SMIQ
Fading Simulation
1125.5555.03
2.71
E-9
2.9.1
Output Power with Fading
With a PATH LOSS setting of 0 dB, a single path of the fading simulator introduces an insertion loss
between 12 dB and 18 dB for the IQ signals applied (with Insertion Loss Setting Mode = NORMAL). This
insertion loss provides a headroom if several paths are superimposed on one another and also for the
statistical influences to which a path is exposed. In the LOW ACP mode, the insertion loss is reduced to
approx. 6 dB to 12 dB. This may lead to the rare case of clipping level being attained in the instrument.
The IQ signals are in such case limited to the maximum level (clipping). The corresponding insertion
loss is automatically corrected in the SMIQ. The output power is kept constant.
Displays:
LEVEL:
The rms value of the output signal is displayed.
PEP:
The (theoretically possible) peak value is displayed. This value is attained if clipping level
is reached both for the I and the Q path. For signals with a high crest factor it is not likely
that the PEP value is attained.
Due to the insertion loss introduced by the fading simulator, the maximum output power of the SMIQ is
reduced by max. 18 dB.
2.9.2 Two-Channel
Fading
For two-channel fading, an SMIQ with two fading options (SMIQB14 and SMIQB15) and a second SMIQ
without fading options is required. Moreover, the SMIQ has to be recabled internally, see description in
Chapter 1, Section "Option SMIQB15 – Second Fading Simulator". After reconnecting the internal
cables, the I/Q baseband signals of the second channel (SMIQB15) are available at connectors I
FADED and Q FADED on the rear panel of the unit. On the second unit, vector modulation has to be
switched on.
Notes:
- Because of the insertion loss introduced by the fading simulator in the first SMIQ, the second
SMIQ is not driven correctly. For the second SMIQ to be driven correctly, the current insertion
loss of the first SMIQ must be determined and entered into the second SMIQ. This correction
can be made by entering a CREST FACTOR in the vector modulation menu of the second
SMIQ. The numerical value to be entered can be taken from the first SMIQ from the line SET
SECOND SMIQ CREST FACTOR TO in the fading menu. After this value has been entered,
the second SMIQ supplies the output level indicated in the menu.
- For calibration of the two output levels (with Fading Simulator) it is necessary to leave the
Fading Simulator in the signal path and to switch off fading. At this purpose, select setting
“CALIBRATE“ with Standard in the Fading Simulator menu.
ï ð
SMIQ
ï ð
SMIQ
I
Q
RF 2
RF 1
Fig. 2-37
Two-channel fading