SCALE SCALE AND REFERENCE LINE
Chapter 7
SCALE AND REFERENCE LINE
GENERAL DESCRIPTION
This chapter describes the use of SCALE and REFERENCE LINE control groups for setting the amplitude scale, and for making amplitude level measurements more conveniently.
R E F E R E N C E L I N E E
DISPLAY LINE
1:
THRESHOLD
SCALE
SCALE keys allow the scaling of the vertical graticule divisions in logarithmic or linear units without changing the reference level value.
LOG.
m (DATA entry) scales the amplitude to 1 dB, 2 dB, 5 dB, or 10 dB per division.
If m is pressed when the scale is linear, 10 dB per division will be automatically entered. The subsequent
(DATA), if any, will then replace the automatic 10 dB/div.
Press
Manual
Operation 61
SCALE
LIN
SCALE AND REFERENCE LINE level, the bottom graticule becomes zero voltage. Reference level, and all other amplitudes, are read out in voltage. However, other units may be selected. See AMPLITUDE UNITS SELECTION, Chapter 11.
If m is pressed when the scale is linear, 10 dB per division will be automatically entered.
LIN
Press (
In LINEAR, a specific voltage per division scale can be set by entering a voltage reference level value. For example, to set the scale to 3 mV/division, key in 30 mV reference level, (Voltage entries are rounded to the nearest 0.1 dB, so the 30 mV entry becomes 30.16 mV which equals - 17.4 dBm.)
DATA Entry m(-j pq @
Changes scale in allowable increments (1, 2, 5, or 10 dB per division).
Enables direct scale selection of allowed values. Other entries are rounded to an adjacent value.
LIN
No DATA entry will be accepted with the linear SCALE selection key, 0
Example
It is convenient to observe AM sidebands in linear as well as logarithmic scales for analysis of both modulation percentages and distortion products.
6.2 Manual Operation
SCALE
AND
REFERENCE
LINE
Modulated AM signal displayed in the 10 dB/division scale shows the carrier, its sidebands, and distortion products.
SCALE
Linear scaling enables the observation of the sidebands proportional to the carrier.
LIN
Press (-J
As in the MARKER m example, Chapter 6, a direct readout of the percent modulation can be made.
The fractional readout is one -half the modulation index (only one sideband is measured).
%AM = 2(.25) x 100 = 50%.
t I I I I III I
Note that the carrier signal need not be placed at the reference level for an index ratio measurement.
I I 1
LOG
Change to a logarithmic scale with m and change the dB/division with @ @ .
The sidebands are 12 dB down from the carrier, verifying the earlier measurement results.
Manual Operation 63
REFERENCE LINE SCALE AND REFERENCE LINE
Harmonic distortion of the modulating signal can be measured as in MARKER m , Chapter 6.
The modulation frequency is 18.8 kHz and the distortion caused by the second harmonic is 2.4% (read out as .024X).
REFERENCE LINE
The reference line functions, DISPLAY LINE (DL) and THRESHOLD (TH), place horizontal reference lines on the display. Their levels are read out in absolute amplitude units.
DISPLAY LINE uses l l measure signal levels with direct readout.
establish a standard for go/no-go test comparisons.
0 eliminate or reduce amplitude errors due to system frequency response uncertainty
THRESHOLD provides: l a base line clipper whose level is read out.
0 a minimum threshold level that can be set.
DISPLAY LINE
DISPLAY LINE [1.1113 (DATA entry) places a horizontal reference line at any level on the graticule. The line’s amplitude, in reference level units, is read out on the left-hand side of the CRT display.
64 Manual Operation
SCALE AND REFERENCE LINE DISPLAY LINE
The DISPLAY LINE can be positioned anywhere within the graticule. When activated after LINE power ON or m , the display line is placed 4.5 divisions down from the reference level.
DISPLAY LINE m erases the line and readout from the CRT display but does not reset the last position. If the display line is activated again before LINE power ON or [a;l:l , it will return to its last position.
DISPLAY LINE position is always accessible for HP-IB and TRACE m , even if never activated. See Chapter 5,
TRACE ARITHMETIC.
t
The DISPLAY LINE readout has the same number of significant digits as reference level.
DATA Entry
(go
I
Moves the line about one division for each full turn. The line moves in display unit increments.
1
m @@
Moves the line one-tenth of the total amplitude scale per step.
@iiJH
Positions the line to the exact entry level. Entry may be in mV, FV -I- dBm,
+ dBmV, or f dB& depending upon which units are selected.
Example
When the amplitude of a number of signals in the same span require a quick readout, the DISPLAY LINE can be used.
Activate the DISPLAY LINE with @
With and read out its absolute amplitude level.
a d%“V
Moving the DISPLAY LINE to each signal reads out its amplitude.
Manual Operation 65
T H R E S H O L D
THRESHOLD
SCALE AND REFERENCE LINE
THRESHOLD (,.,,. (DATA entry) moves a lower boundary to the trace, similar to a base line clipper on directwriting CRT spectrum analyzers. The boundary’s absolute amplitude level, in reference level units, is read out on
The THRESHOLD can be positioned anywhere within the graticule. It operates on TRACE m , m, or for TRACES A, B, and C simultaneously. When activated after LINE power ON or 1’6::] , the THRESHOLD is
The THRESHOLD level does not influence the trace memory; that is, the threshold level is not a lower boundary for trace information stored and output from the trace memories through the HP-IB. TH [ removes the
THRESHOLD boundary and readout from the CRT display but does not reset the position. If threshold is activated again before LINE power ON or I’d::] , it will resume at its last level.
The THRESHOLD readout has the same number of significant digits as reference level.
DATA Entry
Moves the THRESHOLD about one division per rotation. The line moves in (,.,.io
Moves the THRESHOLD one-tenth of the total amplitude scale per step.
I (t*ll.l l pJ
Positions the THRESHOLD to the exact entry level. Entry may be in mV, k dBm, f dBmY or + dB& depending upon units selected.
66 Manual Operation
SCALE AND REFERENCE LINE
Example
The THRESHOLD can be used as a go/no-go test limit.
A series of signals can be tested for a specific
THRESHOLD level by placing the THRESHOLD at the test level.
Press THRESHOLD (,.,,,I 55.2 dBm. Only those signals > - 55.2 dBm will be displayed.
T H R E S H O L D
Manual Operation 67
