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Larcan FM-250 Technical Manual

250w stereo transmitter/exciter
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FM-250 FM BROADCASTING EXCITER
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
Issue Date: 21 Jan 2003

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  • Page 1 FM-250 FM BROADCASTING EXCITER 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 Issue Date: 21 Jan 2003...
  • Page 2 FM-250 FM BROADCASTING EXCITER NOTE AMENDMENT Please take note that any reference to 230V and 50Hz in this manual should be read as 110V and 60Hz respectively. Issue Date: 21 Jan 2003...

  • Page 3: Table Of Contents

    FM-250 FM BROADCASTING EXCITER FM-250 250W STEREO TRANSMITTER/EXCITER TECHNICAL MANUAL CONTENTS: General Description Technical Specifications Operating Information Installation Information Technical Information 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 Exciters produced by Broadcast Solutions Electronics (Pty) Ltd and supplied by LARCAN USA in the United States. 1. The FM-250 Exciter forms a compact, solid state FM Broadcast transmitter with a RF output in excess of 250W in the FM Broadcasting band (87.5MHz to 108MHz). The unit is housed in a 19-inch rack mount case occupying only a 2U space.

  • Page 6: General Description

    FM-250 FM BROADCASTING EXCITER 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 Issue Date: 21 Jan 2003...
  • Page 7 FM-250 FM BROADCASTING EXCITER Issue Date: 21 Jan 2003...
  • Page 8 Display module (980509). f) Stereo coder/Limiter (980512). (Optional). 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).
  • Page 9 FM-250 FM BROADCASTING EXCITER 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 Issue Date: 21 Jan 2003...
  • Page 10 FM-250 FM BROADCASTING EXCITER Figure 1: FM-250 Front Panel Controls Issue Date: 21 Jan 2003...
  • Page 11 FM-250 FM BROADCASTING EXCITER Figure 2: FM-250 Rear Panel Controls and Connectors Issue Date: 21 Jan 2003...
  • Page 12 FM-250 FM BROADCASTING EXCITER Issue Date: 21 Jan 2003...
  • Page 13 FM-250 FM BROADCASTING EXCITER BACK PANEL RS485 (OPTIONAL) INPUTS REAR PANEL PILOT OUT LEFT (XLR) (BNC) 20 LED MULTIMETER REAR PANEL STEREO VU METER STEREO RIGHT (XLR) CODER DISPLAY PILOT INDICATOR 980512 REMOTE FAULT INDICATORS TELEMETRY FUNCTIONAL INDICATORS 980509 REAR PANEL...
  • Page 14 FM-250 FM BROADCASTING EXCITER a) SYNTHESIZER AND MODULATOR (980507) The digital synthesizer derives the final operating frequency from a 10MHz reference (TCXO) using a PLL (Phase lock loop) and dividers. The frequency can be selected Locally (In 100kHz steps via rotary BCD switches) or Remotely (via a external parallel control). The direct carrier modulator uses special techniques to obtain very low distortion and high stereo channel separation (>60dB).
  • Page 15 FM-250 FM BROADCASTING EXCITER The power supply module contains the smoothing capacitors for the ‘off board’ 230V 50Hz a/c mains transformer/bridge rectifier combination. This +52V nominal smoothed supply is then distributed to a choke/capacitor filter at the module. This type of arrangement eliminates all ripple and therefor any AM products on the transmitter, even when the a/c input voltage is extremely low.
  • Page 16 FM-250 FM BROADCASTING EXCITER There is provision for three (50-ohm BNC female) external modulating inputs, one for external MPX (600 ohms unbal. or 1.2k ohms BAL.) And two for auxiliary use (20k ohms unbal.). The RF Output is via an N Type (50-ohm) connector.

  • Page 17: Technical Specifications

    FM-250 FM BROADCASTING EXCITER 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 Issue Date: 21 Jan 2003...
  • Page 18 FM-250 FM BROADCASTING EXCITER TECHNICAL SPECIFICATIONS GENERAL RF SPECIFICATIONS FREQUENCY RANGE 87.5 MHz to 108MHz FREQUENCY CONTROL PLL Synthesizer FREQUENCY INCREMENTS 100kHz steps (Local and Remote control) ± 2ppm (10MHz TCXO) FREQUENCY STABILITY ≥ 250W (Adjustable via front panel control) RF OUTPUT POWER ≥...
  • Page 19 FM-250 FM BROADCASTING EXCITER MONO OPERATION (With built in Mono filter) ≤ ±0.3dB (30Hz to 15kHz) AF RESPONSE ≤ 0.1% (30Hz to 15kHz) MONO DISTORTION ≥ 80dB (20Hz to 20kHz) 50uS de emph S/N RATIO INPUT IMPEDANCE 600 ohms balanced (XLR) +6dBm for ±40kHz deviation (adj.)
  • Page 20 FM-250 FM BROADCASTING EXCITER • RF Power backed off with high VSWR. • RF Power backed off with high RF PA Current. Issue Date: 21 Jan 2003...

  • Page 21: Operating Information

    FM-250 FM BROADCASTING EXCITER 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 Issue Date: 21 Jan 2003...
  • Page 22 FM-250 FM BROADCASTING EXCITER OPERATING INFORMATION FRONT PANEL 1. POWER ON/OFF SWITCH The front panel On/Off switch connects the External A/C and D/C supplies to the equipment. 2. POWER ADJUST CONTROL This single turn potentiometer is used to set the RF output power via the internal ALC Circuit.
  • Page 23 FM-250 FM BROADCASTING EXCITER detection. The signals are derived from the built in stereo decoder and calibrated accordingly. The VU meter scales are as follows: LEFT CHANNEL RIGHT CHANNEL LED STATUS +3dBm +3dBm Over deviation (red) +2dbm +2dbm Over deviation (red)
  • Page 24 FM-250 FM BROADCASTING EXCITER BACK PANEL a) A/C INPUT Standard IEC male connector for 110V 60Hz mains operation. b) A/C FUSE (110V a/c operation) 20mm (10 Amp) fuse connected in live line. c) DC INPUT Terminals for +48V dc operation.
  • Page 25 FM-250 FM BROADCASTING EXCITER n) RS485 OPTION This 9 pin D type (female) connector is used for remote monitoring of meter functions. o) TELEMETRY CONNECTIONS (PL7) FUNCTION PL7 CONNECTOR PINS CONTACT STATUS RF FAULT Pins 1 and 2 Voltage free contacts...
  • Page 26 FM-250 FM BROADCASTING EXCITER p) REMOTE FREQUENCY PROGRAMMING (PL2) 15 pin connector BCD Parallel Code Code information PL2 pin 1 x 0.1MHz These four data lines contain PL2 pin 2 x 0.2MHz the information from 0 MHz to PL2 pin 3 x 0.4MHz...
  • Page 27 FM-250 FM BROADCASTING EXCITER Issue Date: 21 Jan 2003...

  • Page 28: Installation Information

    FM-250 FM BROADCASTING EXCITER 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 Issue Date: 21 Jan 2003...
  • Page 29 FM-250 FM BROADCASTING EXCITER INSTALLATION STAND ALONE CONFIGURATION (Stereo Exciter) The following information sets out the general requirements for installation and operation of the above equipment in a "stand alone" configuration. Note: The Audio program inputs (Left and Right), may vary in level from the standard factory sensitivity setting, and adjustment may have to be made internally (due to the Stereo coders built in Limiter).
  • Page 30 FM-250 FM BROADCASTING EXCITER 2. OPERATION With the electrical connections completed above the unit is now ready for operation. a) SWITCH ON SEQUENCE Adjust the RF power control on the front panel, fully acw. then set the power on/off switch to ON.
  • Page 31 FM-250 FM BROADCASTING EXCITER The front panel deviation adjustment should not be used for the purpose of deviation adjustment in the Stereo operational mode. (This is for use with Wideband operation). With the standard factory setting, the unit should not be over deviating due to the Limiter operation and protection.
  • Page 32 FM-250 FM BROADCASTING EXCITER Issue Date: 21 Jan 2003...

  • Page 33: Technical Information

    FM-250 FM BROADCASTING EXCITER 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 Issue Date: 21 Jan 2003...
  • Page 34 FM-250 FM BROADCASTING EXCITER TECHNICAL INFORMATION 1. SYNTHESIZER MODULE (980507) a) Power supply. The single +21.5V dc input at PL4 pin 4 is routed via diode D25 to capacitor C68, which acts as a dc storage mechanism that allows the synthesizer module to remain temporarily operational during power dips in the final system.
  • Page 35 FM-250 FM BROADCASTING EXCITER input sensitivity of the VCO is approximately 2.2MHz/Volt, with a tuning voltage range between 3 and 12 volts The Fet oscillator TR4 is tuned to the operating frequency via L2 and the above varactor diodes. The output from the oscillator is split and attenuated to the separately screened Pre- scalar (IC12) and a RF output buffer IC11, which provides the final RF output to SK1 (Typically +10dBm).
  • Page 36 FM-250 FM BROADCASTING EXCITER The adjustment to control the deviation flatness is provided by R53. This is used to provide constant deviation by adjusting the dc conditions to Varactor diodes, D21 and D22, when the synthesizer frequency is changed. 2. CONTROL MODULE (980508) a) PSU and Internal Monitoring The Control module has two dc power inputs.
  • Page 37 FM-250 FM BROADCASTING EXCITER IC2/a provides the detection for a Forward RF Alarm, with R10 (FWD Alarm cal) setting the required threshold when the level is low. The output is used to give an Alarm signal via TR1/RL1. d) Reflected RF detection and Alarm The Reflected RF monitoring input is via SK2 (SMB), which provides a RF signal (nominally 0dBm), proportional to the RF reflected power of the Exciter.
  • Page 38 FM-250 FM BROADCASTING EXCITER output power in the Exciter with respect to the Control voltage (The ALC Output is used to control the Gain of the RF PA via the Mosfet gate voltage). This arrangement controls the power output of the RF PA and the other inputs to the circuit are only there for protection purposes, by reducing the output power during fault conditions.
  • Page 39 FM-250 FM BROADCASTING EXCITER PL1 pin 9 Reflected Fault (indication) Provides data for Led D3 PL1 pin 10 Temp Fault (indication) Provides data for Led D4 PL1 pin 11 Psu Fault (indication) Provides data for Led D5 PL1 pin 12...
  • Page 40 FM-250 FM BROADCASTING EXCITER operate Leds D46, D45, D44 and D43, which indicate which switch selection is in operation. The four inputs to the switch are as follows: • Temperature. R47 is used to calibrate this input function. • Current. R52 is used to calibrate this input while R51 sets the offset null (0 Amps).
  • Page 41 FM-250 FM BROADCASTING EXCITER operational only (LK1 in position B) or when operated in stereo, if the pilot signal fails then the Right meter could be inhibited automatically (LK1 in position A). This provides the customer with excellent visual status of the real time program.
  • Page 42 FM-250 FM BROADCASTING EXCITER The main regulator can be disabled via TR4 / D10 which effectively shunts the constant current source to ground thus removing the output voltage. TR4 is switched via an external input from the control module. Resistor R35 is used to monitor the current in the RF PA section and provision is made for external monitoring via R37, R38 and R39.
  • Page 43 FM-250 FM BROADCASTING EXCITER 5. PSU MODULE (980515) a) A/C Supply The a/c input to the power supply is provided by a external 48V a/c Transformer and Full wave Bridge rectifier which is connected to SK1 pin 1 (+) and SK4 pin 1 (0V). This raw dc input which is indicated by Led D2 is smoothed by capacitors C1, C2, C3 and C4.
  • Page 44 FM-250 FM BROADCASTING EXCITER 7. STEREO CODER MODULE (980512) a) Psu and distribution The dc input is supplied via PL4 pins 5 and 6, and is typically between 24V to 40V dc. The ground is connected to PL4 pins 1 and 2.
  • Page 45 FM-250 FM BROADCASTING EXCITER d) High pass filter The output from the Limiter circuit is connected to IC20/a and IC23/a, which form the High pass filters, removing any low frequencies below 10Hz. This is done to remove any dc switching transients contained in the incoming audio program.
  • Page 46 FM-250 FM BROADCASTING EXCITER output has a pulse repetition frequency of 76kHz with a 1.879uS pulse. The outputs of IC9 are routed to a Quad bilateral switch (IC11) which with precision weighting resistors (R53 to R60), a 14 step replica of a 38kHz sinusoid is produced. This has a distinct advantage over direct switching at 38kHz, as any spurious products produced appear at frequencies 532kHz and above and are easy to filter.

  • Page 47: Maintenance Information

    FM-250 FM BROADCASTING EXCITER 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 Issue Date: 21 Jan 2003...
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