F. Adjustinq Dial Calibration
The calibration of the main tuning dial on the R-4A may vary slightly
from band to band due to the tolerance limits of the various crystals.
Therefore, the main tuning dial index has been made adjustable by
means of the small red knob to its right. To set the calibration on
a given band, proceed as follows:
1. Set Band Switch, Preselector,
band.
2.
3.
4.
Set Function switch to CAL.
5.
6.
Set SSB/CW-AM switch to Slow AVC.
Tune in 100 KC crystal calibrator signal for zero beat at the 100
KC point nearest the desired operating frequency.
Slide the red knob at the right of the dial scale until the index
line coincides with the 100 KC dial calibration.
While holding the main tuning knob, push in on its calibrated
skirt and turn until the “0” mark coincides with the indicator
line.
G . Noise Blanker Operation
and Xtal switch to the desired
The noise blanker in the R-4A is an I. F. device which turns off the
receiver during a noise pulse. It is equally effective on all modes
of operation and greatly attenuates most impulse noise.
For normal operation under ” no noise” conditions, the Function switch
should be positioned in other than the N. B. settinq. However, if noise
becomes a problem, simply switch to N.B. It will be noticed that the
noise blanker functions only when needed: that is when the noise is
greater than the desired signal. Due to the effect of AVC in giving
constant AF output, the noise may not appear to decrea se. However,
signals down in the noise will come up and can be copied which were
undetectable previously.
It will also be noted that the N.B. works best on noise pulses which
are very short in duration and which are separated widely in time, (i.e.
automobile ignition noise
) .
The closer the pulses are together, the
less effective the N. B. will be since the noise detector circuitry has
more and more difficulty distinguishing the noise from the desired signal.
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