Why are high frequencies bands chosen in satellite communication?

[curiousman]

Hi all,

I'm an student of Physics so apologies if I'm just some silly questions here.

The higher frequency bands typically give access to wider bandwidths (e.g wifi). Considering that higher frequencies bands (> 30 Ghz) are more susceptible to signal degradation due to ‘rain fade’ (atmospheric rain, snow or ice). Why are they made in order to emit high frequencies? Is information lose once it pass the atmosphere through?

Thanks in advance,
Jose

 

[RUber]

One benefit of high frequencies is that they tend to have less loss overall and are easier to focus at a single target. Think of something really high frequency, like light. You can direct a focused beam of light pretty far without having too much loss from the atmosphere. Lower frequencies have greater spread, and so require much more energy to retain a strong enough signal at the destination...also security can become a concern if you are transmitting information intended for a single receiver.

 

[rootone]

Since satellites generally are data receieving and transmitting devices, a high band width data capacity is very much an advantage.
It's true that higher frequencies can be attenuated more quickly by rain for example, but that is easily compensated for by making the receiver and transmitter components sufficiently sensitive/powerful for whatever is the the job of the satellite.

 

[curiousman]

Thanks guys. Clear enough

 

[davenn]

Thanks guys. Clear enough

both are good answers,
but there is another serious consideration why the 8 - 15GHz is used for satellite and distant space probe comms that wasn't mentioned

that freq range isn't subject to ionospheric reflection that much lower HF, VHF and UHF freq's are ... that is the microwave freqs penetrate the ionosphere more easily
(and apart from the fact that range of bands is already in full use, it doesn't have the freq bandwidth capabilities
that are available much further up the spectrum

Dave

 

[curiousman]

Thank you all!

I was thinking about your answers and I´m still wandering that if non-militar Satellites use to spread the signal in a great area (TV, Internet, Sat Phone,etc).. so the RUber´s point "also security can become a concern if you are transmitting information intended for a single receiver" wouldn´t make any sense.

 

[rootone]

RUber is right that it's easier to make a shorter wavelength transmission more focused.
There are both military and non military satellites for which that can be useful.
The signal does not HAVE to be more focused though.

 

[davenn]

I´m still wandering that if non-militar Satellites use to spread the signal in a great area (TV, Internet, Sat Phone,etc)..

wondering not wandering 2 very different meanings

The geostationary sat's for communications, TV etc have very specific footprints covering various regions/countries etc ... as an example
see this map ... http://www.satbeams.com/footprints?beam=5548