Senstar Corporation B76060 用户手册

 

 

The digital modulation used in the Senstar-Stellar PPD unit is a tri-level 2-FSK format; i.e., the carrier 
frequency is part of the modulated waveform. The base band waveform is redrawn below for a sample 
ID word 366f (hex).

 

 

 

Transmitted data waveforms are generated by the microcontroller (Atmel AT90S2313) and fed to the 
quad digital-to-analog converter (DAC - MAX533-pin 15). This DAC output waveform is fed to the 
reference oscillator voltage controlled, input port (U3 - pin 1). The maximum voltage swing on the 
reference oscillator is 0.5 V to 4.5 V (

≈ +/- 10 ppm). This corresponds to a maximum possible 

deviation swing at the transmitter output of 4.7 kHz peak.   

The DAC has 8-bit resolution and deviation is controlled by setting the DAC output swing in the 
factory. The VCTCXO is modulated with data and the transmitted deviation is measured with a 
modulation analyzer at the antenna output. The test procedure requires the DAC peak-peak voltage 
swing to be varied until the appropriate data average deviation level is recorded. This level is saved in 
the microcontroller EEPROM and modulation limiting is provided via software setting of the DAC 
maximum output voltage. Deviation is tested and confirmed in the factory test station prior to 
shipment. 

The transmitter was designed, using the appropriate data rate and deviation levels, to be 
compliant with Part 90.217(b) of the FCC rules. Per 90.217(b), there is a spectral emissions 
requirement and not a mask requirement. Hence, no data filtering is used.  

 

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