HP 8517B - Manual (Page 49)

HP 8517B S-Parameter Test Set Manual 3-11
If you view the response of a short circuit, notice that:
•
Changing Port 1 attenuator has negligible effect on S
11
marker reading
•
Changing Port 2 attenuator has negligible effect on S
22
marker reading
This is due to the way the attenuators are paired. Both the reference and the
test signal are changed by approximately equal amounts.
When viewing S
21
or S
12
, however, changing Port 1 or Port 2 attenuators
offsets the marker reading by the difference value between Port 1 attenuator
and Port 2 attenuator.
Storing Trace
Memories To compensate for the main frequency response effects due to changing
the attenuators, use the HP 8510C trace memories and trace mathematics
function, as explained below:
1. Connect the thru used for calibration and set the port attenuators to the
value used for device measurement.
2. Recheck the user parameter levels, then press PARAMETER [ S
21
].
3. Press MENUS [DISPLAY] , then {DATA AND MEMORIES} .
Press DISPLAY: {DATA-->MEMORY n} to store the S
21
trace in default trace
memory 1. This trace represents the frequency response difference
between the S
21
signal path calibration and the measurement.
4. Press PARAMETER [S
12
] , then press the following DISPLAY: menu keys:
{SELECT DEFAULTS}
{DEFAULT to MEMORY: 2}
{DATA-->MEMORY 2}
The S
12
trace is now stored in trace memory 2. This trace is the
frequency response difference of the S
12
signal path between calibration
and measurement.
Viewing Normalized
Parameters Use the traces stored in memory 1 and memory 2 to normalize the corrected
data to the new levels after the attenuation is changed. The next example
uses normalization for S
21
or S
12,
only. To view the corrected parameters:
1. Press MENUS [DISPLAY] , then {DATA AND MEMORIES}
2. Press PARAMETER [S
11
] and view the S
11
measurement.
3. Press PARAMETER [S
22
] and view the S
22
measurement.
4. Press PARAMETER [S
21
] , then the following DISPLAY: menu keys:
{SELECT DEFAULTS}
{DEFAULT to MEMORY: 1}
{MATH ( / ) }