JSAT Satellite Services

Satellite Services Satellite Applications and Uses Why Satellite



Frequency  

Is your frequency rain and neighbor proof?

Signals are transmitted back and forth to satellites at different frequencies. The reason: the frequency of the transmitted signal allows us to separate it from other signals (either from the ground or from space) by establishing its place in the radio frequency spectrum.

First of all what is frequency?

Mathematically speaking, the radio signal can be represented by a sine wave as below, which has the property of frequency as well as amplitude. Frequency is the number of oscillations or wavelength cycles per second. Frequency is measured in Hertz (Hz), which is the same as "oscillations per second" or "cycles per second."
 
The higher the frequency (the closer the ripples would be in this diagram) and the shorter the wavelength.

The power of the signal corresponds to the square of the amplitude, so the higher the amplitude, the higher the power. Increasing frequency allows us to move to other portions of the spectrum but does not, in and of itself, change the power.

What frequencies are used?

Essentially all commercial satellite communications transmit and receive in the microwave frequency band, between 1 and 30 GHz.

This table illustrates the position and relative bandwidth available for each of the currently-used satellite bands. Note that this is a logarithmic scale, so that bandwidths above 10 GHz are really ten times what is shown for the same width just above 1 GHz.
 

The microwave portion of the frequency spectrum, showing all of the bands currently used for satellite communications. The most popular bands for broadband services are shown in blue.

Terrestrial radio services employ much of this same spectrum; if the terrestrial and satellite services lie in the same band, that band is indicated as Shared with Terrestrial.

Strengths and weaknesses of common frequency bands.

C-band is useful for many satellite services, particularly TV distribution to cable TV systems and TV broadcast stations. However, the satellite EIRP is typically less than 40 dBW so dish sizes tend to be significantly larger than with Ku band sometimes by a factor of three.

C-band frequencies are not attenuated (or subject to interference) by rain as much as Ku band, and so C-band links are extremely reliable (see reliability discussion, below).

Ku-band is the most versatile part of the microwave spectrum for providing satellite broadband services to small dishes (1 meter or less in diameter) and two-way data communications.

Any video, data or voice service can be provided at Ku band, and there are many satellites that provide Ku-band coverage in the US and elsewhere.

Service can be provided with good reliability, although rain will produce greater signal loss than at C-band. This can be compensated for in the engineering of a Ku-band satellite service, as is routinely done for broadcasting, VSAT data communications, and SNG and emergency communications. The resulting availability will be acceptable for most applications.

Some of the Ku (and Ka) band frequencies are not shared with terrestrial services. This is highly desirable because it means that Ku band dishes can be installed anywhere, while dishes for C-band, which is shared, will have to be located carefully to avoid interference with terrestrial microwave stations.




Through our fleet of satellites and exceptional level of customer care, JSAT International makes it easy to communicate and transmit content across North America.