, 05:34 AM

Any idea how DEMON works ? I mean in real life .. technically. What kind of signal processing does it use ?
Noise demodulation says pretty nothing to me.

My analysis:

Each blade is source of noise. The amount of noise received will vary as the blade travels the circle. Each blade will generate noise signal with amplitude peaks, mostly 1 distinct maximum per turn.
You get several similar phase-shifted signals summed together. For each blade one.

You roughly know the frequency, so you can demodulate the noise, by watching amplitude of the noise. Standard 'radio' demodulation, consisting off cutting minus half-wave and filtering for low frequency would do. Then you can do normal frequency analysis in 1-100 Hz range.

But this would only give you blade frequency. Not blade count, not turn frequency.
It would be hard to find which peaks come from the same blade. Especially sub's blades would be made very precisely, so there should be no distinct blade signature.

Only thing I can think of is dopler. Blades on one side will make slightly different sound then blades on the other side, because of relative speed. This would vary heavily with listener aspect, but there should be some difference almost always.

So .. any idea ?

[dc]Blade · 11-30-06, 07:19 AM

The lines that you see on the DEMON display shown from left to right first show the prop shaft freq, then the count of how many props it has.
The TPK`s from the the classification manual help you demodulate the freq as the blades have already been counted, guess you can call it intel

So from the whole display the only thing that you can get from it is the targets speed, this is then handed to the TMA to give better your contact data, even though it displays to you how many screws the contact has the only purpouse is to realy gain speed knowledge, in real life workings this would be classified im sure

The old school way would have been the 3 minute rule using a maneuvering chart to plot a course and speed, so you can see TMA is a modern version of this too but minus the speed calculations hence DEMON

I hope this helps.

Dr.Sid · 11-30-06, 09:37 AM

I'm asking about how it works, now how it is used. I know that. Thanx anyway.

I'm talking aboud real-life, not DW. I could post is elsewhere, but there I would have to use 3 paragraphs to explain what I'm talking about.

Intel really can tell blade count. But DEMON is used for classification too, not just speed estimate, at least in DW. Maybe in reality it does not give blade count, and it must be input together with TPK.

Somebody who really knows ?

UglyMowgli · 11-30-06, 01:30 PM

At Ms we had some month ago a great description of the DEMON in real life but the post was erased after an official request

as the real sound of submarines I had post ("this is not a place (the internet) to have such sounds" write to me the officals).

Dr.Sid · 11-30-06, 02:25 PM

Uh .. I know this .. I have studied computer science.
In US, any form of publishing some encyption algorithms is illegal. Some rebels was inspired by formulation 'any form' and created many obscure forms of the algorithms, like T-shirts and dramatic reading recorded on CD, just to show stupidity of this.
I hope CIA has file on me, cause I'm from 'eastern block' and I know the algorithms, I even had to implement them as my homework.
I guess things like this too fall in the same basket. Anyway, if americans must shut up, maybe some russia guys here ? :rotfl:

Dr.Sid · 11-30-06, 04:19 PM

After really painful googling I found some thread where British bubbleheads talk about some new sub propeller. They say: impossible to get blade count, hard to get turns.
Maybe blade count really relies on blades differences.

11-30-06, 05:34 AM	#1
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	How DEMON works ? Any idea how DEMON works ? I mean in real life .. technically. What kind of signal processing does it use ? Noise demodulation says pretty nothing to me. My analysis: Each blade is source of noise. The amount of noise received will vary as the blade travels the circle. Each blade will generate noise signal with amplitude peaks, mostly 1 distinct maximum per turn. You get several similar phase-shifted signals summed together. For each blade one. You roughly know the frequency, so you can demodulate the noise, by watching amplitude of the noise. Standard 'radio' demodulation, consisting off cutting minus half-wave and filtering for low frequency would do. Then you can do normal frequency analysis in 1-100 Hz range. But this would only give you blade frequency. Not blade count, not turn frequency. It would be hard to find which peaks come from the same blade. Especially sub's blades would be made very precisely, so there should be no distinct blade signature. Only thing I can think of is dopler. Blades on one side will make slightly different sound then blades on the other side, because of relative speed. This would vary heavily with listener aspect, but there should be some difference almost always. So .. any idea ?

11-30-06, 01:30 PM	#4
UglyMowgli Grey Wolf Join Date: Aug 2003 Location: Canada Posts: 784 Downloads: 10 Uploads: 0	At Ms we had some month ago a great description of the DEMON in real life but the post was erased after an official request as the real sound of submarines I had post ("this is not a place (the internet) to have such sounds" write to me the officals). __________________ Modern Naval Warfare Community Manager

11-30-06, 07:19 AM	#2
[dc]Blade Seaman Join Date: Aug 2006 Posts: 42 Downloads: 0 Uploads: 0	The lines that you see on the DEMON display shown from left to right first show the prop shaft freq, then the count of how many props it has. The TPK`s from the the classification manual help you demodulate the freq as the blades have already been counted, guess you can call it intel So from the whole display the only thing that you can get from it is the targets speed, this is then handed to the TMA to give better your contact data, even though it displays to you how many screws the contact has the only purpouse is to realy gain speed knowledge, in real life workings this would be classified im sure The old school way would have been the 3 minute rule using a maneuvering chart to plot a course and speed, so you can see TMA is a modern version of this too but minus the speed calculations hence DEMON I hope this helps.

11-30-06, 09:37 AM	#3
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	I'm asking about how it works, now how it is used. I know that. Thanx anyway. I'm talking aboud real-life, not DW. I could post is elsewhere, but there I would have to use 3 paragraphs to explain what I'm talking about. Intel really can tell blade count. But DEMON is used for classification too, not just speed estimate, at least in DW. Maybe in reality it does not give blade count, and it must be input together with TPK. Somebody who really knows ?

11-30-06, 02:25 PM	#5
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	Uh .. I know this .. I have studied computer science. In US, any form of publishing some encyption algorithms is illegal. Some rebels was inspired by formulation 'any form' and created many obscure forms of the algorithms, like T-shirts and dramatic reading recorded on CD, just to show stupidity of this. I hope CIA has file on me, cause I'm from 'eastern block' and I know the algorithms, I even had to implement them as my homework. I guess things like this too fall in the same basket. Anyway, if americans must shut up, maybe some russia guys here ? :rotfl:

11-30-06, 04:19 PM	#6
Dr.Sid The Old Man Join Date: May 2005 Location: Czech Republic Posts: 1,458 Downloads: 6 Uploads: 0	After really painful googling I found some thread where British bubbleheads talk about some new sub propeller. They say: impossible to get blade count, hard to get turns. Maybe blade count really relies on blades differences.