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2-NB NOISE BLANKER FOR 2-C RECEIVER
INSTALLATION
The 2-NB Noise Blanker is an accessory for the
Model 2-C Receiver that plugs into a connector mounted on the top of the chassis of the 2-C Receiver at the
rear of the set and is turned on by the Function switch on the receiver's
front panel.
OPERATION
The Noise Blanker is an I.F. device which turns off the receiver I.F. amplifier
during a noise pulse. It is effective on all modes of operation and greatly
attenuates most impulse type noise. It will be noted that the noise blanker
works best on noise pulses which are very short in duration and are separated
widely in time (i.e. automobile ignition type noise). The closer the pulses
are together, the less effective the noise blanker will be since the noise
detector circuitry has more difficulty distinguishing the noise from the
desired signal. For normal operation under "no noise" conditions, the Function switch should
be positioned in other than the N.B. position. The noise blanker functions
only when the amplitude of the noise pulses exceed the amplitude of the
signal.. It will be noted that the S-meter will decrease when the noise
blanker is switched on. This is due to the noise pulses causing AVC action
when the blanker is off causing the S-meter to read high. When the noise
blanker is switched on, the I.F. is turned off during the impulse period and
the AVC is now activated by the signal rather than the noise pulse and the
receiver gain increases. Due to the effect of AVC in giving constant audio
output, the noise may not appear to decrease when the blanker is switched on.
However, switching the blanker on increases the gain as described above and
signals that were buried under the noise will now increase. Very strong signals (30 or 35 dB over S9) will cause a slight distortion in
the audio quality of the signal due to the dynamic range capability of the
N.B. circuitry. This should cause no detrimental effects since signal of
this strength should far exceed noise conditions.
ALIGNMENT
All noise blankers are factory aligned, but may require realignment at some
time due to unusual circumstances.
Remove the cover from the noise blanker,
plug the noise blanker into the 2-C Receiver and place the Function switch in
the N.B. position.
Connect a signal generator or some type of external
source of signal to the receiver antenna and tune the signal in on the SSB
mode as described for SSB Reception in the 2-C manual.
Zero beat the signal and connect a VTVM, DC probe at the anode end of diode D2. (The anode end
is the end opposite the stripes. Diode D2 is located near the left hand end of
the printed circuit board).
Increase the signal level until a readable
negative voltage is measured and tune transformer Tl for maximum voltage.
An input signal of about 3 mv should give -1V DC under tuned conditions.
Signal levels considerably lower than this will result in a positive voltage.
(c) 1998-2012
D. PRODUCTS SA/NV - DRAKE is a registered trade mark of R.L.
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JM CHERRY Last updated on: 24 Dec 2011
