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Model 8902A
lone-Burst Receiver
FUNCTIONS
Special Function
18
(Tone-Burst Receiver)
DESCR I PTlON
Operation
In some FM applications (mobile radio testing,
&ar
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 difficult 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 Function
18
enables the Measuring Receiver 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).
+0.5V
Oscilloscope Photo Dipicting
a 99
m. 5 Delay &tween Transmitier Keying
Pirlse
(Lowcr
Tract,)
nnd A
clivafion qfMOD(JI,A TION OUTPUT/A UDIO INPUT
3-193
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