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Channel Power Measurement

Channel power measurement is one of most common measurements for a radio transmitter.

This test measures the output power, or channel power, of a transmitter over the frequency

range in a specific time interval. Out-of-specification power measurements indicate system

faults, which can be in the power amplifiers and in filter circuits. Channel Power measure

ments can be used to:

Validate transmitter performance

Comply with FCC regulations

Keep overall system interference at a minimum

The following section describes a GSM Channel Power measurement as an example.

GSM Channel Power Measurement

Global Systems for Mobile (GSM) communication is a globally accepted standard for digi

tal cellular communication. There are two frequency bands allocated to GSM mobile

phones, one at 900 MHz, and the other at 1800 MHz. GSM uses a combination of Fre

quency Division Multiple Access (FDMA) and Time Division Multiple Access (TDMA).

Within each band are approximately one hundred available carrier frequencies on 200 kHz

spacing (FDMA), and each carrier is broken up into time-slots so as to support eight sepa-

rate conversations (TDMA). Each channel has an uplink and a downlink, 80 MHz apart.

GSM uses the Gaussian Minimum Shift Keying (GMSK) modulation method.

Due to the nature of TDMA, GSM transmitters ramp RF power rapidly. If the transmitter

keys on too quickly, users on different frequencies, especially those close to the channel of

interest will experience significant interference. This is one of the reasons that spurious

measurements are extensively used in GSM applications.

To make accurate and repeatable GSM measurements, there are a few simple rules to fol-

low:

The resolution bandwidth of the Site Master should be set to 1.0 MHz to cover

the wide GSM band.

The video bandwidth must be set to 100 kHz or greater to obtain the details of

multiple channels in the GSM band.

Max Hold on the Site Master should be set to ON.

NOTE: When Max Hold is on, the Site Master automatically turns the sweep av

eraging function off.

Required Equipment

Site Master S114C/S332C

30 dB, 50 Watt, bi-directional, DC –18 GHz, N(m) – N(f), Attenuator,

Anritsu 42N50A-30

Test Port extension cable, Anritsu 15NNF50 – 1.5C

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Chapter 5 Spectrum Analyzer Measurements

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