Vectronics VEC-821K - Manual (Page 21)

VEC-821K Instruction Manual Super CW Filter Kit
Amateur Radio bands. Once you find a CW signal, switch SW1 to the 110
filter cutoff. The 110 position is the third from the left. When you switch to the
110 cutoff, you will notice that the signal sounds cleaner than before. You can
now fine tune the radio tuning knob for the best received signal. If using a
communications receiver or scanner with a BFO control, use this control to fine
tune the received CW signal. If the receiver or scanner you are using does not
h a v e a BFO control, it will be very difficult trying to tune the signal in
properly. If the signal you are trying to receive is in a "pile up", then try the 80
hertz filter cutoff. Then fine tune the receiver to "pull out" the desired signal.
Operation with an Amateur Radio transceiver is basically the same, but you
would use either LSB, (Lower Side Band) or CW mode. All other connections are
the same.
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" Figure 1.
Most of the time there will be a part that is not installed or not installed
p r o p e rly, a wrong value part in place of another, or a broken part. A close
inspection at this point may reveal some accidental mistake(s).
Intermittent Filter Operation:
A filter that operates intermittently may have poor solder connections, a problem
with broken wires, or a low voltage power source. Self-oscillation may be caused by
a defective U1, U2, or U3. Also, check for dirty or intermittent switch operation.
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 circuit
then do not touch the part with your fingers. If the part is bad, it could be HOT
and could cause a serious burn. The supply voltage (9-volt battery) and/or broken
wires could cause this problem.