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RCA Crystal-Calibrated Marker Generator WR-99A
The 10- and I-Me signals from V4A and V4B are
fed to the mixer/modulator
stage, V5, which mixes
the two signals and feeds them through CI3 and C5 to
grid No. 1 of V2. The output from V5 also contains
harmonics
of the two signals. The 4.5-Mc signal is
generated by V6B, a Pierce oscillator. The 4.5-Mc is
fed through
C37 to grid No. 3 of V2. The 6OO-cps
modulating
signal is generated by a phase-shift oscil-
lator, V6A, which feeds the signal to grid No. 3 of
V2. Any signal fed into the MOD IN terminal is also
fed to grid No.3 of V2.
Crystal diodes CRI and CR2 comprise
a voltage-
doubler
beat-frequency
detector. In this circuit,
the
I-Mc, IO-Mc, or external signals are beat with the vfo
signal from VI to produce an audio-beat signal from
the speaker. V3A and V3B are audio-frequency
ampli-
fiers.
Regulation of the B+ voltage for the vfo stage, VI,
is accomplished
by use of OA2 regulator tube, V7.
IO·Mc Crystel-Oscllfatcr
Adjustment
1. Connect the WR-99A to a 1- and 10-Mc standard
oscillator,
as shown in Figure
15. A Measurements
model III
or equivalent
unit may be used as the
standard.
2. Set the RF control on the WR-99A to "OFF". Set
the CAL/MOD control to "10 MC CAL". Turn the AF
GAIN control about three-quarters
turn clockwise. Set
the standard oscillator to deliver a 10-Mc output signal.
3. With an insulated alignment tool, turn the slug
in inductor L9 until about one-quarter inch protrudes
from the coil form. (See Figure 14 for locations of in-
ternal adjustments.]
4.
Screw the core slowly back into the coil form and
listen for an audio beat between the two 10-Mc signals.
Continue screwing in the core until the beat note disap-
pears;
then, back the core out of the form one full
turn. Switch the CAL/MOD
control between "10 MC
CAL" and "OFF" several times to make sure that the
WR-99A 10-Mc oscillator starts promptly.
1£
oscillator
starts erratically,
back out the cere until oscillation is
satisfactory.
S. Adjust trimmer
capacitor
C24 to zero beat the
two 100Mc signals as closely as possible.
I·Mc Oscillator Adjustment
1. With power applied to the WR-99A, set the RF
control to "ON". Set the RF RANGE switch to band 2
(27-30 Mc).
2. Set the CAL/MOD control to "10 MC CAL" and
set the RF TUNING to read 30 Mc on the dial scale.
With an insulated alignment tool, adjust the core of
L2 to zero beat with the third harmonic of the 10-Mc
crystal oscillator. Check the zero-beat accuracy at the
4O-Mc point. Readjust L2, if necessary.
Figur.
14.
Locations
of tub ..
and
internal
adlustments
in
WR-99A •
. 21 •
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