Boonton 4240 RF Power Meter - Manual (Page 59)

Boonton 4240 Series RF Power Meter
Diode
20 dBm (-10 dBm and 0 dBm for attenuated models 51015 and
1033). This response characteristic is obtained because the sensors are dual diode types, and diodes respond in square-law
not an approximation, but rather an inherent effect. This effect results from the fact
s switches, but behave as signal dependent resistors instead. Even with no signal input,
e diodes have a finite conductance, and this conductance is modulated on a cycle by cycle basis to give a net DC offset
ponse can be seen in Figure 4-12, where a 100% amplitude modulated signal is shown to have virtually no
sensors are also RMS responding below about -
5
fashion at low and medium levels. This is
that the diodes do not turn on and off a
th
proportional to the power.
The square-law res
effect on the measured power at low levels. Of course, frequency modulated and phase modulated signals can be measured at
any level, since the envelope of these modulated signals is flat. Frequency shift keyed (FSK) and quadrature modulated
signals also have flat envelopes and can be measured at any power level.
Figure 4-1 Modulation (510 2. Error Due to AM 13 Diode Sensor)
y -10 d detectors. The
odel 4 0 is so lculate the RF
pe. Ho ever, o RF si nals wi
ansition region from -20 dBm to -10 dBm.
the top
easured. The duty cycle in percent is set into the DUTY entry in the
HANNELS menu. For example, if the signal consists of pulses with a duty cycle of 25%, set DUTY to 25. This will add 6
B to the displayed power and turn on the "Pk" indicator following the units.
t higher power levels (above approximatel Bm for the 51013 sensor), the diodes operate as peak A
M
24 ftware calibrated to ca power based on a shaping transfer function (RF to DC) for each sensor
y measurements f e valid in this ty w nl o g th flat envelopes (CW, FM, PM, FSK, quadrature, etc.) ar
region and in the tr
r pulses where the duty cycle (on-time percentage) is known and A special provision is made for the case of rectangula
vel power of the pulse (pulse power) is to be m le
C
d
Operation
4-13