| The functions performed by repeaters are | | | | attenuation and distortion. Present communication |
| amplification and frequency down conversion. | | | | satellite repeaters use dual mode filters using cavity |
| Repeater amplifies signal from a low power level of | | | | coupling and having centre frequency to bandwidth |
| the order of negative hundred decibels watt to an | | | | ratio of about 100000 and C band and about 10000 at |
| output power level of the order of ten decibel watts | | | | about k band. Accordingly C band filter has bandwidth |
| thus providing again of the order of hundred and ten | | | | of about thirty six mega hertz. |
| decibel. Frequency down conversion avoids | | | | Primary function of carrier processing equipment is |
| interference between strong transmitted signals and | | | | frequency translation that is to bring the uplink signal to |
| weak returning signal sometimes these repeaters | | | | lower frequency down link signal. Frequency translation |
| perform the additional function of detection or | | | | can be done in the following four different ways. |
| demodulation then the repeater or the transponder is | | | | Conventional repeater use either radio frequency-radio |
| called regenerative transponder. | | | | frequency translation or radio frequency- Intermediate |
| Parts of a typical satellite repeater are satellite | | | | frequency-radio frequency translation where as |
| antenna, diplexer, front end electronic system, carrier | | | | regenerative repeater uses either intermediate |
| processing system and power amplifier. In diplexer the | | | | frequency modulation method or demodulation-re |
| same antenna is being used by the satellite for | | | | modulation method. Thus the difference in the |
| receiving the uplink signal and transmitting the downlink | | | | conventional repeater and regenerative repeater lies |
| signal. This is made possible by use of an electronic | | | | only in the structure of its carrier processing unit. Last |
| device called diplexer which serves a two way | | | | unit of the satellite is the power amplifier. Traveling |
| microwave gate. Since two different frequencies are | | | | wave tube amplifiers re popularly used as power |
| used for uplink and down link there is no interference | | | | amplifiers. The size of traveling wave tube depends |
| between the two transmissions and the same antenna | | | | upon the purpose of the satellite. Typical parameters |
| serves satisfactorily. Front end electronic system is | | | | of traveling wave tube amplifiers are saturated output |
| made up of radio frequency filter, equalizer and low | | | | power is eight to twenty watts, saturated gain is fifty |
| noise amplifier. Signal from the diplexer is fed to the | | | | five decibel, carrier to inter modulation noise power |
| radio frequency filter. It is an integrated circuit | | | | ratio at saturation is ten to twelve decibel and |
| microwave filter having merits of better packaging, | | | | amplitude modulation-pulse modulation conversion |
| smaller weight and lesser power requirements. This | | | | coefficient is 4.5 decibels. |
| filter is designed to achieve requisite mask, noise | | | | Tymon Hytem has worked in the electronics feild for |
| rejection and equalization. It should not add any circuit | | | | the past 15 years. He enjoys helping people decide on |
| noise. | | | | electronic gadgets from telephones to XM Radio and |
| Typical filters so used are Butterworth, Cheby Chev or | | | | choosing the perfect XM Satellite Radio system for |
| Bessel filters. The delay introduced by the filter is | | | | their needs. |
| cancelled by an equalizer without introducing any | | | | |