FCC ID: E6T072503FMW300 XT 300 Frequency agile FM Transmitter

XT300 Technical Manual BEXT, Inc. 1045 Tenth Avenue San Diego, Ca 92101 U.S.A. Tel: 619-239-8462 Fax: 619-239-8474 E-mail: support @bext.com Web Site: http://www.bext.com XT300 and XT300/S 300W Mono and Stereo Synthesized Exciter 87.5-108 MHz Technical and Maintenance Manual Pag. 2 Pag. 4 PRELIMINARY INSTRUCTIONS AND WARRANTY INFORMATION WARNING: This is class A equipment. In a residential place this can cause R.F. Burns. In this situation the user is recommended to take appropriate action. Please observe safety precautions when handling this unit. This equipment contains dangerous voltages and currents. This manual is written as a general guide for those having previous knowledge and experience with this kind of equipment. It is not intended to contain a complete statement of all safety precautions which should be observe by people working on this or other electronic equipment. Bext, Inc. doesnt assume responsibility for injury or damage resulting from improper procedures or practices by untrained/unqualified personnel in the handling of this unit. Please observe all local codes and fire protection standards in the operation of this unit. CAUTION: Always disconnect power before opening covers or removing any part of this unit. Use appropriate grounding procedures to short out capacitors and high voltage points before servicing. Any damage to the goods must be reported to the carrier in writing on the shipment receipt. Any discrepancy or damage discovered subsequent to delivery, must be reported to Bext, Inc. within five

(5) days of receipt. Bext, Inc. extends to the original end-user purchaser all original manufacturers warranties which are transferable and all claims are to be made directly to Bext, Inc. per indicated procedures. All manufacturers warranties will be supported by Bext, Inc. to ensure precise and speedy service where possible. Bext, Inc. shall not be liable for any damage of whatsoever nature, arising out of or in connection with the product or its use. Bext, Inc. warranty shall not include:

1) 2) 3) 4) 5) Reshipments of unit to Bext, Inc. for repair purposes Any unauthorized repair/modification Incidental/consequential damages as a result of any defect Nominal non-incidental defects Reshipment costs or insurance of the unit or replacement unit/parts Warranty shall come into force from invoice date and for the period of manufactures warranty. Pag. 5 The warranty is good for a period of 24 months on any Bext, Inc. product, while for products such as transistors, Mos-FET and tubes of the final stages, the warranty is based on the products manufaturers warranty. To claim your rights under this warranty:

a. b. c. Contact the dealer or distributor where you purchased the unit. Describe the problem and ask if he has an easy solution. Dealer and distributors are supplied with all the information about problems that may occur and usually they can repair the unit quicker than what the manufacturer could do. Very often installation errors are discovered by dealers. If your dealer cannot help you, contact Bext, Inc. and explain the problem. If it is decided to the return the unit to the factory, Bext, Inc. will give you a return authorization and all the necessary instructions to send back the goods. When you receive the authorization, you can return the unit. Pack it carefully for shipment, preferably using the original packing, and seal the package perfectly. The customer always assumes the risks of loss (i.e., Bext, Inc. is never responsible for damage or loss), until the package reaches Bext, Inc. premises. For this reason, we suggest that you insure the goods for the whole value. Replacement and warranty parts may be ordered from the following address. Be sure to include the equipment model and serial numbers well as part description and part number. Bext, Inc. 1045 Tenth Avenue San Diego, CA 92101

(619) 239-8462

(619) 239-8474 Fax support@bext.com Bext, Inc. reserves the right to modify the design and specifications of the equipment in this manual without previous notice. Pag. 6 Warning!

The voltages and currents in this equipment are dangerous! Personnel must at all times observe safety precautions. Warning!

Always disconnect power before opening covers, doors, enclosures, gates, panels or shields. Always use grounding sticks and short out high voltage points before servic-

ing. Never make internal adjustments, perform maintenance or service when alone or when fatigued. Do not remove, short-circuit or tamper with interlock switches on access covers, doors, enclosures, gates, panels or shields. Keep away from live circuits, know your equipment and dont take chances. Warning!

In case of emergency ensure that the power has been disconnected. Pag. 7 Treatment of Electrical Shock Chapter 1 DESCRIPTION OF THE XT300 and XT300/S 1.0 INTRODUCTION This manual contains technical information about the XT300 and XT300/S exciters. For more simplicity we will always refer to the XT300, unless specified for clarity. 1.1 GENERAL DESCRIPTION The XT300 is housed in a 3U, 19 rack-mounting container comprising a num-

ber of interconnected modules mounted internally on the main chassis, facilitating removal and substitution. The power output control, audio input level control and analog meter for measurement of the operating parameters, are all mounted on the front panel. The AC line power, audio input, RF output and telemetry connectors are mounted on the rear panel. 1.2 ELECTRICAL DESCRIPTION The XT300 is an exciter working in the 87.5 to 108 MHz band, programmable in steps of 10 KHz. Its power output is continuously adjustable from 10W to 300W into a 50 Ohm load. The XT300 incorperates a stereo coder card which guarentees excellent stereo separation together with low harmonic distortion (only for Stereo Version). It also accepts two SCA Signals. A front panel switch allows stereo operation (only for Stereo Version) or mono/mpx operation which excludes the stereo encoder and uses the right input as the mono input and the left input as the wideband composite input. The specifications feature low audio distortion and intermodulation figures

(typically 0.03%) and a high signal-to-noise ratio (typically -80dB). 1.3 METERS AND INDICATORS The operating parameters of the exciter can be monitored using the analog multimeter situated on the front panel. The parameter to be measured is selected by the rotary selector switch. The frequency control allows frequencies to be selected in steps of 10 KHz. Three red alarm LEDs indicate VCO unlock, excess VSWR on the output and exces-

sive temerature, and the shutdown condition, programed by a remote command. Pag. 10 Three green LEDs indicate the presence of +12V, +15V and +28V voltages which are used to power the various cards inside the exciter. A selector switch allows selection between Mono/Mpx and Stereo functions and another selector switch provides a choice of level input signal. Trimmers are provided for adjustment of left and right channels and a switch allows the stereo subcarrier to be enabled or disabled. 1.4 AUTOMATIC FREQUENCY CONTROL The operating frequency is governed by a thermally-compensated, reference oscillator working within a phase locked loop (PLL). The XT300 reaches frequency lock within a maximum of 30 seconds. 1.5 CONTROL CIRCUITS The control circuits allow automatic control of the output power (internal and external), maintaining the chosen power level across the entire operating band. Fur-

thermore, another circuit protects the final stage against excessive VSWR or short circuits and excessive temperature. Then, there are other protection circuits that act to limit the maximum output power and to protect the equipment against a power supplys overvoltage. 1.6 R.F. POWER AMPLIFIER The RF amplifier is a broadband design and guarantees an adjustable power output of 10 to 300 Watts across the entire band. A low pass filter enables the XT300 to be used as a low power transmitter, connected directly to an antenna. 1.7 SPECIFICATIONS Please refer to Table (A) for the electrical specifications and Table (B) for me-

chanical specifications. Pag. 11 TABLE A ELECTRICAL SPECIFICATIONS Power supply 117-230V +/- 10 %, 50-60 Hz single phase Power Consumption approx. 600 W Cooling Frequencies Output power Forced ventilation 87.5 to 108 MHz in steps of 10 KHz adjustable from 10 to 30 W Automatic Output Level Control Stabilizes the set RF output level Output Impedance 50 Ohm Output Connector Standard N-type Harmonic Suppression Spurious Signal Suppression

> -65 dB

> -80 dB Mono Intermodulation Distortion 0.05 % or less, measured at 1 KHz and 1.3 KHz, ratio 1:1 at 100 % modulation Frequency Stability Modulation Type

+/- 500 Hz (typically +/- 300 Hz) from 0 deg to 50 deg C Direct frequency modulation of the RF oscillator at the fundamental frequency Frequency Deviation

+/- 75 KHz nominal Harmonic Distortion

< 0.05 % (typically 0.01 %) FM Signal-to-Noise Ratio

> 75 dB mono, > 70 dB stereo measured with 75 KHz deviation in the 30 Hz to 15 KHz band RMS. Residual AM (asynchronous) Approx. 0.05 % + 65 dB RMS Pag. 12 Residual AM (Synchronous) 0.1% = 60dB Pre-emphasis 50uS +/- 2% 0r 75 uS +/- 2% selectable Audio Input Impeadance Audio Input Level Audio Frequency Range Audio Input Filter 10 KOhm balanced or 5K Ohm unbalanced

(600 Ohm on request) Selectable from -9 to +6 dBm in five steps Continuous from -12 to +9 dBm 30-15000 Hz, MONO input 30-100000 Hz, MPX input

> 45 dB at 19 KHz (Mono)

> 40 dB from 20 KHz to 100 KHz Mono Frequency Response

+/-0.3 dB from 30 Hz to 15KHz MPX Frequency Response

+/-0.5 dB from 30 Hz to 75KHz Stereo Separation

> 45 dB (typically 50 dB) Pilot Tone Frequency 19 KHz +/- 1 Hz Pilot Tone Level

-20 dBm adjustable Number of SCA inputs 2 SCA Input Impedance 1 KOhm unbalanced SCA Input Level 0 dBm for +/- 7.5 KHz of deviation SCA Input Response

+/- 0.5 dBm from 40 KHz to 100 KHz Pag. 13 TABLE B MECHANICAL SPECIFICATIONS Rack dimensions 483.0 mm (19.0) W 132.5 mm (5.20) H 500.0 mm (19.7) D Operating temperature from -10 deg C to 45 deg C Humidity Weight 95 % max. non-condensing 22 Kg Pag. 14 Chapter 2 ELECTRICAL DESCRIPTION 2.1 INTRODUCTION This section describes, in detail, the operating theory behind the XT300. To aid understand-

ing, the unit has been subdivided into blocks, each of which is fully described below. The block diagram is shown in Fig. 3 2.2 POWER SUPPLY This circuit comprises a board, mounted on a heat sink, which is fixed to the central part of the lower section of the unit. The power supply generates the various modules that make up the XT300. The transformer has a selectable input from 110V to 240V and three outputs:

A. 30/0/30V (9A), B. 36V (0.5A), and C. 20V (1A). This power supply is composed of two main parts: after having undergone filtering for mains-

borne interference, the supply is transformed into four lower voltages, rectified, smoothed and stablized to the following values: +12V, +15V +15 variable and +50V to obtain the higher efficiency switching power supply (85-90%). The +15V supplies the encoder mixer, the PLL card, the VCO card, the meter card and the alarms card. The +12V supplies the fan . The +15V variable supplies the input of the RF power module amplifier driver (BLF244) and the 50V supplies the final power stage (BLF278). The variable voltage of the final stage driver is controlled by the PWR ADJ control which determines the RF power output of the exciter. The automatic control of the output power guarantees the power level set by the PWR ADJ control right across the frequency range and independently of the other variables such as temperature, load variations etc. The system works by comparing the value set by the PWR ADJ control with the actual power output of the unit and compensating accordingly. 2.3 AUDIO INPUT CARD This card is situated on the rear panel of the exciter. The card filters all audio signal inputs to the unit, removing RF interference, before supplying them to the encoder mixer or mono/mpx card. The main operating parameters of the exciter are available for remote monitoring via the telemetry connector. 2.4 STEREO CODER CARD (only for Stereo Version) This card is situated in the lower part of the unit. Pag. 15 The card can function either as a stereo encoder or as a simple mixer for the various audio inputs. The function may be selected by a control situated on the front panel. In the stereo encoder mode, the 19 KHz pilot tone is derived from a quartz crystal reference oscillator. So too is the sampling frequency which allows the L and R sig-

nals to be separated from the multiplexing signal. Plus the suppresion of the 38 KHz frequency. The level of the left and right signals are set by the corresponding selector situated on the front panel. The signals are filtered at 15 KHz and pre-emphasized (50 uS CCIR, 75 uS FCC) before being sent to the multiplexing circuit. The audio signals from the two SCA inputs are mixed in to provide the output. In the mixer mode

(Mono/Mpx) the stereo encoder is bypassed, the right input accepts a mono signal and the left input accepts a multiplex signal up to 100 KHz. The SCA inputs remain un-

changed. Three rectifiers allow the peak levels of the two inputs Left/MPX and RIGHT/MONO to be displayed on the analog meter, and provide the audio detector circuit with the deviation level. 2.5 PLL CARD The PLL card is situated internally, in the upper part of the unit. The circuit includes a reference crystal oscillator (optional high stability), a logic section that includes the frequency dividers and comparator. The reference crystal oscillator gener-

ates a 4 MHz frequency that is divided to generate a fixed 1 KHz signal. This signal is compared to the operating frequency generated by the VCO divided based on the frequency set on the contraves board. An indicator situated on the front panel signals the unlocked condition. The comparator output (AFC signal) is sent to the varicap diodes situated on the VCO card. 2.6 VCO CARD The VCO card is situated internally, in the upper part of the unit. This module includes an audio input stage at low frequency, a voltage controlled oscillator (VCO) and driver stage. The audio signal supplied by the encoder mixer is amplified and then injected into the VCO to provide class F3 modulation. The voltage controlled oscillator (VCO) generates the signal on the frequency set on the contraves. This signal is amplified to 300mW level (25dBm) to drive the final stage and sent to the PLL circuit situated on the PLL card. The operating frequency generated by the VCO is divided down before being compared to a reference frequency, generated by a high stability oscillator (stan-

dard 5 ppm). Pag. 16 The error voltage is filtered and used to compensate the VCO frequency and guarantee its stability. A trimmer is present on this card for adjustment of deviation. 2.7 RF POWER AMPLIFIER The final power stage is mounted on a heat sink to dissipate waste heat and is en-

closed in a totally screened metal container, fixed to the upper-middle part of the central section of the unit. The RF signal coming from the stereo decoder or Mono/

MPX at a power level of about 300mW, reaches the driver stage (BLF244) and is amplified to a level from about 300mW to 8W before being further amplified by the final stage (BLF278) to a level of up to 300W. The resultant signal is then filtered by a low-pass filter which removes any harmonic content. A directional coupler allows the direct and reflected power levels to be measured and displayed on the analog multim-

eter and fedback to the power supply for automatic control of the output power (see power supply description). A BNC connector situated on the rear panel provides a power signal at -60db of the amplifier output power. 2.8 METER CARD This card is situated centrally on the front panel. The card receives direct and reflected power signals from the power supply which, in turn, come from the final power stage. The stereo encoder card supplies deviation and left and right signal lev-

els. These signal levels are then displayed on the analog meter according to the posi-

tion of the rotary selector situated on the front panel. 2.9 FREQUENCY SELECTOR CARD This card is located on the left-hand side of the front panel. The operating fre-

quency selected by the frequency control is represented by a signal which is supplied to the frequency dividers that form part of the PLL circuits found on the PLL card. 2.10 ALARMS CARD This card is fixed in the lower part of the unit. This circuit allows 7 adjustments via trimmers, the threshold of the external and internal output level, internal and exter-

nal VSWR level, temperature and to preset the maximum value of the output power. In case of a fault there is no automatic reset, because the transmitter automatically re-

duces the output power to continue transmitting without interruption, even if at mini-

mum power. Pag. 17 2.11 SOFT START The soft start is mounted on a board placed on the front side of the transmitter. The circuit eliminates the current spikes generated by the transformer when it is pow-

ered. 2.12 MONO/MPX CODER CARD (Mono Version) This card is located in the lower part of the unit. The Mono/MPX card is an Audio Mixer at four inputs: two balanced (Mono and MPX) and two unbalanced

(SCA1 and SCA2). Mono and MPX input level can be set through decade thumbwheel switches on the front panel, on 5 fixed positions and on a variable posi-

tion from -12 dBm to +9 dBm (preset at 0 dBm). Its possible to set the pre-emphasis value at 50uS, 75uS or linear. Then, its possible to insert or remove a low pass filter at 15KHz. 2.13 CLIPPER CARD This card is attached with a sandwich structure on the coder card and is acces-

sible from the lower part of the equipment. Its function is to limit drastically any audio signal that exceeds a prefixed threshold. Therefore, its used to avoid any type of over-

modulation which exceeds maximum peak permitted of +/- 75 KHz. Pag. 18 1 2 3 4 5 6 7 8 9 FRONT PANEL STEREO VERSION VEIW DESCRIPTION (FIG. 1A) STEREO/MONO-MPX Selects STEREO or MONO/MPX operation STEREO LED Indicates the operation of the stereo encoder 19KHz LED Indicates the 19KHz pilot tone presence MODE SELECTOR Button in:

STEREO OPERATION MODE PILOT TONE PRESENT L/MPX &R/MONO LEVEL INPUT LEVEL VOLTAGE LEDs SWR PWR ADJ 10 REM Button out: MONO OPERATION MODE PILOT TONE ABSENT L/MPX AND R/MONO input level adjustable from -12 to +9 dBm; this is possible if the input level switch is completely turned clock wise Input signal attenuator adjustable in 5 steps from -9 to +6 dBm Indicates the presence of the internal operating voltages +12V, +15V and +28V Indicates that reflected power exceeds 30W 10-turn trimmer to regulate the power output of the exciter. AGC maintains the level set by this control Indicates that the exciter has been shut-down by remote control 11 MEASUREMENT SELECTOR The measurement made by the meter corresponds to the position of this selector 12 METER 13 14 15 POWER MHz/KHz L.O. UNLOCK Analog meter used to display the following operating parameters of the exciter:

Direct power Reflected power Deviation Right channel input level Left channel input level f.s. 375W f.s. 37.5W f.s. 100KHz f.s. +3dB f.s. +3dB ON/OFF switch Rotary frequency selector If ON indicates that the VCO is not locked to the reference frequency. The output power will drop to zero in this condition Pag. 19 Pag. 20 Pag. 22 REAR PANEL View Description (Fig, 2) MAINS VOLTAGE SOCKET Mains Voltage Socket VOLTAGE CHANGER Mains Voltage Changer:

Connect: 0-100V for 100V A.C. Input Connect: 0-120V for 120V A.C. Input Connect: 0-220V for 220V A.C. Input Connect: 0-240V for 240V A.C. Input D.C. LINE FUSE Protection for D.C. line R.F. module R.F. MUTE FAN TELEMETRY TERMINALS BNC connector. Connecting the center conductor to ground will cause the RF output power level to drop to zero and stay there until the short is removed. When used with a Bext, Inc. amplifier, this connector should be connected to the REMOTE output of the power amplifier. Fan-assisted cooling for the power stage and power supply Audio GND 10 Pin Telemetry card 1-2 3-10 GND 4 5 6 7 8 9 Forward power Reflected power VPA IPA SWR Alarm/Temp Unlock alarm A.C. LINE FUSE Protection fuse for A.C. line R.F. OUTPUT N-type connector, 50 Ohm R.F. TEST POINT

-60 dB output referred to the output level P.A. FUSE Protection fuse for the Switching Power Supply EXT. RFL FEEDBACK BNC connector, external Reflected Feedback Input EXT. AGC BNC connector, external AGC input RIGHT (MONO) BNC connector for FCC unbalanced version: Cannon XLR for CCIR version with balanced input 1 2 3 4 5 6 7 8 9 10 11 12 13 14 LEFT (MPX) 15 16 SCA1 SCA2 BNC connector for FCC unbalanced version: Cannon XLR for CCIR version with balanced input BNC connector, unbalance SCA1 input BNC connector, unbalance SCA2 input or output

(internally selectable) for pilot tone (i.e. for RDS encoder) Pag. 23 BOTTOM VIEW DESCRIPTION (PHOTO 1) Meter card Stereo coder card (for Stereo Version) Mono/MPX card (for Mono Version) Audio bus card Power supply card Alarms card Audio input card 1 2 3 4 5 6 Pag. 26 UPPER VIEW (PHOTO 2) Frequency Selector card Meter card Soft-Start card R.F. Power Amplifier- Driver Stage Analog Meter Transformer VCO Audio Input card PLL 1 2 3 4 5 6 7 8 9 10 R.F. Power Amplifier-Final Stage 11 Low Pass Filter 12 Switching Power Supply 13 Directional Coupler Pag. 28 CHAPTER 3 INSTALLATION 3.1 INTRODUCTION This chapter contains the information required for installation of the XT300 exciter and for preliminary checks. 3.2 UNPACKING Remove the unit from its packaging and before any other operation, check for damage that the unit may have suffered in transit and check to be sure all front panel controls are functioning. 3.3 INSTALLATION 1) 2) Check that the line voltage selector is correctly set for the local supply. Check also that the A.C. Line Protection Fuse (Fig.2 Item 7) is mounted on the rear panel. The currrent sizes of the fuses are as follows:

220-240V 100-120V 6.3A 12.5A Now ensure that the PWR ADJ control (Fig. 1A Item 9 or Fig. 1B Item 5) is rotated fully counterclockwise, using a small screwdriver (the pot is a ten turn pot so care should be taken to verify the minimum position). Units are normally shipped with this control at minimum. WARNING: When the unit is switched on with the control at its minimum posi-

tion, power output is about 10W. 3) 4) Connect a dummy load with a power rating of at least 300W continous to the R.F. output, situated on the rear panel of the unit. It is advisable to connect a bypass wattmeter in series with this load in order to verify the accuracy of the units own internal wattmeter (see setup 1). Connect a switch, via a cable, to the R.F. Mute connector (Fig. 2 Item 4) on the rear panel so that the switch is able to short the central conductor to its ground. Leave the switch in the short-circuit position. 5) Switch the units ON/OFF switch (Fig. 1A Item 13 or Fig. 1B Item 9) to the OFF position. Pag. 30 6) Connect the line cord. (Fig.2 Item 1)

(It is essential that the unit be properly grounded to ensure both the safety of the operator as well as the correct functioning of the equipment.) 7) Switch the power switch (Fig. 1A Item 13 or Fig 1B Item 9) to the ON position and check that the three green internal voltage LEDs, (Fig. 1A Item 7 or Fig. 1B Item 3) and the red unlock LED (Fig. 1A Item 15 or Fig. 1B Item 11) are all on. Select the desired operating frequency using the corresponding selector. The red UNLOCK LED should switch off within 30 seconds, indicating that the oscillator has locked onto the operating frequency. The frequency selector comprises five figures of which three to the left of the decimal point represent (from left to right) hundreds MHz, tens MHz, and MHz. The two figures to the right of the decimal point represent (from left to right) hundreds of KHz and tens of KHz. EG:

098.45= ninety eight megahertz and four hundred and fifty kilohertz. EG:

103.94= one hundred and three megahertz and nine hundred and forty kilohertz. Furthermore, if a frequency is selected beyond the two limits of the 87.5-108 band, the amplifier will continue to work even though the displayed frequency no longer corresponds to the operating frequency of the unit. Transmitting outside the legal band (87.5-108 MHz) is an offense and may lead to prosecution. 8) After having verified that the UNLOCK LED is off and that the unit is therefore locked to the selected operating frequency, switch the switch connected to the REMOTE connector so as to remove the short circuit between the center conductor and the ground. The R.F. output is now enabled and should correspond to a power level of about 10W. To check this reading, select FWD on the meter selector and read the power from 375W FSD scale. Pag. 31 9) Using a small screwdriver, rotate the PWR ADJ control clockwise; the power output should increase progressively to a maximum of 300W. Check the value with the bypass wattmeter which should be within +/- 10% of the front panel meter. 10) With the power output at 300W, select a new operating frequency well away from the current value. Eg: 107 MHz: the UNLOCK LED should switch to on and the power output should fall to zero at the same time. Only when the UNLOCK LED switches off

(unit locked to new frequency) should the power output resume its previous level. 11) 12) Automatic power control check. It is advisable to start this procedure with the operating frequency set to 87.50 MHz. When locked to this frequency, the PWR ADJ control should be adjusted for an output power of 150W. Now, with no further adjustment of the PWR ADJ control, change the operating frequency in steps of 4-5 MHz, ensuring that the output power remains constant at 150W. SWR alarm check. For this test, adjust the PWR ADJ control for a power output of 10W. Disconnect the output load and check that the SWR LED lights. Now adjust the PWR ADJ control to check that the unit switches on again at a reflected power level of about 10% of the output power. Turn the PWR ADJ control for maximum power and check that the reflected power does not exceed 30W. Reconnect the output load and check that REF falls to zero, the SWR LED goes out and the PWR FWD jumps to 300W. 13) Now short circuit the center conductor of the remote input to ground and the output should drop instantly to zero. Removing the short should cause the power output to return, gradually, to its previous level. 14) Deviation reading check. The maximum input sensitivity is determined by the position of the input level control. In the -12/+9 position, the sensitivity will depend on the L/MPX and R/MONO controls. Put the selector in the DEV position. Connect a low-distortion audio generator to the LEFT and RIGHT inputs. Inject a 400 Hz tone at a level of 0dBm (775mVrms=2.2Vpp). Put the INPUT LEVEL control in the 0dBm position. Select stereo mode (corresponding LED will switch on). Enable the pilot using the relevant switch (the green LED will switch on). With the selector in the R/MONO position, check that the reading is 0dBm, measured on the +3db FSD scale. Repeat the operation for the L/MPX. Check that the deviation reading is 100%. Pag. 32 3.4 OPERATION USING THE INTERNAL STEREO CODER (only for stereo version) 1) 2) 3) 4) 5) 6) Inject the pilot tone checking that the corresponding LED switches on. Select STEREO operation confirmed by the corresponding LED. Select the sensitivity of the audio LEFT/RIGHT inputs to match the signal level being supplied to the unit. Connect the signal source to the LEFT/RIGHT inputs. These are balanced inputs

(see setup 2). Check on the internal analog meter that the L/R signal levels are those expected, selecting the desired input with the corresponding control. The effective modulation level may be measured on the analog multimeter by selecting DEV with the corresponding selector. 3.5 CONNECTION OF AN EXTERNAL STEREO-PHONIC SOURCE 1) 2) 3) 4) Connect the stereo sources output to the MPX input of the unit (see setup 3). Adjust the stereo encoder to obtain just the 19 KHz subcarrier output and ensure the total absence of signal on the LEFT and RIGHT inputs of the encoder. Adjust the output level of the encoder to obtain the correct level as displayed on the analog meter of the XT300. Inject audio signals into the LEFT and RIGHT inputs of the encoder and adjust the sensitivity of the input to obtain a peak reading of MAX= 75KHz with both channels enabled. Pag. 33 3.6 MONOPHONIC TRANSMISSION 1) 2) 3) Connect the signal source (audio mixer, receiver, compressor etc.) to the MONO input. This input is unbalanced (see setup 4). Select the desired input level. Adjust the signal level of the equipment connected to the XT300 (with the audio signal present) for a peak reading of DEV MAX=75KHz NOTE: International standards permit a maximum deviation (DEV MAX) of 75KHz for frequency modulated, radiophonic transmissions. Exceeding this limit will only result in the degradation of the signal quality. In the case of mono transmissions the stereo input is available for frequencies between 15 KHz and 100KHZ (i.e. subcarriers for SCA, RDS etc.). Pag. 34 Pages 35-68 intentionally left blank Page intentionally left blank 71 75