Does anyone here have any knowledge of how "sonar beam-forming" operates? I have read about this recently and it sparked my curiousity.
As I understand there are two methods, phasing shifting and time delay. IOW using delay lines, etc. or a frequency dependent phase shift.
I have heard two FM signals are typically used to achieve this effect, but what type of signals and bandwidth are involved and how do they interact to form the beam as advertised?
Claus Jensen
This sort of tech is hard to find details on (not surprising considering military uses) but start here:
Mark L. Fergerson
Sound propagation underwater and through thermal layers is especially interesting and _very_ military. Active (pingers) and passive buoy systems, separate or in various combos, often used for submarine tracking make this an especially hot topic in some circles.
Jon
It is very oily and very fishy as well.
VLV
"Claus Jensen"
** Read the wiki on it yet ??.... Phil
Yes, and it points out that cell phone towers also have this capability.
I heard this from a tech once. He said that if the telco was given the GPS coordinates of your house, they could improve the reception there continuously. You don't even need to have your phone switched on for them to locate you there. Does that sound correct?
I also found some relevant info here:
"Advances in Bistatic Radar" Nicholas J. Willis, Hugh Griffiths
Parts are available for free reading on Google books.
Claus Jensen
Only if your phone transmits when it is not switched on.
That is adaptive convergence.
However, can you please explain why you believe the phone would need to be transmitting if the GPS coordinates were known?
Are you saying this is beyond the network's technical capability, or that it simply has not been implemented?
Claus Jensen
I suspect it would work a lot better if the phone was switched on. The differences between the real world with trees, topography and metal sheds and the idealised model of wave propagation is important.
The largest selection of open literature on beam forming is in the field of radio astronomy where big phased arrays are used both for massively increased signal with limited steering capability and higher resolution via aperture synthesis. The mathematics is essentially the same although some radar/sonar use chirp or other modulation for disambiguation.
In hardware terms there is an example of a GDBF from Westerbork online at:
Regards, Martin Brown
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.