Specifications

TNC GPS Upgrade Addendum/
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with different connections, we can’t provide you with schematics on how to build this
cable.)
3. Get the APRS software program running. APRS will ask you some questions, simply an-
swer the questions and your TNC and APRS will be ready for dual port mode operation.
Building your own APRS adapter cable
The APRS adapter cable works as follows:
The adapter allows for Hardware Single Port mode (HSP) operation, so you only need one
computer COM port for both your GPS receiver and TNC. The adapter normally has the TNC
switched to the computer until APRS decides it’s time to send its location report. When it’s time
to send position information, the computer running APRS asserts flow control to the TNC to pre-
vent it from sending any more data. The flow control line is also used to switch the adapter to the
GPS receiver. Once the GPS string is received, the computer running APRS releases flow control,
switching back to the TNC.
A pre-made and tested cable can be purchased from Timewave for $30.00, plus shipping and
handling. Visit the Timewave website, http://www.timewave.com.
An APRS adapter cable can be made from the following components and schematic.
ItemItem
ItemItem
Item
DescriptionDescription
DescriptionDescription
Description
QtyQty
QtyQty
Qty
Timewave Part #Timewave Part #
Timewave Part #Timewave Part #
Timewave Part #
Radio Shack Part #Radio Shack Part #
Radio Shack Part #Radio Shack Part #
Radio Shack Part #
1. PCB 1 013-141
2. 1K resistor 1 210-102 271-023
3. 10K resistor 2 210-103 271-034
4. IN4148 diode 2 310-001 276-1122
5. 2N3904 NPN transistor 2 320-001 276-2016
6. DB-25 male connector 1 420-102
7. DB-25 female connector 1 420-105
8. DB-25 hood 1 053-065
9. Screws for hood 1 053-065-1
10. Saddle washers 1 053-065-2
11. Hex nuts 1 053-065-3
12. 6ft shielded cable 1 769-001