Boonton 4240 RF Power Meter - Manual (Page 60)

Boonton 4240 Series RF Power Meter
nly the display is affected by the duty cycle calculation. The m
Operation
4-14
easurement process is subject to the same criteria discussed
periods on the order of tens of milliseconds may
f inadeq ate ave be increased by use
e. For
ccurate pulse power measurement, the power meter should read an average power of -30 dBm or less. This is the power
e at least +
O
above. For thermal sensor no correction is needed for level. However, pulse
e result in unstable readings becaus o u raging. If the filter time constant is too short, it can
f the AVG function. o
For diode sensors, the RMS power region extends up to -30 dBm with a gradual change to peak voltage respons
a
indication when the duty cycle is set to 100%. Somewhat useful measurements can be made up to -20 dBm average power,
but the uncertainty will typically b
1dB.
using the pulse power feature to avoid overload damage to power sensors. Pulses with small
k to average power ratio. The average responding power meter may have a small indicated
4.9 Chart Recorder Operation
he output voltage is equal to the digits
isplayed on the main data display divided by 1100 times 10. In the dBm or dBr modes, the output voltage is directly
ifference of the measured value and the sonsor’s lower limit to the full dynamic range of the
the default upper limit is 23 dB and the lower limit is -75 dB for a particular sensor then at 0
Extra care should be taken when
uty cycle have a very large pea d
power, but the peak signal at the sensor diode or thermal element may easily exceed the maximum ratings.
The chart recorder output is a DC voltage from 0 to 10 volts. In the Watts mode, t
d
proportional to the ratio of the d
sensor times 10. For example if
dBm the corresponding Recorder Output voltage would be: (0 – (-75) * 10) / (23 – (-75)) = 750 / 98 = 7.65 volts. The
sensitivity over a 10 dB range would be (10 * 10) / 98 = 1.02 volts. Refer to Section 3.3.2 Sensor Key to locate the upper and
lower limits of the sensor in use in determining the expected Recorder Ouput response.
The output impedance is 9.06 kilohms, which gives the user the option of loading it with 1 kilohm, thereby reducing the full
scale output to 1 volt. The normal 12-bit resolution is still maintained with this method. With a 1 megohm load, the circuit is
essentially open and the error is small. Absolute accuracy is +5%.
4.10 Bar Graph Operation
The meter presents the power proportionally in the following manner.
tts Mode. The m Wa
re eter follows the digital display as a percentage of the full scale. The bar graph consists of 100 segments
sulting in a 1% resolution. A main data display of 1100.0 µW drives the meter to 100 percent of full scale while a display
. The meter reads full scale at 10 dB increments.
isplay reads 0 dBr.
at –5 dBr or less.
of 561.0 µW drives the meter to 51 percent of full scale
dBm Mode. The meter follows the digital display as a percentage of the full scale. The bar graph consists of 100 segments
resulting in a resolution of 0.1 dB/segment. A main data display of 0.00 dBm (or any 10 dB increment) drives the bar graph
to zero percent of full scale while 5.00 dBm and 9.99 dBm drives the meter to 45 percent and 90 percent of full scale
respectively. A value of –7 dBm would drive the meter to 27 percent of full scale while a value of –2 dBm would drive the
meter to 72 percent of full scale.
dBr Mode. Selecting the dBr mode positions the bar graph to 50 percent of full scale when the digital d
The analog meter thereafter reads 100 percent of full scale at +5 dBr or more and zero percent of full scale