Why must a satellite have a distinct up link and down link frequencies?

Answer 1

These are frequencies used for satellite communications.

Usually in the Gigahertz bands.

Uplink is on a differenct channel to downlink, to avoid interferece.

The Uplink, is the signal sent to the satellite, via a dish antenna, which focuses the signal in the direction of the satellite.

On board the satellite, this signal is changed and re-transmitted, on a different frequency (Downlink), and beamed back to earth.

This way huge distances can be covered on earth, despite the curvature and with minimal power.

Answer 2

Because the uplink frequency can be sent from a way bigger antenna. If Up and Down were running on the same frequency, they would end up both garbled from meshing with each other.....separate frequency paths guarantee clear transmission In some cases, such as satellite communications, the uplink frequency (Earth to satellite) is of a higher value than the downlink to mitigate the free space spreading losses, and the tropospheric losses (gases, clouds, rain), all of which are related to wavelength and therefore to frequency (wavelength=speed of light in vacuum/frequency).

Higher the frequency, lesser the wavelength. So high frequency can be received using smaller antenna in satellite, which is more practical. Whereas in earth we can have bigger antennas..

Answer 3

A satellite is a repeater in space. It must receive on one frequency, and transmit on another. When it comes to transmitting, it is more efficient to generate high power at a LOWER frequency.

On the other hand, the higher the frequency, the narrower the beam width from the same diameter antenna. This becomes important in a crowded geostationary orbit with satellites orbiting only a few degrees apart. If you increase frequency and the diameter of the dish antenna on earth remains the same, the effective radiated power of the signal increases because the beam width decreases (becomes more focused).

As a final reason to support a higher input frequency for satellite transmission, when the space program first began, the transmit klystron tubes and power transistors available were so inefficient that they required massive amounts of input power to generate a small amount of power output. This power could easily be supplied on earth, but hard to come by and store in space when the bird is in the shadow of the earth, and the solar panels are not charging the spacecraft's batteries.

Conclusion: Using a higher receive frequency and a lower transmit frequency will reduce the power requirements for a communications satellite, and allow closer satellite spacing and lower earth station transmit power with a smaller antenna. This is because the ground temperature of the earth which contributes to the thermal noise is large and so the frequency is increased to increase the signal to noise ratio. A more conplicated explanation involves Boltzmann'a constant and a very complicated equation.

At higher frequency attenuation is more hence power will be required for signal transmission to ensure that it reaches the destination with the required minimum power.Higher power requirements will involve use of high power amplifiers with high ratings and heat sinks.This will increase weight and power supply ratings of the equipments.This does not make any difference to the ground station.But for the satellite this will result in higher power consumption, which will reduce its efficiency. Hence the ground station uses high power equipments to generate high frequency which can reach the satellite

Answer 4

Up-link frequency is the highest in satellite communication. This is because in order to penetrate the atmosphere, more power is needed on earth. This can only be accomplished with high power applications. Up-link frequency is at a higher power, and therefore the best solution.

Answer 5

Usually Signals are sent from earth to satellite with high frequencies, reason of high frequency is as the frequency increases the antenna aperture which is the cross sectional area of an antenna or size of antenna decreases. Transpoders inside satellite reduces signal frequency to overcome interference. and send them to earth with low frequency. low frequency so it will require large antenna size which is not a problem on earth.

Aperture A = (lambda)^2 / 4 *pi

Aperture cross sectional area of Antenna

Lambda wavelength of signal, (high frequency low wavelength)

Answer 6

This is done to avoid crosstalk.

If, for example the up and down -links were on the same frequency, it would work much like a walkie-talkie, meaning only one person could send, and one receive, at any given point in time.

By giving each direction its own carrier wave, it allows both deviced to send and receive simultaneously, which greatly speeds communication.

Answer 7

Before describing the solution of above query let firstly define uplink and downlink frequencies

Uplink frequency: In satellite telecommunications terminology, uplink means the signal sent from Earth to the satellite.

Downlink frequency: In satellite telecommunications terminology downlink means the signal from the satellite to earth.

And now what about the frequencies Why kept different??

The main reason for keeping these frequencies apart is to avoid

interference between the upcoming and outgoing signals since they

received and sent from a single body that is our satellite.

Answer 8

Simply to provide faster transmissions. If you transmit and receive data or communications on the same frequency, you have to wait until the sender has finished transmitting before you can send a reply.

This is because you cannot simultaneously transmit and receive on the same frequency, your receiver would only hear your transmitter and it would 'howl round'.

Simultaneous two-way or 'duplex' transmissions using different frequencies to send and receive - mean that both the sender and receiver can transmit at the same time. This speeds up the the rate at which data can be sent, as neither party has to wait for the other to stop sending before they start.

This is known as 'Duplex'

Think of it as the difference between a walkie-talkie and a mobile phone. With a walkie-talkie - one person speaks while the other listens. With a mobile phone, both people can speak at the same time.

Answer 9

High frequencies are more difficult to generate and manipulate. Consequently, the higher frequency is assigned to the ground station which has far more resources than the space component.