User Guide

NHB–3
Technical Documentation
PAMS
Tuning Instructions
Original 26/97
11
3. I/Q Modulator Amplitude Balance and Phase Shift Tuning
The purpose of this tunig operation is to adjust the I/Q modulator d.c. offsets
and the I/Q modulator amplitude balance and phase shift.
I/Q modulator d.c. offsets, amplitude balance and phase shift tuning:
– Connect spectrum analyzer (with attenuator if needed) to phone antenna
connector.
– Select adjustment menu option ”TX I/Q Tuning” and press <Enter>.
– Check that TX power level is level 5, Cont. mode channel is 661 and TX
data type is 1.
– Adjust spectrum analyzer centre frequency to 1880 MHz, Ref level to
30 dBm and Span 200 kHz (500 kHz can be used to see both sides of the
spectre)
– Set also Res BW to 10 kHz, Video BW 1 kHz and Sweep time 1.0 s.
– Set triggering to Free Run
–67.71 kHz +67.71 kHz
CHF
> 30 dB
> 35 dB
Set this value
to minimum
Amplitude &
phase difference:
Set this value
to minimum
D.C. offset
tunings:
– Select option ”TX I DC offset”.
– Adjust the level of centre frequency (CHF signal) to minimum by varying D/A
converter value with <+> and <–> keys (or occasionally cursor left and right
keys).
– The amplitude difference between CHF–67.7 kHz and CHF should be
>30 dB (See picture).
– When value is OK move to the next option with cursor keys.
– Select option ”TX Q DC offset”.