Larcan FM-250 Technical Manual Download Page 7

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FM-250 FM BROADCASTING EXCITER

Issue Date: 21 Jan 2003

Summary of Contents for FM-250

Page 1: ...ssue Date 21 Jan 2003 FM 250 250W STEREO TRANSMITTER EXCITER TECHNICAL MANUAL LARCAN Denver Office LARCAN TTC 1390 Overlook Drive 2 Lafayette CO 80026 USA Tel 303 665 8000 Fax 303 763 9900 E Mail sales earthnet net Web www larcan com ...

Page 2: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 NOTE AMENDMENT Please take note that any reference to 230V and 50Hz in this manual should be read as 110V and 60Hz respectively ...

Page 3: ...ONTENTS 1 General Description 2 Technical Specifications 3 Operating Information 4 Installation Information 5 Technical Information 6 Maintenance information LARCAN Denver Office LARCAN TTC 1390 Overlook Drive 2 Lafayette CO 80026 USA Tel 303 665 8000 Fax 303 763 9900 E Mail sales earthnet net Web www larcan com ...

Page 4: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...

Page 5: ...M Broadcasting band 87 5MHz to 108MHz The unit is housed in a 19 inch rack mount case occupying only a 2U space The Exciter features a range of customer options including a built in high quality Stereo coder 2 The FM 250 Exciter offers a standard specification better than the general requirements of the major broadcasters in the world This level of performance is only found in the best equipment t...

Page 6: ...21 Jan 2003 FM 250 250W STEREO TRANSMITTER EXCITER TECHNICAL MANUAL General Description LARCAN Denver Office LARCAN TTC 1390 Overlook Drive 2 Lafayette CO 80026 USA Tel 303 665 8000 Fax 303 763 9900 E Mail sales earthnet net Web www larcan com ...

Page 7: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...

Page 8: ...onal g Fan Psu module 980518 2 FEATURES The FM 250 Exciter has standard features including the following a Remote Internal frequency selection standard with Thumbwheel switch option available b Remote telemetry with voltage free contacts standard c 48V Battery operation standard d Wideband input MPX with two auxiliary inputs SST SCA RDS e Comprehensive metering including VU meters Built in Stereo ...

Page 9: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 Refer to the Front panel layout in figure 1 Rear panel controls and connectors in figure2 and the Block diagram of FM 250 in Figure 3 ...

Page 10: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 Figure 1 FM 250 Front Panel Controls ...

Page 11: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 Figure 2 FM 250 Rear Panel Controls and Connectors ...

Page 12: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...

Page 13: ...EL D 25 PL7 DEVIATION ADJ OPTIONAL PL3 PSU PL4 PL5 THUMBWHEEL OPTION PSU PCB 980508 PL1 OV SK1 ALC TEMP CNTRL FWD REFL PL3 PL1 PL2 SK1 SK2 PL1 PL2 PL3 DISPLAY PCB 980509 26 way ribbon cable PL6 20 LED MULTIMETER STEREO VU METER PILOT INDICATOR FAULT INDICATORS FUNCTIONAL INDICATORS DEVIATION ADJ OPTIONAL RF POWER ADJ RS485 OPTIONAL REAR PANEL PL1 PL8 500VA TRANSFORMER RF MONITOR FRONT PANEL BNC OV...

Page 14: ...ratings Wideband techniques are used throughout the PA and a built in harmonic filter is used at the output to suppress all harmonics Directional couplers are used to sample the output for control and monitoring purposes A temperature sensing device is provided for thermal monitoring This device is situated at the final RF Stage to provide accurate temperature monitoring of the RF PA Heatsink Curr...

Page 15: ...vides instant viewing of Transmitter deviation from Left and Right channels The Stereo pilot indication is also provided with the meter Alarm indications are provided by Front panel LED s enabling instant viewing of transmitter functions Front panel adjustments are available for control of RF Output power and Deviation level Connection for the optional RS485 Module is provided on the Display enabl...

Page 16: ...tor for the RS485 module h MONO FILTER optional The Mono filter option provides the user with a XLR F 600 ohm balanced input and 15kHz low pass filter with an internal output connection to the Synthesizer and modulator Pre emphasis switching 50uS or 75uS is provided on board and is switched via the Pre emphasis switch on the back panel An Audio Limiter is supplied as standard issue with internally...

Page 17: ... 21 Jan 2003 250W STEREO TRANSMITTER EXCITER TECHNICAL MANUAL Technical Specifications LARCAN Denver Office LARCAN TTC 1390 Overlook Drive 2 Lafayette CO 80026 USA Tel 303 665 8000 Fax 303 763 9900 E Mail sales earthnet net Web www larcan com ...

Page 18: ...ONSE 0 2dB 30Hz to 100kHz STEREO SEPARATION 60dB 30Hz to 15kHz STEREO DISTORTION 0 1 30Hz to 15kHz WIDEBAND S N RATIO 80dB 20Hz to 20kHz 50uS de emph INPUT IMPEDANCE 1k2 ohms balanced other on request DEVIATION SENSITIVITY 3 5V p p for 75kHz deviation adj STEREO OPERATION With built in Stereo coder Limiter AF RESPONSE 0 3dB 30Hz to 15kHz STEREO SEPARATION 60dB 30Hz to 15kHz STEREO DISTORTION 0 1 3...

Page 19: ... OPERATING ALTITUDE 2500m above sea level COOLING SYSTEM Forced air 4 x 24Vdc blowers PHYSICAL DIMENSIONS 480mm x 485mm x 88 8mm PHYSICAL MASS Approximately 16kg STANDARD ALARM SETTINGS AND LOCAL INDICATIONS adjustable RF FAULT INDICATION 175W Red led on front panel VSWR FAULT INDICATION 20W Red led on front panel VSWR FAULT TRIP INDICATION 25W Red led front panel 10Sec re cycle TEMP FAULT INDICAT...

Page 20: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 RF Power backed off with high VSWR RF Power backed off with high RF PA Current ...

Page 21: ...te 21 Jan 2003 250W STEREO TRANSMITTER EXCITER TECHNICAL MANUAL Operating Information LARCAN Denver Office LARCAN TTC 1390 Overlook Drive 2 Lafayette CO 80026 USA Tel 303 665 8000 Fax 303 763 9900 E Mail sales earthnet net Web www larcan com ...

Page 22: ...ses a linear scale 20 led green custom bar display The meter has a push button selector with individual LED s yellow for indicating the four selectable Functions Temperature RF PA Heatsink temperature with 100 C f s d RF PA Current RF final stage current with 10A f s d RF Forward power RF Output power with 320W f s d RF Reflected power RF Output Reflected power with 32W f s d 5 ALC METER This dedi...

Page 23: ...ht VU meters If the pilot is lost the led will extinguish and if desired the Right channel VU meter can be actively disabled in this circumstance Internal link option This would normally happen for instance if Mono had been selected 7 INDICATORS FRONT PANEL FUNCTION INDICATION STATUS RF ENABLED Green led Indicates ext command on PLL LOCK Green led Indicates PLL is in lock PRE EMPHASIS Yellow led I...

Page 24: ...plementary signals RDS SST SCA g LEFT INPUT Balanced 600 ohm XLR female input for Left channel Stereo coder or Mono filter installed h RIGHT INPUT Balanced 600 ohm XLR female input for Right channel Stereo coder installed i PRE EMPHASIS SWITCH Slide switch for pre emphasis switching Stereo coder or Mono filter installed j PILOT OUTPUT BNC female with pilot 19kHz sine wave output 1V p p Stereo code...

Page 25: ...s 5 and 6 Voltage free contacts s c for fault PSU FAULT Pins 7 and 8 Voltage free contacts s c for fault STEREO OPERATION Pins 9 and 10 Voltage free contacts s c for stereo PLL LOCK Pins 11 and 12 Voltage free contacts s c for Lock ENABLE COMMAND Pins 13 o c to enable ground to disable MONO STEREO COMMAND Pins 14 o c for Stereo ground for Mono 12V 20mA SOURCE Pins 15 Supply for Test jig Leds GROUN...

Page 26: ... 4MHz 9MHz in BCD code PL2 pin 8 x 8MHz PL2 pin 9 x 10MHz These three data lines contain PL2 pin 10 x 80MHz the information 80MHz 90MHz PL2 pin 11 x 100MHz and 100MHz PL2 pin 12 Data enabled 5V Logic 1 output PL2 pin 13 Lock indication Open collector for Lock PL2 pin 14 Remote enable Connect to 0V for Enable PL2 pin 15 Ground 0V Example Freq pin 11 pin 10 pin 9 pin 8 pin 7 pin 6 pin 5 pin 4 pin 3 ...

Page 27: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...

Page 28: ... 21 Jan 2003 250W STEREO TRANSMITTER EXCITER TECHNICAL MANUAL Installation Information LARCAN Denver Office LARCAN TTC 1390 Overlook Drive 2 Lafayette CO 80026 USA Tel 303 665 8000 Fax 303 763 9900 E Mail sales earthnet net Web www larcan com ...

Page 29: ...cessary then the unit top cover has to be removed and a new frequency selected on the Synthesizer module 980507 This is simply done by setting the direct readout on the rotary BCD switches 1 ELECTRICAL CONNECTIONS Ensure that the power on off switch on the front panel is switched off before proceeding a A C MAINS SUPPLY 110V 60Hz Connect a c power cable to IEC connector on back panel b DC SUPPLY 4...

Page 30: ...METER All the Leds on the ALC meter should be OFF when PWR ADJ is set to minimum d MULTIMETER Select the four functions in turn and check the meter readings TEMPERATURE Room ambient PA CURRENT 0 Amps no Leds on FORWARD POWER 0 Watts no Leds on REFLECTED POWER 0 Watts no Leds on e DECODED MPX VU Meters The Left and Right VU meters will be indicating the incoming program levels and should be operati...

Page 31: ...to approximately 12 C above Room temperature WIDEBAND OPERATION The connection for this mode of operation is almost the same as for the Stereo mode the difference being in the connection of the Program inputs The Wideband system does not use the Left and Right program inputs or the pre emphasis switch not normally supplied The Composite input or MPX is connected to the MPX input on the unit back p...

Page 32: ...FM 250 FM BROADCASTING EXCITER Issue Date 21 Jan 2003 ...

Page 33: ...te 21 Jan 2003 250W STEREO TRANSMITTER EXCITER TECHNICAL MANUAL Technical Information LARCAN Denver Office LARCAN TTC 1390 Overlook Drive 2 Lafayette CO 80026 USA Tel 303 665 8000 Fax 303 763 9900 E Mail sales earthnet net Web www larcan com ...

Page 34: ... in steps of 100kHz from 87 5MHz to 108MHz Provision is made for external operation of the switching process via PL2 which is activated by connecting pin 14 and 15 on PL2 which disables the rotary BCD switches via diode D12 This in turn switches on transistor TR1 that provides the logic 1 signal for the external data on pin 12 of PL2 Led D38 provides indication of remote operation Provision is als...

Page 35: ... dc supply to IC11 RF output buffer The RF output is attenuated by 40dB e Out of Lock detection In the case of an Out of Lock condition the Phase detector IC9 pin 1 will provide an input to IC8 b pin 4 that will switch off the Lock led D18 and output buffer IC11 as described above f Signal inputs and Phase correction The MPX input at SK2 BNC can be operated in a Balanced or Unbalanced mode by inse...

Page 36: ...output to the Stereo coder module option PL5 pin 4 This provides the 21 5V dc output to the Synthesizer module PL6 pins 24 and 25 This provides the 21 5V dc output to the Display module IC6 b 12V Psu sensing This provides Psu fault indication via TR10 RL6 b RF Psu Monitoring PL2 pins 3 and 4 provide a differential current monitor for the RF PA power supply via IC4 a This configuration gives good c...

Page 37: ...gh reflected power persists When the output of IC2 d is low the Reflected Alarm is held on via D7 which latches the Alarm indication during re cycling via IC2 b e Temperature detection and Alarms The temperature sensing Thermistor which is mounted in the RF PA module is input at PL1 pins 1 and 2 The nominal resistance of the Thermistor is 4700 ohms at 25 C R41 Temp cal is adjusted to obtain a volt...

Page 38: ...sizer in Lock The Pilot detection is routed from the Display module via PL6 pin 6 and TR5 RL4 c The PLL Lock detection is derived from the Synthesizer module via PL5 pin 1 and TR6 RL5 c The Enable input on PL7 pin 13 requires a ground connection to disable the RF PA This is done via D29 D23 and TR4 to PL2 pin2 The Mono Stereo input on PL7 pin 14 requires a ground connection for Mono This is only u...

Page 39: ...and 3V is offset via R19 which is connected to the 5V supply This allows the meter to operate on a positive voltage only at a scale factor of 1V Led 9 Leds The input signal at IC1 pin 5 Linear scale bargraph driver is used to drive the Leds D13 to D21 of the ALC Meter The Bargraph drivers are operated in dot mode but configured to run in bar mode by connecting the Leds in series this reduces the c...

Page 40: ... The Left and Right outputs are then filtered by Fourth order Low pass networks IC13 a IC13 b IC13 c and IC13 d which remove the 19kHz and 38kHz products produced in the Decoding process and prevent errors in the VU meter operation e VU Meters and peak detection circuits The Left and Right outputs from the Stereo decoder are routed via R28 Left meter level and R37 Right meter level which are used ...

Page 41: ...ltage output Temperature pin 11 0 to 1 2Vdc voltage output ALC meter pin 13 5 to 3Vdc voltage output Pilot status pin 15 0 7V for pilot 0V no pilot These outputs are routed to the Analog to Digital converters in the RS485 module and the meter scales and alarms are calibrated and set in the software 4 RF PA MODULE 980510 a Psu and Regulator The RF PA requires two dc input supplies The VR supply is ...

Page 42: ...the Mosfet input The output wideband transformer 1 2 T2 has a centre tap in which the dc input is applied This provides optimum balance in the push pull mode of operation and ac de coupling is provided via L2 and associated components R25 is provided to set the gate voltage for the output mosfet which is operated in Class C See manufacturers data sheet for individual gate voltage settings D C bloc...

Page 43: ...olation between the supplies This output is used to supply the main RF PA Fuse F1 10A provides protection on the a c supply d RF PA Aux supply The battery supply and raw dc supply are combined via D4 and D5 for isolation to provide the auxiliary supply to the RF PA via R5 and PL4 pin 1 This supply is smoothed by C6 to reduce the a c ripple e Control supply The battery supply and raw dc supply are ...

Page 44: ...ured as a differential amplifier which is required to remove any common mode signal when the input is operated in balanced mode The input circuitry has the capacity to operate up to 20V p p 19dBm Trimmers R9 Left and R37 Right are provided to allow for level adjustment to customer requirements which generally vary from 6dBm to 9dBm Note This is the main adjustment in the final Exciter IC1 b is a b...

Page 45: ...IC22 b is configured as a fifth order 19kHz low pass filter Adjustment is provided by C101 The filter is adjusted by monitoring TP4 which is the output of a differential amplifierIC29 with very high common mode rejection This unique feature enables very simple set up of the 15kHz filters by allowing the Left or Right filterto be measured individually and also allowing simple differential measureme...

Page 46: ...MOS switching and the final output from the weighting resistors is routed to IC17 via R73 h 19kHz Bandpass filters The 19kHz square wave above is routed to IC16 a and IC16 b which are configured as bandpass filters centered at 19kHz These filters convert the 19kHz square wave to a sinusoid with 0 1 distortion R63 and R67 adjust the filters for maximum amplitude at 19kHz and the output from IC16 b ...

Page 47: ...e 21 Jan 2003 250W STEREO TRANSMITTER EXCITER TECHNICAL MANUAL Maintenance Information LARCAN Denver Office LARCAN TTC 1390 Overlook Drive 2 Lafayette CO 80026 USA Tel 303 665 8000 Fax 303 763 9900 E Mail sales earthnet net Web www larcan com ...

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