Model
8901B
Operation
Tone-Burst Receiver
FUNCTIONS
Special F’unction
18
(Tone-Burst Receiver)
DESCRIPTION
In some FM applications (mobile radio testing, for example),
after
a
transmitter
is
keyed, it issues
squelch tones for a brief interval. Often,
it
is
necessary
to
measure the frequency of the squelch tones.
This measurement
is
made difEcult by the noise in the demodulated audio during the short delay
between the keying of the transmitter and the appearance of the audio tones.
Special F’unction
18
enables the Modulation Analyzer
to
be configured
as
a
tone-burst receiver. This
function inserts a user-selectable delay between the instant the instrument senses an
RF
signal
at its
RF INPUT and the time when
it
turns on the output
of
MODULATION OUTPUT/AUDIO
INPUT.
When an external counter
is
connected
to
this output, the squelch tone
will
reach the counter only
when
a
valid measurement can be made. The time delay
is
selectable from
1
through
99
milliseconds.
The following photo illustrates a
99
ms delay between transmitter keying (lower trace).
M
0
D
U LATl
ON
OUTPUT
TRANSMITTER
KEYING PULSE
+0.55V
1.1
vp.p
-0.55V
+0.5V
l.ovp.p
-0.5V
___~
Oscilloscope Photo Depicting
a
99
ms
Delay Between Pansmitter Keying Pulse
(Lower Bace) and Activation
of
MODULATION OUTPUTIAUDIO INPUT
Tone-Burst Receiver
3
-
165
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