Boonton 4530 Peak Power Meter User Manual User Manual
Page 153
Boonton Electronics
Chapter 5
4530 Series RF Power Meter
Making Measurements
5-11
Meas Mode:
Pulse
Frequency:
0.815 GHz (or whatever operating frequency is in use)
Averaging:
8 (use less for faster response time, more for better noise rejection)
TimeSpan:
20 ms (shows the full 15ms 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:
-2.0 ms (moves leading edge of pulse 2ms to the right to center pulse in display)
Trig Holdoff:
88.000 ms (delay for almost a full frame, and arm trigger 2ms before next expected edge)
Marker Mode:
Vertical (set markers to measure power at time offsets)
Marker1 Pos:
0.0ms (set Marker 1 at the beginning of pulse)
Marker2 Pos:
15.0ms (set Marker 2 at the end of pulse)
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 iDEN 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, 6-timeslot frame may be viewed by setting the timespan to 100ms, and power of each timeslot can
be measured by moving marker positions to each timeslot.
An alternative method for measuring average and peak power for the iDEN reverse link (handset) is to use
modulated mode. Peak power is measured directly. Overall average power may be accurately measured, and
average power during the burst may be calculated by multiplying the overall average by 6 since the burst is
active during one of every three timeslots. This can be done by setting the measurement offset to 7.78dB (10
x log10[6]). Note, however, that this will make the peak power and peak-to-average ratio read 7.78dB too high,
since the peak power does not vary with duty cycle. Since the pulse repetition rate is relatively slow, the
integration filter should be set for an integral number of frames, or at some multiple of 90mS. This ensures that
the signal will be averaged over one or more full cycles, and the average reading will be the same no matter
where in the frame the reading is synchronized. The following table shows how to use modulated mode for
this measurement.
Meas Mode:
Modulated
Frequency:
0.87 MHz (or whatever operating frequency is in use)
Filter:
360ms (average power over four full frames. Any multiple of 90ms is OK.)
Offset:
7.78dB (multiply power by 6.0 to account for the 1/6 duty cycle of the signal)
Query Cmnd:
FETCh1:ARRay:CW:POWer?
(returns array including average and peak power)
5.6.4
Measuring Bluetooth.
The Bluetooth signal is a frequency hopping multiplexing scheme that uses variable
length packets to transmit digital data. Each packet occupies one or more fixed-length 625
µs timeslots. One
common type of packet is the DH1 (high rate data packet), which uses one timeslot. Although the timeslot is
625
µs in duration, the transmitting device may only be active for 366µs of the timeslot, unless a multi-timeslot
packet is being set. This allows time for signal propagation and for frequency switching at the end of the
timeslot. The master and slave devices usually transmit during alternate timeslots, and these packets may
repeat at a rapid rate, so the transmitted signal envelope for a continous series of DH1 packets will appear as
a 366
µs pulse repeating at a 1250µs (800Hz) rate. The modulation format is GFSK (Gaussian Frequency Shift
Keying), which has a relatively flat power envelope while the pulse is on, so typically only average power
during the burst is of interest. The first and last 2.7% (0.4ms) is excluded from the average to allow for RF
power settling at the edges of the timeslot. This is accomplished by using Pulse Mode, and setting markers
at the desired points in time.