Table of Contents
Advertisement
10 Transient Spectrum, Spectrum due to Switching
10.1 What is transient spectrum
In the GSM-system is all communication between the base station and the phone done switched,
in shape of bursts.
The burst is a squared output power pulse with step up- and down ramping.
Every time the voltage of the squared pulse changes rapidly there will be formed a number of
over tones.
The over tones have got different frequencies and amplitudes.
The amount of over tones and what amplitude they have got depends on how steep the up- and
down-ramping are, the higher up- and down-ramping, the higher amplitude and frequency of the
over tone.
The over tones form a spectrum that is called transient spectrum or "Spectrum due to
switching".
To be able to get lower amplitudes for the over tones in the transient spectrum, the up-and down
ramping does not change momentarily from zero-to-max/max-to-zero.
Instead is this done with two help steps, these two help steps are called Low and High
Intermediate Power level.
Fig.10.1. below shows what the control signal POWLEV from N800,DAC 2, looks like.
The times in the figure are approximates measured at an approved phone at full Power level.
The control voltage POWLEV then passes through an exponential amplifier and a Bessel low
pass filter in N450 where the transient disturbance is reduced.
This gives a control voltage without the straight, vertical edges and the sharp corners that pro-
duces the over tones.
4/00021-3/FEA 209 544/18 B
Fig. 10.1
Trouble Shooting Guide, Advanced
43(121)
Advertisement
Table of Contents
