Skip to main content

Satellite Communication - Part 2

Image
By

Communications by Satellite

Satellite communication "Transponder" operates like REPEATER, which is very similar to Terrestrial Radio Communication.
The term "Transponder" here, in satellite itself, easier for satellite operator to maintain power liniarization if divided into some lot of frequency. Usually,1 transponder consist of 36 MHz in bandwidth (certain satellite use 72 MHz bandwidth).

Main functional similarities between Terrestrial Communication and Communication via / by Satellite are :
  • Input signal at antena (F-in = F-Rx) relatively weak and coming from many directions.
  • Mixing (F-Rx) with Local Oscilator, therefore results Frequency Translation (F-out not equal to F-in).
  • F-out (F-Tx) of Repeater is filtered, amplified, then with relatively very High Power is transmitted by Antenna, for greater distance and wide area coverage (benefit of using satellites)
  • Repeater's site is always placed on high surface, structure , etc, to fulfill and guarantee its desired area coverage.
  • it has a certain Band-Width and Frequency (MHz) allocations.

Ok, time to explain why F-out and F-in (to satellite) is not equal and therefore occur a Frequency translation. The reasons behind this are :
  • 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
  • Separate frequency paths guarantee clear transmission. 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, means lesser the wavelength. So, high frequency can be received using smaller antenna in satellite, which is more practical (due the effort for throwing the satellite to its orbit), whereas in earth we can have bigger antennas.

Labels

Labels:

Comments

Post a Comment

Popular posts from this blog

Satellite Communication - Part 4 (CPI)

By
Cross Polar Isolation (CPI) In installation and pointing/peaking antenna, Orthogonal Mode Transducer (OMT) must be set to be as precise as possible to get the best CPI value. above is picture of OMT Feed assembly include with BUC and LNB The minimum value for CPI is 30 dB (better will be good) in Linier Polarized Antennas. The reason is for our receive (Rx)-side as not to get interferenced (distrubed) by other (polarity) Down-Link users, therefore our transmit (Tx) shoild as well not interfere other users that operates at 90 deg (Orthogonal) Polarization. Note : In LH/RH Circular Polarizations, usually CPI of 27dB (=AR of 1.09) is acceptable enough. picture above is careless/miss-aligned OMT setting
Post a Comment
Read more

Satellite Communication : Transmission Bands

By
A satellite link is a radio link between a transmitting earth station and receiving earth station through a communications satellite. A satellite link consists of one uplink and one downlink; the satellite electronics (i.e., the transponder) will remap the uplink  frequency to the downlink frequency. The transmission channel of a satellite system is a radio channel using a direct-wave approach, operating in at specific RF bands within the overall electromagnetic spectrum as seen below : The table below shown some key of physical parameters of relevance to satellite communication,  The frequency of operation is in the super high frequency (SHF) range (3-30 GHz). Regulation and practice dictate the frequency of operation, the channel bandwidth, and the bandwidth of the subchannels within the larger channel. Different frequencies are used for the uplink and for the downlink. Frequencies above about 30 MHz can pass through the ionos...
Post a Comment
Read more

High Throughput Satellite Service - more than modems and transmission

By
The advent of High Throughput Satellite (HTS) has been significant amount of new satellite capacity come online in recent years, prompting industry-wide disruptive innovation. This lower cost capacity enables a new era of satellite communications, with innovative new applications spreading around the world. However, there are a number of factors that must be considered for the operation of a successful HTS service. The satellite industry is undergoing a dramatic evolution as more and more High Throughput Satellite (HTS) capacity is introduced to markets around the world, like Intelsat Epic , Inmarsat Global Express , Viasat-2 , SES-12 ,etc. HTS is bringing more and lower-cost capacity that enables the satellite industry to cost-effectively provide large-scale internet services to rural and other hard-to-serve areas around the world. To enable these services, many providers are focusing on selecting the optimal ground system, and rightly so, because the ground system is a key e...
Post a Comment
Read more