Uniden PB010, Руководство по обслуживанию

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RF amplifier biasing is different for AM/FM/CW and SSB; ЛМ/FM/CW is Class C, and SSB is
d a s s AB (linear). The bias is changed by TR52, which in the SSB mode disables the Col-
lector B+ régulation of TR49-TR51 and allows the füll 13.8 VDC to be applied to the TR45
& TR 4 4 Collectors insetad.
In ail modes, a small sample of the 27 MHz signal is detected by D101 & D102 and used to
drive the S/RF meter for a relative RF power output indication. VR8 allows calibration
of the output reading.
IV. CW (PB010 only):
CW transmission is basically identical to AM transmission; i.e., the carrier is turned
on and off by a CW key rather than the microphone button. The only real différence is
that on CW, TR55 turns off when the key is pressed, which turns on D75 & TR31, grounding
the mike audio so it cannot modulate the carrier. TR35 is an audio oscillator. When the
CVî key is pressed, it oscillâtes. At the same time, TR39 disconnects the normal RX
speaker audio so it won't be heard; instead the CW monitor tone is heard. D82 disables
the Roger Веер oscillator so it also will not be heard on the air. The time constant
produced by C219/R284 of switch TR55 provides a small delay before the radio returns to
the RX mode so that annoying speaker noise and thumping will not be heard between Morse
characters.
V. AMC CIRCUIT:
TR53 is the AMC Detector which samples modulated AM audio from TR51. When overmodulation
occurs it turns on to drive TR34, which in turn drives TR32. TR32 is shunted directly
across the mike input line. The harder it turns on, the more the audio modulating signal
is reduced. VR14 allows setting the 100% modulation limit. The AMC functions only in the
AM mode.
VI. ALC CIRCUIT:
TR48 is the ALC sensor which detects peak RF power on SSB modes. If the power exceeds
the level determined by VR12, it drives TR34 and TR32 to reduce the mike audio level and
consequently the RF power level. In the AM mode, the TR48 Emitter voltage is pulled up
to B + , making it inoperative.
VII. UNLOCK DETECTOR:
Pin 8 of the MC145106 (or Pin 6 of the MB8719) is normally at logie high level, about 8
VDC. If the PLL circuit becomes unlocked, this pin qoes LOW (about 0.0 VDC), switching
appropriate diodes and transistors which disable the TX and RX circuits, preventing off-
frequoncy operation.
VIII. ROGER ВЕЕР OSCILLATOR:
TR33 is an audio oscillator. It is powered by the TX-only 8 VDC source, TR38. Pressing
the mike button turns on D92, grounding the TR33 audio before it would normally pass
through R217 to the mike amp. D91 also turns o n , activating a timing delay circuit con-
sisting of C270, R206, and one section of IC4. When the mike button is released, the
timing circuit keeps the Collector of TR38 at B+ and therefore in the TX mode for a short
time longer than normal. Since releasing the mike button simultaneously turns D92 off,
the tone burst from TR33 can pass to the mike amp and be heard on the air.
IX. PUBLIC.ADDRESS (PB042, PC999 only):
A signal from the mike amp IC4 goes to TR30 (PB042), the PA preamp. The signal is fed to
the audio power amp IC501 and then to the PA SP jack.
X. MODULATION METERING (PB042, PC999 o nly):
A sample of the audio modulation goes to DC amp TR29 (PB042), is rectified by D62 & D63,
and used to drive the modulation metering circuit. VR3 allows meter calibration. In the
PC999 chassis, an RF signal sample is used instead from TP9. The sample is rectified by
D74 and used to drive the metering circuit.
XI. SWR METERING (PB010 only):
The small circuit board, PC958 is actually a microstrip section of 50-ohm transmission
line. R601 & R602 form a résistance bridge which is perfectly balanced whenever a 50-
ohm load is connected to the ANT. socket. Similarly, C602 & C601 form a capacitive
voltage divider which produces equal RF voltages whenever a 50-ohm load is connected to
the ANT. socket. With a pure 50-ohm load, the RF currents and voltages in the bridge are
exactly equal but of the opposite phase, thus canceling each other out and producing no
SWR meter reading. (1:1 SWR match.) D601 samples the Forward RF power and D602 the
Reflected RF power. D601 also allows full-scale forward power meter calibration. As the
ANT. socket load becomes more and more reactive, the bridge becomes unbalanced and a
différence voltage is produced in proportion to the unbalance; this voltage drives the
SWR meter and indicates the relative degree of unbalance or 'mismatch'.