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carry eight separate channels. Each channel has an upstream line and a downstream line with a
frequency interval of 80 MHz between them. The GSM system uses Gaussian Minimum Shift Keying
(GMSK) modulation. Since the RF output power of TDMA and GSM transmitters will suddenly jump, it
will significantly interfere users at different frequencies, especially those in the adjacent channel, if the
transmitting switch is turned on too fast. Fortunately, the interference can be quantitatively analyzed
through measurement of GSM system channel power.
Measurement Setup
In order to ensure the accuracy and repeatability of the measurement, the following simple rules should
be observed:
a) The resolution bandwidth of the microwave analyzer should be set to 1 MHz to cover the GSM
system of broadband.
b) The video bandwidth should be set to 100 kHz or greater in order to obtain details of the multiple
channels within the GSM system.
c) Use the maximum hold state when measuring.
Measurement steps
Steps for measuring the GSM signal channel power using the S5105D/E/F microwave analyzer are:
a) Reset the microwave analyzer to its default state:
Press
【
Reset
】
, [Factory State] .
b) Receive a GSM signal via the antenna or a GSM signal via the cable at the spectrum input of the
microwave analyzer.
c) Set the reference level of Analyzer:
Press
【
Amplitude
】
, [Ref Level] , -10 [dBm]
d) Set the resolution bandwidth and video bandwidth:
Press
【
BW
】
, [RBW Auto Man] , set the resolution bandwidth to 10kHz;
Press [VBW Auto Man] ,set VBW to 10kHz ;
e) Switch to the channel power measurement setup menu:
Press
【
Measure
】
, [Ch Power>] to switch to the channel power measurement menu.
f)
Set center frequency:
Press [Center Freq] and set the center frequency to the GSM signal frequency with numeric keys, which
is set to 850MHz in this example.
g) Set the channel power bandwidth:
Press [Ch BW] and set the channel power bandwidth with the figure keys. Enter 200kHz for GSM
signals.
h) Set the channel power span:
Press [Span] and set the channel power sweep bandwidth with the figure keys. Enter 800kHz for the
GSM signal.
i)
Turn on the maximum hold function:
Press [Trace], [Max Hold] .
j)
Turn on the channel power measurement function:
Press
【
Measure
】
, [Ch Power>] , [Ch Power Off On] to turn on the channel power measurement.
When the channel power measurement function is turned on, the detection mode is automatically set to
the mean detection mode. The measurement result is displayed at the bottom of the screen, and the two
vertical dashed lines on the screen indicate the bandwidth of the channel power as shown in Figure
5-25.
