Specifications

Description
The HP 3048A can be configured with a down converter under manual or
system control. Typically down converters translate the frequency of the
DUT to a lower frequency The critical parameter to the HP 3048A is Phase
Detector Input frequency. Because the down conversion is done prior to
the phase detector, the system is essentially measuring a lower frequency
source. When downconverting a signal by mixing against a local oscillator,
the noise of the DUT is translated to the IF without any change in the noise
level except for added noise due to the LO. When manually controlling
the down converter you must input the down converted frequency (IF)
as the Detector Input Frequency in the Instrument Parameter display.
If the Detector Input Frequency is less than 95 MHz, the system will
automatically enable the 2 MHz Low Pass Filter internal to the HP 11848A
Interface. With the 2 MHz LPF enabled, the measured offset range is
limited to 2 MHz.
The Carrier Frequency entered in the Instrument Parameters display should
reflect the correct DUT frequency so the graphic display of the Carrier
Frequency is correct. The entered Carrier Frequency is used:
• To label the graph,
• To compute Sigma vs. Tau and S
y
{f), and
• To derive the correct frequency band selection and Detector Input
Frequency for a system controlled HP 11729C.
HP 11729C Carrier Noise Test Set
The HP 11729C is the only down converter fully supported under system
control, When configured under System Control the system automatically
selects the correct comb line filter on the HP 11729C and determines the
correct Detector Input Frequency from the entered Carrier Frequency.
Detector Input Frequency = \Garrier Frequency — Center Frequency of Comb Line\
6-32 Down Converters rev.05SEP89