Tigertronics RTX-12 Quick Start Manual

Grants Pass, Oregon

- INTRODUCTION -

The RTX-12A and RTX12OEM are half-duplex 1200 baud
radio modems, designed especially for telemetry and remote
data transfer applications using inexpensive "voice grade"
radios. While the standard RTX modem is Bell 202
compatible, an optional CCITT v.23 model is available.
The RTX modems provides an inexpensive solution to
interfacing computers and microcontrollers to radio links.
The modem utilizes FSK audio tones to provide reliable
communications over narrow bandwidth channels.
modem is easily interfaced to radios designed for either
telemetry or voice communications (hand-held, mobile or
base). The data interface is designed to be compatible with
both standard RS-232 levels and CMOS logic levels. The
total power consumption is less than 25 milliwatts, making
it ideal for battery powered applications. When operated
from a standard RS-232 port, no external power source is
required. The modem has it's own micropower voltage
regulator, allowing it to operate from a single polarity
unregulated power source as low as +4.8 volts. Thus, it can
be powered directly from the +5 volt logic supply in
microcontroller applications.
The RTX-12 is available in two different versions: The
RTX-12A and the RTX-12OEM.
functionally and electrically identical. The only difference
between them is their physical layout and the connectors
used for the radio and data interfaces. The RTX-12A is
packaged in a custom injection molded case and is designed
to plug directly into a standard 25-pin RS-232 serial port.
Connection to the radio is through an RJ-11 connector
(cable included). The RTX-12OEM model is intended for
embedded applications and is provided without an
enclosure. This modem is extremely small (1-1/4" x 1-
1/2") and is easily installed inside other equipment. A
single 10-pin header provides connections for both the radio
and controller. An optional color coded ribbon cable is
available for this modem.
Model RTX-12 Radio Modem
154 Hillview Drive Grants Pass, Oregon 97527 (541) 474-6700 Fax: (541) 474-6703
The
Both versions are
Both the RTX-12A and the RTX-12OEM are normally
supplied with full transmit and receive capability. However,
in high volume applications, either modem can be specially
ordered in a Transmit or Receive Only version.

- RADIO INTERFACE -

The radio interface on the RTX-12 consists of four signal
lines and is described in detail below. Please refer to the
"Specifications" section for the specific connector and pin-
out used with each version of the modem.
Ground - This is the signal ground for both microphone and
receive audio from the radio. It is also connected to power
ground in the modem.
PTT - This line is used to "key" the transmitter.
modem switches this line to ground with a FET transistor,
when it receives a transmit command. The transistor can
"sink" currents as high as 50ma. When interfacing older
radios that use mechanical switches (relays) in the PTT
circuit, precautions must be taken to insure that voltage and
current limits are not exceeded (see specifications). Special
provisions have been made to key the PTT of some "hand-
held" radios. See the "HT Operation" section for details.
Rx Audio - This is the receive audio input to the modem. It
is high impedance and capacitively coupled inside the
modem. The nominal input level is 300mv p-p. A factory
option is available to attenuate this input and/or provide a
lower impedance if required. Care should be taken not to
overdrive this input (see specifications).
Mic Audio - This is the transmit audio output from the
modem. The output is capacitively coupled and should be
connected to the microphone input of the radio. The level
of this output can be adjusted by the "LEVEL" control on
the RTX-12 from zero to 290mv p-p (Hi Z). The output is
factory adjusted to 20mv p-p into a 1000 ohm load. This
level should be correct for most modern radios that use
"electret" type microphone inputs.
available to modify the output level.
CAUTION - Be sure that the cable you plug into the RJ-11
connector (RTX-12A only) does not have the wires in
reverse order! Verify the orientation as follows: When
viewing the connector from the rear of the RTX-12A,
oriented such that the release lever is UP, the left most wire
MUST BE YELLOW.
The
A factory option is