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SRK Electronics MFTX100 Скачать руководство пользователя страница 64

MFTX AM TRANSMITTERS

SRK Electronics

64

14. Circuit description

14.1 Theory of operation

The MFTX range of transmitters uses a unique phase-to-amplitude modulation
technique to implement AM. All models follow the general scheme described
below.

As can be seen from the diagram above, there is no modulation stage.  Instead
the RF amplifiers are fed with 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 are 1, 2, 4 and 6 amplifiers in the
MFTX50/100, 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 (36V for MFTX50).  Appropriate
capacitive storage is included on the DC supply to allow extended periods of
+125% positive modulation.

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Содержание MFTX100

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

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

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

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

Страница 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...

Страница 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...

Страница 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...

Страница 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...

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

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

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

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

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Страница 91: ...MFTX AM TRANSMITTERS SRK Electronics 91...

Страница 92: ...MFTX AM TRANSMITTERS SRK Electronics 92...

Страница 93: ...MFTX AM TRANSMITTERS SRK Electronics 93...

Страница 94: ...MFTX AM TRANSMITTERS SRK Electronics 94...

Страница 95: ...MFTX AM TRANSMITTERS SRK Electronics 95...

Страница 96: ...MFTX AM TRANSMITTERS SRK Electronics 96...

Страница 97: ...MFTX AM TRANSMITTERS SRK Electronics 97...

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

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

Страница 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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