Watkins-Johnson Company WJ-8711A, Installation, Operation And Maintenance Manual

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LOCAL OPERATION WJ-8711A DIGITAL HF RECEIVER
3-32
The value can be altered by the Auxiliary Parameter edit knob or by pressing the SQUELCH key to toggle
between off and a numeric value. The numeric entry keys can be used to enter a numeric value in units of -
dBm, terminated with the SQUELCH key.
Terminal 12 (MUTE) of TB1 on the rear panel is provided for the input of external squelch
control in system setups. When an external mute is asserted (mute line pulled low), the receiver's squelch is
activated and the squelch value in the display is overwritten with "MUT". When the external mute is
disasserted (mute line pulled high or not driven), the display returns to the last squelch value that was selected.
3.5.5
ATTENUATING OR AMPLIFYING INPUT SIGNALS VIA THE RF
INPUT PATH SELECTION
Depending on the receiver's tactical location, signals may be, in general, too powerful or not
powerful enough for ideal reception. In these situations the input signals can be attenuated or amplified by
selecting the appropriate RF input path for the input signals. The RF INPUT key is used to make the
selection, which can be PREAMP, NORM, or ATTN. The selection is indicated by the lit LED.
When PREAMP is selected, all input signals are amplified by 10 dB. When ATTN is
selected, all input signals are attenuated by 15 dB. When NORM is selected, the input signals are unaffected
at this point.
3.5.6
SELECTING THE GAIN CONTROL MODE
Two basic gain control modes are available: automatic (AGC) or manual. In the AGC mode,
the receiver automatically adjusts the gain level (depending on the level of the received signal) to provide
optimum signal level for demodulation. Two modes of AGC are available: fast or slow. The fast AGC mode
provides a 15 millisecond attack time and a 25 millisecond decay time which makes it a more suitable
selection when monitoring signals in the AM and FM detection modes. The slow AGC mode provides a 15
millisecond attack time and a 4 second decay time which is best suited for monitoring signals in the CW, USB,
LSB, and ISB detection modes. Attack time and decay time are defined as the length of time that it takes for
the audio outputs to return to a nominal level after a moderate instantaneous increase or decrease in the input
signal level has occurred, respectively.
The selected gain mode is displayed in the upper Auxiliary Parameter display, directly above
the AGC key. The selections are FST (for fast AGC), SLO (for slow AGC), and MAN (for manual gain
control). To select the gain control mode, press the AGC key, lighting its LED. Use the Auxiliary Parameter
edit knob or continue pressing the AGC key until the desired mode is displayed.
In the manual gain mode (MAN), the operator can manually adjust the gain of the receiver
with the MANUAL GAIN knob.
3.5.7
AIDING CW DETECTION WITH THE BFO FUNCTION
The BFO (beat frequency oscillator) function is available, while in the CW detection mode, to
aid in the detection of CW tones. A BFO frequency can be applied to the received CW signal to alter its audio
pitch.
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