9. Intermodulation Response Immunity
9.1 Test purpose
To measure that the capability of a pager receives a wanted signal at the normal frequency for a successfully page response. It caused by two equal level unwanted signals with a specific frequency relationship to the wanted signal at nominal operating frequency, one of which is modulated with normal coded signal having at specific intermodulation frequency.
9.2 Conformance requirement
The limit of the intermodulation response immunity shall be no less than 42dB.
9.3 Method of measurement
a. signal generator 1, 2, and 3 are set as follows,
Signal generator 1:
Frequency range: Fc (Carrier frequency)
Modulation: FM EXT.DC
Deviation: ±4.5KHz for POCSAG
±4.8KHz for FLEX
Amplitude: +3dB for the best sensitivity
Signal generator 2:
Frequency range: Fc±50KHz
Modulation: No
Signal generator 3:
Frequency range: Fc±100KHz
Modulation: 400Hz tone
Deviation: ±3KHz
b. initially, signal generator 2 and 3 shall be switch off. The amplitude of signal generator 1 shall be adjusted, as described in sub-clause 6.1 to record the measured output level for the best pager sensitivity.
c. as step b, add 3dB
d. signal generator 2 shall then be switched on (unwanted signal), and its frequency adjusted the frequency to Fc+50KHz without modulation.
e. increase the output level of signal generator 3, and adjust the frequency to Fc+100KHz with modulated signal.
f. adjust the output level of the unwanted signals of signal generator 2 and 3 to the lowest and equal level until the receiving signal is not obtained by a successful page.
g. the level of unwanted signals of two signal generators shall then be reduced until the receiving signal to be received successfully at 8 times out of 10 pages.
h. the unwanted signal output level of two signal generators shall be adjusted for a successful response. The level of the output signal shall then be recorded.
i. the intermodulation response immunity for receiving signal at the frequency is the ratio in dB of the unwanted signal level recorded in step h with the level of the wanted signal in step c.
9.4 Test requirement