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4 8472B Operating and Service Manual
Operating Information
Operating Information
The crystal detector can be used as a demodulator to obtain a pulse envelope
which can then be observed on an oscilloscope. It can also be used as a
general purpose detector.
CAUTION
• Static discharge can damage the detector element. A 100 pF capacitor
(1.2 m [4 ft] of coax cable) charged to 14 volts stores .1 erg, the
maximum pulse rating of the detector element.
• Connect cables to test equipment and discharge the center conductor
before you connect to the detector.
• DO NOT NEEDLESSLY HANDLE THE DETECTOR ELEMENT
USED IN CRYSTAL DETECTOR. Static electricity which builds up on
a person, especially on a cold dry day, must never be allowed to
discharge through the crystal detector.
• Avoid exposed leads to or from the crystal detector, since these are often
touched accidentally.
The power applied to the detector can be either modulated or continuous
wave (CW). If modulated at a 1000 Hz rate, a SWR meter can be used as an
indicator. For CW detection, a dc milliammeter or millivoltmeter can be used
as the indicator.
NOTE When using the crystal detector with an oscilloscope, and the waveshapes to
be observed have rise times of less than 5
µs, the coaxial cable connecting
oscilloscope and detector should be as short as possible and shunted with a
resistor.
Ideally, this resistor should be 50
Ω to terminate the coaxial cable properly.
However, with 50
Ω resistance, the output video pulse may be too small to
drive some oscilloscopes. Therefore, the cable should be shunted with the
smallest value of resistance that will obtain suitable deflection on the
oscilloscope; typically the value will lie between 50
Ω and 2 k Ω. The larger
the resistance, the more degradation of rise time.