Free Space Path Loss for Deep space/Interstellar Communications

[pavannanduri]

for distances which are in terms of Astronomical Units (AU) and Light Years how should we treat the free space path loss? do we have to treat it the same way as we normally do for Satellite Communications?

or do we have to take into account something different?

also anyone - can you please throw some light on the fading, interference and attenuation at those distances.

 

[jeffrey samuel]

really a thread of keen interest i am keen in knowing more awaiting more replies here

 

[LvW]

for distances which are in terms of Astronomical Units (AU) and Light Years how should we treat the free space path loss? do we have to treat it the same way as we normally do for Satellite Communications?
or do we have to take into account something different?

Since the physical/mathematical background for definition of the "space loss" is an idealized isotropic radiator it is independent on the distance and applies also for very large distances (several AU's).

 

[FvM]

can you please throw some light on the fading, interference and attenuation at those distances

Are you aware of the mechanisms bringing forth these effects, e.g. multi-path, properties of the ionosphere? If so, you surely can imagine why they don't occur in space.

 

[albbg]

I think that, roughly, inside our solar system the path loss can be calculated as the path loss between two points in LOS, then:

PathLoss = -28 + 20*Log[d(meters)*f(MHz)]

eventually compesated by the atmospheric absorption, function also of the angle of arrival of the EM wave. As far as I know the lunar missions link budgets were based on such a simple calculations.

Outside our solar system (I can't quantify "how far from us") I think that the scattering effect due to interstellar dust and cosmic objects becomes more and more heavy so those effects should be taken into account as both simple attenuation and multipath fading with a doppler spread quite high since celestial bodies are moving and I'm referring mainly to the smaller.

 

[jeffrey samuel]

radio waves are em and so do they get distorted by radiations from sun to large extent

 

[FvM]

radio waves are em and so do they get distorted by radiations from sun to large extent

Sounds like you are going to shake Maxwell's theory to the very foundations. :wink:

Is the solar radiation blowing off the electromagnetic waves?

 

[jeffrey samuel]

i am curious that is it never know if it is possible and all

just tell whether the solar radiation interfere with radio waves

 

[biff44]

That's why captain Kirk used subspace communications. As soon as that is invented, you will be all set.

 

[jeffrey samuel]

That's why captain Kirk used subspace communications. As soon as that is invented, you will be all set.

i am sorry to say that i am unaware of charecters in cartoons much any way thanks for clearing it

 

[pavannanduri]

Hello All,

thanks for the replies. i mean when we are dealing with distances in terms of light years and astronomical units, the disturbances that surface in atmospheric cover have to given lesser priority when compared with the intergalactic noise, cosmic noise and radiation from solar flares.

and if unfortunately if the frequency of our signal and the radiation emitted in space are both of equal frequency then how can we detect and process our signal (say for example at voyager I) from the noise which is disturbing and even more to the extent of damaging

 

[FvM]

Although there are apparently different opinions about additional effects in deep space, I would assume validity of Friis equation for the time being.

Received power will be respectively low and has to be compensated by high antenna gain and very low effective transmission bandwidth.

 

[vfone]

Why bother? If some of the space waves needs 30.000 years to reach the Earth, doesn't matter if you wait another year or two for the reflected ones. :wink:

 

[E Kafeman]

The planet GJ 1214b, found by Hubble, is about 50 light years from earth and is a possible exoplanet with water. It gives possibilities for some kind of intelligent life. If they have a high gain directive antenna pointing against earth, can they now watch Lucy Show and Bonanza.

If we in the future could travel slightly faster then the radio waves , away from earth, is it possible to watch Lucy Show in slow motion but backward because transmitted radio waves containing the beginning of the show, have traveled further away.
Guess it can be a serious problem if traveling at warp speed and at the same time picking up important messages which actually can be backwards.
"Now beam, not, wait"