Rev. 07/14 RITRON DTXM SERIES II DTXM-X60 FAMILY PROGRAMMABLE WIRELESS FM MODEM TRANSCEIVERS VHF/220 MHz/340-400 MHz/UHF 6.25 kHz/12.
1 INTRODUCTION 1.1 GENERAL The DTX Plus Series II modem is a wireless modem designed to operate on the frequency bands at VHF, UHF, and 220 MHz. It supports over-the-air data rates of 4800 bps in a 5.0/6.25/7.5 kHz channel, 9600 bps in a 12.5/15 kHz channel, and 19.2 kbps in a 25/30 kHz channel. The modem supports three protocols, the legacy packet protocol of the DTXM-X54 series, a small-packet streaming protocol, and a no-overhead streaming protocol with no error detection/correction.
F designates the regulator option I=Internal regulator (10-16 VDC operation with regulated RF power amplifier) D=No regulator (7.5 VDC operation) L=RF PA is unregulated, but the remainder of the modem is regulated (10-watt versions) Example: A DTXM-460-OBN6I would be a UHF module for operation between 450 and 470 MHz with a BNC RF connector, narrow (12.5 kHz channel spacing) IF bandwidth, 6 watts maximum output power, and an internal regulator to allow operation from 10 to 15 volts. 1.3 FCC REGULATIONS 1.
2 SPECIFICATIONS 2.1 GENERAL FCC Rule Parts IC Rule Parts Data rate (bps) 6.25 kHz channel 12.5 kHz channel 25 kHz channel Modulation Voice Data Over-the-Air Protocols Number of Channels Operating Bandwidth VHF 220 MHz 340-400 MHz 400-430 MHz UHF Synthesizer Step Size VHF 220 MHz 300-430 and UHF Emissions Bandwidth Voice Not allowed 12.5 kHz channels 25 kHz channels Data 6.25 kHz channels 12.
FM Hum and Noise 6.25 kHz channel 12.5 kHz channel 25 kHz channel Current Drain 1 watt 2 watts 6 watts 10 watts 2.3 35 dB min. 40 dB min. 45 dB min. 1.1 A max. 1.6 A max. 2.2 A max. 2.6 A max. RECEIVER Sensitivity Voice (12 dB SINAD) Data (10-3 BER) Adjacent Channel Selectivity 6.25 kHz channel 12.5 kHz channel 25 kHz channel Spurious and Image Rejection IMD Rejection FM Hum and Noise 6.25 kHz channel 12.5 kHz channel 25 kHz channel Conducted Emissions Squelch Attack Time Receive Current Drain 0.
3 DTXM I/O CONNECTOR AND INDICATORS 3.
This is the positive power supply input for the modem. Pin 7 Receiver Alginment This pin is the output pin of the modem IC’s input operational amplifier. It is used during alignment to set the receiver gain and DC offset for proper modem IC receiver decoding. This pin must be left unconnected by the user! Pin 8 RD (Receive Data) RS-232 data to be received from the modem is available at this pin.
3.2 INDICATORS The DTXM Modem has two indicators on the side of the unit, one green RX LED and one red TX LED. They function as follows: GREEN RX LED-This LED can be programmed to be illuminated under a variety of conditions. The choices are: Never (Off), whenever power is applied (Power On), when receiving, whether or not an actual signal is on the frequency (RX Synthesizer Lock), and when receiving and an actual data packet is being received (RX Data).
4 OPERATION 4.1 CHANNEL SELECTION Via the 15-pin connector, the DTXM supports one channel if the A/B pin (pin 4) is programmed for high/low power and two channels if the A/B pin is programmed as a channel select input. Channel A is set when the A/B pin is activated and the A/B pin is in the logic high state i.e. above 2.0 volts DC or left unconnected (There is an internal pullup resistor on the A/B pin). Channel B is set when the A/B pin is activated and the A/B pin is in the logic low state i.e.
Warning: Although the output power can be set as low as 1 watt, and the module is certified as low as 1 watt, operation below 2.5 watts output power is not recommended. At low power levels, the output power can vary by 50% or more with variations in ambient temperature. Transmit Mode – 3 watt output power Supply Voltage Internal Regulator 7.5 V 11.0 V 12.5 V 16.0 V No Yes Yes Yes Current Drain 1.8 A 1.4 A 1.2 A 0.
Blowing air across the unit and/or adding a heat sink to the rear of the unit where the PA module is located can significantly improve the duty cycle/key-down times. Ritron offers an option where the case screws at the rear of the module are longer allowing heat sinks to be attached. Also, a fan option is available from Ritron which can significantly increase the duty cycle, up to 100% at room temperature in some cases.
4.5 INSTALLATION The DTXM modem has two connectors, a BNC for the RF (Antenna) connection and a 15-pin Dsubminiature for the data/programming interconnection. The BNC connector should be connected to a suitable antenna or RF dummy load or attenuator, depending upon the installation. If an antenna is connected, it should be placed at least 10 ft. away from the radio itself to prevent RF interference. Also, any antenna must present a good 50-ohm RF load (low VSWR) at the operating frequency.
The button at the upper right is the Programmer Configuration button and is used to set the serial communications baud rate for communications between the programmer and the host computer. It defaults to 38400 baud, but can be set to other common serial rates. In addition, if the host computer baud rate is unknown, the Test Configuration button can be selected to auto-detect the baud rate. Selecting OK confirms the choice of baud rate.
particular model use. In addition, there are five other tabs and five buttons that can be selected. These are summarized below: 5.2 PAGE TABS The page tabs show up on all of the pages. Clicking on a tab moves one to that page. Frequency-as explained above, this page allows the observing and entering of operating frequencies. The other tabs are shown below and their contents will be detailed in later sections. General-shows the general operating parameters of the modem.
5.4 GENERAL TAB PAGE The General Page is shown below: The selections are: A/B Input One or Two Channel-Determines the function of the A/B pin. This pin can be used to control the power selection, high or low, for one channel, channel A or it can be used to choose between channel A and channel B, in which case, the output power is high for both. Comm Port Baud Rate-Determines the baud rate for communications between the data device and the radio modem.
TX Low Power/TX High Power-This allows setting the RF output power for the two states of the low/high power pin. The low-power selection corresponds to the low logic level of the pin while the highpower selection corresponds to the high logic level. Note that the high-power selection does not necessarily have to be greater than the low-power selection. Each is independent of the other and only corresponds to a state of the power select pin.
Test Patterns (via Test Pin)-Selecting any of the selections in this box will cause a test pattern to be transmitted when the Test Pin (PTT) is active. If no selection is made, activating the Test Pin will cause the radio to transmit in analog/voice mode. The choices are: Bit Error Rate (BER)-A pn pattern is generated which allows for the computation of bit error rate, setting deviation, or observing an eye pattern. The pattern is 511 symbols long with no synchronization symbols and repeats continually.
5.6 ANALOG TAB PAGE The analog page allows selection of the analog/voice mode parameters and is shown below: The selections are: TX pre-emphasis-Selects whether the external audio signal is pre-emphasized i.e. had its high-frequency audio content boosted or whether the signal is sent with a flat audio response. Voice signals typically use pre-emphasis. RX de-emphasis-Selects whether the external audio output signal is de-emphasized i.e.
Carrier Detect On (dBm)-Sets the RF signal level in dBm such that the carrier detect pin will go active and the output audio, if squelch is selected, will go unmute. Carrier Detect Off (dBm)-Sets the RF signal level in dBm such that the carrier detect pin will go inactive and the output audio, if squelch is selected, will be muted. Note: The Carrier Detect On level must be set to be higher (less negative) than the Carrier Detect Off level. 5.
5.8 RESTORE EE PAGE This page allows the configuration of the radio to be saved for loading into other DTX Series II radio modems. This page is shown below: If it is desired to save the current configuration, one of the three boxes should be checked.
