Measuring the I/Q Spectrum of a Mobile
GSM uses the GMSK modulation scheme with a symbol rate of 270.833 kBit/s
and four different phases that can be occupied during one symbol interval.
If a constant series of zeros or ones is transmitted, the rotation of
the I/Q vector causes a side band at 270.833/4 Hz = 667.70825 Hz from
the carrier. Compared to the side band, the original carrier frequency
is suppressed by -30 dB to -40 dB. The following example program measures
the carrier signal, the upper and the lower side band using the RF
Spectrum and the RF Power vs Time measurement groups. No additional
options are needed.
To keep the syntax as short and simple as possible, the programs were
written with the aid of Winbatch, a batch job tool organizing and
simplifying the transfer of commands and data between the controller and
the instrument.
Winbatch uses device names such as
CMUBASE, CMUGSMNS, CMUGSMSIG which are previously defined and assigned
to the primary address, secondary address, and some general device settings.
With these device names, a complete command line reads:
CMUBASE: <CMU_Command>
where <CMU_Command> may be any of the commands (setting
commands or queries) specified within the function group and mode identified
by the device name CMUBASE. Program sequences consisting of commands
that are defined in several function groups and modes can be re-used with
an exchanged device name.
In addition to these data transfer commands, Winbatch provides
WHILE, GOTO, and IF statements to express conditions and
define loops. Program examples utilizing these statements can be found
in the manuals for network tests, e.g. GSM-MS. For the following
example, configure your Winbatch settings such that CMUBASE
is the device name for the CMU BASE system and CMURF denotes
function group RF (Non Signalling).
ECHO ON
FPRINT ............................................................................
FPRINT INITIALISATION ROUTINE:
FPRINT ASK FOR THE IDENTIFIER OF THE CMU, RESET THE INSTRUMENT,
FPRINT DEFINE THE SECONDARY ADDRESSES FOR ALL AVAILABLE FUNCTION GROUPS
FPRINT ............................................................................
CMUBASE: *IDN?
|
Identification query |
CMUBASE: *RST;*OPC?
|
Reset the instrument; prevent the following command to be
executed before *RST is complete |
CMUBASE: *CLS
|
Clear output buffer, set status byte |
CMUBASE: SYST:REM:ADDR:SEC 1,"RF_NSig"
|
Define function group RF Non Signalling; the CMU Base
system is always assigned secondary address 0 |
FPRINT .............................................................................
FPRINT CONNECTORS
FPRINT .............................................................................
CMURF: INP:STAT RF2
|
Define input connector RF2 |
CMURF: OUTP:STAT RF2
|
Define output connector RF2 |
FPRINT .............................................................................
FPRINT RF GENERATOR SETTINGS
FPRINT .............................................................................
CMURF: SOUR:RFG:FREQ 900 MHZ
|
Set RF generator frequency |
CMURF: SOUR:RFG:MOD SSB
|
Switch on frequency offset (single side band modulation) |
CMURF: SOUR:RFG:MOD:SSB:FREQ 67.7 KHZ
|
Set offset frequency |
CMURF: INIT:RFG;*OPC?
|
Switch on RF generator |
FPRINT .............................................................................
FPRINT SPECTRUM ANALYZER SETTINGS
FPRINT REFERENCE LEVEL ONLY EXISTS IN THE MANUAL MODE (Defines display area)
FPRINT .............................................................................
CMURF: SENS:SPEC:FREQ:CENT 900 MHZ
|
Set center frequency for spectrum measurement |
CMURF: SENS:SPEC:FREQ:SPAN 500 KHZ
|
Set frequency span |
CMURF: SENS:SPEC:FREQ:BAND 20 KHZ
|
Set resolution bandwidth of the spectrum analyzer |
CMURF: CONF:SPEC:CONT:REP SING,NONE,NONE
|
Single shot measurement, no stop on error |
FPRINT .............................................................................
FPRINT SPECTRUM MEASUREMENT AT 900 MHZ + OFFSET 67.7 KHZ, 1 POINT
FPRINT .............................................................................
CMURF: CONF:ARR:SPEC:RANG 900.0677 MHZ,1
|
Select single measurement point at 900.0677 MHz |
CMURF: READ:ARR:SPEC?
|
Start single shot spectrum measurement, wait until it is
terminated, and return result (1 value) |
FPRINT .............................................................................
FPRINT HAVE A LOOK AT SPECIFIC OFFSETS (SUPPRESSED CARRIER AT 900 MHZ)
FPRINT .............................................................................
CMURF: CONF:ARR:SPEC:RANG 900 MHZ,1
|
Select single measurement point |
CMURF: READ:ARR:SPEC?
|
Start single shot spectrum measurement, wait until it is
terminated, and return result (1 value) |
FPRINT .............................................................................
FPRINT HAVE A LOOK AT SPECIFIC OFFSETS (THE OTHER SIDEBAND 900 MHZ - 67.7 KHZ)
FPRINT .............................................................................
CMURF: CONF:ARR:SPEC:RANG 899.9323 MHZ,1
|
Select single measurement point |
CMURF: READ:ARR:SPEC?
|
Start single shot spectrum measurement, wait until it is
terminated, and return result (1 value) |
FPRINT .............................................................................
CMURF: ABOR:SPEC
|
Abort spectrum measurement and free resources |
FPRINT .............................................................................
FPRINT PRODUCE A RAMPED SIGNAL
FPRINT .............................................................................
CMURF: SOUR:RFG:PULS:STAT ON;*OPC?
|
Select pulsed signal (as opposed to CW) |
FPRINT .............................................................................
FPRINT CONFIGURE THE POWER/T MEASUREMENT
FPRINT .............................................................................
CMURF: SENS:POW:FREQ:CENT 900.0677 MHZ
|
Set center frequency for power vs. time measurement |
CMURF: SENS:POW:FREQ:BAND 20 KHZ
|
Set resolution bandwidth of the RF analyzer |
CMURF: SENS:POW:TIME:SPAN 1MS
|
Set evaluation time of power measurement |
CMURF: TRIG:SOUR IFP
|
Trigger meas. by IF signal level (recommended) |
CMURF: LEV:MAX -10
|
Set expected maximum input level |
CMURF: CONF:ARR:POW:RANG 3E-4,1
|
Select single measurement point at 0.3 ms |
CMURF: CONF:POW:CONT:REP SING,NONE,NONE
|
Single shot measurement, no stop on error |
CMURF: SYST:ERR?
|
Read error queue |
CMURF: INIT:POW
|
Initiate power vs. time measurement |
CMURF: READ:ARR:POW?
|
Start single shot measurement, wait until it is terminated,
and return result (1 value) |
FPRINT .............................................................................
FPRINT HAVE A LOOK AT SPECIFIC OFFSETS (SUPPRESSED CARRIER AT 900 MHZ)
FPRINT .............................................................................
CMURF: SENS:POW:FREQ:CENT 900 MHZ
|
Set center frequency for power vs. time measurement |
CMURF: READ:ARR:POW?
|
Start single shot measurement, wait until it is terminated,
and return result (1 value) |
FPRINT .............................................................................
FPRINT HAVE A LOOK AT SPECIFIC OFFSETS (THE OTHER SIDEBAND 900 MHZ - 67.7 KHZ)
FPRINT .............................................................................
CMURF: SENS:POW:FREQ:CENT 899.9323 MHZ
|
Set center frequency for power vs. time measurement |
CMURF: READ:ARR:POW?
|
Start single shot measurement, wait until it is terminated,
and return result (1 value) |
SETLOCAL
|
Quit remote control mode |