DE
DANIELS
ELECTRONICS
VT-3H040 VHF Enhanced Transmitter Instruction Manual
2-1
2
SYSTEM OVERVIEW
2.1
Transmitter Operation
Several modules are integrated by the VT-3H040 Transmitter Main board to provide the
complete transmitter. The Transmitter Main Board, Front Panel Board and Audio Processor are
generic in that they apply to both transmitter models. The Front Panel Board and Audio
Processor are soldered directly to the Transmitter Main Board and are treated collectively in the
Transmitter Main Board Manual. The operating frequency range is determined by the choice of
Amplifier and Frequency Synthesizer, both of which plug in to the Transmitter Main Board and
can be changed with minimal effort. Circuitry and jumpers on the Transmitter Main Board
control the operation of all modules and the operation of the transmitter, overall. Technical
details and a complete description of transmitter operation can be found in the Transmitter Main
Board Manual.
The VT-3H040 transmitter requires two power supplies; a reg9.5 Vdc supply and a
+13.8 Vdc supply, the latter of which is connected only to the Amplifier Module. The
(nominally) +13.8 Vdc supply's range is +11 Vdc to +16 Vdc. The current drawn from the +13.8
Vdc supply (while transmitting at the rated power) varies between 450 mA to 1000 mA with
temperature, operating frequency and power supply voltage. The current drawn by the 13.8 Vdc
line should not exceed 1100 mA. The +9.5 Vdc current drawn by the transmitter in its quiescent
state depends on what modules are enabled during the inactive (PTT off) state. This aspect of
transmitter operation is controlled by jumper settings on the Transmitter Main Board (refer to the
Transmitter Main Board Manual). The m9.5 Vdc quiescent current is typically 15 mA
and occurs when the Synthesizer and Audio Processor are disabled while the transmitter is off
(Mode 1). If Synthesizer and Audio Processor operation is maintained continuously (Mode 4),
the +9.5 Vdc quiescent current is approximately 185 mA. Maintaining continuous operation of
some modules dramatically decreases the turn on time of the transmitter.
The front panel depicted in Section 3.1 bears a DPDT toggle switch (mounted on the Front Panel
Board; see the Transmitter Main Board Manual) which controls the operation of the VT-3H040
Transmitter. When in the 'OFF' position, the transmitter is turned off; however, the +13.8 Vdc
remains on the Transmitter Main Board terminals and on the Amplifier Module. When in the
'KEYED' position, +9.5 Vdc is supplied to the transmitter circuitry and the transmitter is
continously transmitting. When this switch is in the 'NORM' position, +9.5 Vdc is supplied to the
transmitter circuitry although the transmitter remains quiescent until keyed from one of several
Push-To-Talk (hereafter PTT) inputs. The red indicator LED is illuminated during transmit.
Microphone, RF output and optional reference input are mounted on the front panel; power and
other signal connections are provided by a type 'F' connector at the rear of Transmitter Main
Board. Details on their function can be found in the Transmitter Main Board Manual.
