Hum Bug Reference Manual Page 13
Quest Scientific
Step Three: Observe the operation of the Hum Bug in
BYPASS
mode. In this mode the input
and output of the Hum Bug should be identical. Here are some explicit steps to help you with
the procedure.
•
Make sure that you are recording a noisy signal.
•
Turn on the Hum Bug.
•
Press the
BYPASS
key. The red LED should be on. Note that the
HOLD
function
will also become active.
•
Using your oscilloscope, confirm that the input and output of the Hum Bug are
identical. If not, check the calibration on the oscilloscope. If you are not sure that the
calibration is correct you can use a single channel on the oscilloscope to alternately
observe the input and output.
•
Initiate normal operation by pushing the
BYPASS
key again. Make sure that
HOLD
is also disengaged. Both the
BYPASS
and
HOLD
switches should have their green
LEDs illuminated.
•
Watch any 50/60 Hz noise present on the input signal gradually disappear from the
output signal. The
LED Indicator
will flash red as the noise replica grows to the
required size. When adaptation is complete the
Indicator
should be off.
•
Toggle
BYPASS
mode on (red LED) and off (green LED) to observe the signal with
and without noise cancellation.
•
Compare the input and output signals. You should find that the primary signal of
interest is not modified by the Hum Bug.
Step Four: Observe the Hum Bug adapt to changing noise conditions. One easy way to
change the level of noise is to place your hand near the recording electrode. Alternatively, turn
on a light or a nearby instrument known to cause noise in your recordings.
•
Cause a change in the noise level and/or wave-form and then observe the Hum Bug
adapt to the change. Rapid changes require time for full cancellation whereas the
output will remain relatively free from noise when noise on the input is slowly
evolving.
•
Activate the
HOLD
function (red LED) and then cause a change in the input noise.
The level of noise cancellation present before
HOLD
was activated should continue
but the Hum Bug should not adapt to the change in noise level.
•
Return to normal operating mode by turning off the
HOLD
function and observe the
Hum Bug
catch up
to the new noise level on the input.
