4
Operating Guide
46
Keysight N4000/1/2A Operating and Service Manual
Service
Principles of operation
Referring to the SNS block diagram in
, a co28 V
is supplied from the NFA through the multi-pin “Connector” block when the SNS
is connected to the noise figure analyzer. A voltage inverter is used in the N4000A
and N4001A to input approximately –25 V to the current regulator.
The current regulator applies a negative bias current to the noise diode for the
N4000A and N4001A models. The N4002A utilizes a positive bias, so the voltage
inverter is not necessary. The current regulator block also provides the switching
necessary to produce the noise “On” and “Off” states.
The 2-wire bus interface allows for data transfer to and from the noise source. The
data stored in the EEPROM includes model, serial number, diode current setting,
and SNS calibration data.
The power supply pr5 V to the 2-wire bus interface, EEPROM, and digital
temperature sensor.
The digital temperature sensor is a digital thermometer, thermally coupled to the
microwave assembly.
When the smart noise source is in its “On” state, the noise diode produces
broadband noise which is input to the attenuator.
The attenuator sets the final Excess Noise Ratio (ENR) and output impedance of
the smart noise source. A 16 dB attenuator is used in the N4000A to provide
nominal ENR values of 5 dB. A 6 dB attenuator is used in the N4001A and N4002A
models for nominal ENR values of 15 dB.
The standard output connector is a Precision 3.5 mm. A Type-N connector is
optional.
Troubleshooting
Check the connectors and perform the operator’s check described in the
section of this manual. If the operator’s check results
indicate a problem, or if the connectors are damaged, please contact Keysight
Technologies. Our representatives can help isolate the problem and make
arrangements for repairs if necessary.
