Use Manual

SETUP

OPERATION

The DTX-145M uses two connectors for operation and one for factory use. The sub D-15 contains signal, control and

power lines and the RF connector receives low level signals and transmits power. The third connector on the unit is

used for initial factory flash programming of the unit. The radio’s eight transmit and receive frequencies are programmed

via a PC. Pins 1, 2 and 3 of the DB-15 connector select the channel. The receiver bandwidth is fixed in either a wide or

narrow bandwidth and should be ordered as such from the factory. The transmitter can be programmed for either wide

or narrowband deviation on a channel by channel basis. A monitor input activates both speaker and auxiliary outputs,

allowing a modem to continually search for a signal. A high/low RF power control pin allows selection of transmitter

power level. Separate microphone and auxiliary inputs allow either pre-emphasized voice or flat data to be transmitted.

Only one input should be driven at a time. Separate speaker and auxiliary outputs allow either de-emphasized voice or

flat data output. A carrier detect output is pulled high when the channel is busy. Alternately, the MON ITOR input can be

used as a carrier and tone detector output. Adjacent to the DB-15 connector, a dual colored LED appears on the sub D-

15 edge of the board. It has the following functions:

Bright RED while transmitting

Bright GREEN when carrier is present on channel

Bright blinking RED when PLL is unlocked, PA overheats or TX regulator voltage not present while attempting to

transmit

Dull blinking red when receiver PLL is unlocked or TX regulator remains on in receive mode.

INSTALLATION

The antenna should be installed in a location to minimize radiation to the DTX-145M board and DB-15 connector

harness. Antenna positioning is also important in minimizing interference to the receiver. PCs and motors are notorious

producers of electrical noise. In a noisy environment the receiver squelch level can be raised to avoid unwanted

spurious reception.

To maximize transmission power, the power supply cable should be of sufficient gauge to minimize voltage drop.

Measuring the voltage between pin 6 and pin 15 on the DB-15 connector while transmitting will show the actual radio

voltage. For higher duty transmitter cycles, heating of the board should be considered. An external heat sink can be

added to the bottom of the board only version using the two mounting holes on both sides of the RF PA shield. On the

shielded board model the shield will help heat sink the unit. On the encased model the heat is conducted out of the

aluminum end cap opposite the connectors. When transmitting with higher duty cycle usage at elevated ambient

temperatures, without heat sinking, the internal board heat may push the reference oscillator Y301 temperature higher

than the 60 ºC specified limit for 2.5 ppm (VHF). Some form of additional cooling may be employed to avoid this

situation. Operating at voltages higher than 14 volts with high duty cycle usage can generate additional heat from the

regulator. The transmitter voltage regulator regulates the voltage to around 13.5 volts. The regulator will dissipate power

while transmitting when the supply voltage exceeds 13.5 volts. A thermistor, or temperature sensitive resistor,

monitoring the voltage regulator temperature will trigger a transmitter shutdown with excessive heat. Also, a thermistor

monitoring the final RF FET will trigger a transmitter shutdown if it overheats.