VEC-821K Instruction Manual
Super CW Filter Kit
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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.
No Speaker Audio:
No speaker audio can be a symptom of a bad SW1, a broken wire or a
bad C9. Check the voltage from the 9-volt battery. A broken wire at the
audio input to the filter could attribute to no speaker audio. The audio
amplifier chip (U3) could also be defective.
If technical assistance or factory repair is desired, please refer to the
warranty instructions on the inside front cover.
THEORY OF OPERATION AND SPECIFICATIONS
Circuit Description:
The VEC-821K uses two LM747 operational amplifier integrated circuits
to form four low Q cascaded stages with no insertion loss. This results in
a very narrow bandwidth and extremely high skirt rejection with minimal
audible ringing, making good signal copying possible. The center
frequency is between 750-800 hertz. The filter also has an LM380 Audio
Amplifier which can drive an 8 ohm speaker or headphones.
Specifications:
Bandwidth:
80Hz, 110Hz, 180Hz (switch selectable)
Skirt Rejection:
At least 60dB down 1 octave from center
frequency for 80Hz. bandwidth.
Center Frequency:
750-800Hz
Insertion Loss:
None
Power Required:
9-volts DC; 9-volt battery
PCB Dimensions:
3" x 3"
ENCLOSURE
Vectronics has designed a matching enclosure just for your VEC-821K
Super CW Filter Kit. The matching enclosure is an all metal box which
includes knobs, hardware, decals, and rubber feet. The Vectronics
model number for the matching enclosure is VEC-821KC.
