Axcera-335B FCC Type Acceptance Report Parts List/Tune

Axcera-335B FCC Type Acceptance Report Parts List/Tune

Axcera-335B FCC Type Acceptance Report Parts List/Tune-up

Info

7. PARTS LIST/TUNE-UP INFO

7.1 Parts List

The exciter, 750-watt amplifier trays, and the output filter assembly can be subdivided as follows:

Exciter:

-Video input

-Audio input

-Sync-tip clamp/modulator with SAW filter

-AM FCC identifier

-IF crystal oscillator

-Phase correctors

-Aural frequency modulated oscillator

-Automatic level control

-Linearity correctors

-Channel crystal oscillator

-Frequency multiplier

-Filter/mixer

-Filter/amplifier

-Metering circuits

-Control and protection circuits

-Power supply

750-Watt Amplifier Trays:

-AGC control

-Phase shifter

-Filter/amplifier

-VHF amplifier

-Overdrive protection

-VHF driver amplifier

-3-way splitter

-VHF final amplifier

-3-way combiner

-Power supply

Output filter assembly:

-Bandpass filter with traps

-VHF coupler

-VHF splitter/combiner assemblies

7.2 Tune-up Information

The 335B transmitter was aligned at the factory and should not require additional alignments to achieve normal operation.

This transmitter operates 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.

Check that the RF output at J2 of (A9-A5) the coupler is terminated into a dummy load of at least 500 watts. While performing the alignment, refer to the Test Data Sheet for the transmitter and compare the final readings from the factory with the readings on each of

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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 VHF exciter circuit breakers on the AC distribution panel behind the rear cabinet door.

7.2.1 Low-Band VHF Exciter Tray with Baseband Video and Audio Inputs

The (A4) low-band VHF exciter tray (1304463) has adjustments for video levels, audio modulation levels, and other related parameters.

Connect an NTSC baseband video test signal input (1 Vpk-pk) to transmitter video input jack J2 on (A12) the remote interface panel. Jacks J1 and J2 on the VHF exciter tray are loop-through connected and the unused jack can be used as a video source for another transmitter by removing jumper W4 on jack J3 on (A5) the sync tip clamp modulator board (1265-1302). Connect a baseband audio input (+10 dBm) to the balanced audio input terminal block TB1-1 (+), TB1-2 (-), and TB1-3 (ground). If stereo/composite audio is provided, connect it to BNC jack J6, the composite audio input jack on the remote interface panel. Jacks J3 and J13 on the rear of the exciter panel are loop-through connected and the unused jack can be used as an audio source for another transmitter by removing jumper W1 on jack J15 on the aural IF synthesizer.

Look at the front panel meter on the VHF exciter tray. In the Video position, the meter indicates active video from 0 to 1 Vpk-pk. The normal video input level is 1 Vpk-pk on the meter. If this reading is not at the proper level, the overall video level can be changed by adjusting video level control R12 on the sync tip clamp/modulator board.

Switch the meter to the Audio position to show the audio deviation (modulation level) of the signal from 0 to 100 kHz. The aural IF synthesizer board was factory set for a ±25 kHz deviation with a balanced audio input of +10 dBm. If the reading is at not the correct level, adjust balanced audio gain pot R13 on the aural IF synthesizer board, as needed, to attain the ±25 kHz deviation. The aural IF synthesizer board was factory set for a ±75 kHz deviation with a composite audio input of 1 Vpk-pk. If this reading is not correct, adjust composite audio gain pot R17 on the aural IF synthesizer board, as needed, for the ±75 kHz deviation.

7.2.2 VHF Exciter Tray with the 4.5-MHz Composite Input Kit

With the 4.5-MHz composite input kit, (A4) the VHF exciter tray (1070820) is able to operate using either the separate video and audio baseband inputs or the single 4.5-MHz composite input. The 4.5-MHz composite input kit includes a composite 4.5-MHz filter board (1227-1244) and a 4.5-MHz bandpass filter board (1265-1307).

To align the VHF exciter using baseband video and audio, refer to the alignment instructions described in Section 7.2.1. Select the baseband input operation by applying a baseband select, using a jumper or closed contacts, connected between J7-6 and J7-7 on the rear of the tray.

To operate the transmitter using the 4.5-MHz composite input, remove the baseband select command from J7-6 and J7-7 on the rear of the tray.

Connect a multiburst test signal from an envelope delay measurement set to the input of the rear interface panel at J2. On (A24) the composite 4.5-MHz filter board (1227-1244), connect an oscilloscope between J7, the center pin, and pin 1 or 3, which are ground.

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Adjust C21, if necessary, for the best frequency response. Adjust R32 for a signal level of

1 Vpk-pk on the oscilloscope. The output, as measured at J6 and J7 on the board, should be video-only with a minimum 4.5-MHz aural subcarrier.

On (A25) the 4.5-MHz bandpass filter board (1265-1307), adjust the filter with L2, C3, L4, and C7 for a frequency response of no greater than ±.3 dB from 4.4 MHz to 4.6 MHz.

Adjust C19 for an overall peak-to-peak variation of less than ±.3 dB from 4.4 MHz to 4.6

MHz. Recheck the frequency response; it may have changed with the adjustment of the envelope delay.

7.2.3 VHF Exciter Tray with either Baseband or 4.5-MHz Composite Input

The IF section of (A4) the VHF exciter tray (1070820) includes adjustments for automatic level control (ALC), linearity (amplitude predistortion), and phase (phase change vs. level) predistortion for the correction of the nonlinearities of the RF amplifier trays. The upconverter section also includes adjustments to the local oscillator chain tuning and the local oscillator center frequency tuning. Both of these were completed at the factory and should not require adjustments at this time.

Move the Operate/Standby switch on the VHF exciter tray to Standby. The setup of the RF output includes an adjustment to the drive level of the two VHF amplifier trays, the adjustment of the linearity and phase predistortion (which compensate for any nonlinear responses of the amplifier trays), and the gain and phasing adjustments of the two VHF amplifier trays.

Verify that all of the red LEDs on the ALC board are extinguished. The following list describes the meaning of each LED when they are illuminated:

• DS1 (Input Fault) – Indicates that an abnormally low or no IF is present at the input of the board

• DS2 (ALC Fault) – Indicates that the ALC circuit is unable to maintain the signal level requested by the ALC reference. This is normally due to excessive attenuation in the linearity signal path or the IF phase corrector signal path or because jumper W3 on J6 is in the Manual ALC Gain position.

DS3 (Video Loss) – Indicates a loss of video at the input of the board

DS4 (Mute) – Indicates that a visual Mute command is present (not used in this configuration)

• DS5 (Modulator Enable) – Indicates that the modulator IF output has been selected

(this is only used if a receiver tray is present in the system). DS5 is always on with no receiver.

The ALC is muted when the transmitter is in Standby. To monitor the ALC, turn off the two amplifier on/off circuit breakers on the AC input assembly in the rear of the cabinet and switch the transmitter to Operate. Adjust the power adjust gain pot on the front panel of the VHF exciter tray to obtain +0.8 VDC on the front panel meter in the ALC position. On the ALC board (1265-1305), move jumper W3 on J6 to the Manual position, between pins

2 and 3, and adjust R87 on the ALC board for +0.8 VDC on the front panel meter in the

ALC position. Move jumper W3 back to Auto (between pins 1 and 2); this is the normal operating position. The detected IF signal level at J19-2 of the ALC board is connected to the transmitter control board that distributes the level to the two VHF amplifier trays

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where it is used as a reference for the automatic gain control (AGC) in each amplifier tray.

7.2.4 IF Phase Corrector Adjustment

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.

Locate (A9) the IF phase corrector board (1227-1250) mounted in the VHF exciter. The amplitude correction portion of the board is not utilized in this configuration. As a result, jumper W3 on J10 should be in the Disable position, to +6.8 VDC, and R35 and R31 should be fully counter-clockwise (CCW). R68 is the range adjustment and should be set in the middle of the range. The phase correction Enable/Disable jumper W2 on J9 should be in the Enable position, to ground.

Switch the input video test source to select an NTSC 3.58-MHz modulated staircase or ramp test waveform. Set up the station demodulator and monitoring equipment to monitor the differential phase or intermodulation products of the RF output signal. There are three corrector stages on the IF phase corrector board, each with a magnitude and a threshold adjustment that are adjusted, as needed, to correct for any differential phase or intermodulation problems. Adjust the R3 threshold for the cut-in point of the correction and the R7 magnitude for the amount of the correction that is needed.

Jumper W1 on J8 is set to give the desired polarity of the correction shaped by the threshold R11 and the magnitude R15 adjustments. After setting the polarity, adjust the

R11 threshold for the cut-in point of the correction and the R15 magnitude for the amount of the correction that is needed. Finally, adjust the R19 threshold for the cut-in point of the correction and the R23 magnitude for the amount of the correction that is needed.

Note: Adjusting these pots changes all visual parameters and should be done

cautiously.

7.2.5 Linearity Corrector Adjustment

The IF linearity correction function consists of three non-linear cascaded stages, each having magnitude and threshold adjustments, 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. The magnitude adjustment determines the amount of gain change for the part of the signal that exceeds the corresponding threshold point. Refer to the VHF exciter tray control locations drawing, ALC board (1265-1305), to find the adjustments for the first through third linearity corrector stages. Because the stages are cascaded, the order of correction is important. The first stage should cut in near white level, with the cut-in point of the next stage toward black, and with the last stage primarily stretching sync.

To adjust the linearity correctors from scratch, ensure that the transmitter is operating at full power with the desired A/V ratio. Check that jumper W1 on J4 of the ALC board is enabled between pins 1 and 2. Make sure that the ALC voltage is set to +0.8 VDC as monitored on the front panel meter in the ALC position.

Insert a modulated ramp video test signal into the transmitter. Demodulate the output signal of the transmitter and observe the waveform on a waveform monitor while also looking at the signal on a spectrum analyzer. On the IF ALC board (1265-1305), preset

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pots R34, R37, and R40 (threshold) fully CCW and the magnitude adjustments R13, R18, and R23 fully clockwise (CW). On the IF phase corrector board (1227-1250), preset pots

R7, R15, R23, and R35 fully CW and R3, R11, R19, and R31 fully CCW.

Set the waveform monitor to differential step filter and the volts/division scale to .1 volts.

Center the display to the blanking level (approximately).

Gradually adjust pots R3, R11, and R19 CW on the IF phase corrector board, as needed, to minimize the observed thickness of the intermodulation as seen on the display.

Adjust pots R34, R37, and R40 CW on the IF ALC board, as needed, to give correction at sync or at low luminance levels as viewed at the left-most edge of the waveform monitor.

The intermodulation beat products between the colorburst and the aural carrier at 920 kHz above visual carrier should also be observed on the spectrum analyzer while performing the preceding adjustments. The frequency will vary for different video systems. When the adjustments are performed properly, the intermodulation products on the spectrum analyzer should be at least -52 dB down, with a red field input, from peak visual carrier.

The intermodulation distortion, as displayed on the waveform monitor, should be no more than 1 IRE. Pot R31 on the IF phase corrector board is used for any extra intermodulation correction that may be needed.

Note: Any adjustments to the above pots affect other visual parameters and some slight adjustments to all of the pots may be needed to meet all specifications simultaneously.

If the transmitter is being driven very hard, it may not be possible to get enough sync stretch while maintaining a flat differential gain. In this case, some video sync stretch may be used from the sync tip clamp/modulator board; the sync stretch adjustment is R48.

Switch the transmitter to Standby.

7.2.6 Phase and Gain Adjustment of Multiple VHF Amplifier Trays

The following procedure was completed at the factory and should only be followed if one of the VHF amplifier trays is replaced.

Adjust the gain controls located on the VHF Amplifier Trays full CCW. Switch On the front panel AC Circuit Breaker on the bottom VHF amplifier tray. Place the Transmitter in

Operate and adjust the Gain control on the Amplifier Tray for 50% output power and adjust the Phase control to mid range. Monitor the output power of the Transmitter by connecting a Spectrum Analyzer to a sample of the output. Adjust the Spectrum Analyzer for Zero Span operation. The power could be monitored by watching the meters on the panel but the power change is easier to see on the analyzer.

Turn On the AC to the middle amplifier tray and adjust its' output power to 50%. While monitoring the output power of the Transmitter, adjust the Phase Control until the power reaches a peak. If the Phase adjust reaches its end of travel, add a 4 inch cable 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, add a 3 inch cable to J1 of the 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.

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Turn On the AC to the top amplifier tray and adjust its' output power to 50%. While monitoring the output power of the Transmitter, adjust the Phase Control until the power reaches a peak. If the Phase adjust reaches its end of travel, add a 4 inch cable to the RF

Input (J1) of the amplifier. Readjust 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, add a 3 inch cable to J1 of the 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.

Increase the output power on the bottom and middle amplifier trays to 90%.

Adjust the Phase Control on the middle amplifier tray to peak the System output power.

Increase the output power on the top amplifier to 90% and adjust the Phase control for maximum System output power.

Monitor the Reflected Power on all of the VHF Amplifier Trays. The Reflected Power should read <5%. If an amplifier is showing high reflected power, adjust the Phase control as needed to minimize Reflected Power. Be careful not to increase Reflected Power on the other Amplifier Trays. The Amplifier Trays should interact in such a way that the phasing of any one amplifier tray will affect the Reflected on the other amplifier trays.

Raise or lower the output power of each tray as needed to achieve 100% Output Power.

The output power of each tray should be 90% to 100%.

7.2.7 Calibration of the Forward Output Power Level of the Transmitter

Note: The following procedure should only be performed if the power calibration is suspect.

Switch the transmitter to Standby and preset R51, the aural null pot on the visual/aural metering board (1265-1309), fully CCW. Adjust R48, the null offset pot on the visual/aural metering board, for 0% Visual Output. Perform the following adjustments with no aural present; this is accomplished by removing jumper cable W1, the aural IF loop-through, that is connected to J16 on (A5) the sync tip clamp/modulator board (1265-1302).

Connect a sync and black test signal to the video input jack of the VHF exciter tray. Switch the transmitter to Operate.

Set up the transmitter for the appropriate average output power level: sync + black 0 IRE setup/wattmeter=1963.5 watts; sync + black 7.5 IRE setup/wattmeter=1798.5 watts.

Note: The transmitter must have 40 IRE units of sync.

With the front panel meter in the % Visual Output position, adjust R28, visual calibration, on (A19) the visual/aural metering board (1265-1309) for 100%.

With the spectrum analyzer set to the zero span mode, obtain a peak reference on the screen. Reconnect jumper cable W1 to J16 on (A5) the sync tip clamp/modulator board.

While in the Visual Output Power position, adjust L3 for a minimum visual power reading.

Turn the power adjust pot on the front panel until the original peak reference level is attained. Peak L1 and C8 for a maximum aural power reading and then also adjust R20 for a 100% Aural Power reading. Switch the transmitter to the Visual Output Power position and adjust R51, the aural null pot, for 100% Visual Power.

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7.2.8 Calibration of the Reflected Output Level of the Transmitter

Check that the transmitter is at 100% forward power. Switch the transmitter to Standby and move the reflected cable to the other Incidental port on the A16 Coupler. Switch the transmitter to Operate and adjust R39 on the visual/aural metering board (1265-1309) for a 10% reading in the Reflected Power position. At this 10% reference power reading, the

VSWR LED mounted on the front panel of the exciter should be illuminated. If this LED is not lit, adjust R22 on the transmitter control board in the VHF exciter tray until the VSWR

LED just turns on. Turn the power adjust pot slightly CCW and the LED should go out.

Turn the pot CW until the LED just turns on. The reflected output power is now calibrated.

Switch the transmitter to Standby. Move the cable on A16 Coupler back to the Reflected port.

Switch the transmitter to Operate and adjust the front panel power pot for a 100% Visual

Power reading.

7.2.9 3-Way Combiner Assembly

There are no adjustments to (A8) the 3-way VHF combiner assembly.

Note: The bandpass filter is factory swept and should not be tuned without the proper equipment. Do not attempt to tune the filters without a sweep generator or, preferably, a network analyzer. If tuning is required, consult the

Axcera Field Support Department before attempting to make any adjustments.

7.2.10 Bandpass Filter Assemblies

The harmonic and bandpass filters are factory swept by the filter manufacturer and should not be tuned without the proper equipment. Do not attempt to tune the filters without a sweep generator or, preferably, a network analyzer. If tuning is required, consult the Axcera Field Support Department before attempting to make any adjustments.

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7.2.11 750-Watt Low-Band VHF Amplifier Trays

NOTE: The following procedure should be followed only if complete alignment

of a VHF amplifier tray is needed.

The (A6, A7, and A11) low-band VHF amplifier trays have been adjusted at the factory to meet all specifications, including phase adjustment to match the multiple trays in an amplifier array when they are combined. The trays should not need to be adjusted to attain normal operation. If necessary, any adjustments to the boards in this tray should be performed in the Manual Gain position, with S1 on (A13) the AGC control board

(1142-1601) in Manual. The idling currents for the amplifier boards are adjusted with no

RF drive applied. Remember to put S1 back to the Auto AGC position after any adjustments. Auto AGC is the normal position during operation of the transmitter.

Connect a dummy load with a rating of at least 750 watts to J2, the RF output jack of the tray being aligned, before beginning the alignment procedure.

Switch the VHF amplifier tray on and the transmitter to operate.

7.2.11.1 AGC Control Board

Using a calibrated wattmeter, check that the tray is operating at the rated power. Remove the sample forward power connection J4 from the (A13) AGC control board (1142-1601).

The output power level should drop to 20% because of the VSWR cutback and DS4, the

VSWR Cutback LED, should be illuminated. The front panel Module Status LED should not be lit.

Reconnect J4 and adjust R59 so that it begins to cut back on the output power level when the reflected level increases above 20%.

In the Power Supply Voltage position, the front panel meter is calibrated to +30 VDC using

R86 on the AGC control board.

7.2.11.2 Phase Shifter Board

There are no adjustments to (A2-A1) the phase shifter board (1198-1602). The front panel has adjustments for phase that are made during the amplifier array setup procedure. Typically +7 dBm input and +7 dBm output.

7.2.11.3 Filter/Amplifier Board

The (A2-A2) VHF filter/amplifier board (1198-1606) has approximately 14 dB of gain.

Tune the channel filter capacitors C29 and C20 (loading), C26 and C23 (center frequency), and C24 (coupling) at J6 on the board for the best response. Set voltage adjust pot R19 for +24 VDC at the anode of CR5.

The idling current, no RF drive applied, of the device Q1 is set for 250 mA. To set the current, remove the RF drive, measure the voltage across R16 (a 1 Ω resistor on the filter/amplifier board) and adjust R13 for .25 volts (using Ohms’ Law: [E=I x R] : [E=250 mA x 1 Ω ] : E=250 mV). Typically the board has a +7 dBm input and a +19.5 dBm output level.

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7.2.11.4 Low-Band VHF Amplifier Board

The (A3-A1) VHF low-band amplifier board (1198-1605) has 22 dB of gain and is biased for 3 amps of idling current, no RF drive applied. Adjust voltage adjust pot R10 for +24

VDC at pin 0 of the regulator IC U1. To set the bias, remove the RF drive from the board, measure the voltage across R6 and R7 (two 1 Ω resistors in parallel on the high-band driver board), and adjust R4 for 1.5 volts (using Ohms’ Law: [E=I x R] [E=3 amps x .5 Ω ]

: E=1.5 volts).

Connect a spectrum analyzer to output jack J2 on the board and adjust C15 for peak output. Typically +19.5 dBm input and +41.5 dBm output.

7.2.11.5 Overdrive Protection Board

The typical input level to the (A3-A2) overdrive protection board (1198-1601) is +41.5 dBm during normal operation with a typical output of +41.3 dBm.

To set up the overdrive circuit, check that the output power level of the transmitter is at

100% and adjust R11 on the board for a reading of .4 VDC at TP1. Increase the output power level of the transmitter to 110%, sync only, and adjust R12 until the output power begins to drop off. Return the output power level of the transmitter to 100%.

7.2.11.6 3-Way Splitter Board

There are no tuning adjustments for (A3-A3) the 3-way splitter board. The board takes the

+41.3 dBm input and splits it into three equal +36.3 dBm outputs.

7.2.11.7 VHF Low-Band Amplifier Pallet

These pallets, P400-VHF-L, are supplied by Delta RF Technology, Inc. Refer to the data sheets in the subassembly section of this manual for more information. Each board has approximately 18 dB of gain and with an input of +36.3 dBm the output is typically +54.3 dBm.

7.2.11.8 3-Way Combiner Board

There are no adjustments to the (A5-A1) 3-way combiner board. The three +54.3 dBm inputs are combined to produce the 750 watts, +58.8 dBm, peak of sync output at J2 of the combiner assembly.

7.2.11.9 Calibration of the Visual Plus Aural Output Power and VSWR Cutback

Check that a dummy load of at least 750 watts is connected to the output of the tray that is to be calibrated. Place switch S1 on the AGC control board in the Manual position before beginning the setup.

To adjust the visual output power levels:

1.

Remove the J16 cable from (A5) the sync tip clamp/modulator board (1265-1302) in the VHF exciter tray. Set the Manual AGC switch S1, on the (A13) AGC control board

(1142-1601) in the VHF L.B. amplifier tray, to the Manual position. Turn the transmitter to the Operate position.

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2.

3.

Connect a sync and black test signal to the video input jack of the remote interface panel.

Adjust the manual gain pot R5 on the AGC control board for:

Sync + black 0 IRE setup; wattmeter=1963.5 watts

Sync + black 7.5 IRE setup; wattmeter=1798.5 watts

NOTE: The transmitter must have 40 IRE units of sync.

4.

Obtain a zero span reference of the visual-only carrier on a spectrum analyzer. Replace the J16 connector on the sync tip clamp/modulator board in the VHF exciter tray.

Adjust R5 on the AGC control board until the same visual reference is obtained. Adjust

R44 on the AGC control board for 100% Forward Power.

Lower the forward power reading to 80% on the front panel meter using R5, the manual gain adjust on the AGC control board. Adjust R65, the AGC fault adjust on the AGC control board, until the green Module LED DS3 on the front panel just begins to light. Use

R5 to readjust the forward power to 100%.

Switch off the tray and reverse the J6 and J7 cables on the 3-way combiner enclosure.

Switch on the tray and adjust the front panel meter, in the Reflected Output Power position, to a 100% reading using R53, the reflected power meter adjust on the AGC control board. Adjust the reflected output power to a 20% reading using R5 on the AGC control board. Adjust R59, the VSWR cutback adjust on the AGC control board, until the red VSWR Cutback LED DS4 on the front panel lights. This sets up the VSWR cutback circuitry.

Readjust R5 for 100% on the meter to achieve a 750 watts peak of sync output + 75 watts aural power. However, if the system requires less output power per amplifier tray, adjust each tray by the same amount to give the desired total output power.

Switch off the tray and return the J6 and J7 cables on the 3-way combiner assembly, back to their original positions. If the tray was originally operating below 100% output power, the AGC fault adjust was set for 20% below the operational % Output Power of the tray.

See the Test Data Sheet for the transmitter for the actual readings for the tray. Place S1 on the AGC control board in the AGC position. This is the normal operating position after the setup is completed.

The VHF amplifier tray is aligned, calibrated, and ready for normal operation. Repeat as needed for the other VHF amplifier trays.

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7.2.12 Board Level Alignment Procedures

7.2.12.1 (Optional) 4.5-MHz Composite Input Kit

If the (optional) 4.5-MHz composite input kit is purchased, the tray is capable of operating by using either the 4.5-MHz composite input or the baseband audio and video inputs. The kit adds (A24) the composite 4.5-MHz filter board (1227-1244) and (A25) the 4.5-MHz bandpass filter board (1265-1307) to the transmitter. When the 4.5-MHz intercarrier signal generated by the 4.5-MHz composite input has been selected by the 4.5-MHz composite input kit, the 4.5-MHz generated by the aural IF synthesizer board is not used.

When the 4.5-MHz intercarrier signal generated by the baseband video and audio inputs with baseband has been selected by the 4.5-MHz composite input kit, the composite 4.5-

MHz filter board and the 4.5-MHz bandpass filter board are not used.

The tray has been factory tuned and should not need any alignments to achieve normal operation. To align the tray for the 4.5-MHz composite input, apply the 4.5-MHz composite input, with the test signals used as needed, to the video input jack (J1 or J2 [loop-through connections]) on the rear of the tray. Select the 4.5-MHz composite input by removing the baseband select from J18-6 and J18-7 on the rear of the tray.

To align the exciter using baseband video and audio inputs, apply the baseband video, with the test signals used as needed, to the video input jack (J1 or J2 [loop-through connections]) and the baseband audio to the proper baseband audio input on the rear of the tray. For balanced audio input, connect TB1-1(+), TB1-2(-), and TB1-3 (GND). For composite/stereo audio, connect the composite audio input jack (J3 or J13 [loop-through connections]) and connect a baseband select from J18-6 and J18-7 on the rear of the tray.

7.2.12.2 Delay Equalizer Board

The jumper W1 on J5 of the sync tip clamp/modulator board, if present, must be in the

Enable position between pins 2 and 3.

1.

2.

Note: This board has been factory tuned and should not be re-tuned without the proper equipment.

To tune this board:

Connect a sinX/X test signal into jack J1-2 on the delay equalizer board.

Monitor the video output of the board, at video sample jack J2, with a video measuring set, such as the VM700, adjusted to measure group delay.

3. Tune the four stages of the board using the variable inductors (L1 to 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 out of the board as into the board.

7.2.12.3 Composite 4.5-MHz Filter Board

This board is part of the 4.5-MHz input kit and will only function properly with a 4.5-MHz composite input signal and the 4.5-MHz composite input selected. To align this board:

1. Connect the test signal from an envelope delay measurement set to the video input of the tray at J1 or J2.

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2. Connect an oscilloscope to jack J7, video out, between the J7 center pin and pin 1 or

3 (ground). Adjust C21, frequency response, if needed, for the best frequency response. Adjust R32, video gain, for a signal level of 1 Vpk-pk on the oscilloscope.

The output at J6 and J7 on the board should be video-only, without the 4.5-MHz aural subcarrier.

7.2.12.4 (Optional) 4.5-MHz Bandpass Filter Board

This board is part of the 4.5-MHz input kit and will only function properly with a 4.5-MHz composite input signal and the 4.5-MHz composite input selected. To align this board:

1.

Adjust the filter with L2, C3, L4, and C7 for a frequency response of no greater than

±0.3 dB from 4.4 MHz to 4.6 MHz.

2. Adjust C19 for an overall peak-to-peak variation of less than ±0.3 dB from 4.4 MHz to 4.6 MHz.

3. Recheck the frequency response; it may have changed with the adjustment of the envelope delay. If necessary, re-tune the board.

7.2.12.5 IF Carrier Oven Oscillator Board

To align this board:

1. While monitoring J3 with a spectrum analyzer, observe the 45.75-MHz visual IF

(typical +5 dBm).

2.

3.

Connect a frequency counter to J3 and adjust C17 for 45.750000 MHz.

Connect a frequency counter to J1 and check for 50 kHz, which is the aural phase lock loop (PLL) reference.

7.2.12.6 Sync Tip Clamp/Modulator Board

3.

4.

5.

To align this board:

1.

Determine if jumper W4 on jack J3 is present. Jumper W4 terminates the video input into 75 Ω . Remove jumper W4 if a video loop-through is required on the rear chassis at jacks J1 and J2.

2. Set the controls R20, the white clip, R24, the sync clip, and R45, the sync stretch cut-in, to their full CCW position. Set R48, the sync magnitude, fully CW and place the jumper W7 on jack J4 to the Clamp-Off, Disable, position.

Connect a 5-step staircase video test signal to the input of the transmitter.

Monitor TP2 with an oscilloscope. Adjust R12, the video gain pot, for 1 Vpk-pk.

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.

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6.

Monitor TP2 with an oscilloscope. Adjust pot R41, manual offset, for a blanking level of -0.8 VDC. The waveform shown in Figure 7-1 should be observed at this point.

Move jumper W2 on J4 to the Clamp Enable position. Adjust pot R152, depth of modulation, for a blanking level of -0.8 VDC.

Note: This waveform represents the theoretical level for proper modulation depth. Step 9 below describes how to set the modulation depth through the use of a television demodulator or a zero-spanned spectrum analyzer tuned to the visual IF frequency.

8.

7.

9.

Figure 7-1. Waveform

The following test setup is for the adjustment of the depth of modulation and ICPM at IF:

A. Remove the cable that is on J18 and connect the double-sideband, 45.75-MHz visual IF signal from J18 to a 10-dB splitter/coupler. Connect the coupled port of the splitter/coupler to the RF input of a television demodulator. Connect the direct port to a spectrum analyzer.

B.

Connect the 75Ω video output of the demodulator to the video input of a waveform monitor. For ICPM measurements, also connect the quadrature output of the demodulator to the horizontal input of the waveform monitor using a

250-kHz, low-pass filter. (An oscilloscope can be used in place of a waveform monitor).

C. Set the controls of the demodulator to the following:

Detector mode – Cont

Sound trap – In

Zero carrier – On

Auto – Sync

Audio source – Split

De-emphasis – In

Move jumper W7 on J4 to the Clamp Disable position. Readjust pot R41, 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.

Check the demodulated video for a proper sync-to-video ratio (sync is 28.6% of the

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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. Readjust R41, manual offset, if needed, for the correct depth of modulation.

10. Move jumper W7 on J4 to the Clamp Enable position. Readjust pot R152, depth of modulation, for the correct depth of modulation.

11. Set the waveform monitor to display ICPM. Preset R53 fully CCW, adjust C78 for the greatest effect at white on the ICPM display, and then adjust R53 for minimum ICPM.

12. Recheck the depth of modulation and, if necessary, adjust R152, depth of modulation.

13. On a spectrum analyzer, adjust pot R70 for a level of approximately -10 dBm at J18.

14. Remove the input video test signal. Place the front panel meter in the video position and, while monitoring the meter, tune pot R144, zero adjust, for a reading of zero.

15. Replace the input video test signal (the 5-step staircase). Turn the front panel meter to the video position and adjust R20 on the transmitter control board for a reading of 1 volt (10 on the 0 to 10 scale). This board does not have sync metering.

16.

Reconnect the plug to J18 and move the spectrum analyzer test cable to the 41.25

IF output jack J16. Tune C59 and L17 to L20 to maximize the 41.25-MHz aural IF signal and minimize the out-of-band products. Adjust pot R97 for -20 dBm at J16.

17. Reconnect the plug to J16 and move the spectrum analyzer test cable to IF output jack J20. Preset R62, the visual IF gain pot, to the middle of the range. Insert a multiburst test signal into the transmitter and observe the visual frequency response with the spectrum analyzer set at 1 dB/division. Tune R63 and C30, the IF frequency response adjustments, for a flat-frequency response (±0.5 dB).

18. While still monitoring J20 with a spectrum analyzer, readjust R62, visual IF gain, for a 0 dBm visual output level. Adjust R85, A/V ratio, for a minus 10 dB aural-to-visual ratio or to the desired A/V ratio. Reconnect the plug to J20.

19. Using an input video test signal (the 5-step staircase) with a 100 IRE white level, monitor TP2 with an oscilloscope. Set control R24, the sync clip, just below the point where sync clipping begins to occur. Similarly, set R20, the white clip, to just below the point at which the white video begins to clip.

7.2.12.7 Aural IF Synthesizer Board, 4.5 MHz

1. To set up the test equipment for this board:

A.

Connect the 600Ω balanced audio output from an audio oscillator to the balanced audio input terminals of the tray at TB1-1 (+), TB1-2 (-), and TB1-3

(ground) on the rear chassis.

B. Connect the combined IF output at J21 (IF sample) on the clamp modulator board to the input of an IF splitter. Connect one output of the splitter to the

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video demodulator and the other output to the spectrum analyzer.

C. At the front of the demodulator, connect a short cable from the RF-out jack to the IF-in jack.

D. Connect a cable from the 600Ω audio output jack of the demodulator to the input of an audio distortion analyzer.

2. Set the output frequency of the audio oscillator to 400 Hz and the output level to

+10 dBm.

3. Center the aural carrier on the spectrum analyzer with the spectrum analyzer set to the following:

Frequency/Division – 10 kHz

Resolution bandwidth – 3 kHz

Time/Division – 50 msec

Trigger – Free run

A. Adjust L5 for approximately +3.5 VDC at TP2.

B. The green LED DS1 should be illuminated, indicating a locked condition. If not, re-tune L5 for a locked condition.

4. Adjust R13, balanced audio gain, on the aural IF synthesizer board for a ±25-kHz deviation.

5.

6.

Check the distortion on the aural distortion analyzer (THD=< 0.5%).

Disconnect the 600Ω balanced audio input to the tray. Connect a 75Ω stereo audio input (400 Hz at 1 Vpk-pk) to composite audio input jack J3 on the rear of the tray.

Follow the procedures in the stereo generator instruction manual for matching the level of the generator to the exciter. Use R17 to adjust the composite audio gain.

7. Check the distortion level on the distortion analyzer (THD=< 0.5%)

7.2.12.8 ALC Board (Part 1 of 2)

Table 7-2 describes the functions of each LED on (A8) the ALC board.

Table 7-2. ALC Board LEDs

LED FUNCTION

DS1 (Red LED)

Indicates that an abnormally low IF signal level is present at IF input connector J1

DS2 (Red LED)

Indicates that the ALC circuit is unable to maintain the level requested by the ALC reference due to excessive attenuation in the linearity or the IF phase corrector signal path or because jumper W3 on J6 is in manual gain

DS3 (Red LED)

DS4 (Red LED)

Indicates a video loss fault

Indicates that a Mute command is present

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DS5 (Green LED)

Indicates that the output from the modulator is selected as the input to the board

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1.

To align the ALC board, preset the following controls on the tray:

A. ALC Board (1265-1305)

Connect jumper W1 on J4 to Disable, between pins 2 and 3 (to disable linearity correctors). Connect jumper W3 on J6 to Manual, between pins 2 and 3 (for manual gain control).

Adjust R87, the manual gain pot, to mid-range.

B. IF Phase Corrector Board (1227-1250)

Move W2 on J9 to Phase Correction: Enable. Move W3 on J10 to Amplitude

Correction: Disable.

2.

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 look to see if DS1, the Input

Fault LED, is illuminated. Reconnect J32 and make sure that DS1 is extinguished.

3. Jumper W3 on J6 should be in the Manual position. Monitor jack J3 with a spectrum analyzer.

4. With a multiburst video signal present, tune C4 for a flat-frequency response of

±0.5 dB.

5. Before proceeding with the second part of the ALC board alignment, check to see that the IF phase corrector board (1227-1250) is functioning properly.

7.2.12.9 IF Phase Corrector Board

2.

3.

4.

See Section 7.2.4 of this chapter for the system alignment procedures for the IF phase corrector board. The signal level into the board should be approximately the same as the output of the board.

The IF input jack of the IF phase corrector board is fed from J3, the IF O/P jack of (A8) the

ALC board. The IF output jack of the IF phase corrector board is fed to J7, the IF I/P jack of (A8) the ALC board.

7.2.12.10 ALC Board, NTSC (Part 2 of 2)

To align this board:

1.

Input a multiburst video test signal. Connect a spectrum analyzer to J11. Tune C63 for a flat-frequency response of ±0.5 dB.

Move the Operate/Standby switch on the front panel to the Operate position.

Place jumper W3 on jack J6 in the Manual mode and adjust R87 for 0.5 volts at TP4.

Place jumper W3 on J6 in the Auto mode and adjust the front panel power adjust control A20 fully CW. If the (optional) remote power raise/lower kit is present, then adjust switch S1 on the board to maximum voltage at TP4. Adjust R74, the range adjust, for 1 volt at TP4.

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5. Tune front panel power adjust control A20 for 0.5 VDC at TP4. If the (optional) remote power raise/lower kit is present, move switch S1 on the board to mid-range and then tune (A20) the front panel power adjust control for 0.8 VDC at TP4.

6. Disconnect the plug that is on J12, the IF output, and monitor J12 with a spectrum analyzer. Verify an output of approximately 0 dBm. If necessary, adjust R99 to increase the output level. If less of an output level is needed, move jumpers J27 and

J28 to pins 2 and 3 and then adjust R99. Reconnect J12.

7. Move W2 on J5 to the Cutback Enable position. Remove the input video signal and verify that the output of the transmitter drops to 25%. Adjust R71, the cutback level, if necessary. Restore the input video.

Caution: The following step affects the response of the entire transmitter.

8.

Connect a video sweep signal to the input of the tray. Monitor the output of the system with a spectrum analyzer. Adjust C71 with R103 and C72 with R106, as needed, to flatten the response. C71 and C72 are used to adjust the frequency of the correction notch that is being applied to the visual response of the transmitter. R103 and R106 are used to adjust the depth and width of the correction notch.

9. Refer to Section 7.2.5 of this chapter for the system alignment procedures for the linearity correctors. Controls R13, R18, and R23, the magnitude controls, should be set fully CW. Controls R34, R37, and R40 are the linearity cut-in adjustments.

7.2.12.11 Channel Oscillator Board, Dual Oven

This board is mounted in (A14) the channel oscillator assembly (1145-1202). To align the board:

1.

Connect the main output of the channel oscillator (J1) to a spectrum analyzer, tuned to the crystal frequency, and peak the tuning capacitors C6 and C18 for maximum output. Tune L2 and L4 for maximum output. The output level should be about +5 dBm. The channel oscillator should maintain an oven temperature of 50° C.

If a spectrum analyzer is not available, connect a digital voltmeter (DVM) to TP1 on the x4 multiplier board. Tune capacitors C6 and C18 for maximum voltage, then also tune L2 and L4 for a maximum voltage output at TP1.

2.

Connect the sample output of the channel oscillator (J2) to a suitable counter and tune C11, coarse adjust, and C9, fine adjust, to the crystal frequency.

Note: Do not re-peak C6, C18, L2, or L4. This may change the output level.

Note: While adjusting C9 and C11 to the crystal frequency, the peak voltage monitored at TP1 of the x4 multiplier board should not decrease. If a decrease does occur, there may be a problem with the crystal. Contact Axcera Field

Support for further instructions.

Note: If the VCXO board (1145-1204) in the VCXO assembly (1145-1206) is used, the fine-frequency adjust C9 is not located on the VCXO board. Use R9 on the FSK with EEPROM board.

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3. Reconnect the main output (J1) of the channel oscillator to the input (J1) of the x2 multiplier.

7.2.12.12 FSK Identifier Board with EEPROM

The FSK identifier board with EEPROM generates a Morse code identification call sign by controlling the shifting of the amplitude of the aural carrier in the exciter tray. This gives the station a means of automatically repeating its identification call sign at a given time interval to meet FCC requirements.

The starting circuit is made up of U1B and U1D, which are connected as a flip-flop, with gate U1A used as the set. U1A automatically starts the flip-flop each time U3 completes its timing cycle. At the start of a cycle, U1B enables clock U2. U2 applies the clock pulses that set the speed, which is adjusted by R2, and the identification code is sent to 12-bit binary counter U4. R2 fully CW is the fastest pulse train and R2 fully CCW is the slowest pulse train. U4 provides binary outputs that address EEPROM U5.

The data output of U5, which is serial, is connected to U6A, whose output shifts low and high. This output is applied to the IF attenuator board, which shifts the amplitude of the aural carrier according to the programming of U5.

7.2.12.13 IF Attenuator Board

The IF attenuator board is operated with the FSK identifier board to produce an amplitudemodulated aural IF signal for broadcasting the required FCC station identification call sign at the proper time intervals.

The board contains a PIN attenuation circuit consisting of CR1 and the two resistors R2 and R3. The bias output of the FSK identifier board is applied to J3 of the IF attenuator board. As the bias applied to J3 increases and decreases, the amplitude of the aural IF signal that enters the board at J1 and exits at J2 will increase and decrease. This produces an amplitude-modulated IF signal at J2, the aural IF output jack of the board.

7.2.12.14 x2 Multiplier Board

While monitoring the board with a DC voltmeter, maximize each test point voltage by tuning the broadband multipliers in the following sequence:

1. Monitor TP1 with a DVM and tune C4 for maximum voltage. Monitor TP2 with a

DVM and tune C6 for maximum voltage. Repeak C4 and C6 for maximum voltage.

2. Connect a spectrum analyzer, tuned to two times the crystal frequency, to the x2 multiplier output jack J2. While trying to keep the out-of-band products to a minimum, monitor the output and peak the tuning capacitors for maximum output.

The output of the x2 multiplier (+15dBm) connects to (A11-A1) the filter/mixer board.

7.2.12.15 VHF Filter/Mixer Board

Typically a +15dBm RF input at J3, a 0dBm combined IF input at J7, and a RF output of

0dBm at J2.

To align the board:

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1. Monitor J4, the LO output of the board, with a spectrum analyzer and adjust C12 and C18 for maximum output (+14 dBm) at the LO frequency and minimum outof-band products. Adjust C13 and C17 for the best frequency response for the LO frequency.

2. Adjust C3 and C6 to determine the center frequency. Use C2 and C7 to locate the upper and lower channel-edge shaping. C4 is used to determine the channel bandwidth.

7.2.12.16 Low-Band VHF Filter/Amplifier Board

The filter/amplifier board has been factory swept and adjusted for a 6-MHz bandwidth.

NOTE: This board should not be tuned without the proper equipment.

The output of the filter/mixer board connects to the board at J7 (0dBm). It is filtered on the board with the filtered output connecting to J1 on the board that is amplified by U1 to a nominal +12 dBm visual and +2 dBm aural level set by adjusting R9. The output at J2 is fed to J4 on the A11 enclosure and from there to J15 the RF output jack on the rear of the tray.

To align the board, use a multiburst or sweep video signal inserted into the exciter tray.

Check that there is a cable connected from J6 to J1 on the filter/amplifier board.

Monitor J2, the RF output of the board, and peak C17 for the maximum signal level.

Tune the manual gain adjust R9 for a +12 dBm peak visual output.

This completes the detailed alignment procedure for the VHF Exciter Tray, the VHF L.B.

Amplifier Tray, and also the detailed alignment procedures for the entire 335B transmitter.

If a problem occurred during the alignment procedure, please call Axcera field support at

724-873-8100 for assistance.

This completes the tune-up procedures for the 335B transmitter.

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