6 settings for some common signal types – Boonton 4530 Peak Power Meter User Manual User Manual
Page 151
Boonton Electronics
Chapter 5
4530 Series RF Power Meter
Making Measurements
5-9
5.6 SETTINGS FOR SOME COMMON SIGNAL TYPES
The following list discusses some of the common telecommunication formats that are frequently measured. While this
list should give enough setup information to read back the most used measurements, some of the advanced features of
the 4530 Series can return other data as well. This information is not intended as a tutorial on each of the signal types,
but rather a guide on how to get started.
5.6.1
Measuring GSM and EDGE.
The GSM (Global System for Mobil Communications) signal is a Time
Division Multiple Access (TDMA) multiplexing scheme that uses a repeating sequence of 8 time slots in a
frame. The data frame duration is 4615
µs, and each time slot is 577µs. Handsets transmit during one of the
eight timeslots. Base stations transmit during all timeslots, but usually at different levels for each timeslot.
The power envelope of the GMSK modulation is relatively flat during each timeslot, and it is generally desired
to measure the average power during the “active” portion of the timeslot, or the middle 90%, or 520
µs. The
first and last 5% (28
µs) is excluded from the average to allow for RF power ramping at the edges of the timeslot.
This is accomplished by using Pulse Mode, and setting markers at the desired points in time.
EDGE is an extension of the GSM format (Enhanced Data for GSM Evolution) which uses uses 8PSK modula-
tion during the burst. This modulation does not share the flat envelope of GSM’s GMSK, so there is a
significant peak-to-average ratio, and the measurement of this is generally of interest. The setup shown
below will return the peak-to-average ratio as well as average power during the burst.
Meas Mode:
Pulse
Frequency:
0.90 GHz (or whatever operating frequency is in use)
Averaging:
4 (use less for faster response time, more for better noise rejection)
TimeSpan:
1 ms (shows the full 577
µs burst and both edges)
Trig Source:
Sensor 1 (triggers on RF signal)
Trig Slope:
Positive (trigger on leading edge of pulse)
Trig Mode:
Pk-To-Pk (automatically sets based on signal level)
Trig Position:
Left (position trigger point at left edge of screen)
Trig Delay:
-0.2 ms (moves leading edge of pulse 200
µs to the right to center pulse in display)
Trig Holdoff:
4.500 ms (delay for almost a full frame, and arm trigger 100
µs before next expected edge)
Marker Mode:
Vertical (set markers to measure power at time offsets)
Marker1 Pos:
30
µs (set Marker 1 at beginning of timeslot’s “active interval”)
Marker2 Pos:
550
µs (set Marker 2 at end of timeslot’s “active interval”)
Query Cmnd:
FETCh1:ARRay:PULse:POWer?
(returns array inclulding average pwr betwn markers)
Other measurements may include timing information such as burst rate, width, and transition times of the
leading and trailing edges of the burst.
To measure GSM basestation signals reliably, it is necessary to either limit the basestation to transmitting
during only one timeslot, or provide an external trigger pulse that is synchronized with the frame. Otherwise,
it is difficult to guarantee that the power meter will synchronize with the desired portion of the frame (timeslot).
The entire, 8-timeslot frame may be viewed by setting the timespan to 5ms, and power of each timeslot can be
measured by moving marker positions to each timeslot.
5.6.2
Measuring NADC.
The IS-136 NADC (North American Digital Cellular) signal is a Time Division Multiple
Access (TDMA) multiplexing scheme that uses a repeating sequence of three time slots in a 20ms frame. The
full frame length is actually six time slots (40ms), with two time slots active, but there is little difference
between the two, and measuring either the first or second set should produce the same result. The data frame
duration is 20ms, and each time slot is 6667
µs. Handsets transmit during one of the three timeslots (or two of
the six, depending how you view things). Base stations transmit during all timeslots, but usually at different
levels for each timeslot. The power envelope of the DQPSK modulation varies during each timeslot, and it is
generally desired to measure the average power and peak-to-average ratio during the “active” portion of the
timeslot, or the middle 96%, or 6.4ms. The first and last 2% (100
µs) is excluded from the average to allow for
RF power ramping at the edges of the timeslot. This is accomplished by using Pulse Mode, and setting
markers at the desired points in time.