The input to the receiver must be compatible with the output of 

 the downconverter , and the receiver output must be compatible with 

 the input requirements of the demodulator. 



DE MODULATOR / DECODE R 



The output of the receiver is fed to a separate demodulator/decoder 

 external to the receiver at a convenient intermediate frequency (IF). 

 The demodulator portion converts this IF signal to a series of d.c. 

 pulses. The decoder portion separates the clock and the data stream 

 to recover the information. 



If the user purchases a spec;ial receiver for DCS reception, the 

 demodulator/decoder may be built into the receiver. In either case, 

 the demodulator/decoder will recover the data from the phase shift 

 signal. In principle, the output of the decoder should be the 

 same as the sensor data input to the radio set transmitter at the 

 remote platform. 



FRAME SYNCHRONIZER 



Following the decoder, a frame synchronizer must be provided to 

 recognize the 15-bit Maximal Length Sequence (MLS) synchronizing 

 data pattern and ensure that the data bits are outputted in the 

 proper sequence. 



DATA PROCESSING EQUIPMENT 



Where a large amount of data is to be received, or where the data 

 must be processed, automatic processing equipment is necessary. 

 The design of this equipment depends on the requirements of the 

 user and cannot be discussed in general . 



III. DCS SIGNAL POWER 



The energy available in the received signal plays an important 

 role in determining the necessary quality and, hence, cost of the 

 receiving system. Unfortunately, the received signal level can 

 vary over a wide range; a lOdB variation may be typical (a numerical 

 variation of 10). There are various causes for this variation, all 

 of which are beyond the control of the user. The most probable 

 cause is satellite loading; i.e., the number of other platforms 

 transmitting at the same time. 



During emergency situations many more platforms may be programed 

 to respond in their emergency mode than would normally be 

 transmitting. Unfortunately, this tends to lower signal levels at 

 a time when the data are most needed. 



The power radiated by the satellite in the DCS band under normal 

 conditions is 2.5 watts. This power is known as the equivalent 

 isotropic radiated power (EIRP). This 2.5 watts is available to be 

 shared equally by all channels. Thus, if everything were ideal and 



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