Ref Set - HP 8642A Operating Manual

Operation
Model 8642A/B
Relative Amplitude (cont'd)
Display
? fcj kj.fcj kj kj kl) ia kJ in t_
FREQ
[ 7 ) 7 T1 TJ
iu.kj J J JD
AMPTD REL
The AMPTD REL annunciators indicate that the amplitude display is a relative
output. All subsequent amplitude settings will be entered and displayed in units of dB
relative to the absolute amplitude when the Relative Zero function was selected.
After setting the amplitude reference, the dBm key operates as a dB terminator (note
the dB printed above the dBm key). For example, after setting the output to read in
dB relative units, just key in 20 dB to output 20 dB relative to the absolute amplitude
when the Relative Zero function was selected.
REF SET
How to Set a Reference to a Specific Amplitude
(In units of dBm, V, mV, uV, EMF V, EMF mV, or EMF uV.)
Setting a specific RF amplitude as the amplitude reference causes subsequent
amplitude settings to display the current output amplitude as dB relative to the
amplitude reference.
[ AMPTD 1 REF SET ( I SHIFT 1 I AMPTD I ) followed by the value of the desired
reference amplitude (in dBm, V, mV, or uV).
REF SET Example 1
Configure the front panel to allow all amplitude setting values to be entered and
displayed as offset from a IV amplitude reference.
First select fTNSTR PRESET 1 to put the instrument in a known state, then:
LOCAL
(keys)
ENTRY
[ AMPTD 1 [ SHIFT ]
ENTRY
REF SET
( FREQ I
DATA
UJS
APRS 1 VL
Display
I kls klf.fcj \u fcj fell KJ fcj hi z_
5 3.0
HI
3-7*
The AMPTD REL annunciators indicate the displayed amplitude is relative to a
reference amplitude. The displayed amplitude is -153.0 dB; the actual output
amplitude is the displayed amplitude plus the amplitude reference. To convert the
amplitude reference to dBm, first exit the relative mode, then select your reference
amplitude as the absolute output amplitude (IV in this case), then press the dBm key.
The equivalent value for IV is 13 dBm; therefore, - 1 5 3 dB + (+13 dBm) = - 1 4 0 dBm.