Data Sheet Chapter 5

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4-6 kW UHF Translator Chapter 5, Detailed Alignment Procedures

837B, Rev. 0 5-1

Chapter 5

Detailed Alignment Procedures

The 837B translator was aligned at the

factory and should not require any

additional alignments to achieve normal

operation.

This translator takes the On channel RF

input to the Receiver Tray and converts it

to the desired UHF On Channel RF Output

at the systems output power level.

If the (Optional) Modulator Kit is

purchased, this translator can also

operate using the baseband audio and

video inputs or, if the (Optional) 4.5-MHz

composite input kit is purchased, either a

single composite video + 4.5-MHz input

or separate baseband video and audio

inputs.

Make sure that the RF output at J2 of the

(A11) coupler is terminated into a

dummy load of 4000 to 6000 watts,

depending on your systems output

power. While performing the alignment,

refer to the test data sheet for the

translator and compare the final readings

from the factory with the readings on

each of the trays. They should be very

similar. If a reading is off by a significant

amount, the problem is likely to be in

that tray.

Switch on the main AC and the UHF

exciter circuit breakers on the AC

distribution panel behind the rear cabinet

door of the Exciter Cabinet.

5.0 UHF/VHF Receiver

Tray.)(1142479 or 1265-1100;

Appendix C)

Connect a UHF or VHF Input that is

at the desired Channel Frequency, to

J1 50Ω or J5 75Ω located on the rear

of the (A7) VHF/UHF Receiver Tray.

Check that the On/Off Switch located

on the rear of the Tray is On.

Note

: If the Red LED, DS1 is lit, +12

VDC is present at the input of the

Receiver Tray and may damage any test

equipment connected to it. Remove the

fuse F1, DS1 will not be lit, before

connecting test equipment to the input

jack of the Receiver Tray.

5.0.1 (A7) UHF Filter, DC Multiplexed

{(1035-1204, 50

Ω

or 1035-1207,

Ω

), VHF Filter, LB, DC Multiplexed

(1035-1902, 50

Ω

or 1035-1903,

Ω

) or VHF Filter, HB, DC

Multiplexed (2065-1024, 50

Ω

2065-1023, 75

Ω

); Appendix D)}

The input UHF or VHF signal (-61 dBm to

-16 dBm) is fed to the filter which has

been factory swept for 6 MHz Bandwidth

at the Channel frequency and should not

be tuned in the field. The output of the

filter is directed to the J1 input of (A8)

the Dual Stage Amplifier Assembly.

5.0.2 (A8-A1) Dual Stage Amplifier

Board (1227-1501; Appendix D)

Mounted in: (A8) a Dual Stage Amplifier

Assembly (1227-1503).

The Dual Stage Amplifier Board has been

factory set to the channel frequency and

contains no customer tuning

adjustments. The board has

approximately +13 dB or +26 dB of gain,

depending on whether Jumper W1 on J5

is in place.

5.0.3 (A9) UHF Filter {(1007-1101),

VHF LB Filter (1034-1202) or VHF HB

Filter (2065-1000); Appendix D}

The UHF or VHF Filter has been factory

swept for 6 MHz Bandwidth at the

Channel Frequency and should not be

tuned in the field. The output of the filter

(-50 dBm to -5 dBm) is fed either

through the additional amplifier stage on

the Variable Gain Amplifier Board or to

Summary of content (20 pages)

PAGE 1
4-6 kW UHF Translator Chapter 5, Detailed Alignment Procedures Chapter 5 Detailed Alignment Procedures The 837B translator was aligned at the factory and should not require any additional alignments to achieve normal operation. This translator takes the On channel RF input to the Receiver Tray and converts it to the desired UHF On Channel RF Output at the systems output power level.
PAGE 2
4-6 kW UHF Translator (A10-A1) Board. the Chapter 5, Detailed Alignment Procedures Downconverter/Filter Assembly (1145-1206), containing a VCXO Board (1145-1204), will be used instead of the standard Channel Oscillator Board. The adjustment will be the same as above except that the frequency is adjusted by moving the Jumper W1 on Jack J6, located on the IF PLL Board (1109-1002), to Pins 2 & 3, Fixed Bias, and adjusting R15 on the IF PLL Board for -3 VDC at FL2 of the VCXO Assembly.
PAGE 3
4-6 kW UHF Translator Capacitors to minimize the seventh and the ninth harmonics, they should be at least -30 dB down, without affecting the x8 Multiplier Output. If a Spectrum Analyzer is not available a DC voltmeter can be used as follows but the harmonic frequencies must be minimized to prevent interference with other Channels. 1. 2. While Monitoring each Test Point with a DC voltmeter, maximize the voltage by tuning the Broadband Multipliers in the following sequence.
PAGE 4
-6 kW UHF Translator 5.0.9 (A11-A2) (Optional) SAW Filter/Amplifier Board (1035-1211; Appendix D) Chapter 5, Detailed Alignment Procedures 1. Monitor the Aural Notch Test Output of the board at J5 and move the Jumper W1 on Jack J4 to between Pins 2 & 3, Test Position. Adjust C17 to the Aural IF Frequency, then adjust R10 to eliminate or minimize the Aural IF signal. Move the Jumper W1 on Jack J4 back to between Pins 1 & 2, Operate Position. 2.
PAGE 5
4-6 kW UHF Translator The Receiver Tray is now set up and ready for normal operation. 5.1 UHF Exciter Tray with Baseband Video and Audio Inputs (Must have Optional Modulator Kit.)(1142458 or 1245-1100; Appendix C) This tray has adjustments for video levels, audio modulation levels, and other related parameters. Connect an NTSC baseband video test signal input (1 Vpk-pk) to the translator video input jacks J2 or J1 on the rear of the tray.
PAGE 6
4-6 kW UHF Translator response; it may have changed with the adjustment to the envelope delay. 5.3 UHF Exciter Tray with Receiver Tray, or either (Optional) Baseband or (Optional) 4.5-MHz Composite Input The IF section of the UHF exciter tray includes adjustments for automatic level control (ALC), linearity (amplitude predistortion), and phase (phase change vs. level) predistortion for correction of the nonlinearities of the RF amplifier trays.
PAGE 7
4-6 kW UHF Translator 3. Tune the four stages of the board using the variable inductors (L1-L4) and potentiometers (R7, R12, R17, and R22) until the signal attains the FCC group delay curve. The stages are arranged in order of increasing frequency. Adjust R29 as needed to attain the same level coming out of the board as is going into the board. 5.3.2 (A24) (Optional) Composite 4.5-MHz Filter Board (1227-1244; Appendix D) The (A24) (optional) composite 4.
PAGE 8
4-6 kW UHF Translator Chapter 5, Detailed Alignment Procedures 4. Connect a 5-step staircase video test signal to the input of the transmitter. 5. Monitor TP2 with an oscilloscope. Adjust R12, the video gain pot, for 1 Vpk-pk. 6. Change the video input test signal to a multiburst test pattern. While monitoring TP2, adjust C8 and R32 for a flat-frequency response. Change the input video test signal back to the 5-step staircase. 7. Monitor TP2 with an oscilloscope.
PAGE 9
4-6 kW UHF Translator manual offset, for the correct depth of modulation by observing the demodulated waveform on the waveform monitor or on the spectrum analyzer set to zero span. 10. 11. Check the demodulated video for the proper sync-to-video ratio (sync is 28.6% of the total white video signal). If sync stretch is needed, adjust R45, sync stretch cut-in, until sync stretch occurs. Adjust R48, sync stretch magnitude, for the proper amount of stretch.
PAGE 10
4-6 kW UHF Translator input terminals of the tray at TB1-1 (+), TB1-2 (-), and TB13 (ground) on the rear chassis. B. C. D. 2. 3. Connect the combined IF output at J21, the IF sample on the clamp modulator board, to the input of an IF splitter. Connect one output of the splitter to the video demodulator and the other output to the spectrum analyzer. Connect a short cable at the front of the demodulator from the RF-out jack to the IF-in jack.
PAGE 11
4-6 kW UHF Translator control); adjust R87, the manual gain pot, to mid-range. • 2. IF phase corrector board – Move jumper W2 on J9 to the phase correction enable position; move the jumper W3 on J10 to the amplitude correction disable position. The combined IF output of the sync tip clamp modulator board is cabled to jack J32 of the ALC board. Remove J32 from the board and check to see that DS1, Input Fault, is illuminated. Reconnect J32 and check to see that DS1 is extinguished. 3.
PAGE 12
4-6 kW UHF Translator adjusted for the frequency of the correction notch being applied to the visual response of the translator. R103 and R106 are used to adjust the depth and width of the correction notch. Chapter 5, Detailed Alignment Procedures Caution: Do not repeak C6, C18, L2, or L4. This can change the output level. 5.3.
PAGE 13
4-6 kW UHF Translator frequencies must be minimized to prevent interference with other channels. While monitoring each test point with a DC voltmeter, maximize each test point by tuning the broadband multipliers in the following sequence: • Monitor TP1 with a DVM and tune C4 for maximum (typical 0.6 VDC). • Monitor TP2 and tune C6 and C10 for maximum (typical 1.2 VDC). • Monitor TP3 and tune C12 and C18 for maximum (typical 2.0 VDC). • Monitor TP4 and tune C20 for maximum.
PAGE 14
4-6 kW UHF Translator 5.4.3 (A1) UHF Filter (1007-1101; Appendix D) Apply a multiburst test signal to the translator. Monitor J2 with a spectrum analyzer and tune C1 and C3 for peak output with a flat-frequency response. There is approximately 1 dB loss through the filter. Chapter 5, Detailed Alignment Procedures The working point setting is factory implemented by means of potentiometers R9, R11 and R12 and should not be altered. 5.4.
PAGE 15
4-6 kW UHF Translator 5.4.15 Calibration of Output Power and VSWR Cutback of the Tray Place a wattmeter and dummy load of at least 600 watts at the output of the tray that is to be calibrated and switch the front panel meter to the % Output Power position. Preset R16, manual gain, on (A8) the amplifier control board fully CCW. Move switch S1 on the amplifier control board to the Manual position.
PAGE 16
4-6 kW UHF Translator to the RF Input (J1) of the amplifier. Re-adjust the Phase to peak the System output power. If the Phase Control again reaches its end of travel before a peak in power is reached, remove the 2 inch cable and add a 3 inch cable to J1 of amplifier and readjust phase for peak output power. The adding of cables should be done during the adjustment anytime the range of the phase adjust needs extended. 7. Repeat steps 5 and 6 for the remaining Amplifiers. 8.
PAGE 17
4-6 kW UHF Translator Begin the power calibration with the Amplifier Array adjusted to {2200 Watts (4kW) or 2750 Watts (5kW) or 3300 Watts peak of sync Visual + 10% Aural for 6 kW transmitter)}. Side A Forward Power Calibration. In (A6) the Metering Control Panel, located in the UHF Exciter Cabinet, find the (A9) Dual Peak Detector Board (1159965). Adjust R9 for 100% on the Side A Power Meter. Side B Forward Power Calibration.
PAGE 18
4-6 kW UHF Translator 5.9 Calibration of the Forward Output Power Level of the Translator Note: - Perform the following only if the power calibration is suspect. Switch the Translator to Standby and preset R51, Aural Null pot, located on the Visual/Aural Metering Board (1265-1309) in the Metering Panel, full CCW. Adjust R48, the Null Offset pot, located on the Visual/Aural Metering Board, for 0% Visual Output.
PAGE 19
4-6 kW UHF Translator Return CB1, the Main AC circuit breaker for the Side A Amplifier Array, to the On position. 5.12 IF Phase Corrector Adjustment of the Translator As shipped, the exciter was preset to include linearity (gain vs. level) and phase (phase vs. level) predistortion. The predistortion was adjusted to approximately compensate the corresponding non-linear distortions of the amplifier trays and should not require additional adjustments.
PAGE 20
4-6 kW UHF Translator Chapter 5, Detailed Alignment Procedures 5.13 Linearity Corrector Adjustment for Translator is set to +0.8 VDC as monitored on the front panel meter in the ALC position. The IF linearity correction function consists of three non-linear cascaded stages, each having adjustable magnitude and threshold, or cut-in points, on the ALC board. The threshold adjustment determines at what IF signal level the corresponding corrector stage begins to increase gain.