Vectronics VEC-841K - Manual (Page 23)

VEC-841K Owner's Manual Tunable SSB/CW Audio Filter Kit
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The maximum filter settings are when the FREQUENCY and SELECTIVITY
controls are set fully clockwise. This is the highest "Q" setting for the filter,
noting that at maximum selectivity you may experience a "ringing" effect. This
is normal. The most usable setting for the Selectivity control is when it is back
off in the counter-clockwise direction about 10-15% of the maximum setting.
Use the FREQUENCY control to either "peak up" desired signals while SW1 is
in the PEAK position. While SW1 is in the NOTCH position, the
FREQUENCY control can be used to "notch" or "null" unwanted interference.
The PEAK/NOTCH switch (SW1) is a dual function switch. The IN position is
NOTCH, while the OUT position is PEAK. How you are using the VEC-841K,
dictates what position SW1 will be in. Placing SW1 in the PEAK position you
will be able to PEAK desired signals to bring them up where they are more
readable and out of the SSB noise. Using the filter with SW1 in the NOTCH
position, you can actually notch or null out nearby adjacent signals and
interference.
You can also use a pair of mono headphones with a 1/4" mono plug attached.
Connect your headphones to the phones jack, J5.
IN CASE OF DIFFICULTY
No Signal Filtering:
A newly constructed filter that fails to work upon initial power up, generally
requires a very close and careful inspection of all work. Please go back through
all steps of assembly and inspection, referring to the "Parts Placement Diagram".
Most of the time there will be a part that is not installed or installed properly, a
wrong value part in place of another, or a broken part. A close inspection at this
point will reveal some accidental mistake.
Intermittent Filter Operation:
A filter that operates intermittently may have poor solder connections, a problem
with broken wires, or low voltage power source. Self-oscillation, may be caused
by a defective U1, U2, or U3. Also check for dirty or intermittent switch
operation. Also, if you made the jumper going from Points C and D too long,
self-oscillation can occur.
Filter Stops Filtering:
A working filter that fails "in-service" generally indicates a failure of one or
more of the integrated circuits U1, U2, or U3. If you suspect a bad integrated