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Azur Electronics

OPERATING HP 8555A
RF SECTION
CALIBRATION  
 
Before the Spectrum Analyser can be used, it must be calibrated using the following procedure. This sets the HP 8552B IF Section X & Y gain & position and the HP 8555A RF Section amplitude calibration.  
[Based on HP 8552B & 8555A Operating and Service Manuals]

NOTE: Ensure the 8552B / 8555A D-type connectors are correctly mated. 
Poor mating is often the cause of X & Y display problems! A quick check is to ensure that switching the INPUT ATTENUATION lights all the lamps around the LOG REF LEVEL control. 

 
1. Initial Setup  
 
Switch the HP 141T Display Section LINE ON.  
Press NON STORAGE mode CONV button.  
Intensity to 12 o’clock approx.  
Focus to 12 o’clock approx.  
Allow to warm up for 30 minutes approx.

Set 8555A Controls as follows: 
BAND 0 to 2.05GHz
FREQUENCY 30MHz  
FINE TUNE Centred  
BANDWIDTH 100kHz  
SCAN WIDTH PER DIVISION  
PER DIVISION 10MHz  
INPUT ATTENUATION 10dB  
TUNING STABILIZER On
SIGNAL IDENTIFIER Off  
Terminate in 50Ω the FIRST LO OUTPUT and THIRD LO OUTPUT.  
 
Set 8552B Controls as follows:  
MANUAL SCAN Centred  
BASELINE CLIPPER CCW  
SCAN TIME PER DIVISION 10ms  
LOG REF LEVEL -30dBm  
LOG REF LEVEL Vernier 0  
LOG LINEAR 10dB LOG  
VIDEO FILTER OFF  
SCAN MODE INT  
SCAN TRIGGER AUTO  
 
2. Focus and Astigmatism  
 
Adjust INTENSITY as needed.  
 
Set LOG REF LEVEL maximum CCW (this minimises noise on the baseline).  
 
Adjust VERTICAL POSITION to set the trace to the -50dB graticule line.  
 
Set SCAN TIME PER DIVISION to 10s.  
 
Adjust FOCUS and ASTIG for the smallest round dot possible.  
 
3. Trace Alignment  
 
Set SCAN TIME PER DIVISION to 10ms.  
 
Adjust TRACE ALIGN to set the trace parallel to the horizontal graticule line.  
 
4. Horizontal Position and Gain  
 
Adjust HORIZONTAL POSITION so the display is centred on the CRT.  
 
Adjust HORIZONTAL GAIN so the displayed scan width is exactly 10 divisions on the CRT.  
 
Some interaction between HORIZONTAL POSITION and GAIN controls may require readjustment.


Display shows horizontal line at -50dBm graticule line and  
1st L.O. feed through at 0MHz (centre position is 30MHz)
5. Vertical Position and Gain  
 
Adjust VERTICAL POSITION to set the trace to the -80dB graticule line.  
 
Set LOG REF LEVEL to 0dBm.  
 
Set FREQUENCY to 50MHz.  
 
Connect 8552B CAL OUTPUT to 8555A RF INPUT using a BNC to BNC 50Ω coax cable and a N-type to BNC Adaptor.

Display shows horizontal line at -80dBm graticule line and  
Calibration signal at 30MHz and -30dBm  
2nd harmonic at 60MHz and -40dBm approx  
3rd harmonic at 90MHz and -45dBm approx
Adjust FREQUENCY to centre the 30 MHz signal on the CRT.  
 
Reduce SCAN WIDTH PER DIVISION to .2MHz.  
 
Adjust FREQUENCY FINE TUNE to keep signal centred.  
 
Set LOG REF LEVEL maximum CCW.  
 
Adjust LOG REF LEVEL and VERNIER so maximum signal amplitude is exactly on -70dBm graticule line.  
 
Rotate LOG REF LEVEL 7 steps clockwise. The amplitude of the signal should increase one vertical division per 10dB step.  
 
Adjust VERTICAL GAIN to place maximum signal amplitude exactly on the top graticule line.  
 
Repeat the previous 3 steps to obtain optimum setting.


Display shows Calibration signal at 30MHz  
Note noise on baseline
6. Amplitude Calibration  
 
Set LOG REF LEVEL to -30dBm.  
 
Adjust AMPL CAL to place maximum signal amplitude exactly on the top graticule line.  
 
The Spectrum Analyser is now calibrated in the LOG display mode from -130dBm to +10dBm.  
 
7. Linear Mode  
 
Set LOG REF LEVEL to 1mV/DIV on blue scale.  
 
Set the LOG – LINEAR switch to LINEAR.  
 
Set LINEAR SENSITIVITY to 1mV on blue scale (Vernier 0 position).

Display showing the 30MHz calibration signal at 7.1mV
The left hand side vertical graduations 0 to 8 are calibrated in absolute voltage.  
 
Maximum signal amplitude should be 7.1mV (-30dBm is 7.07mV across 50Ω), if necessary adjust AMPL CAL to achieve this.  
 
The Spectrum Analyser is now calibrated in the LINEAR display mode from 0.1µV to 100mV.  
 
8. Reset  
 
Return the 8552B and 8555A controls to their starting position.  
 
 
 
NOTE: For safe operation, maximum RF Input level (with INPUT ATTENUATION >= 30dB) is +33dBm, 2W, ±20Vdc 10Vrms, 14.4Vp. To avoid damage to the Mixer, initially utilise maximum input attenuation and/or an external attenuator!