| From: | Adam Getchell <acgetche@****.UCDAVIS.EDU> |
|---|---|
| Subject: | Jamming laser communications (WARNING! Physics) |
| Date: | Fri, 3 Mar 1995 17:30:07 -0800 |
> You are definetly on the right track, you can also defocuss the beam alittle
> to give you better coverage.
Okay, let's do some back of the envelope calculations.
Emitter: Intensity I, Aperture = .01 meters, Divergence =
.1mRad, Distance to Receiver ,000 meters
Jammer: Intensity I, Aperture = .01 meters, Divergence = 1
mRad (de-focussed), Distance to Emitter variable
Receiver: Dish radius = 10 meters
We neglect atmospheric and beam losses, and employ the small
angle approximation.
Emitter flux = I/ (4*pi*r1^2), Jammer flux = I/(4*pi*r2^2). All
we care about is the ratio between the two. When Eflux/Jflux is high,
the jammer is not noticeable. When this ratio drops much below 3 (a
breakpoint in a normal distribution), we need to examine the actual
Maxwell-Boltzman distributing for the frequency and/or the Routh array to
determine signal stability.
Case 1: Jammer equidistant from Emitter and Reciever at 10 km.
Shines on emitter. r1 = .01 meters, r2 = 10000*.001 = 10 meters
Emitter flux/Jammer flux = 1.0 x 10^6 -->No significant effect
Note: I have not precisely calculated the beam divergence of the
two to find (Divergence Emitter) cross (Divergence Jammer). This
calculation would be more complex, and would only add in geometric
effects that would increase the above ratio. (I would also have to
specify the exact geometry of intersection)
Case 2: Jammer shines on receiver. r1 = 10000*.0001 = 1 meter,
r2 = 10000*.001 = 10 meters
Eflux/Jflux = 100 -->No significant effect
Case 3: Jammer at a range of 500 meters from Emitter.
Shines on emitter. r1= .01 meters, r2 = 500*.001 = .5 meters
Eflux/Jflux = 2500 -->No significant effect
Case 4: Jammer at a range of 500 meters from Receiver. Emitter is
10 km from Receiver. Both shine on receiver. r1 000*.0001= 1 meter,
r2 = 500*.001 = .5 meters.
Eflux/Jflux = .25 -->Possible effects
Jammer signal strength is 4 times the emitter's signal.
Note that only in case 4 does the jammer have a possibility of
working. Even so, by simply polarizing the laser beam rectilinearly the
jammer's signal strength can be cut in half, while circularly polarizing
the beam will cut the signal strength down to a minute fraction,
depending upon the polarization frequency.
Also note that the jammer must know the exact location of the
emitter to within 10 meters at least, and within half a meter for short
ranges. In case 4, the only successful possibility, the jammer must be
within a very short distance of the receiver array. However, because the
information content of the jammer is likely to be quite different than
the real signal, noise filtering algorithms can counteract much of the
jammers' effects.
I believe your laser "jammer" exceeds the bounds of practicality.
> Sinbad Sam
========================================================================
Adam Getchell "Invincibility is in oneself,
acgetche@****.engr.ucdavis.edu vulnerability in the opponent."
http://instruction.ucdavis.edu/html/Adam/getchell.html
