025-9209K 65
APPENDIX A
COMMUNICATING OVER TWO-WIRE BALANCED LINE (600
)
Zetron’s Model 1700, 1708, and 1716 RTUs all have similar data transmission circuitry. That
circuitry is designed to operate with most makes and models of two-way radios. This
applications note is designed to assist in connecting the Model 17xx units over wireline for
data transmission over long distances.
R2
RTU
P3
+12 VDC
GND
PTT OUT
PTT COM
COR
GND
TXREQ
TXAUD
RXAUD
600
600
Dedicated Leased Line
Impedance Matching
Transformer
R1
1
10
External Devices: R1=560, R2=10K, T1=(600 ohm)
Jumper Positions
JP3: Pos B (PTT to GND)
JP9: Pos B (600 ohm TX)
T1
Figure 8. Leased Line Interface Circuit
Notes
Loss of signal will result from lack of proper grounding. Transformer will have to be a
balanced 600Ω transformer for this to work properly, otherwise there will be additional
signal loss. Transformers can be purchased through Zetron, part # 305-0022, or through a
vendor. Resistor values should be observed.
Leased Lines
This application is for a dedicated leased line. Normal dial-up lines will not work. RTUs do
not have the capability of dialing and waiting for a response. In this situation, when the unit
reports a change of state, it will simply send the information.
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