Midian TRA, Instruction Manual

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and Mod Pot R58. When U4-B is ready to re-encode the
tones, it will switch the modulation path over to the DAC
output coming in from Pin 1 of U4-B.
Transmit telephone audio is applied to the low pass filter
when the micro switches on U4-B Pin 2. With JU6
installed, the output impedance is approximately 1KW,
and the output impedance is approximately 27KW if
jumper JU6 is not installed.
U5-C is the VOX amplifier which feeds transistor Q4,
which acts as a detector instantly charging C19 which has
about a 50 msec time constant. This signal causes
Schmidt trigger U5-D to tell the micro to key up the
transmitter with an additional VOX delay time which has
been programmed in
Vox Hold Timer . The micro asserts
PTT out by turning on Q9.
Squelch is controlled by Transistor Q8 and the polarity is
selected by Jumper JU7. When using positive squelch
the 47K resistor may be lowered if more current is
needed. The horn transistor Q10 is a VMOS power FET
and provides a momentary ground to honk the horn for the
time programmed in
Horn Period .
Channel Scanning. There are two types of channel
scanning on the TRA, binary and step scanning. The
binary scan uses a three line address on P1-2, P1-6 and
P1-12. When binary is employed remove Q11 and install
a jumper from its base to its collector. In the step
scanning Q11 is normally installed and the base collector
jumper is omitted. Q11 is an open collector circuit which
can be used to step push button type radios. The type of
scan is selected in
Scan Step . Busy Lockout, #
Channels to Scan controls busy lock out and the number
of channels to scan. When using the step scan feature a
maximum of 16 channels is available When using the
binary method a maximum of 8 channels is available.
This is due to the limitation of 3 binary address lines.
MIDIAN CONTACT INFORMATION
Midian Electronics Inc.
2302 East 22
nd
Street
Tucson, Arizona 85713 USA
Orders: 1-800-MIDIANS
Service: 520-884-7981
Fax: 520-884-0422
E-mail:
sales@midians.com
Web: http://www.midians.com/