EXTERNAL MODULATION
(cant)
The equation defining the relationship of instantaneous modulation voltage to the
envelope amplitude is:
x VcarrierlVp-p}
2
1
-)
+
2
Vmodulation
VenveJope(Vp-p}
where Vcarrier
=
the 3314A's displayed amplitude and
-10V
Vmodulation
+
10V
Observations:
-The carrier amplitude is 1/2 the displayed value when VmoduJation
OV.
-The envelope
=
when Vmodulation
=
-lV.
-The carrier is 180
0
out of phase when Venvelope is negative IVmodulation is
more negative than
-
1V} .
-The Reduce Input light will come on when modulation is
100%.
The Reduce Input light will come on whenever the AM modula-
tion is
100%. AM modulation
100% can be sensed from the HP-IB when bit
#1 of the Status Byte is unmasked. The Reduce Input light's HP-IB equivalent is
ER50". Envelope distortion occurs when the output
'
clips
at approximately 10%
over the maximum amplitude allowed in each amplitude range. Note: Amplitude
modulation
>
100%
will not necessarily distort the AM
envelope. The
AM
envelope is distorted when distortion sidebands are present, not when the ratio of
total sideband power to carrier power is greater than 1. A synchronous AM detec-
tor is required to recover the modulating signal undistorted. Note that a non-
synchronous detector such as a peak detector, cannot recover the modulating
signal, undistorted. The Reduce Input light
are inhibited while in either
of the
Lock modes when the phase locked loop is unlocked.
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