XR12 Troubleshooting Manual
Detailed Circuit Descriptions
Page 2-10
Issue 3.0 2009-07-28
Linear integrator
The linear integrator circuit converts the
f
PDM
square wave on its input to a triangular waveform at its
output. The triangular waveform has negative and positive voltage excursions of equal amplitude and
duration. The long R/C time constant formed by C27/R11 ensures a linear rise and fall time.
Integrator peak detector
The integrator peak detector circuit detects the positive going excursions of the linear integrator's
triangular waveform. A portion of the resulting positive dc voltage (nominally 1.8 V) at U8A's output,
is applied to the inverting input of differential amplifier U3A. The
carrier ref + audio
output of U3A is
offset by this voltage which is proportional to the triangular waveform voltage peaks. This offset
effectively sets the
carrier ref + audio
's zero power reference to the triangular waveform's peak voltage.
This technique ensures no RF output is produced when the carrier ref input (J1-2) is 0 V. It also
ensures the RF output is reduced to near 0 W at the 100% modulation envelope valleys when
operating at the transmitter's rated carrier level.
Interphase pdm generator
The interphase PDM generator consists of two variable pulse duration generators (PDM1 and
PDM2). Both produce identical 0 V to +15 V rectangular waveforms at the PDM repetition rate, but
they are 180
0
out of phase with each other. The waveform on/off ratio (duty cycle) is directly
proportional to the carrier level and amplitude of the modulating audio.
PDM1 generator
The PDM1 generator consists of U10B, Q4, Q5, and their associated components. The compensated
carrier ref + audio
input from the integrator peak detector circuit is applied to differential amplifier
U10B's non-inverting input, where it is compared to the triangular waveform from the linear
integrator circuit. When the compensated
carrier ref + audio
is more positive than the triangular
waveform, U10B's output is an open collector. +15 V is applied through R60 and R62 to the
balanced drive formed by Q4/Q5. Q4 turns on and a15 V to K1-3 as the
PDM1
output (Q5
is off). For the remainder of the triangular waveform's period, the compensated
carrier ref + audio
is
less positive than the triangular waveform. U10B's output is a current-sink-to -15 V and Q4 turns off.
Q5 turns on and clamps the
PDM1
output to ground. The minimum 'on time' (zero RF power)
occurs at the negative peaks of the triangular waveform. See
for a timing
diagram.
Summary of Contents for XR12
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Page 100: ...XR12 Troubleshooting Manual Detailed Circuit Descriptions Page 2 32 Issue 3 0 2009 07 28...
Page 108: ...XR12 Troubleshooting Manual Parts Lists Page 3 8 Issue 3 0 2009 07 28...
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Page 214: ...XR12 Troubleshooting Manual Reading Electrical Schematics Page 5 6 Issue 3 0 2009 07 28...
Page 223: ...Issue 3 1 2014 05 07 SD 9 Figure SD 9 NAPX05E 02 Dynamic Carrier Control PWB Sheet 1of 2...
Page 224: ...Issue 3 1 2014 05 07 SD 10 Figure SD 10 NAPX05E 02 Dynamic Carrier Control PWB Sheet 2 of 2...
Page 233: ...Issue 3 1 2014 05 07 SD 19 Figure SD 19 NAP34A RF Power Module Overall Sheet 1 of 2...
Page 234: ...Issue 3 1 2014 05 07 SD 20 Figure SD 20 NAP34A RF Power Module Modulator Stage Sheet 2 of 2...
Page 235: ...Issue 3 1 2014 05 07 SD 21 Figure SD 21 NAPC150A RF Drive Control PWB Sheet 1 of 3...
Page 236: ...Issue 3 1 2014 05 07 SD 22 Figure SD 22 NAPC150A RF Drive Control PWB Sheet 2 of 3...
Page 237: ...Issue 3 1 2014 05 07 SD 23 Figure SD 23 NAPC150A RF Drive Control PWB Sheet 3 of 3...
Page 238: ...Issue 3 1 2014 05 07 SD 24 Figure SD 24 NASM07H Modulator Assembly...
Page 239: ...Issue 3 1 2014 05 07 SD 25 Figure SD 25 NAA51A 03 RF Amplifier Assembly...
Page 245: ...Issue 3 1 2014 05 07 SD 31 Figure SD 31 NAPS10C RF Drive Power Supply PWB...
Page 248: ...Issue 3 0 2009 07 28 MD 1 Figure MD 1 XR12 Transmitter...
Page 257: ...Issue 3 0 2009 07 28 MD 10 Figure MD 10 NAPP02 01A RF Current Probe PWB...
Page 259: ...Issue 3 0 2009 07 28 MD 12 Figure MD 12 NAFP103 05 Forward Reflected Power Probe A1 DETAIL...
Page 263: ...Issue 3 0 2009 07 28 MD 16 Figure MD 16 NAPC150A RF Drive Control PWB...
Page 265: ...Issue 3 0 2009 07 28 MD 18 Figure MD 18 NASM07H Modulator Assembly...
Page 266: ...Issue 3 0 2009 07 28 MD 19 Figure MD 19 PA Input Output PWB 176 1065 04 and 05...
Page 267: ...Issue 3 0 2009 07 28 MD 20 Figure MD 20 NAA51A 03 RF Amplifier Assembly...
Page 268: ...Issue 3 0 2009 07 28 MD 21 Figure MD 21 NAPI47B Modulator Input Output PWB...
Page 271: ...Issue 3 0 2009 07 28 MD 24 Figure MD 24 Relay Assy 202 7019...
Page 272: ...Issue 3 0 2009 07 28 MD 25 Figure MD 25 Fan Tray 202 7020 J1 B1 B2...
Page 273: ...Issue 3 0 2009 07 28 MD 26 Figure MD 26 NAPS10C RF Drive Power Supply 62 V...
Page 275: ...Issue 3 0 2009 07 28 MD 28 Figure MD 28 Rectifier Assembly 202 7017...
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