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OPERATING HP 141T
SPECTRUM ANALYSER
February 2011

Understanding the HP 141T Spectrum Analyser is my first attempt at using spectrum analysis. Most of my test equipment is fairly easy to use and I have had previous experience with similar items and their applications. Spectrum Analysers are one (of the many) areas where I have little knowledge, although I appreciate their general function, so these are my working notes.

HP Spectrum Analyser Equipment from top to bottom:
8556A; 8553B; 8445B; 141T; 8555A; 8552B; 8444A; 8443A;
plus special cables.

November 2014

The Spectrum Analyser measures frequency against amplitude, unlike an Oscilloscope that measures time against amplitude. If you want to see a signal at say 1GHz, this is the way to do it. This Spectrum Analyser has a frequency range of 20Hz to 18GHz and an amplitude range of -130dBm to +10dBm.

HP 141T Display Section with HP 8553B RF Section
and HP 8552B IF Section plug-ins.


The CRT display is 8 x 10 with frequency horizontal, Log Ref levels -10dBm, -20dBm, -30dBm, -40dBm, -50dBm, -60dBm, -70dBm on the right hand side vertical and Linear Ref levels 7, 6, 5, 4, 3, 2, 1 on the left hand side vertical.

Display showing a pulse at the centre frequency
PLUG-INS

There are various plug-ins available.

The horizontal 'X' signal is provided by the HP 8552B IF Section which is the lower plug-in. There are 2 versions: the 8552A and 8552B. The B version is the higher specification and the one that I have. This has a scan timebase of 0.1ms to 10s.

The vertical 'Y' signal is provided by the RF or LF Sections which are the upper plug-in. There are 4 versions: the HP 8553B RF Section for 1kHz to 110MHz; the HP 8554B RF Section for 100kHz to 1,250MHz; the HP 8555A RF Section for 10MHz to 18GHz; and the HP 8556A LF Section for 20Hz to 300kHz. I have all four of these Sections.


TRACKING GENERATORS

There are 2, well actually 3, Tracking Generators. The HP 8443A Tracking Generator Counter for 100kHz to 110MHz and the HP 8444A Tracking Generator for 500kHz to 1.3GHz. The 8556A also includes its own tracking generator.


PRESELECTOR

The HP 8445B Automatic Preselector is a YIG tuned filter for use with the Spectrum Analyser 8555A (10MHz to 18GHz) RF Section. The Preselector can be tuned exactly to the Analyser's reception frequency and eliminates harmonic mixing image and multiple responses from 1.8GHz to 18GHz. Below 1.8GHz the image and multiple responses are eliminated by a low-pass filter.

SPECIAL CABLES

There are various special cables to inter-connect the equipment.

Special Cables for the Spectrum Analyser
CALIBRATION
 
Before the Spectrum Analyser can be used, it must be calibrated using the following procedures:

   Operating HP 8552B IF Section

   • Operating HP 8553B RF Section 
 
   • Operating HP 8554B RF Section 
 
   • Operating HP 8555A RF Section 
 
   • Operating HP 8556A LF Section


These procedures calibrate the IF Section to work correctly with the RF and LF Sections as required.

SWEPT MEASUREMENTS

Set Up for Swept Measurements

This is the setup for swept measurements over the 10MHz to 1.3GHz range using the 8444A Tracking Generator. The display shows the fall off at 1.4GHz approx.

First the 8444A is connected to the 141T. At the rear, a special cable connects the 8444A 3rd Local Oscillator input to Aux A on the 141T. At the front: the 8444A Scan Output connects to the 8552B Scan In/Out; the 8444A First LO Input connects to the 8555A First LO Output; the RF Output could connect to the 8555A Input but in this case connects to the 8445B Input.

The 8445B is connected to the 141T. At the rear, a special cable connects the 8445B to Aux B on the 141T. At the front, a special rigid cable connects the 8445B Output to the 8555A Input.

The 8443A is not used.

The DUT (Device Under Test) is inserted between the 8444A Output and the 8445B Input. For convenience of making measurements between direct and via the DUT, I use 2 HP 8761A SPDT RF Switch which operate between DC and 18GHz.

The 8620C Sweep Oscillator with appropriate plug-ins could be used instead of the 8444A to provide swept measurements up to 18GHz.

The 8443A and 8553B could be used for swept measurements in the 1kHz to 110MHz range.

The 8556A can be used with its own tracking generator over the range 20Hz to 300kHz.

... more to follow ...