OPERATION
Checking the battery and offset voltage:
The battery and offset voltage should be checked regularly to
ensure proper functioning of the detector.
1. Turn on the module using the power switch.
2. Connect the “Bias Monitor” port to a voltmeter.
3. Press and hold the “Batt Chk” button and observe the bias
monitor output. The photodiode bias voltage is momentarily
applied to the “Bias Monitor” SMA connector. A reading of 5 V
on this connector is typical with a new battery; the battery
should be replaced when the voltage reaches 3.5 V.
4. Release the “Batt Chk” button and observe the voltage level on
the voltmeter. Without an optical input, this voltage is the DC
offset plus dark current. This “dark voltage” should be less than
10 mV.
5. If needed, keep the voltmeter connected to the module to
optimize coupling to the fiber.
Making the Microwave Connection
Connect the microwave output connector of the photodetector
module to a 50-
Ω
input test instrument such as an oscilloscope
or spectrum analyzer, or other 50-
Ω
load using the proper torque.
To avoid connector damage and signal distortion, be sure that the
instrument you intend to connect to the module has a compatible
connector. See Appendix 2: Using the Correct Microwave Connector
for a list of connector compatibilities.
Aligning the Photodetector to the Optical Input:
To avoid signal distortion, the optical fiber used to deliver the
optical signal to the photodetector module should be single
mode at the operating wavelength and the cable length should
be no longer than necessary.
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