Ritron RIT17-442 UHF FM Transmitter User Manual SST 454 THEORY OF OPERATION

Ritron Inc UHF FM Transmitter SST 454 THEORY OF OPERATION

users manual

DTX-442 PROGRAMABLE VHF FM TRANSCEIVER MODULE OPERATING AND SERVICE MANUAL RITRON INC. 0
TABLE OF CONTENTS SECTION TOPIC PAGE 1. INTRODUCTION General Model Identification FCC REGULATIONS Licensing 5 Exposure to Radio Frequency Energy DTX-442 SPECIFICATIONS GENERAL RECEIVER 3 TRANSMITTER 3 DESCRIPTION OF INPUT/OUTPUT OPERATION MAINTENANCE INFORMATION 5 Surface Mount Repairs 5 Precautions for handling CMOS 6 Synthesizer shield 6 6. PROGRAMMING THE RADIO 9 PROGRAMMING THE RADIO USING A PC COMPUTER 9 Programmable Features 9 COMPUTER SOFTWARE COPYRIGHTS 9 7. DTX-442 THEORY OF OPERATION INTRODUCTION 10 POWER SUPPLY AND VOLTAGE DISTRIBUTION 10 REFERENCE OSCILLATOR 10 SYNTHESIZER 11 RECEIVER 11 Receiver Front End 11 FM Receiver Subsystem 11 Voice and Tone Conditioning 12 TRANSMITTER 12 Voice and Tone Conditioning in Transmitter 12 MICROCONTROLLER 14 8. DTX-442 ALIGNMENT PROCEDURE RECOMMENDED TEST EQUIPMENT 14 RADIO PREPARATION 14 REFERENCE FREQUENCY AND TRANSMITTER POWER 14 TRANSMITTER VOICE AND DATA DEVIATION 15 RECEIVER FRONT END TUNNING 15 RECEIVER SQUELCH 15 1 INTRODUCTION 1
General RITRON's DTX-442 transceiver module is designed to operate in the UHF band from 450 to 470 MHz. The transceiver is a single board unit with a 50 ohm BNC or SMA RF connector and a DB-15 connector providing input/output control. The unit supports voice through a microphone input and a nominal 1 watt speaker output. It supports up to 9600 bps 4-level FSK through its auxiliary in and auxiliary out ports. Each radio can be dealer or factory programmed to contain a unique set of eight operating frequencies and options. When all three channel select inputs are tied to ground the radio operates on channel 1. The channel selection is done in a binary manner on the CS2, CS1 and CS0 inputs. Separate RX and TX Quiet Call (CTCSS) or Digital Quiet call (DCS) tones can be programmed per channel. Transmitter wide or narrow deviation can be programmed on a per channel basis. The unit is set up to transmit 2 or 5 watts when operating at 13.8 VDC. The standby current at 13.8 VDC is 20 mA or less. Model Identification The standard DTX-442 is contained in an aluminum case with a BNC and DB-15. A standalone board version is also available. The DTX-442 model, serial number and FCC Identification are displayed on a label located on the top of the radio VCO shield for board versions or on the non-connector end for cased units. The following breakdown explains the model number. The model number form is: “ DTX-442-OABC ” Where: A is the connector type: B = BNC S = SMA 0 = no connector B designates the IF bandwidth: N = Narrow W = Wide C designates the case: D = deletion of case No designator = case present Examples: DTX-442-OBN 450 to 470 MHz narrowband receiver in case with BNC connector DTX-442-OSWD 450 to 470 MHz wideband receiver with SMA connector and no case Units without case are delivered with a vertical female DB15 connector. 2
FCC REGULATIONS Licensing The FCC requires the radio owner to obtain a station license for his radios before using them to transmit, but does not require an operating license or permit. The station licensee is responsible for ensuring that transmitter power; frequency and deviation are within the limits specified by the station license. The station licensee is also responsible for proper operation and maintenance of the radio equipment. This includes checking the transmitter frequency and deviation periodically, using appropriate methods. Exposure to Radio Frequency Energy: The DTX-442 transceiver consists of a transmitter and a receiver. The transmitter is active when the Push-to-Talk line is connected to ground or when activated electronically and emits radio frequency (RF) energy at a power level up to 5.0 watts. This product has been evaluated for compliance with the maximum permissible exposure limits for RF energy at the maximum power rating of the unit with the whip antenna available from RITRON. To ensure compliance with the Occupational/Controlled Exposure maximum limits, all persons must be at least 20 cm (7.9 inches) from the antenna while the unit is transmitting. Other antennas may require lesser or greater distances to meet the limits depending upon their gains relative to that tested. Higher gain antennas are capable of yielding a higher RF energy density in the strongest part of their field and would, therefore, require a greater separation from the antenna. The antenna tested for this product for RF exposure was the RITRON RAM-1545 with the included 25 feet of coaxial cable. This is the only antenna available from RITRON for use with this product. Other antennas may require lesser or greater distances to meet the limits depending upon their gains relative to that tested. Higher gain antennas are capable of yielding a higher RF energy density in the strongest part of their field and would, therefore, require a greater separation from the antenna. If other antennas are used, it is incumbent upon the installer to insure that the RF exposure limits for General Population/Uncontrolled Exposure are met. See 47CFR1.1307(b)(1)-(3) and/ or OET Bulletin 55, Edition 97-01 for more information on RF exposure guidelines. FCC Label: An FCC label must be visible on the unit as installed in its final configuration. If the unit is to be used as shipped from RITRON, this would be no problem since an FCC label is affixed to the top of the VCO shield. If the DTX-442 is to be installed in an enclosure, the installer must ensure that either the FCC label on the unit is visible through a door, window or other opening, or add a label to the outside of the enclosure. If a label is to be added to the outside of the enclosure, the label must be of a type which is not easily removed or damaged and contain wording: Contains FCC ID: AIERIT17-442. 3
DTX-442 SPECIFICATIONS GENERAL FCC ID: AIERIT17-442 FCC Rule Parts: 90 Frequency Range: 450 to 470 MHz RF Channels: 8 Independent TX/RX frequencies Transmit/Receive bandwidth: 20 MHz Synthesizer Step Size: 12.5 kHz Frequency Stability: +/-2.5 PPM (-30 to +60 C) Tone/Code Signaling: CTCSS (Quiet Call) and DCS Maximum Data rate: 9600 bps with 4-level FSK Power Supply: 8 to 15 VDC Battery Drain: RX Standby: 20 mA at 13.8 VDC RX Receive: 250 mA Transmit: 1.1 Amp @ 5 Watts at 13.8 VDC Dimensions: 5”H x 3”W x 1.25”D Weight: 3.8 oz. Antenna Fitting: BNC female or SMA female Transmitter Duty Cycle: 100 % up to 30 C (above 30 C degrades linearly to 0% at 60 C) 4
DTX-442 SPECIFICATIONS RECEIVER Specifications Wide band Narrow band 25 kHz 12.5 kHz Sensitivity (12 dB SINAD): 0.25 µV 0.25 µV Adjacent channel: -70 dB -60 dB Spurious rejection: -65 dB -65 dB Image rejection: -55 dB -55 dB Intermodulation: -60 dB -60 dB FM hum and noise: -46 dB -40 dB Conducted spurious: -57 dBm -57 dBm Receiver attack time(TX to RX): < 25 ms < 25 ms Noise squelch attack time: < 15 ms < 15 ms (for 20 dB quieting) RSSI squelch attack time: < 5 ms < 5 ms RSSI squelch sensitivity: Manually adjustable; factory set for –108 dBm Noise squelch sensitivity: Manually adjustable; factory set for –121 dBm AUX OUT frequency response: 6 - 3000 Hz @ +1 / -3 dB Audio Output >700 mW into 8 Ω, with less than 5 % THD TRANSMITTER RF Power Output: 1.0 watts @ 13.8 VDC < .4 A 5.0 watts @ 13.8 VDC < 1.1 A Voice Emission Designator: 15K2F3E 10K6F3E Data Emissions Designator: 9K4F1D Deviation: +/- 5.00 kHz +/- 2.50 kHz Transmitter attack time: 20 ms 20 ms FM Hum and Noise: -45 dB -39 dB Audio Distortion: < 5 % < 5 % Spurious and Harmonics: -20 dBm max Aux In frequency response: 7 Hz to 2700 Hz @ +1 / -3 dB 5
DESCRIPTION OF INPUT/OUTPUT The DTX-442 is equiped with a 15 pin female sub D connector with the following functions: Pin# Function 1 least significant channel select bit (CS0) 2 channel select 1 (CS1) 3 Most significant channel select (CS2) 4 Microphone input 5 High/ low power select (pull low to get low power) 6 + 8 to 15 VDC input 7 auxilary input 8 auxilary ouput 9 PC programing port 10 N/A 11 Auxilary monitor input (pull to ground to open squelch) 12 Speaker output 13 Carrier detect output (pulls to 5 VDC through 390 ohms) 14 PTT (pull to ground to transmit) 15 ground Channel Select (pins 3,2,1) Three lines control the channel selection; CS2, CS1, CS0. The inputs have binary weighting of 4, 2 and 1 respectively. Tying an input to ground gives it a zero weighting. Thus, if no inputs are tied low channel eight is selected. Microphone (pin 4) An electret microphone can be connected to the microphone input at pin 4. A 22 k ohm resistor internal to the DTX-442 supplies power to the microphone. High/ Low Power Input (pin 5) Pulling this input to ground will yield about a 2 watt transmit power. Unconnected it will transmit up to 5 watts. Actual power output will depend on supply voltage. Power Input (pin 6) A power source of 8 to 15 VDC with 1.2 Amp capability should be connected here. Once power is applied to pin 6 of the radio the microcontroller will start and load the receive frequency of the channel designated by CS2, CS1 and CS0 (pins 3, 2 and 1). Auxiliary Input (pin 7) This input (pin7) has a frequency response from 2 Hz to 3000 Hz. The input gain is set up to produce +/- 1.5 kHz deviation (3.0 kHz for wideband) when a 300 mV peak-peak signal is applied. The gain can be adjusted by an internal potentiometer R375 for other input levels. Auxiliary Output (pin 8) An output loading of 600 ohms or greater should be applied to this output. With a 600 ohm load the output exhibits a frequency response of 6 Hz to 3000 Hz. Higher load impedances will lower the low end frequency response. The output is adjustable with an internal potentiometer R360. It is preset at the factory to give 1 volt peak to peak output when receiving a +/- 1.5 kHz (3.0 kHz for wideband) deviated signal. Programming Port (pin 9) This line is a bi-directional programming port to be connected to a RITRON programming cable. The other end of the programming cable connects to the PC’s serial port 25 pin D-sub connector. The appropriate DTX-442 programming software must be run for configuring the transceiver. Monitor Input (pin 11) Bringing this input to ground will switch the auxiliary and speaker outputs on. Normally the AUX_OUT and SPEAKER_ OUT are switched on only when a carrier with required tone is detected. 6
Speaker (pin 12) A speaker with 8 ohms or higher should be connected to pin12. As much as 1 watt of audio power at 10% THD is possible. The speaker volume is preset by an internal potentiometer (R350) to yield 2 volts RMS into 8 ohms. If your application requires a different audio level two options exist. One is to open the transceiver unit by removing the 4 corner screws on the connector end of the radio case, pull out the PCB and reset the volume potentiometer (R350). The second is to place a power resistor or potentiometer in series with the output and speaker to reduce or adjust volume. Carrier Detect Output (pin 13) This line will be pulled to 5 volts through a 390 ohm resistor when a carrier is present. If a valid tone carrier detect is needed use pin 11 as an output. Push-To-Talk (pin 14) Pulling the PTT input (pin14) low activates the transmitter, and must be held low while transmitting. Alternately, a microphone with a PTT switch (switched to ground through < 3 k ohm) can be connected to pin4 to activate transmission. A programmable time-out-timer will shut down transmission when PTT is held down too long. 7
PROGRAMMING THE RADIO PROGRAMMING THE RADIO USING A PC COMPUTER RITRON’s programming kit, DTXL-PCPK-2.0, allows programming of the DTX-442 model radios using a PC compatible computer. The PC Programming Kit Includes: 1) Ritron Transceiver programming software, DTXL-PCPS-2.0, which is contained on 3.5" diskettes. 2) Ritron PC to radio adapter cable, 9/RTC-PAS, which is terminated at one end with a DB-25F connector, at the other end with a 6 pin modular plug. 3) Another cable, DTXP-PAC, with a modular jack (which mates to the previous cable) on one end with a DB-15M on the other end to mate to the radio. Power leads are also provided. Red is positive. The PC Programming Kit Requires: A PC compatible computer with Windows 95 or later. The computer must have an RS-232 serial port available. A hard disk drive is recommended. Programming the DTX-442: To program the DTX-442 do the following: 1) Connect the PC’s RS-232 port to 9/RTC-PAS and DTXP-PAC programming cable. Connect DTXP-PAC to DTX-442 2) Apply 8 to 15 VDC power to pin 6 of the DB15 (Red wire) 3) Insert disk 1 in floppy disk drive. View the disk contents and double click on setup.exe. Follow the instructions on screen. When finished the software will be resident on the PC’s hard disk. Using the Programming Software Upon starting the software a form appears identifying the radio frequency band and channel information. The channel information will not be correct, however, until the radio is read. If no radio is connected when the software is started the model displayed will be that of the last radio read by the software and the default parameters for that radio. To read the radio contents click radio on the menu bar and then read radio. Allow several seconds for the reading to take place. To change a parameter click a white field or double click the channel field to access it. Once changes are made to program the radio click radio the program radio. Again allow several seconds for programming. Files can be saved and read using the File menu option. Channel features can be programmed differently on each channel. One channel can have wide band deviation (+/- 5 kHz) on the transmitter and another narrow band (+/- 2.5 kHz). Transmit and receive frequencies and QC or DQC tones on a channel can be different. A channel can also be moved or deleted. A transmit time out timer of up to 254 seconds can be programmed. Entering 255 will disable the time out timer. An ID string of up to 72 characters can be entered to allow PC programmers to identify radios. Computer Software Copyrights The RITRON, Inc. products described in this manual include copyrighted RITRON, inc. computer programs. Laws in the United States and other countries grant to RITRON, inc. certain exclusive rights in its copyrighted computer programs, including the exclusive right to distribute copies of the programs, make reproductions of the programs, and prepare derivative works based on the programs. Accordingly, any computer programs contained in RITRON, inc. products may not be copied or reproduced in any manner without the express written permission of RITRON. The purchase of RITRON, inc. products does not grant any license or rights under the copyrights or other intellectual property of RITRON, inc., except for the non-exclusive, royalty fee license to use that arises in the sale of a product, or as addressed in a written agreement between RITRON, inc. and the purchaser of RITRON, inc. products. 8
MAINTAINANCE Surface Mount Repair RITRON surface mount products require special equipment and servicing techniques. Improper servicing techniques can cause permanent damage to the printed circuit boards and/or components, which is not covered by RITRON’s warranty. If you are not completely familiar with surface mounted component repair techniques, RITRON recommends that you defer maintenance to qualified service personnel. Precautions for Handling CMOS Devices This radio contains complementary metal-oxide semiconductor (CMOS) devices, which require special handling techniques. CMOS circuits are susceptible to damage by electrostatic or high voltage charges. Damage can be latent, with no failure appearing until weeks or months later. For this reason, take special precautions any time you disassemble the radio. Follow the precautions below, which are even more critical in low humidity environments. 1) Storage/transport - CMOS devices that will be stored or transported must be placed in conductive material so that all exposed leads are shorted together. CMOS devices must not be inserted into conventional plastic “snow” or plastic trays of the type that are used for other semiconductors. 2) Grounding - All CMOS devices must be placed on a grounded bench surface. The technician that will work on the radio/CMOS circuit must be grounded before handling the radio. Normally, the technician wears a conductive wrist strap in series with a 100K Ohm resistor to ground. 3) Clothing - Do not wear nylon clothing while handling CMOS circuits. 4) Power off - Remove power before connecting, removing or soldering a PC board that contains CMOS devices. 5) Power/voltage transients - Do not insert or remove CMOS devices with power applied. Check all power supplies to be used for testing CMOS devices, making sure that no voltage transients are present. 6) Soldering - Use a grounded soldering iron for soldering CMOS circuitry. 7) Lead-straightening tools - When straightening CMOS leads, provide ground straps for the tool used. Synthesizer Shield The synthesizer shield should not be removed, unless a component must be replaced. This shield is soldered to the main PC board. The shild can be removed by sucking or wicking the solder up around the perimeter. If this should prove difficult a side cutters can cut the top off after which the walls can be removed. A replacement shield will then be needed. 9
DTX-442 THEORY OF OPERATION POWER SUPPLY AND VOLTAGE DISTRIBUTION The DTX-442 is powered by an 8 to 15 VDC external power supply. F601 is a 3A fuse in series with J301 for short circuit protection. Zener diode D601 prevents over voltage damage by blowing the F601 fuse when over 18 volts is applied. If reverse battery voltage is applied F601 will blow by conducting current through D601. The DTX-442 is designed to consume low current by using a switching DC/DC converter called a buck converter. Receiver standby current is less than 20 mA at 13.8 volts. The buck converter outputs about 40 mA at 6.4 volts. The conversion efficiency of the buck converter is about 90%. Lowering the supply voltage will cause more current to be drawn from the supply. The buck converter’s output of 6.4 volts feeds a 5 volt low drop out regulator U602 and a 6 volt regulator U402. The 5 volt regulator supplies the logic and audio processing ICs and the 6 volt regulator supplies the frequency synthesizer. A voltage regulator consisting of Q601, 2 and 3 limits the RF final PA and audio PA voltages to +13.8 volts. This circuitry is enabled by Q604 only when receiving a carrier, when transmitting or when AUX_MON is enabled. A +8 volt regulator consisting of Q201 and Q202 supply power to the pin diode switches CR101 and CR201 and VCO buffer stage Q210 during transmission. REFERENCE OSCILLATOR Reference oscillator Y301 is a temperature controlled, voltage controlled oscillator (TCVCXO) operating at 14.4 MHz. The Pin 4 output of the TCVCXO provides a reference for the frequency synthesizer U401 at Pin 8. The reference oscillator also feed pin 7 of the U301 microcontroller through a buffer amplifier Q310 and a Schmit inverter U303 to obtain a14.4 MHz clock. The Y301 pin 4 output is also multiplied (tripled) up to 43.2 MHz by Q104 and its associated circuitry to provide a receiver second local oscillator signal. SYNTHESIZER The DTX-442 radio is built around a PLL synthesizer that consists of a receiver voltage-controlled oscillator (VCO) and transmit VCO. U401 contains both a prescaler and synthesizer controller. The prescaler squares and divides the VCO output present at pin 5 by either 8 or 9, determined by a synthesizer controller logic signal. The prescaler changes once every reference cycle at the appropriate time to yield the right frequency. U401 contains a digital phase detector that works as follows. When the receive/transmit mode is switched, a new synthesizer operating frequency is selected. Microcontroller U301 clocks new data into U401 internal buffer in synchronization with clock pulses. The channel information is stored in EE memory of U301 and is loaded into RAM when the channel is selected. Two separate VCO are used in the synthesizer. The transmit VCO operates from 450 to 470 MHz. The receive synthesizer works 43.65 MHz lower than the transmit band. The transmit VCO is turned on by Q405 and the receive VCO by Q408. The transmit VCO has a modulation varactor diode CR401. The loop filter C403, C404,C405, R407 and R408 transform the pin 2 output signal to a DC voltage for application to the VCO tuning varactor CR405 for receiver or CR402 for transmitter. The synthesizer system is “locked” when the phase and frequency of both the reference and the divided VCO signal are the same. Output pin 1 of U401 is brought low for about 1 milliseconds after the frequency is loaded to speed up lock time. Internally the charged pump phase detector current is increased to momentarily widen the loop bandwidth thereby reducing settling time. When the synthesizer is locked pin 14 goes high. If the loop becomes unlocked pin 14 goes low. RECEIVER Receiver Front End The signal from the antenna passes through the transmitter lowpass filter and then goes to the tunable bandpass filter L101 and L102. Q101 amplifies the signal about 15 dB before going through another bandpass filter and mixer matching stage. The receiver is turned on by Q107 and Q108 supplying RX_5v when RXEN of U301 goes high. The amplified received input signal is applied to the base of mixer Q102. The 1st local oscillator signal from the synthesizer module is buffered and filtered by bandpass amplifier Q106 and then applied to the source of 10
Q102. L195, C114, C115 and C135 tune the drain output of Q102 to 43.65 MHz and apply it to Y101 and Y103, a 43.65 MHz four-pole crystal filter. Q103 and associated components amplify the 43.65 MHz IF signal and apply it to the input of the 2nd mixer at Pin 16 of U101. FM Receiver Subsystem A multi-function integrated circuit, U101 and associated components form the FM-receiver subsystem. The subsystem performs the following functions as a 2nd mixer, IF amplifier and FM detector. The second local oscillator at 43.2 MHz is applied to the 2nd local oscillator input at Pin 1 of U101. The 43.65 MHz signal at Pin 16 and the 2nd local oscillator are mixed, with the resulting 450 KHz output signal appearing at Pin 3. This signal is filtered by a 450 kHz 6-pole ceramic filter YF101 and applied to the input of the limiting IF amplifier at Pin 5. IC101 pin 6 de-couples the IF amplifier. An internal quadrature detector, whose center frequency is determined by the 450 kHz quadrature resonator Y102, detects the FM IF signal. One input of the quadrature detector is connected internally to the IF signal from pin11 while the other input is the phase-shifted signal from Y102 at Pin 10. Demodulated audio appears at Pin 9, where a lowpass filter R323 and C309 removes spurious second IF output prior to application to the voice, tone or squelch conditioning audio circuitry. Two types of squelch circuits exist on the DTX-442, an RSSI squelch and a noise squelch. Both types can be used simultaneously or one or the other can be used. The RSSI (receive signal strength indicator) squelch, which is typically set around –108 dBm, must be set to open at a higher level than the noise squelch. This is necessary since the RSSI measures total power in the receiver IF bandpass. All background noise, which at VHF can be high, is seen as signal. The advantage of the RSSI squelch is that it opens and closes the audio paths very quickly. The noise squelch has the advantage that it can be set at a much lower level, typically –120dBm for a 12 dB SINAD. It takes longer to open and close the squelch. If both are used simultaneously, since they are wired ORed together at U301 pin 32, the squelch will open quickly and close slowly for strong signals. If only RSSI is desired for fast audio closure R145 can be removed or R144 can be set fully counterclockwise. Voice and Tone Conditioning in Receiver Three post demodulation paths are provided in the DTX-442. U304c provides DC level translation to bias succeeding op amp stages at about 2.5 volts. The audio path goes through a fourth order 300 Hz highpass filter U305c and d. C326, R353 and R351 de-emphasis the audio. The 1 watt audio amp is turned on by Q311 and Q312. The data path goes through U304a and b. U304a inverts the signal to provide a non inverted data output. U307a is an adjustable gain buffer stage. This stage is squelched by Q311. Sub-audible signals go through a third order 250 Hz lowpass filter U304d, R342, and C316. Pin 27 of U301 decodes the CTCSS or DCS signal. In the case of CTCSS an internal discrete Fourier transform looks for the wanted tone. Decode bandwidth is about +/-2 Hz. Receiver Current Consumption The radio will monitor the channel until a carrier becomes present. When an on channel carrier appears, the carrier detect line (pin 13) will be pulled high through a 390 ohm resistor. If the correct CTCSS or DCS tone is present the radio will unsquelch the speaker and auxiliary output lines. In standby mode the radio consumes 20 mA or less. When unsquelched both the internal regulator and the audio PA are turned on. Total current consumption goes up to about 65 mA. If only the auxiliary output and no voice is needed current consumption can be saved by disabling the internal regulator and audio PA when a carrier is present. This is done by removing R617 and R606 and will bring current consumption down to about 33 mA during receive. TRANSMITTER The transmit VCO feeds buffer stage Q210 which feeds the predriver Q209 and in turn the RF final Q208. The final is a FET device. The power supply to the driver and the final FET biasing is controlled by a feedback power controller. The power control circuitry maintains a constant current supply to the final Q208 transistor. A constant current across the frequency band will yield a level power output if the amplifier efficiency is similar. U201a is a differential amp monitoring current through the four paralleled 1 ohm shunt resistors. U201b is a comparator op amp. Potentiometer R222 is used to set the high level power to 5 watts. When excess current producing power greater than 5 watt goes through the four 1 ohm resistors the output of U201a drops. This in turn causes U201b pin 7 output to drop forcing the voltage on the collector of Q205 to drop thereby reducing power. In the low power mode Q309 gets turned off when U301 pin 9 goes low. This causes less current to flow through the 11
power control pot R222 and raises the voltage on U201b pin 6 causing a lower power output. R222 is preset in the factory to give 2 watts in low power mode and 5 watts in high power mode. A low-pass filter comprised of filter L201, L202, C201, C027, C203 and C204 removes harmonics from the transmitter output before applying the RF signal to the antenna. Two PIN diodes CR101 and CR201 along with associated components form the antenna switching circuit. When transmitting both pin diodes are turned on. CR101 shunts transmitting power to ground at the receiver input to prevent receiver overload. With the DTX-442 in receive mode no voltage is applied to the PIN diodes and they do not conduct. This opens CR201 to prevent the transmitter amplifier from affecting the receiver tuning. Incoming signals from the antenna pass through L203 to the receiver front end. Voice and Tone in Transmitter In transmit mode two audio paths and one tone path exist. The microphone input is high gain pre-emphasized path. R366 and C354 form the pre-emphasis network. Signal limiting occurs in U308a. “Splattered” higher frequency components are later filtered out by the fifth order 3000 Hz low pass filter consisting of U308a, c and d. The data path (AUX_IN) with a flat frequency response goes through an adjustable gain amplifier U305a. The gain should be adjusted so the required deviation is transmitted. Deviation limiting occurs in U305a. It is preset in the factory to give +/- 3 kHz deviation with 100 mV peak to peak input. The CTCSS and DCS sub-audible tone are generated by the U301 pin 13. These tones are generated by the pulse width modulated (PWM) output at pin 13 of the microcontroller. The 8 bit PWM output operates at 14.4 kHz. A simple RC filter consisting of R319, R373 and C338 suppress higher order frequency components. The fifth order 3 kHz lowpass filter further attenuates the 14.4 kHz components. Both the VCO and the reference oscillator are modulated by all signals resulting in a flat frequency response from DC to 2500 Hz. The FM deviation of the VCO is set by the “deviation” potentiometer R388. The reference oscillator’s deviation is adjusted by the “balance” pot R304. The balance pot is adjusted to give a minimal tilt on a DCS generated waveform. The transmit loop bandwidth of the synthesizer is about 100 Hz. The CTCSS deviation from 67 to 254 Hz lies between 600 and 900 Hz in wideband mode. Typical Performance The DTX-442 is an eight-channel synthesized transceiver unit capable of rapid data reception and rapid data transmission at rates up to 9600 bps when using 4-level FSK. The unit maintains 20 mA or less current consumption at 13.8 VDC when in the receive standby mode. The current drain goes up as the voltage goes down. The transmitter also exhibits good efficiency. The following table shows typical DTX-442 performance when set to 5 watts output. Power Transmit Transmit Radio TX Receive Supply Power Current Efficiency standby current (VDC) (watts) (Amps) (%) (mA) 8 1.75 0.55 39.8 28.5 9 2.35 0.61 42.8 25.5 10 3.05 0.70 43.6 23.3 11 3.75 0.77 44.3 21.7 12 4.52 0.80 47.1 20.0 13 5.00 0.80 48.1 19.0 14 5.00 0.80 44.6 17.9 15 5.00 0.80 41.7 17.0 With the unit set to 2 watts the power would rise to around 2 watts and stay there as the supply voltage goes up. MICROCONTROLLER 12
The DTX-442 transceiver is electronically controlled by U301, an 8-bit flash programmable microcontroller. U301 has A/D inputs and PWM outputs for processing analog signals. Radio characteristics are stored in internal EE memory. Its RS232 port is used in programming the radio’s personal characteristics such as frequencies and tones. PIN DESCRIPTION 1 Input is pulled LOW when the PTT input is grounded to initiate transmitter operation. 2 Input is pulled high when high/low power input is grounded. This produces a low RF output power. 3 GROUND 4 +5 VDC VCC supply voltage. 5 GROUND 6 +5 VDC VCC supply voltage 7 XTAL1 is 14.4 MHz reference input from Y301. 8 Input is normally high when PLL is locked and low when unlocked. 9 Output goes high to produce high power RF output. 10 Output drops low momentarily to produce synthesizer latch enable (LE) pulses. 11 Output goes high to enable receiver (RXEN). 12 Output goes high to enable transmitter (TXEN). 13 TONE OUT generates the QC (CTCSS) or DQC (DCS) waveforms via an 8 bit PWM prior to modulating the VCO in transmit mode. Also generates alert tones heard on the speaker. 14 SQUELCH output goes high to apply power to audio amp U306 for receiver speaker audio or radio alert tones. 15 DATA output sends serial data to frequency synthesizer U401 to program frequency information. Also used for flash programming (MOSI) 16 CLK output sends serial data clock pulses to frequency synthesizer. Also used in flash programming (MISO). 17 output is set permanently low to allow CS0 to be a channel select input bit. 18 AVCC supplies +5VDC. 19 Input is used to measure receiver RSSI. 20 AREF supplies the reference level for the A/D and is connected to the regulated +5 VDC. 21 AGND supplies A/D ground. 22 Not used 23 Input is pulled low when the CS2 frequency bit input is tied to ground. 24 Input is pulled high when CS0 channel select bit is pulled low. 25 Output is set permanently low to allow CS1 to be a channel select input bit. 26 Input is pulled high when CS1 channel select bit is pulled low. 27 CTCSS IN is an A/D input sampling the CTCSS or DCS waveform. 28 Not used 29 RESET is held low to start the radio in a known state on power up. 30, 31 SERIAL DATA PORT links the microcontroller to communications from an external data terminal via programming port pin 9 of J301. This allows programming of the DTX-442 EE memory used to store channel frequency and configuration information. 32 CARDET gets pulled low when a RF carrier is detected by the U101. 13
DTX-442 ALIGNMENT PROCEDURE An authorized RF service technician must perform test and alignment of the DTX-442. Do not attempt service of the DTX-442 if not completely familiar with frequency synthesized radio operation. RECOMMENDED TEST EQUIPMENT 1) 0 to +15 VDC, 1A current-limited power supply 3) Oscilloscope 2) RF Communications Test with: 4) VTVM or DMM - FM Deviation Meter - RF Wattmeter 5) RITRON PC Programming Kit - Frequency Counter - SINAD Measuring Device RADIO PREPARATION 1) Remove the DTX-442 from case. 2) Connect the FM communications test set to the antenna connector. 3) Connect RITRON programming cable to radio and PC. 4) Apply 13.8 VDC to the red wire with the black to ground. 5) Run RITRON software and read the radio. 6) Program two channels for band edge tune up, one on the low side of the operating band and one on the high side and another in the middle. (Hint: use a bit of an offset from even frequencies to avoid receiver interference. A good choice is 450.1, 460.1 and 470.1. All of these will be wideband mode. 7) Type in these RX and TX frequencies in three channels. 8) Program the radio with these parameters. REFERENCE FREQUENCY AND TX POWER The DTX-442 is preset at the factory for 5 watts in high power and 2 watts in low power at 13.8 VDC. If you need to change or readjust do the following: 1) Make sure that the unit is at room temperature and power supply at 13.8 VDC. 2) Set the RF communications test set to the transmit mode. 3) Select low edge channel on channel select inputs CS2, CS1 and CS0. 4) Make sure the Hi/low power pin 5 is ungrounded. This selects high power. 5) Ground PTT pin 14 of J301 to transmit. 6) Transmitter frequency error should be less than +/-200 Hz ( assuming your equipment is calibrated) 7) Adjust the trimmer cap on the rectangular reference frequency oscillator Y301 if not within specs. 8) Adjust the power pot R222 to give 4.8 watts (+/- 0.2) 9) Confirm the upper edge frequency produces the same results. 10) If upper edge power is too low spike L208 to reduce inductance and increase high side power. To access L208 remove the copper tape over the access hole on the transmitter shield. The 2 turn inductor will appear beneath this opening. If the high side power is too high squeeze the 2 turn windings closer together to increase the inductance. 11) Check low edge power again. Readjust L201 to balance band edge powers. Replace copper tape over hole. 14
DTX-442 ALIGNMENT PROCEDURE TRANSMITTER VOICE & DATA DEVIATION If the transmitter voice deviation needs adjustment perform the following. 1) Set the RF communications test set to the transmit mode. 2) Set audio filtering from <20 Hz to 15 kHz. 3) Set to FM demodulation with +/- peak deviation. 4) Connect oscilloscope to the demodulated output. 5) Select the mid band channel on channel select inputs CS2, CS1 and CS0 which has no tone on it. 6) Connect sinusoidal 1 kHz audio source to pin 4 microphone input and set to 100 mV peak-peak . 7) Ground PTT (pin 14) to transmit. 8) Adjust deviation pot R388 for peak deviation of 4300 +/- 100 Hz. 9) Stop transmitting, remove mic input and inject a 50 Hz +/- 20 Hz square wave into AUX_IN (pin 7) with the signal amplitude of your data source generator. Adjust R375 to get 3.0 +/- .1 kHz (1.5 +/- .05 for narrowband) deviation. 10) Adjust the balance pot R304 to give a flat sloop on the demodulated output oscilloscope waveform. 11) Readjust R375 to maintain 3.0 kHz deviation. 12) Stop transmitting by releasing the /PTT line on pin 14. *NOTE: Sub audible tone deviation is automatically set to be within 600 to 900 Hz after this adjustment on wide band tone channels. Maximum voice and tone deviation on wide band channels will then be 4800 to 5300 Hz. Narrow band tone deviation will be 350 to 500 Hz with overall deviation of 2400 to 2650 Hz. RECEIVER FRONT END TUNNING If the DTX-442 receiver appears to be less sensitive on one of the band edges the front end tuning coils may need readjustment. Connect a SINAD meter to the SPEAKER output (pin 12). Unsquelch the audio amp by grounding pin 11. Set the generator to the upper band edge frequency programmed at –120 dBm with +/- 1.5 kHz deviation. Adjust coil cores L101 and L102 in until SINAD starts to drop. Back off slightly to maintain best SINAD. Now, set generator to the lowest frequency programmed at –120 dBm. Similar SINAD readings as the high band edge frequency should be obtained. If not, adjust coils slightly. Recheck high end and balance performance. RECEIVER SQUELCH The DTX-442 is capable of two squelch operating modes. Also, both can operate simultaneously. See the theory above. The units can be configured as the user requires. When a low level signal appears the noise squelch opens when the carrier level with 1.5 kHz deviation is –120dBm or greater. When the signal appearing is –106dBm or greater the RSSI squelch opens the audio with an even faster attack time. The above levels are factory set levels. Ambient noise will affect the level at which the RSSI should be set. The squelch level ideally should be set on the desired frequency, in the actual location the radio will be used and connected to the desired antenna. The level should be set high enough to reject most false signals. If a very fast receiver decay time (or squelching after signal disappears) is needed the noise squelch should be defeated by turning the R144 pot fully counterclockwise. To adjust squelch levels for simultaneous use do the following: Set RSSI squelch level first: 1) Temporarily defeat noise squelch pot by turning R 144 to counterclockwise minimum setting. 2) Adjust RSSI pot R123 fully counterclockwise to squelch audio. Be sure AUX_MON line is high to allow squelching. 3) Set generator to –106dBm on channel desired with 1.5 kHz deviation and 1 kHz tone. Add any CTCSS or DCS as needed. 4) Turn R123 clockwise until audio opens. Go no further if you want only RSSI squelch functionality. Now set noise squelch: 15
1) Select a channel. 2) Adjust squelch pot R144 fully counter clockwise. 3) Adjust the communications test set generator on frequency with an output level of –120dBm. The deviation should be +/- 1.5 with a 1 kHz audio signal. 4) Slowly adjust squelch pot R144 clockwise until squelch opens. 5) Reduce generator level until radio squelches. 6) Increase generator level until audio opens. Confirm squelch hysteresis is between 0.5 and 5 dB. 16

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