© Copyright Wood & Douglas Ltd 1998 version: 1.
Contents Section 1 An overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Section 2 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 USER CONNECTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Section 3 Technical description . . . . . . . . . . . . . . .
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Section 1 An overview Wood & Douglas are an independent UK company dedicated to the design and manufacture of high quality RF designs for the telemetry, security, broadcast and video markets world-wide. The information given in this manual is Copyright Wood & Douglas and is provided to the original purchaser for the purposes of operation and routine maintenance.
1.1 GENERAL DESCRIPTION The ST500 can be configured for analogue or digital operation and is available in the frequency range of 405 - 470MHz with a 12.5kHz channel spacing. The transmitter requires a nominal 12 volt DC supply connected via PL7. However the unit will function correctly within the limits of +6.0V to +14.0V. The output power of the transmitter is normally preset to 100mW nominal.
Section 2 Operation 2.1 USER CONNECTIONS Connection to the ST500 transmitter is made via three headers, PL1, PL2 and PL3, which plug directly into the user's own equipment. The location of these connectors is shown in the General Arrangement drawing given at the back of this manual. The details of these three connectors are detailed below: PIN NAME 1 0V 2 Tb Xb E b 3 FUNCTION REMARKS 0 volts common ground transmit enable o/c = transmitter disabled LOW <+0.8V = transmitter enabled 1KÙ nom.
PIN NAME 1 0V 2 RF O/P 3 0V FUNCTION REMARKS 0 volts common ground RF output 50 ohms output 0 volts common ground Connector PL2 pin detail PIN NAME 1 +VIN 2 0V FUNCTION REMARKS positive supply +6.0V to +14.0V 0 volts common ground Connector PL3 pin detail 1891 1210 1.
Section 3 Technical description Refer to the circuit diagram WD1632 at the rear of this manual. 3.1 POWER SUPPLY DC power is connected to the transmitter module via PL3. The positive side of the supply is fed to TR2 which acts as a series switch; when PL1 pin 2 is connected to 0V to enable the transmitter then base current flows to TR2 via D6 and R54 and turns TR2 on.
RV2 is connected as a variable resistor and consequently controls the amplitude of the modulation signal to both oscillators; RV2 therefore sets the overall frequency deviation of the transmitter. RV3 controls the amplitude of the modulation signal to only the UHF oscillator.
control loop while C39 and C38 provide low-pass filtering at frequencies outside the bandwidth of the control loop. This is necessary in order to filter out residual narrow pulses which appear at the output of the phase comparator in IC6. C37 is provided for decoupling purposes at RF frequencies. IC6 also provides a ‘lock detect’ output at pin 7. This output is rectified and filtered by D1 and C23, then fed via R29 and R26 to pin 18 of microprocessor IC3.
Microprocessor IC3 provides an output at pin 11 (‘+Vtx’) when the transmitter is enabled and no out-of-lock condition is detected. This output is a stepped voltage ramp (which limits at +5V) and is fed via R45 to potentiometer RV4. C43 smooths out the steps in the voltage ramp. The wiper of RV4 is connected to the non-inverting input of operational amplifier IC4a. The inverting input of IC4a is connected to the emitter of TR4 while the output of IC4a is fed via D5 and R36 to the base of TR4.
3.5 FREQUENCY PROGRAMMING 3.5.1 Introduction The ST500 has an internal memory which can store up to 128 RF channels (16 randomly programmed and 112 sequentially programmed). The frequency and set-up information is programmed into the unit by a synchronous PCM interface protocol. The software supplied with the ST500 transmitter is the ST500PRG.exe program. The software can be run on a PC with the serial port connected to PL1 of the ST500 transmitter via a suitable adaptor as shown in Figure 2.
ST500 Programmer Synth. step freq. Chan Chan Chan Chan Chan Chan Chan Chan Chan Chan Chan Chan Chan Chan Chan Chan 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 458.5 MHZ << 458.5125 MHz 458.525 MHz 458.5375 MHz 458.55 458.5625 MHz 458.575 MHz 458.5875 MHz 458.6 MHz 458.6125 MHz 458.625 MHz 458.6375 458.65 MHz 458.6625 458.675 MHz 458.6875 Start table 458.7 Max. Freq. 458.95 MHz Table step 1 x 12.5 12.5 KHz Ref. (TCXO) freq. 12.
3.5.4 Parallel Channel Selection To enable parallel channel selection mode select the F8 (Select channel) function key and then enter ‘999' as the new frequency. The screen then displays ‘parallel mode selected’.
3.5.6 Programming Sequential Channels To generate a new frequency table the following parameter values must be entered: - start frequency - the maximum frequency - the table step as a multiple of 12.5kHz. The maximum frequency is calculated from the start table frequency and the table step.. Therefore if the calculation exceeds the maximum frequency then this parameter will be increased automatically. When the frequency table has been generated the user then selects F6 to program the unit.
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Section 4 Technical specifications Frequency range Switching bandwidth Frequency stability Number of RF channels : : : : RF output power into 50 ohm : : : : 405 - 470 MHz 8 MHz +/-2ppm up to 128 (16 randomly programable, 112 sequential), serial select/reprogram, 1200 baud RS232 or 1 of 8 parallel select 100 mW adjustable to 5mW 1 - 10 mW version available <200nW (-37dBm) <60 mS : : : : : : : 200 mV to 5V p-p AC coupled +3 to 12V square wave DC coupled 9Hz to 3kHz at -3dB +/-1.5kHz nom (±2.
