122 Chapter3
Making EDGE (with GSM) Measurements
Making the EDGE ORFS Measurement
❏ Offset Freq - Only available when Measure is set to Single Offset
(Examine). The Step hardkeys (⇑ or ⇓) will step through the offset list
as selected by the
Offs Freq List key. Other offset frequencies can be
entered using the RPG knob or the Data Entry keys.
❏ Trig Source - in this measurement, trigger source and burst sync are
linked. Refer to the explanation under
Burst Sync.
❏
Burst Sync - Synchronization is different on ORFS compared to other
measurements. Since offsets may be very low power and acquired
using very narrow filters, the burst edges are not well defined and
there certainly is not enough information to perform a
demodulation. Therefore all synchronization is performed on the
carrier. The timing reference (“T0”) is then re-used on the offsets.
Since “T0” on the carrier is determined with respect to the trigger
point, the trigger point on the offsets is very important. Once “T0” is
determined, the 50% and 90% points can be found.
Therefore, the trigger must be synchronous with respect to a rising
edge of a burst. The RF Burst trigger will do this if the offset is
within about 7 MHz of the carrier. Remember that since the RF
Burst trigger is wideband, the carrier will still cause the signal to
trigger. Assuming the trigger threshold remains constant, the
trigger with respect to the burst will remain constant. Since the
Frame Trigger uses an internal frame timer (clock), its period is set
so that it occurs synchronously with respect to the transmitting
frame. If an external trigger is used, it is important that it is
synchronous with the burst.
Because of these requirements, only the trigger source can be
selected while the measurement selects the burst sync type based on
the trigger source.
NOTE Video trigger source is not allowed, because when the instrument is
tuned to offset frequencies away from the carrier, the video trigger
threshold will not be reached (due to the low power level of the offset.)
Trigger Source Measurement Defined
Burst Sync
Free Run None
RF Burst RF Amplitude
Ext Front External
Ext Rear External
Frame Training Sequence
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