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

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WJ-8711A DIGITAL HF RECEIVER LOCAL OPERATION
3-33
The BFO frequency ranges from -8000 Hz to +8000 Hz with 10-Hz resolution. For example,
if the tone of the received CW signal is at 5,000 Hz, entering a BFO frequency of -1000 Hz would change the
CW tone heard at the audio outputs to 4,000 Hz. Conversely, entering a BFO frequency of +1000 Hz would
change the CW tone to 6,000 Hz.
The current BFO frequency is displayed in the upper Auxiliary Parameter display, directly
above the BFO keys. To change the BFO frequency, first press the BFO key to light the LED and enable the
BFO parameter entry mode. The parameter can then be adjusted with the Auxiliary Parameter edit knob or
can be overwritten with a new value by using the numeric entry keys.
The +/- ZERO key is used to change the sign of the frequency to positive or negative, or can
be used to automatically set the BFO to zero. Continue pressing this key until the positive (+) or negative (-)
sign is displayed or until 0000 is displayed as desired.
3.5.8
PASSBAND TUNING IN CW DETECTION MODE
The passband tuning function is available only while the receiver is in the CW detection
mode. This function has the effect of shifting the IF bandwidth without changing the frequency of the audio
output signals so that unwanted CW signals can be placed outside of the IF bandwidth while keeping the
wanted CW signals inside the bandwidth. This is especially useful in FSK demodulation applications for
monitoring mark and space frequencies while other CW signals close in frequency are present.
The passband tuning parameter can be any value from -2000 to +2000 Hz in 10-Hz steps.
When the passband tuning function is used, the tuned frequency and BFO frequencies are adjusted in
accordance to the entered passband tuning parameter. The BFO frequency counteracts the effect of the tuned
frequency, which allows the output audio tones to remain at the previously adjusted frequencies. For example,
entering a passband tuning parameter of +1000 shifts the tuned frequency up by 1000 Hz which also shifts the
IF bandwidth. Any signals received within the IF bandwidth are applied with a BFO offset frequency of -1000
Hz which brings the demodulated tone back down to its original audio frequency.
The passband tuning mode is entered by pressing the SPECIAL FUNCTION key until the
upper Auxiliary Parameter display appears as follows:
P B T U N s n n n n
Hz mSec
where "s" is the positive (+) or negative (-) sign and "nnnn" is the offset frequency. The Auxiliary Parameter
edit knob can be used to adjust the parameter.
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