Telephonics MCB-RT-1601 Color Weather and Search and Rescue Radar User Manual maintenance manual

Telephonics Corporation Color Weather and Search and Rescue Radar maintenance manual

Contents

maintenance manual

MAINTENANCE MANUALRT-1601 RECEIVER-TRANSMITTER815 Broadhollow Road 631-755-7000Farmingdale, N.Y. 11735 FAX 631- 755-72001SECTION 1 DESCRIPTION AND OPERATION1. GeneralThis section provides a general description of the circuit functions and operation of the RT-1601 Receiver-Transmitter.Subsequent information includes operation, equipment part numbers, block diagram discussion, and theory of operation.NOTE: General information for the RDR-1600 Weather Radar System, such as system leading particulars, systemoperation, and a system operational check is contained in the Radar System Installation Manual, TM106601 Maintenanceinformation for the DA-1203A Radar Antenna is contained in PART 1 of the Weather vision System AntennasMaintenance Manual, I.B. 21000A.2. OperationThe receiver-transmitter (R-T) operates by emitting very short, intense pulses of microwave energy, which arereflected within the range of the radar system. A portion of the radiated energy, reflected by an object havingreflective characteristics, is returned along the same general path to the aircraft where it is received andconverted into digital data that is representative of the target size. The digital data is then routed to the radarindicator where it is processed to give a visual presentation of the target.The receiver-transmitter is housed in a short ½ ATR form factor case. Overall dimensions can be found on thereceiver–transmitter outline drawing. The mounting tray for the R-T unit, which is designed for front loading,provides positive positioning and holding of the unit to the aircraft. The mounting tray is mounted to the aircraft,and the R-T unit can easily be removed and replaced for servicing. Depending upon installation requirements,different models of the mounting tray are available.For ease of maintenance, all circuits are contained on plug-in boards. These PC boards are interconnected byway of a ribbon cable, which makes all connections between PC boards. An interconnect PC board replacesthe conventional wiring harness arrangement.The RT-1601 uses a frequency trimmable magnetron for reliable interrogation of beacon transponders; inputfrequency in an accurate 9375 +5 MHz.The RT-1601 functions as short-range pulse radar for high resolution ground mapping (search) and a long rangepulse for conventional weather. The reflected signal is received by the system’s sector scanning antenna,amplified and digitized by the R-T unit, and then routed to the radar indicator. All system power requirementsare routed via the R-T unit to the radar indicator and the antenna.3. Equipment Part NumbersTable 1 lists the TELEPHONICS part number for the RT-1601 Receiver-Transmitter. A brief descriptionof the unit is also provided. Table 2 lists the major assemblies in the RT-1601
MAINTENANCE MANUALRT-1601 RECEIVER-TRANSMITTER815 Broadhollow Road 631-755-7000Farmingdale, N.Y. 11735 FAX 631- 755-72002TELEPHONICSPART NUMBER TYPE DESCRIPTION379-2011-001 RT-1601 Provides X-band output to sector-scanning antenna. Reflected signal is amplified byreceiver, digitized, and routed to the radar indicator. The magnetron is frequencytrimmable and is designed to operate at 9375 +5 MHz to permit reliable triggering of thebeacon transponder. Operating parameters permit optimum performance in each of thefive modes (3 search modes, weather mode, and beacon mode) complies with TSOcertification C102 for ground target approach to within 1000 feet.Table 1. RT-1601 Receiver-Transmitter Part NumbersMODULE OR ASSEMBLY NAME PART NUMBER REFERENCESERIES CONNECTORSInterconnect (Mother) Board 3606464-05013606464-0502 1200 J1204, J1205, J1208, J1217, J1218Front Panel Connector Board 3606465-0501 1100 P1101, P1103Receiver Board 3606458-0501 2000 J2006, J2016, P2020, P2021Mode-Decode Board 379-2040-001 8000 J8023Power Supply Assembly 4007721-0504 5000 J5011PS Control Board Assembly 4007714-0501 5000Power Supply Module 4007715-0501 5000Local Oscillator Assembly 4007932-0501 6000 P6012Beacon Amplifier Assembly Beacon Receiver Module 3606473-0501 7000 P7016, P7019Table 2:RT-1601 Subassemblies and Connectors4. Block Diagram Discussion (Refer to figure 1)A. Waveform Synchronization and Transmitter FunctionA crystal-controlled oscillator located in theMode Decode board generates basic synchronizationsignals for the radar system. The clock frequency is counted down to 1536 Hz for range selectionsof 10 NM or less in search-one and search-two modes. For all other ranges and modes the clockfrequency is counted down to 200 Hz. Either the 1536 Hz or the 200 Hz system trigger keys thetransmitter and provides other timing functions. The system trigger also keys the suppression pulsegenerator to turn off sensitive equipment when the R-T unit transmits. The System trigger is appliedto the timing circuit, which controls the AFC gate, the STC-function gate, the AFC-AGC trigger, andthe test-pattern-generator circuits. The system trigger is buffered and routed to the modulator driver
MAINTENANCE MANUALRT-1601 RECEIVER-TRANSMITTER815 Broadhollow Road 631-755-7000Farmingdale, N.Y. 11735 FAX 631- 755-72003where selection of either the modulator short pulse (0.2 usec) or the modulator long pulse (2.35usec) is selected.Pulse width selection is made depending on the operation mode selected on the radar indicator.Modulator long pulse is selected for modes using a 200-Hz trigger; modulator short pulse isselected for modes using an 1536 Hz trigger. With either modulator pulse, a negative-going, 330-volt, 110-ampere pulse is applied to the pulse transformer. The pulse transformer supplies themagnetron with a 5.5 kV, 4.5 A, negative-going pulse that causes the magnetron to oscillate at its9375 MHz resonant frequency. A 10-kW nominal peak power RF output pulse is generated by themagnetron and is directed through the four-port, E-plane circulator to the radar antenna.B. Receiver FunctionThe R-T unit employs a dual-conversion, superheterodyne receiver. Signals received by the radarantenna are routed through the four-port, E-plane circulator, and the TR limiter to a alanced mixer.A TR limiter is a microwave switch used to prevent damage to the receiver crystals, from themagnetron oscillator high power microwave pulses or from other radars in the vicinity. Thebalanced mixer combines the echo signal with a signal from the first local oscillator (operating at9401.3 MHz) to produce a difference frequency of 26.3-MHz. After amplification in the preamplifierstage, the 26.3-MHz signal is mixed with a 36.6-MHz signal from the second local oscillator toproduce a 10.3-MHz I-f signal.A bandwidth switch selects either a 2-MHz bandwidth for search-mode operation or a 0.5-MHzbandwidth for weather-mode operation. The 10.3-MHz logarithmic-gain amplifier following thebandwidth switch provides for a great variance (approximately 50 dB) in signal levels usable by theR-T unit. Following the logarithmic-gain amplifier, is the video detector and buffer. The detected,buffered video (in the search 1 mode) is acted upon by the FTC circuit (fast time constant) and it isused to remove noise caused by the sea clutter. In the A/D converter following the FTC circuit theamplitude of the detected video signal is compared to three preset dc thresholds. A two-bit logiccode tells the radar indicator the highest threshold level exceeded by the echo return. The two-bitcodes for the four thresholds, in increasing level, are 00, 01, 11, and 10.C. AFC FunctionAfter the system trigger, while the magnetron is oscillating, the first local oscillator frequency mustbe adjusted to ensure a correct i-f echo-return signal. The AFC-AGC trigger circuit turns on theAFC gate, and the I-f signal from the preamplifier is supplied to the AFC mixer. Using the 36.6-MHz signal from the second local oscillator, the mixer converts the 26.3-MHz I-f signal to a 10.3MHz second I-f. The discriminator following the 10.3-MHz buffer checks the I-f frequency. If thesecond I-f is exactly 10.3-MHz the AFC circuits remain stabilized. However, if the second I-f is notexactly 10.3 MHz, the discriminator produces a deviation voltage. The deviation voltage isamplified, integrated, buffered, and applied to the varactor in the first local oscillator to adjust thelocal oscillator frequency. An inverse-logarithmic-gain buffer amplifier is used between theintegrator and the first local oscillator to cancel the logarithmic voltage-to-frequency characteristic of
MAINTENANCE MANUALRT-1601 RECEIVER-TRANSMITTER815 Broadhollow Road 631-755-7000Farmingdale, N.Y. 11735 FAX 631- 755-72004the first local oscillator. If the first local oscillator is not very nearly 26.3 MHz above the magnetronfrequency when the magnetron fires, the 10.3-MHz second AFC I-f will be outside the discriminatorcapture range. In this case the stop-sweep, or reset, circuit will initiate integrator reset and AFCsweep. To ensure that the first local oscillator does not lock on the difference frequency 26.3 MHzbelow the magentron frequency, the AFC sweep circuit causes the first local oscillator to start at itshighest frequency and sweep down. If the first local oscillator does not lock up during the down-sweep, the integrator is reset when the time voltage reaches zero volts and the sweep begins again.D. AGC Function (Wx AGC and BCN AGC)The AGC circuit in the RT-1601 is noise –level actuated. Gain of the preamplifier circuits isadjusted in response to the noise level received by the AGC threshold circuit from the video-detector buffer. Video detector output must not be monitored immediately after the transmittedradar pulse, however, as the returning echo signal would simulate a high noise level. The AFC-AGC trigger circuit prevents the false reading by shutting off the AGC threshold circuit during theecho-return time. In beacon, weather, or search-three operating modes (when the pulse repetitionrate is 200 Hz), the AGC-AFC trigger turns off the AGC threshold circuit for about three millisecondsafter the magnetron fires. This is long enough to allow the echo to return, but still leaves time forthe AGC threshold circuit to be turned on for noise-level sampling before the next magnetron firing.To prevent any return after 0.7 milliseconds from affecting the AGC noise-level sampling, the AFC-AGC trigger circuit turns on the AFC side-step circuit. This causes the firs local oscillator to bedriven off-frequency. Therefore, any echo return after 0.7 millisecond in search-one or search-twomodes is ignored. The AFC side-step is also used as a 3000 microsecond gate.E. STC (Sensitivity Time Control) FunctionThe STC function generator is initiated after the transmitter output pulse. The generator causes thegain of the 26.3-MHz preamplifier to increase exponentially. The weaker returns from distantobjects are thus amplified more than the strong returns from nearer objects. Thus, objects of thesame size or density are made to look equal on the radar indicator, regardless of their distance.F. Test FunctionWhen the system is placed in the test mode, a test ground generated by the radar indicator inhibitsthe transmitter and keys a test pattern generator. The triangular wave developed by the test patterngenerator is injected into the video-detector buffer. A resultant test pattern display on the radarindicator is indicative of system performance. The test pattern exhibits three colors, in five bands.G. Beacon AmplifierWhen operating in beacon mode, or dual mode (e.g., weather plus beacon), the R-T unit musttransmit the standard 9375-MHz signal and receive the 9310-MHz transponder signal. To processthe 9310-MHz signal, a separate beacon I-f amplifier (91.3 MHz) and beacon video detector are
MAINTENANCE MANUALRT-1601 RECEIVER-TRANSMITTER815 Broadhollow Road 631-755-7000Farmingdale, N.Y. 11735 FAX 631- 755-72005used. The R-T unit first local oscillator operates at 9401.3-MHz to convert the standard 9375-MHzsignal to a 26.3-MHz intermediate frequency. The same first local oscillator converts the 9310-MHztransponder signal to 91.3 MHz. The 91.3-MHz signal is amplified by the preamplifier and the 91.3-MHz I-f amplifier, detected, and then applied to the video-detector buffer.5. Detailed Theory of OperationA. Power Supply(1) General (See figure 1.)The power supply for the R-T unit converts +28 Vdc into the dc voltages needed for unitoperation: +23V, +6V, +15V, -20.5V and –330V. Two series transistors mounted on themain frame are driven by the power supply circuits to provide regulated -23 Vdc. Anoverload circuit in power supply limits current. Since +28 Vdc is continuously applied to theR-T unit, a power supply on-off switch circuit is used to control R-T unit operation inresponse to demands from the radar indicator. All voltages except the +23 Vdc aredeveloped by chopping the +23 Vdc, then transforming, rectifying, and filtering the choppedvoltage. The high voltage control and overload circuit, in addition to protecting the highvoltage ac-dc converter from overload, provides the trigger enable signal. Trigger enable isgenerated after a 80-second, turn-on delay from the time-delay circuit, and is used toswitch-on –330 Vdc to the magnetron modulator as well as to enable the modulator triggeron the mode decoder board. A fan is provided for cooling the power supply.Figure 1 POWER SUPPLY BLOCK DIAGRAM
MAINTENANCE MANUALRT-1601 RECEIVER-TRANSMITTER815 Broadhollow Road 631-755-7000Farmingdale, N.Y. 11735 FAX 631- 755-72006MAGNETRONLONG PULSEMODULATORSHORT PULSEMODULATORMIXERVCO1st L.OVid-DetecBEACON RECEIVERData ComparatorAFCDiscriminatorMixerWX ReceiverVid-DetecBWControlPRFGenerator STCGeneratorGainControl FaultMonitorLogAMPLogAMPLogAMPNC-104FUNCTIONSMode Control and TimingGENPowerSupplyAGC GatePulsePulseGain AdjData bitsSystem TriggerBWControlTransmitterAnalog VideoMode DecodeSysTriggerSTCSTCAFC Sweep9401.3Mhz26.3MhzToAntenna9375MhzT-RLimitter91.3Mhz91.3MhzFTC10.3Mhz9375Mhz+/- 5Mhz453 Datato display429 DataMode SetMode Set36.6Mhz2nd L.O36.6Mhz10.3MhzTest PulseTest FuncGeneratorSwitchBCN enPreAMPSTCFigure 2 RT-1601 BLOCK DIAGRAM

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