Parts List

2-6 Transmitter Main Board Instruction Manual
2.1.4.2 Crystal Controlled Transmitter
The OC-3 Crystal Control Oscillator module is a direct replacement for the synthesizer module and
therefore uses the same connections as the synthesizer to connects to the MT-3 Transmitter Main
Board. The channel select lines and switches FSW1 to FSW4 are not used by the crystal control
module as the transmitter's operating frequency is determined by the Crystal Control Oscillator
module's crystal frequency. A frequency multiplication factor, described in the manual for this
module, relates the crystal frequency to the operating frequency .
2.1.5 Amplifier Circuits
The MT-3 series Amplifier has 6 connections that are cabled to the transmitter board: +13.8 Vdc,
+9.5 Vdc, Enable, Forward Power Sense, Reverse Power Sense, and Ground. The +13.8 Vdc
supply (JP1-3) is always on while the +9.5 Vdc supply (JP1-2) is always switched by a PTT
signal. The enable line (JP1-1) is active low and is controlled by the Qualified PTT signal from
the synthesizer module or crystal controlled oscillator module.
Jumpers J12, J13, J14, and J15 are used to configure the amplifier's forward and reverse power
sense lines (JP1-4 and JP1-5). Normally jumpers J13, J14, and J15 are in the 'x' position which
directly connects the amplifier's forward and reverse power sense lines to the backplane connector
(pins B26 and Z26 respectively). The forward and reverse power sense lines from the Amplifier
can be open collector or linear outputs depending on how they are configured in the amplifier
module. In open collector configuration the lines are active low, that is, the output will go low
when a 'fail' condition is detected. If both lines from the amplifier module are configured as open
collector outputs, the power sense lines can be 'OR'ed together to make a general fail indicator
(jumper J12 in, jumpers J13, J14, and J15 in the 'y' position). The Fail Indicator is also an open
collector output; however, the Fail Indicator is active high (the output goes high when a 'fail'
condition is detected). When the transmitter is configured with the general fail indicator option,
pin Z26 (VSWR reverse) is not used and pin B26 becomes the Fail Indicator output.
2.1.6 Time-Out-Timer Circuitry
The MT-3 Transmitter also has an associated programmable push-to-talk (PTT) time-out-timer
(TOT) circuitry on the Tra nsmitter Main Board. The TOT circuitry is powered via J34 from the
continuous +9.5 Vdc supply and is programmable for various time -out periods.
The TOT input trigger (enabled by J33) is normally high and in this state the timer is disabled.
When the input trigger level falls below +2.0 Vdc, the timer is activated, the TOT output trigger
(enable by J35) is pulled low, and the transmitter is keyed. If the input trigger rises above +2.4 Vdc
or if the time-out period is exceeded, the output trigger will go high, disabling the transmitter. If the
time-out period is exceeded, the TOT input trigger must go high and then low again in order to
rekey the transmitter.