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SRK Electronics MFTX100 Operation And Service Manual Download Page 100

MFTX AM TRANSMITTERS 

SRK Electronics 

 

 

 

 

100

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 

1.05 

16/5/19 

Added MFTX50 specifications 

 

Summary of Contents for MFTX100

Page 1: ...FTX50 MFTX100 MFTX200 MFTX400 MFTX600 50W 100W 200W 400W 600W MF AM BROADCAST TRANSMITTER Operation and service manual Manual version 1 05 Issued 16 September 2019 This manual covers all units from se...

Page 2: ...L 23 7 2 1 1 Right mono audio input connector 23 7 2 2 2 Left audio input 23 7 2 3 3 RF output connector 23 7 2 4 4 Mains input connector 23 7 2 5 5 Earth stud 23 7 2 6 6 Air vent 23 7 2 7 7 Analogue...

Page 3: ...PF MENU 40 9 5 1 Setting filter type 40 9 5 2 Setting cutoff frequency 40 9 6 RF PA1 RF PA6 41 9 7 ALARMS 42 9 8 DATE TIME MENU 43 9 8 1 Reading elapsed days 43 9 8 2 Setting date and time 43 9 9 NIGH...

Page 4: ...MFTX400 block diagram 68 14 2 4 MFTX600 block diagram 69 14 3 CONTROL UNIT 70 14 4 RF POWER AMPLIFIER 72 14 5 OUTPUT FILTER 73 15 ABBREVIATIONS 74 16 BILL OF MATERIALS 76 16 1 MFTX50 100 TOP LEVEL 76...

Page 5: ...or three supplies may be included in the power supply MFTX600 only There are three separate mains feeds to the power supply from the transmitter The DC output of the power supply is fed back to the t...

Page 6: ...ging in the mains cord MFTX200 100 or 50 13 All fans should start and the LCD should light showing the summary screen 14 You can now change any settings as desired using the front panel control 15 App...

Page 7: ...600W carrier rest power Power efficient design Pseudo frequency agile Electronically balanced professional audio inputs In built audio processor Over SWR and over temperature protection Loss of audio...

Page 8: ...io signal to noise ratio 60dB Squarewave tilt 40Hz 5 Squarewave overshoot 2 Carrier shift 5 Modulation capability 125 positive peak modulation Audio input impedance 10 000 ohms Audio input connectors...

Page 9: ...to noise ratio 60dB Squarewave tilt 40Hz 5 Squarewave overshoot 2 Carrier shift 5 Modulation capability 125 positive peak modulation Audio input impedance 10 000 ohms Audio input connectors XLR 3 pin...

Page 10: ...l to noise ratio 60dB Squarewave tilt 40Hz 5 Squarewave overshoot 2 Carrier shift 5 Modulation capability 125 positive peak modulation Audio input impedance 10 000 ohms Audio input connectors XLR 3 pi...

Page 11: ...signal to noise ratio 60dB Squarewave tilt 40Hz 5 Squarewave overshoot 2 Carrier shift 5 Modulation capability 125 positive peak modulation Audio input impedance 10 000 ohms Audio input connectors XL...

Page 12: ...signal to noise ratio 60dB Squarewave tilt 40Hz 5 Squarewave overshoot 2 Carrier shift 5 Modulation capability 125 positive peak modulation Audio input impedance 10 000 ohms Audio input connectors XLR...

Page 13: ...freight and travel costs SRK warrants that any replacement parts provided to the Customer are newly manufactured and are free from defects in materials and workmanship If the replacement parts are fou...

Page 14: ...receipt by the customer Upon receipt the transmitter should be visually inspected to ensure that no damage has occurred in transit The packing should be stored and used should it be necessary to retu...

Page 15: ...ere 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 The MFTX400 has been designed to be mounted in a standard 19 r...

Page 16: ...el The transmitter must be installed on a flat stable surface The transmitter must be installed in the upright position The transmitter must be installed in a location free from vermin and the ingress...

Page 17: ...al wiring must be carried out in accordance with local laws standards and regulations If power supply voltages regularly fall outside specifications then a voltage regulator must be installed between...

Page 18: ...tenna system and must be connected to the earthing point indicated on the rear of the transmitter The cable used to connect this earth should be as thick as possible with 8 AWG being the smallest size...

Page 19: ...transmitter must be tuned to minimise reflections Whilst the transmitter is designed to withstand high levels of reflection for short periods continually high levels of reflected power will degrade th...

Page 20: ...here 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 ma...

Page 21: ...supply options including multiple redundant switch mode supplies or a linear supply The MFTX600 has capacity for up to three supplies and there is a switched mains supply for each controlled by the ma...

Page 22: ...ect modify and store parameters This is a compound control By rotating clockwise or anticlockwise screens and parameters can be scrolled through Pressing the knob allows the selected parameter to be m...

Page 23: ...s input becomes the left channel input Otherwise this input is not used 7 2 3 3 RF output connector RF is output on this connector normally connected to the antenna via an ATU or combiner network This...

Page 24: ...res Full details can be found in section 10 1 7 2 8 8 Serial remote control connector This is an RS232 port which enables full control and monitoring of the transmitter See section for full details se...

Page 25: ...r via the serial remote control For details on how to do this please consult the relevant section of this manual The functions described in this section are RF functions o Set RF power o Forward and r...

Page 26: ...t the output RF power generated by the transmitter at 0 modulation sometimes referred to as carrier rest Thus under program audio conditions the forward power will be fluctuating but always equal to o...

Page 27: ...n fact under extreme conditions they can read up to 2 5 times the carrier rest value 8 1 3 Carrier frequency The transmitter is partially frequency agile This means that the user can set the carrier f...

Page 28: ...ndalone operation an internal reference is available The internal or external reference can be selected either by the using the front panel settings or via the serial port Should the external referenc...

Page 29: ...tio of carrier power to audio level is entirely determined by the gain setting 8 2 2 Modulation metering The transmitter includes metering of peak positive and negative modulation The peak hold functi...

Page 30: ...KHz 2 6KHz 3 7KHz 2 9KHz 4 1KHz 3 3KHz 4 6KHz 3 8KHz 5 3KHz 4 4KHz 6 2KHz 5 3KHz 7 4KHz 6 6KHz 9 2KHz 8 8KHz It is strongly recommended that this filter be used even if external audio processing is av...

Page 31: ...acitor that will keep time without mains power for up to three weeks Any longer without power will require the time and date to be set when next powered up The clock does not automatically compensate...

Page 32: ...e that the serial remote control function FD allows the control knob to be disabled for non secure applications See section 10 2 for further details The transmitter is a complex piece of equipment wit...

Page 33: ...shows the current modulation depth in percent Freq shows the transmitter s operating frequency in kilohertz TX status shows the overall alarm status If none of the alarms is active then OK is shown If...

Page 34: ...ilst flashing rotating the knob in the clockwise direction will increase the power up to maximum Rotating the knob in the anti clockwise direction decreases the power Once the desired power has been s...

Page 35: ...jacent to and pointing towards RF Momentarily pressing the knob will cause the RF status to flash Whilst flashing rotating the knob in the clockwise direction will turn the RF on Rotating the knob in...

Page 36: ...o 100 Rotating the knob in the anti clockwise direction decreases the gain The gain can be set to any value in the range zero to 100 in 1 increments Once the desired gain has been set the control knob...

Page 37: ...us of the stereo generator is shown next to Stereo Stereo may be turned off or on by rotating the control knob until the flashing arrow is adjacent to and pointing towards Stereo Momentarily pressing...

Page 38: ...y This will ensure that this value is set when the unit is next switched on 9 4 2 Setting the positive limit level The positive limit level can be set by rotating the control knob until the flashing a...

Page 39: ...limit up to 255 Rotating the knob in the anti clockwise direction decreases the limit The negative limit can be set to any value in the range zero to 255 in increments of 1 Once the desired limit has...

Page 40: ...filter type 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...

Page 41: ...itored and appears as follows Only the relevant screens are available depending on the transmitter model Temp shows the internal temperature of the PA Driver volts shows the driver supply voltage PA v...

Page 42: ...s FAIL and RF power will be turned off GEN shows the status of the RF generator module If there is an error with communication with the RF generator then FAIL will appear in this field TEMP shows the...

Page 43: ...nd time The time and date are shown in the format hour minute second day month year The time is always in 24 hour format Pressing the control knob momentarily will allow the time and date to be set Th...

Page 44: ...the knob anticlockwise will disable night time power switching 9 9 2 Setting night time power start and stop times Pressing the knob will cause the From hour to start flashing The start and stop time...

Page 45: ...the control knob will cause the Internal or External field to flash Rotating the knob clockwise will set the carrier reference to internal Rotating the knob anticlockwise will set the carrier referenc...

Page 46: ...MFTX AM TRANSMITTERS SRK Electronics 46 9 11Unit data The unit data screen gives various unit specific parameters...

Page 47: ...ontrol and monitoring The analogue remote control is a very basic analogue interface which allows the transmitter to be turned on off and audio and other alarms to be monitored The serial remote contr...

Page 48: ...isplay 10 1 2 TX OK relay When all alarms are OK except the audio alarm the TX OK terminals are shorted together by a relay contact internal to the transmitter If any alarm becomes active except the a...

Page 49: ...output The alarm tally output is a voltage source that generates an output of between 0V and 7V in 1V increments Each time the alarm tally is incremented this output voltage is incremented At 7V the...

Page 50: ...ically for human interaction machine to machine control can be implemented by using the syntax for each command as described in the relevant section The only additional consideration is time between t...

Page 51: ...wer FR Returns LPF response Butterworth or Bessel FT Returns night power finish time HP Returns a summary of all commands LO Returns location LO Sets location MD Returns the modulation depth ND Disabl...

Page 52: ...ed output power SP Returns the set output power SP Sets set power Audio related commands AC Returns compressor status AC Turns compressor on or off AF Returns LPF status AF Turns LPF on or off AG Retu...

Page 53: ...power start time ST Sets time TD Returns current time and date Alarm related commands BS Returns BITE status RS Resets over SWR alarm RT Resets alarm tally to zero TY Returns alarm tally PA1 PA6 comm...

Page 54: ...ble operation with no user intervention All alarms will recover automatically upon the removal of the cause of the alarm Whilst some alarms will result in the output of the transmitter being turned of...

Page 55: ...r one second then return to the same set power This allows any ionization to be dissipated If another two failures occur within a minute of the first the output power is halved and the process repeats...

Page 56: ...h the analogue remote control interface if the interlock circuit is open the transmitter will reduce its output power to zero As soon as the interlock circuit is closed the transmitter will restore fu...

Page 57: ...MFTX AM TRANSMITTERS SRK Electronics 57 11 3GEN alarm If the RF generator module fails to communicate properly with the main microprocessor the GEN alarm will be triggered...

Page 58: ...ed off until the internal temperature falls to below 70 C whereupon the alarm becomes inactive and full output is restored As no user intervention is needed to clear this alarm if the cause of the ove...

Page 59: ...tive if the modulation depth falls below 3 continuously for more than 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 alternativ...

Page 60: ...ittle routine 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...

Page 61: ...MFTX AM TRANSMITTERS SRK Electronics 61 12 1Example log sheet TBA...

Page 62: ...l at which the transmitter s high SWR protection is tripped Normally set to 10 of the transmitter s rated output 13 3POT3 Reflected power calibration This pot is adjusted so that the measured forward...

Page 63: ...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 8Directional coupler null This adjustment allows the refl...

Page 64: ...h two signals RF and RF whose relative phase is adjusted to produce amplitude modulation RF and RF are used to drive a number of RF amplifiers Each amplifier produces 100W at 0 modulation Thus there a...

Page 65: ...uded in the output filter assembly Audio processing RF generation remote control metering protection and front panel interface is provided by the controller unit Audio is processed in the analogue dom...

Page 66: ...MFTX AM TRANSMITTERS SRK Electronics 66 14 2Block diagrams 14 2 1 MFTX50 100 block diagram...

Page 67: ...MFTX AM TRANSMITTERS SRK Electronics 67 14 2 2 MFTX200 block diagram...

Page 68: ...MFTX AM TRANSMITTERS SRK Electronics 68 14 2 3 MFTX400 block diagram...

Page 69: ...MFTX AM TRANSMITTERS SRK Electronics 69 14 2 4 MFTX600 block diagram...

Page 70: ...well as threshold and compression ratio This microprocessor communicates with the main microprocessor over a two wire I C bus Compressed audio is passed to a peak limiter formed by U8 and U15 The pos...

Page 71: ...easure the forward and reflected power 50VDC and 20V auxiliary supply voltages The forward and reflected voltage samples from the directional coupler within the output filter are precision rectified b...

Page 72: ...p and coupled into the gates of the output transistors by transformers T1 and 2 Gate protection is provided by D1 to 8 The output transistors Q1 4 are configured as a full bridge with the two output...

Page 73: ...relevant schematic for details The harmonic filter also incorporates impedance matching the convert the 50 j0 ohm load impedance to a value suitable to load the RF amplifiers The directional coupler...

Page 74: ...50 for RF or 600 for audio Hz Hertz IDC DC current K Kilo kilo ohm Kg Kilogram KHz Kilohertz LPF Low Pass Filter nF nanofarads m metre milli M Mega mega ohms MF Medium Frequency 300KHz to 3MHz MHz Me...

Page 75: ...MFTX AM TRANSMITTERS SRK Electronics 75 VGA Variable Gain Amplifier VSWR Voltage Standing Wave Ratio W Watt s...

Page 76: ...MFTX AM TRANSMITTERS SRK Electronics 76 16 Bill of materials 16 1MFTX50 100 Top level TBA...

Page 77: ...MFTX AM TRANSMITTERS SRK Electronics 77 16 2MFTX200 Top level TBA...

Page 78: ...MFTX AM TRANSMITTERS SRK Electronics 78 16 3MFTX400 Top level TBA...

Page 79: ...MFTX AM TRANSMITTERS SRK Electronics 79 16 4MFTX600 Top level TBA...

Page 80: ...MFTX AM TRANSMITTERS SRK Electronics 80 16 5Control unit...

Page 81: ...MFTX AM TRANSMITTERS SRK Electronics 81 16 6RF power amplifier TBA...

Page 82: ...MFTX AM TRANSMITTERS SRK Electronics 82 16 7MFTX100 output filter TBA...

Page 83: ...MFTX AM TRANSMITTERS SRK Electronics 83 16 8MFTX200 Output filter TBA...

Page 84: ...MFTX AM TRANSMITTERS SRK Electronics 84 16 9MFTX400 Output filter TBA...

Page 85: ...MFTX AM TRANSMITTERS SRK Electronics 85 16 10MFTX600 Output filter TBA...

Page 86: ...MFTX AM TRANSMITTERS SRK Electronics 86 17 Schematics 17 1MFTX100 Overall Schematic TBA...

Page 87: ...MFTX AM TRANSMITTERS SRK Electronics 87 17 2MFTX200 Overall Schematic TBA...

Page 88: ...MFTX AM TRANSMITTERS SRK Electronics 88 17 3MFTX400 Overall Schematic TBA...

Page 89: ...MFTX AM TRANSMITTERS SRK Electronics 89 17 4MFTX600 Overall Schematic TBA...

Page 90: ...MFTX AM TRANSMITTERS SRK Electronics 90 17 5Control Unit Schematic...

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Page 98: ...MFTX AM TRANSMITTERS SRK Electronics 98 17 6RF Power Amplifier Schematic...

Page 99: ...MFTX AM TRANSMITTERS SRK Electronics 99 18 PCB Layouts TBA...

Page 100: ...ate 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...

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