PUBLICATION TSM 20-332 TECHNICAL MANUAL 30 WATT VHF AMPLIFIER FOR MX30V SERIES TV TRANSMITTER/TRANSLATOR LARCAN INC.
Section MX30V series - 30 Watt Title VHF AMPLIFIER Page NOTICES, ETC.................................................................3 SAFETY AND HEALTH WARNINGS.....................................4&5 GENERAL SERVICE INFORMATION 1) Parts Lists Explained...................................5 2) Interpreting LARCAN Drawing Numbers.....................5 3) The LARCAN Assembly Prefix Numbering System.............6 4) List of Prefix Numbers for the 10 W Transmitter.........7 5) Production Changes..............
MX30V series - 30 Watt VHF AMPLIFIER PUB98-31 RF Output System: Filter and Directional Coupler (Prefixes 6 & 7): 1. HB Helical Resonator Bandpass Filter Description........31-1 2. HB Low Power Bandpass Filter Description................31-3 3. LB Low Pass & Notch Filter Description..................31-4 4. PUB98-32 RF Power 1. 2. 3. RF Directional Coupler Description......................31-5 Amplifier (Prefix 2): Introduction and General Description....................
INTRODUCTION This manual describes the LARCAN 30 watt VHF amplifier designed for NTSC channels 2 through 13. Models 40D2232G1 is for channels 7 through 13, 40D2232G2 for channels 2, 3, and 4, and model 40D2232G3 is for channels 5 and 6. These amplifiers are used in the LARCAN-USA MX30V series transmitters and translators.
class AB as a linear amplifier. This amplifier is capable of more than 50 watts RF output when driven by the preamplifier in the present system, but uses the identical dual FET device that is used in higher powered LARCAN transmitters. The Sound/Aural signal of the transmitter is internally diplexed and corrected at IF with the visual/vision signal within the exciter, and is amplified in common with the visual/vision signal in the amplifier chain.
ELECTRICAL AND MECHANICAL SPECIFICATIONS DOC/FCC (NTSC) Power Output: ................................................................Visual 30 W peak, Aural 3W Diplexing: ........................................................................internal, 10:1 V to A Frequency Range: ........................................................54-216 MHz (channels 2 thru 13) Amplifier Output Impedance: ....................................................................... 50 Ù Output Connector: ................
VHF AMPLIFIER CHASSIS Contents: Part 1 Topic Page Chassis Description...........................................30-1 List of Figures: Fig 1 2 3 1. Title Drawing Reference Chassis Assembly Diagram.............................40D2232 sht 1 Wiring Diagram, Amplifier, AC Line to Neutral........30C1987 sht 1 `power-one' Power Supply Data..................................... Amplifier Chassis Assembly 40D22328G1 through 40D2232G3: Figure 1.
VHF AMPLIFIER CHASSIS powered from the 48 volt amplifier power supply. As built, the cooling fan pulls warmed air from the heatsink so the cooling air enters through the perforations in the chassis front panel.
Contents: Sec Topic Page 1 2 HB Helical Resonator Bandpass Filter Description (50W HB only)31-1 HB Low Power Bandpass Filter Description......................31-3 3 4 LB Low Pass & Notch Filter Description........................31-4 RF Directional Coupler Description............................31-5 List of Figures: Fig Title Drawing Reference 1 2 Bandpass Filter response...........................text, page 31-2 Bandpass Filter schematic..........................
1. Bandpass Filter: (continued). LARCAN bandpass filter implementations generally consist of a cascaded series of coupled resonators. Some use helical resonators; essentially a self supporting high Q coil (the helix) mounted inside a metallic shield enclosure. One end of the coil is solidly connected to the shield enclosure and the other end is open circuited except for a small trimmer capacitance to ground.
This is the electrical equivalent of a series of five coupled helical resonators. Similar lower power filters are built using conventional air wound coils and ceramic trimmer capacitors, and these will be described next: 2. 20B704G1 Low Power Bandpass Filter for High Band: Please refer to Figure 5.
used with the sweep generator, there is no way to properly set up the input and output matching. Our recommendation: don't mess with the filter adjustments at all.
3. 20B1118G1 Low Pass and Notch Filter for Low Band: Please refer to Figures 6 and 7. Ten adjustable inductors, four fixed inductors (which also can be adjusted slightly by spreading their turns with a suitable tool), and twenty-one fixed capacitors, make up the complete filter. Functionally, it consists of two sections of shunt m-derived low pass network, followed by four bridged-tee notch networks. Its signal direction is intended to be one way only, as indicated in Figure 7.
signal from the transmitter should be seen on these reflected ports. The desired directivity is achieved by the capacitance between the main line and each sampling line. The presence of this capacitance changes the relative phase of the RF signal seen in the sampling line such that the capacitively coupled signal adds to the inductively coupled signal at the end of the line nearest the signal source, and subtracts from it at the other end, thus the sample becomes directive.
Contents: Sec Topic Page 1 Introduction and General Description..........................32-1 2 3 Preamplifier Circuit Board Assembly...........................32-2 RF Power Amplifier............................................32-2 List of Figures: Fig Title Drawing Reference 1 PA & Preamplifier Assembly.....................30C1899 sht 1 rev 1 2 Preamplifier Board Assembly, Low Band..........10A1453 sht 9 Preamplifier Schematic, Low Band..............
panel. The heatsink fan can move approximately 100 cfm of cooling air, and has a DC motor that is powered by the same +50 volts that operates the amplifier.
1.RF Power Amplifier & Heatsink Assembly 30C1899G1 - G2 - G3: Most LARCAN exciters produce their best linearity at or near their maximum rated output levels, and often the overall system gain is sufficient to result in overdrive of later stages of the transmitter. The transmitter or translator lineup may therefore include an in-line attenuator between the exciter and the preamplifier, to prevent overdrive from certain models of exciter-modulator.
requirements which are much more stringent in the internally diplexed case. This is because the 30 dB (or thereabouts) of aural to colour subcarrier isolation normally provided by the diplexer is not there, and it simply means that internally diplexed system intermod numbers have to be much better.
3. SRF 3943-2 RF Power Amplifier: Figures 3, 4, 5, 7, 8, and 9. The Power Amplifier (PA) is configured in push-pull, using dual N-channel enhancement mode Field Effect RF power transistors which are packaged into a single case and operated in class AB. The Low Band and High Band versions of the PA differ slightly due to the frequency ranges to be covered. 3.
operation. DC is applied to the FET drains through L3, L4 for the Q1A half, and L5, L6 for the Q1B half. L3 and L6 are short sections of microstrip line which transform the apparent RF impedances of L4 and L5 to higher values as seen by the FET. RF and lower frequencies are bypassed with paralleled C9, C10, and C17 for the "A" half of the amplifier, and C11, C12, and C18 for the "B" half.
3.2 Low Band PA Setup Procedures 1. Set up a 48 V power supply, current limited to a little more than 1.2 amps. 2. Remove both fuses on the power amplifier. Turn both bias potentiometers to their maximum resistance position ( minimum gate voltage). 3. Apply the 48V supply to the B+ terminal. Verify that the bias (gate) voltage is at or near minimum by measuring the dc voltage at the gates of the device. This voltage should be less than 1V.
3.3 High Band PA Circuit Description board) (20B1222G2 input board, 20B1226G1 output The PA consists of two, source grounded N-channel, insulated gate Field Effect Transistors (FETs) packaged in a single case, and operating in a push-pull configuration in class AB. A single specially characterized device designated SRF 3943-2 is used for this High Band amplifier.
1. Set up a 48V power supply, current limited to a little more than 1.2 A. 2. Remove both fuses on the amplifier. Turn both bias potentiometers to their maximum resistance (minimum gate voltage). 3. Apply the 48V supply to the B+ terminal. Verify that the bias (gate) voltage is at or near minimum by measuring the voltage at the gates of the device. This voltage should be less than 1V. Install one of the fuses adjust one of the potentiometer for 500 mA drain current.
Contents: Sec Topic Page 1 Control & Metering Panel Description..........................33-1 2 Amplifier Control Circuit Board Description...................33-2 List of Figures: Fig 1 2 1. Title Drawing Reference Amplifier Control Board Assembly.....................30C1829 sht 8 Amplifier Control Board Schematic..........................20B2438 Control Panel: Amplifier control and monitoring is performed by the Control and Metering Panel.
2. Amplifier Control Circuit board Assembly 30C1829G2: Figures 1 and 2. There are seven connectors on the Control circuit board. perform the following functions: These connectors J2 connects elsewhere in the amplifier, such as the thermal switch, relay, and to the 50 ì A meter. J3 connects to the external interlocks. J4 interconnects with J3 of the Metering board. The transmitter interlock chain begins with the +12V at K1-7.
2. Amplifier Control Circuit board Assembly 30C1829G2: Figs 1 and 2. Finally, when the interlock chain is complete, the +12V is applied to the solenoid of the power supply primary contactor through J2-10, and the cooling fans and power supply are all turned on. The DS3 LED marked EXT 2 is lighted, as is the optodiode in U3A. The output active low from U3A at pin 15 informs the remote control via J5-15 that the EXT 2 interlock is intact.
Contents: Sec Topic Page 1 RF Metering Board Description.................................34-1 2 RF Metering Board Test and Calibration........................34-3 List of Figures: Fig 1 2 1. Title Drawing Reference Metering Board Assembly..................................20B1235G7 Metering Board Schematic................................20B1245sh2 RF Metering Board 20B1235G7: Figures 1 and 2. The function of this board is to monitor the forward & reflected power.
voltage when the op-amp output is almost touching ground. If the pot is turned beyond this point, the output stage of the op-amp will be driven into saturation thus unable to respond to low power levels.
1. RF Metering Board 20B1235G7: Figures 1 and 2. (continued). The output of U1-7 (U2-7) drives the RF power meter through R32 (R30) which set the meter deflection with a known RF signal. U1-7 (U2-7) drives. Forward calibration is done with full rated power and a forward RF sample from the directional coupler applied to J1. R32 is adjusted for a 100% reading on the forward power meter position.
indicates 10% output. This means that in severe VSWR conditions such as in an open circuit, the amplifier will automatically cuts back to 10% thus protecting itself. 3. Replace the cables in their proper connections. RFL meter reading should be nill and the FWD meter reading should be back to 100%. If the FWD reading is much less than 100%, R36 was probably overadjusted.
Contents: Sec Topic Page 1 RF Pin Attenuator Board Description.......................................................................34a-1 2 AGC/Overpower Protection Setup ...........................................................................34a-1 List of Figures: Fig Title Drawing Reference 1 2 Pin Attenuator Board Assembly.....................................................................10A1255G1 Pin Attenuator Board Schematic.............................................................
