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

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WJ-8711A DIGITAL HF RECEIVER LOCAL OPERATION
3-29
to its left to increment by one (for example 0.009000 to 0.010000). When
tuning down, the highlighted digit goes as far as 0 and the remaining digits
remain unaffected (further counterclockwise rotation of the wheel is ignored).
The position of the highlighted digit can be changed with the
←
(left) and
→
(right) keys.
↑
and
↓
The
↑
(up) and
↓
(down) keys can be used when very small adjustments to the
tuned frequency need to be made. These keys operate under the same
principles as the tuning wheel, whereas they change only the highlighted
value and the receiver dynamically tunes to the displayed frequency. Each
press of the key causes the value to change by one.
Step Tune
The tuned frequency can also be adjusted in steps by using the tuning wheel
or
↑
(up) and
↓
(down) keys in the step tune mode. The step tune mode is
enabled when the STEP TUNE key LED is lit. When enabled, the current
step size is displayed in the Memory/Scan display and the cursor in the
FREQUENCY display disappears.
The step size can be adjusted with the Memory/Scan edit knob. It can be any
value from 0.001 kHz to 25.0 kHz. When using the
↑
and
↓
keys or the
tuning wheel in the step tune mode, the tuned frequency changes in value
according to the displayed step size.
3.5.2
SELECTING A DETECTION MODE
Five detection modes are available for signal demodulation: AM (amplitude modulation),
SAM (synchronous amplitude modulation), FM (frequency modulation), CW (continuous wave), LSB (lower
sideband), USB (upper sideband), and ISB (independent sideband). Operation with these detection modes is
further described below.
•
AM Detection Mode. In this mode, the audio present at the front panel
PHONES jack and the LINE A, LINE B, SPEAKER, and DC AUDIO
terminals of TB1 on the rear panel is provided by the unit's AM detector.
•
SAM Detection Mode. Synchronous AM provides a detection mode that
causes the receiver to lock on the carrier frequency in both frequency and
phase. This mode improves the signal-to-noise ratio of the audio output. In
addition, this mode provides greater immunity to signal loss due to fading.
The operation of the receiver in the Synchronous AM Mode can be enhanced
by employing the Variable AGC Threshold feature. During instances of
severe fading on AM signals, the synchronous AM demodulator attempts to
synchronize itself to the distorted fading signal. Loss of signal lock may
occur in some cases. By using the Variable AGC Threshold feature, the
operator can reduce the gain applied to the faded signal so that it will be too
weak to force the synchronous AM demodulator out of lock.
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