SRK Electronics MFTX100 Operation And Service Manual
100w/200w/400w/600w mf am broadcast transmitter
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- Page 1 SRK Electronics MFTX100 MFTX200 MFTX400 MFTX600 100W/200W/400W/600W MF AM BROADCAST TRANSMITTER Operation and service manual Manual version 1.04 Issued 6 November 2017 This manual covers all units from serial number 889...
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Page 2: Table Of Contents
..........................28 UDIO UNCTIONS 8.2.1 Gain control .......................... 28 8.2.2 Modulation metering ......................28 8.2.3 Compressor ........................... 28 8.2.4 Limiter ........................... 28 8.2.5 Low Pass Filter ........................29 8.2.6 Stereo ............................ 29 ..........................30 IME FUNCTIONS 8.3.1 Clock............................30 SRK Electronics... - Page 3 ALARMS ............................53 11.1 ....................54 ALARM AND FLASHOVER ALARM 11.2 .......................... 55 NTERLOCK ALARM 11.3 ..........................56 ALARM 11.4 ........................57 EMPERATURE ALARM 11.5 ..........................58 UDIO ALARM MAINTENANCE ..........................59 12.1 ........................60 XAMPLE LOG SHEET SRK Electronics...
- Page 4 CIRCUIT DESCRIPTION ........................63 14.1 ........................63 HEORY OF OPERATION 14.2 ........................... 65 LOCK DIAGRAMS 14.2.1 MFTX100 block diagram ....................... 65 14.2.2 MFTX200 block diagram ....................... 66 14.2.3 MFTX400 block diagram ....................... 67 14.2.4 MFTX600 block diagram ....................... 68 14.3 ..........................
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Page 5: Mftx Quick Start Guide
Once set to the desired value, pressing the knob again will cause the value to be stored in NV RAM and will allow another parameter to be selected. SRK Electronics... - Page 6 Therefore discrepancies between the set power and indicated forward power will almost certainly occur, especially if running into a reflective load. In practice, set power should be adjusted to give the desired forward power. SRK Electronics...
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Page 7: Overview
MFTX AM TRANSMITTERS 2. Overview The MFTX100, MFTX200, MFTX400 and MFTX600 are 100W, 200W, 400W and 600W carrier rest AM transmitters designed for continuous unattended service in MF broadcast applications. Amongst others, the MFTX transmitters have the following features: • 10-100W, 20-200W, 40-400W and 60-600W carrier rest power •... -
Page 8: Specifications
MFTX AM TRANSMITTERS 3. Specifications MFTX100 RF output power (0% mod) 10-100W, settable in 1W steps RF output power (peak) 500W RF output connector N female Harmonics and spurious >-65dBc Factory set frequency range 531-1701KHz User set frequency range within ±3% of factory setting... - Page 9 105-264VAC Supply connector IEC 3 pin male Earth stud Cooling Convection/Forced air Size 3U rack case, 300mm deep Weight <10Kg Ambient temperature -5°C to +50°C Humidity 0 to 95% RH, non-condensing Altitude 0 to 4000m above sea level SRK Electronics...
- Page 10 105-264VAC Supply connector IEC 3 pin male Earth stud Cooling Forced air Size 5U rack case, 450mm deep Weight <15Kg Ambient temperature -5°C to +50°C Humidity 0 to 95% RH, non-condensing Altitude 0 to 4000m above sea level SRK Electronics...
- Page 11 105-264VAC Supply connector IEC 3 pin male Earth stud Cooling Forced air Size 7U rack case, 450mm deep Weight <25Kg Ambient temperature -5°C to +50°C Humidity 0 to 95% RH, non-condensing Altitude 0 to 4000m above sea level SRK Electronics...
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Page 12: Warranty
Customer or by a third party or from damage caused to the equipment by external influences, including, but not limited to lightning strike, power surges or irregularity, ingress of water or other moisture, impact or temperature fluctuations in excess of the tolerances set out in the specifications. SRK Electronics... -
Page 13: Unpacking
The packing should be stored and used should it be necessary to return the transmitter to the manufacturer. The customer should ensure that all items are present and then store them in a safe place. SRK Electronics... -
Page 14: Installation
Departure from the instructions contained herein may void any warranty provided by SRK. The MFTX100 has been designed to be mounted in a standard 19” rack frame, where it will occupy 2 rack units. The MFTX200 has been designed to be mounted in a standard 19” rack frame, where it will occupy 3 rack units. -
Page 15: Environmental
All ventilation orifices must be clear to allow adequate air flow. If installed in a rack, the equipment immediately above or below the transmitter should not overhang the fins of the heatsink on the rear of the transmitter (MFTX100 and 200 only). SRK Electronics... -
Page 16: Electrical Supply
If power supply voltages regularly fall outside specifications then a voltage regulator must be installed between the supply inlet and the transmitter. Whilst the transmitter does include live-neutral mains supply MOV protection, external three way protection is also recommended for long term reliability. SRK Electronics... -
Page 17: Earthing
The earth itself must be of high quality buried copper, at least 1.5m deep and preferably in ground that is habitually humid (eg, the base of a gutter down pipe). SRK Electronics... -
Page 18: Antenna
Whilst the transmitter is designed to withstand high levels of reflection for short periods, continually high levels of reflected power will degrade the long term reliability of the transmitter. Operating SWR should be kept to below 1.9:1. SRK Electronics... -
Page 19: Audio Feed
In situations where the audio feed to the transmitter is over any form of land line, suitable protection must be included external to the transmitter to ensure voltage transients do not enter the transmitter. These may be in the form of high power zener diodes and/or gas discharge tubes. SRK Electronics... -
Page 20: External Power Supply (Mftx600 Only)
(controlled by the main breaker). The nominal 50VDC from the supply is fed back into the transmitter via the blue Anderson connector. Note that this connector must be fully engaged and this may require some force. This is normal. SRK Electronics... -
Page 21: External Views
The output level of this connector is about 5V RMS when driving a 50Ω load and at full power. 7.1.4 (4) Air vents These vents allow convection or forced air cooling of the transmitter and must not be obstructed. SRK Electronics... -
Page 22: Rear Panel
7.2.6 (6) Air vent Allows free air convection cooling of the transmitter (MFTX100 and MFTX200) or forced air (MFTX400 and MFTX600), along with the vents on the front panel. -
Page 23: 7) Analogue Remote Control Barrier Strip
See section for full details see section 10.2. 7.2.9 (9) Heatsink The heatsink is the main form of cooling for the transmitter and should have free space both above and below the fins to allow proper operation. MFTX100 and MFTX200 only SRK Electronics... -
Page 24: Transmitter Operation
Forward and reflected power metering o Carrier frequency o Carrier reference • Audio functions o Gain control o Modulation metering o Compressor o Limiter o Low pass filter o Stereo • Time functions o Clock o Night-time power SRK Electronics... -
Page 25: Rf Functions
Consider the two RF waveforms shown below. The one on the left is a carrier with no modulation. The one on the right is the same carrier with 100% sqaurewave modulation (time scales are exaggerated for the sake of clarity). SRK Electronics... -
Page 26: Carrier Frequency
The carrier can be phase locked to an external reference frequency. This allows multiple transmitters to be phase and frequency locked to minimize interference. The external reference is applied to the EXT REF BNC on the rear of the transmitter and must have the following characteristics: Nominal frequency 10MHz SRK Electronics... - Page 27 Should the external reference be selected, but none connected to the EXT REF BNC, the carrier frequency will drift down to approximately -13 PPM of its nominal value. No damage will occur to the transmitter. SRK Electronics...
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Page 28: Audio Functions
-95% and +125%, but can be changed by the user, or the limiter can be turned off completely. Note that setting the negative limit excessively low, or the positive limit excessively high, will affect the other limit level. SRK Electronics... -
Page 29: Low Pass Filter
All other audio processing settings are applied to both left and right audio channels. The stereo function can only be turned on if the optional board is fitted. This board can be retrofitted in the field with no additional modifications. SRK Electronics... -
Page 30: Time Functions
8.3.2 Night-time power If enabled, the transmitter can be programmed to automatically switch to a different set power during the hours of darkness. In this way it is possible to limit co-channel interference at night due to sky wave propagation. SRK Electronics... -
Page 31: Front Panel Operation
The following sections detail the meaning and use of each screen or menu and are listed in the order they are displayed when rotating the control knob in the clockwise direction. Rotating the knob in the anticlockwise direction causes the screens to appear in the reverse order. SRK Electronics... -
Page 32: Summary Screen
AUDIO is shown (depending on which alarm is active). If more than one alarm is active then FAIL is shown. See section 11 for more details about individual alarms. The summary screen is shown when the transmitter is first switched on. No parameters can be changed whilst displaying the summary screen. SRK Electronics... -
Page 33: Rf Menu
The range of frequencies that can be selected is dependent upon factory settings and would have been specified when the transmitter was first purchased. However, all frequencies are in multiples of 9KHz or 10KHz, depending on factory settings. SRK Electronics... -
Page 34: Turning Rf On And Off
This will ensure that this value is set when the unit is next switched on. 9.2.4 Reading forward and reflected power The forward and reflected power are available at “Fwd Pwr=” and “Ref Pwr=” respectively SRK Electronics... -
Page 35: Audio Menu
The status of the audio low pass filter is shown next to “LPF=”. The LPF may be turned off or on by rotating the control knob until the flashing arrow is adjacent to and pointing towards “LPF=”. Momentarily pressing the knob SRK Electronics... -
Page 36: Enabling And Disabling Audio Compressor
Note that stereo can only be turned on if the optional stereo card is fitted to the control unit. If the stereo card is not fitted then pressing the knob whilst the arrow is next to “Stereo=” will have no effect. SRK Electronics... -
Page 37: Limiter Menu
The positive limit is calibrated in arbitrary units in the range 0 to 255. Care should exercised when setting the positive limit as an excessively high value can effect negative peaks. SRK Electronics... -
Page 38: Setting The Negative Limit Level
The negative limit is calibrated in arbitrary units in the range 0 to 255. Care should exercised when setting the negative limit as an excessively low value can effect positive peaks. SRK Electronics... -
Page 39: Lpf Menu
Once the cutoff frequency has been set, the control knob should be momentarily pressed once more to ensure the new value is stored in memory. This will ensure that this value is set when the unit is next switched on. SRK Electronics... -
Page 40: Rf Pa1 - Rf Pa6
“Temp=” shows the internal temperature of the PA. “Driver volts=” shows the driver supply voltage. “PA voltage=” shows the DC supply voltage for the PA. “PA Current=” shows the DC current drawn from the main power supply by the SRK Electronics... -
Page 41: Alarms
“AUDIO OK” relay contact of the analogue remote control interface will go open. This can be used to reset the program source or select an alternative. “F’OVR=” show the status of the internal flashover detector. If an internal flashover occurs then “FAIL” will show in this field. SRK Electronics... -
Page 42: Date/Time Menu
The second, day, month and year are set in the same way and in that order. A final press of the knob once the year has been set causes the clock to be programmed with the set time and date. SRK Electronics... -
Page 43: Night Power Menu
“to” times, the output power will immediately be set to the night-time power. Note that it is not necessary for the night-time power to be lower than the set power, or for the “from” and “to” times to be in the evening and morning respectively. SRK Electronics... -
Page 44: Carrier Reference
Once the reference has been set, the control knob should be momentarily pressed once more to ensure the new value is stored in memory. This will ensure that this value is set when the unit is next switched on. SRK Electronics... -
Page 45: Unit Data
MFTX AM TRANSMITTERS 9.11 Unit data The unit data screen gives various unit specific parameters. SRK Electronics... -
Page 46: Remote Control
The serial remote control is a sophisticated RS232 based interface that allows all parameters and controls to be accessed. SRK Electronics... -
Page 47: Analogue Remote Control
The differential voltage on this contact should be limited to 120VAC or 24VDC and the current should be less than 0.5A AC or DC. Both terminals are galvanically isolated from all other circuitry within the transmitter, but the common SRK Electronics... -
Page 48: Alarm Tally Output
0V and 7V, in 1V increments. Each time the alarm tally is incremented, this output voltage is incremented. At 7V, the output returns to 0V upon the next alarm. The output resistance of this voltage is 100Ω. No external voltage should be injected in to this output. SRK Electronics... -
Page 49: Serial Remote Control
“>” character before starting to send a new command to avoid losing command characters. 10.2.1 Serial command list (alphabetical) Below is a list of all serial commands in alphabetical order. For more information regarding any particular command please consult the relevant section that follows. Command Description SRK Electronics... - Page 50 Sets positive limit value Returns front panel status Returns the RF on/off status Returns the reflected output power Resets over SWR alarm Resets alarm tally to zero Sets date Returns stereo generator status Turns stereo generator on or off SRK Electronics...
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Page 51: Serial Command List (By Function)
Returns negative limit value Sets negative limit value Returns positive limit value Sets positive limit value Returns stereo generator status Turns stereo generator on or off Toggles LPF response between Butterworth and Bessel Time and night power related commands SRK Electronics... - Page 52 AT1? Returns PA1 temperature Returns PA voltage Unit related commands Returns elapsed days Disable front panel Enable front panel Returns location Sets location Returns front panel status Returns serial number Miscellaneous commands Returns a summary of all commands SRK Electronics...
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Page 53: Alarms
Whilst some alarms will result in the output of the transmitter being turned off or reduced, the output will return to normal once the alarm in question becomes inactive. The individual alarms are as follows: SRK Electronics... -
Page 54: Swr Alarm And Flashover Alarm
The level of reflected power needed to trigger a high SWR alarm is factory set to 10W, 20W, 40W and 60W for the MFTX100, 200, 400 and 600 respectively. This is an absolute value and is independent of actual output power set. This allows larger transmitters to have a greater tolerance to reflected power, even if run at a much lower power. -
Page 55: Interlock Alarm
As soon as the interlock circuit is closed the transmitter will restore full output. This alarm may be used for an external emergency shutdown, or for hot standby applications. SRK Electronics... -
Page 56: Gen Alarm
MFTX AM TRANSMITTERS 11.3 GEN alarm If the RF generator module fails to communicate properly with the main microprocessor the GEN alarm will be triggered. SRK Electronics... -
Page 57: Temperature Alarm
As no user intervention is needed to clear this alarm, if the cause of the over temperature is still present then the transmitter will cycle in and out of this alarm condition indefinitely. Operation of this alarm generally indicates inadequate ventilation or inappropriate installation. SRK Electronics... -
Page 58: Audio Alarm
30 seconds. This alarm is used to detect a loss of external audio and may be used to reset the audio source or select an alternative source. The audio alarm is deactivated immediately the modulation depth exceeds 2%. SRK Electronics... -
Page 59: Maintenance
The heatsink and ventilation grills should be regularly inspected and cleaned if necessary. Any air filters should be removed and cleaned as needed. It is also good practice to log all parameters on a monthly basis to allow changes in operating conditions to be identified. SRK Electronics... -
Page 60: Example Log Sheet
MFTX AM TRANSMITTERS 12.1 Example log sheet SRK Electronics... -
Page 61: Adjustments
Allows the contrast of the LCD on the front panel to be adjusted. 13.6 POT6, alarm tally analogue voltage trim This pot allows the analogue voltage of the alarm tally on the analogue remote control interface to be adjusted to exactly 1.00V per alarm. SRK Electronics... -
Page 62: Dc Supply Adjustment
The output of the DC supply is nominally 50V. Hover, it can be adjusted up or down to make the carrier rest power of the transmitter correct. 13.8 Directional coupler null This adjustment allows the reflected power to be set to zero when driving a non- reflective load. SRK Electronics... -
Page 63: Circuit Description
100W at 0% modulation. Thus there are 1, 2, 4 and 6 amplifiers in the MFTX100, MFTX200, MFTX400 and MFTX600 respectively. The DC supply to the RF amplifiers is derived from a self contained switch mode power supply that generates a nominal voltage of 50V. - Page 64 The output of the RF generator consists of two squarewaves at the carrier frequency (RF+ and RF-). The relative phase of these squarewaves sets the instantaneous RF voltage at the output of the transmitter. SRK Electronics...
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Page 65: Block Diagrams
MFTX AM TRANSMITTERS 14.2 Block diagrams 14.2.1 MFTX100 block diagram SRK Electronics... -
Page 66: Mftx200 Block Diagram
MFTX AM TRANSMITTERS 14.2.2 MFTX200 block diagram SRK Electronics... -
Page 67: Mftx400 Block Diagram
MFTX AM TRANSMITTERS 14.2.3 MFTX400 block diagram SRK Electronics... -
Page 68: Mftx600 Block Diagram
MFTX AM TRANSMITTERS 14.2.4 MFTX600 block diagram SRK Electronics... -
Page 69: Control Unit
The RF generator module is a sealed unit that contains advanced digital processing that directly converts the processed audio into two carrier waves (RF+ and RF-) of variable phase difference. RF drive to the RF amplifiers is taken directly from the RF generator module. SRK Electronics... - Page 70 Analogue remote control as well as PSU control (where implemented) is performed the main microprocessor via the IO expander, U40. The main microprocessor (U24) controls all functions of the transmitter, either directly or indirectly. Serial communications via the telemetry port is level shifted by U21. SRK Electronics...
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Page 71: Rf Power Amplifier
The DC supply is also fused to prevent serious damage if one or more of the output transistors fails. This fuse is shunted by a resistor/LED combination to indicate fuse failure. Temperature measurement is provided by U3. This signal is passed to the control unit for monitoring and protection. SRK Electronics... -
Page 72: Output Filter
This ensures high directivity and a flat frequency response. The spark gap for the MFTX100 is a gas discharge tube of suitable voltage rating. For all other models it is an adjustable stainless steel ball gap. -
Page 73: Abbreviations
Pulse Duration Modulation (aka PWM) picofarads Parts Per Million Pulse Width Modulation (aka PDM) Ohms Radio Frequency Relative Humidity Root-Mean-Square Real Time Clock Standing Wave Ratio Total Harmonic Distortion Transmitter Rack unit, 1.75” Microfarad Microsecond Volt(s) or voltage AC voltage DC voltage SRK Electronics... - Page 74 MFTX AM TRANSMITTERS Variable Gain Amplifier VSWR Voltage Standing Wave Ratio Watt(s) SRK Electronics...
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Page 75: Bill Of Materials
MFTX AM TRANSMITTERS 16. Bill of materials 16.1 MFTX100 Top level SRK Electronics... -
Page 76: Mftx200 Top Level
MFTX AM TRANSMITTERS 16.2 MFTX200 Top level SRK Electronics... -
Page 77: Mftx400 Top Level
MFTX AM TRANSMITTERS 16.3 MFTX400 Top level SRK Electronics... -
Page 78: Mftx600 Top Level
MFTX AM TRANSMITTERS 16.4 MFTX600 Top level SRK Electronics... -
Page 79: Control Unit
MFTX AM TRANSMITTERS 16.5 Control unit SRK Electronics... -
Page 80: Rf Power Amplifier
MFTX AM TRANSMITTERS 16.6 RF power amplifier SRK Electronics... -
Page 81: Mftx100 Output Filter
MFTX AM TRANSMITTERS 16.7 MFTX100 output filter SRK Electronics... -
Page 82: Mftx200 Output Filter
MFTX AM TRANSMITTERS 16.8 MFTX200 Output filter SRK Electronics... -
Page 83: Mftx400 Output Filter
MFTX AM TRANSMITTERS 16.9 MFTX400 Output filter SRK Electronics... -
Page 84: Mftx600 Output Filter
MFTX AM TRANSMITTERS 16.10 MFTX600 Output filter SRK Electronics... -
Page 85: Schematics
MFTX AM TRANSMITTERS 17. Schematics 17.1 MFTX100 Overall Schematic SRK Electronics... -
Page 86: Mftx200 Overall Schematic
MFTX AM TRANSMITTERS 17.2 MFTX200 Overall Schematic SRK Electronics... -
Page 87: Mftx400 Overall Schematic
MFTX AM TRANSMITTERS 17.3 MFTX400 Overall Schematic SRK Electronics... -
Page 88: Mftx600 Overall Schematic
MFTX AM TRANSMITTERS 17.4 MFTX600 Overall Schematic SRK Electronics... -
Page 89: Control Unit Schematic
MFTX AM TRANSMITTERS 17.5 Control Unit Schematic SRK Electronics... - Page 90 MFTX AM TRANSMITTERS SRK Electronics...
- Page 91 MFTX AM TRANSMITTERS SRK Electronics...
- Page 92 MFTX AM TRANSMITTERS SRK Electronics...
- Page 93 MFTX AM TRANSMITTERS SRK Electronics...
- Page 94 MFTX AM TRANSMITTERS SRK Electronics...
- Page 95 MFTX AM TRANSMITTERS SRK Electronics...
- Page 96 MFTX AM TRANSMITTERS SRK Electronics...
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Page 97: Rf Power Amplifier Schematic
MFTX AM TRANSMITTERS 17.6 RF Power Amplifier Schematic SRK Electronics... -
Page 98: Pcb Layouts
MFTX AM TRANSMITTERS 18. PCB Layouts SRK Electronics... -
Page 99: Change History
19. Change History Version No. Release Date Description of change(s) 1.00 28/8/16 First issue 1.01 5/5/17 Various additions 1.02 8/5/17 Added theory of operation. Fixed typos 1.03 19/10/17 Added block diagrams, schematics and adjustments 1.04 6/11/17 Updated specifications section SRK Electronics...
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