12-11
Module I/O Specifications
A5 Premodulation Filter and NSM
The PMF_DATA signal is difficult to measure accurately without a high speed
oscilloscopeor logic analyzer. Using a Spectrum Analyzer, an increased noise floor can be
seen when probed about the centre frequency of 270 kHz. Using an oscilloscope, the
signal can be measured at 4.4 Vp-p. On a DVM, 2.25 Vdc.
The 10 MHz Reference signal can be measured on an oscilloscope at 880 mVrms and
2.6Vp-p. On a Spectrum Analyzer, the marker will be approximately +10dBm.
NOTE: The Premodulation Filter and NSM assembly are used to convert User Digital Data and
clock signals into GMSK.
Outputs
The NSM_CLK signal can be sensed on the SERVICE Screen using the
’nsm_pmf_clk_pres_int_sense’latch, a value of 1 for lock and ’0’ for OOL (Out Of Lock)
state. An OOL condition can cause high phase and frequency error problems. See
Figure 4-1on page 12-12 for typical oscilloscope readings. On a Spectrum Analyzer, the
peak marker should be >+6 dBm.
From A34 GSM-RTI Assembly
PMF_DATA J1(1)
Level: TTL
Rate: 270.833 kbps
Format: Non-differential data encoded
From A15 Reference GSM-RTI Assembly
10 MHz Ref B J2(33)
Frequency: 10 MHz ± 500 Hz
Wave Shape: Sine
Level: >10 dBm
Harmonics: <−25 dBc
To A27 DAC/Upconverter
NSM_IF_CLK J2(1)
Frequency: 17.3333 MHz ± 250 Hz
Level: TTL