9-2015

RF & WirelessFigure 12: Adjacent Channel with P25 LSMinterfererFigure 13: Adjacent Channel withmodulation offFigure 14: Spurious response with a400 Hz tone @ 1.5 kHz deviationFigure 15: Spurious Response withmodulation offety of adjacent channel modulation types.This can easily be done by loading the vectorsignal generator with a number of modulationtypes and then switching through themduring receiver testing. In cases where theFigure 17: Intermodulation Rejection setupFigure 16: Intermodulation Rejection block diagraminterferer of interest is not available in thepre-defined modulation types, the AnritsuMS2830A Signal Analyzer supports capturingsignals off the air and then replayingthem at other frequencies and power levels.Figures 10 and 11 show CCDF measurementcomparisons between a P25 Phase 1C4FM modulation and a P25 Phase 1 LSMQPSK modulation. The blue trace is thereference trace of Gaussian noise for reference.The C4FM signal has no AM contentand the yellow trace is just a vertical line- the peak power is essentially the same asthe average power. The QPSK signal hasamplitude peaks 5.3 dB greater than theaverage, and 10% of the time the amplitudeis 3 dB greater than the average. If anadjacent channel is a P25 LSM signal, thevictim receiver will likely have reducedadjacent channel rejection.Figure 12 shows a spectrum display of anadjacent channel measurement using a P25LSM interferer. Figure 13 shows the samesetup with the test signal modulations turnedoff to show the power levels of -112 dBmfor the sensitivity +3 dB and -66 dBm forthe interferer - a difference of 46 dB.Spurious Response RejectionThe spurious response rejection is the abilityof a receiver to prevent a single unwantedsignal from causing degradation to thereception of a desired signal. The measurementprocedure for a 12.5 kHz P25 Phase 1radio is defined by the TIA-102.CAAA-Cstandard. The setup for this measurementhf-praxis 9/2015 59