Digital Traffic Network

This week, my amateur radio station became an official digital traffic network (DTN) station. The main operating digital mode is PACTOR, an evolution of both AMTOR and packet radio. PACTOR uses a combination of simple phase shift keying (FSK) modulation, and the ARQ protocol for robust error detection and data throughput. PACTOR is most commonly used on frequencies between 1 MHz and 30 MHz.

I first looked into PACTOR last fall. I abandoned the idea when I learned that the terminal node controllers (TNCs) cost hundreds of dollars, an investment I was not comfortable making at the time. In December, I asked around about becoming a DTN station operator. I was told that the operational mode was PACTOR and I balked about having to obtain the necessary TNC. Then I was told that a used TNC would be provided. All I had to pay was a $15 dollar shipping charge. That was more than acceptable. Soon, the loaner TNC arrived. It was about 25 years old and supposedly could handle the required PACTOR digital node.

Advanced Electronic Applications, Inc. PK-232MBX TNC

I found a appropriate AC/DC adapter, but I had to jury-rig a mic cable to connect it to my radio and the 5 pins on the back of the TNC. I also had a audio cable on hand for the radio output to the TNC. An RS-232/serial port USB adapter cable connects the TNC to my laptop PC.

Breadboard for connecting a CAT6 twisted-pair cable to the TNC

The AirMail software was downloaded and installed on my laptop. That needed to be configured to interface with the TNC. The TNC was switched on and AirMail was opened. Following initialization of the HF mode, the TNC successfully initialized. My radio AGC was set to 6 and for 40 watts output. It was then tuned to a frequency for a nearby PACTOR station. Then the receive threshold was properly set on the TNC. I tried to connect to a PACTOR station but no joy.

After several days of troubleshooting, with the assistance of two fellow amateur radio operators, I tried a loopback test on the TNC. This involved disconnecting the TNC from the radio and connecting the mic and audio input pins, on the TNC, with a jumper wire. Then a terminal software app was setup to connect the TNC with itself. This test failed and indicated the problem was with the TNC.

I was able to obtain an identical TNC on eBay for a modest and very affordable price. When it arrived, I quickly set it up for a loopback test. The test was successful. I then connected it to my laptop and radio, and it successfully connected to a PACTOR station. The operators of two PACTOR stations modified their configurations to recognize my station. Then I was able to send and retrieve national traffic system (NTS) messages.

I now routinely log in to retrieve NTS messages from The 3rd Region Hub for The Western Pennsylvania Section, on every even numbered day, sharing the responsibility with another amateur radio operator who checks in on odd numbered days. After retrieving messages, I relay them via The Western Pennsylvania Phone Traffic Net, or deliver them via phone, email or US Mail. I also originate my own messages to send via the NTS.

Contact me if you wish to originate an NTS message.

2 thoughts on “Digital Traffic Network

  1. Laura March 8, 2021 / 9:20 PM

    Nice job, Bill. I was lost with the terminology but happy the second TNC worked.


  2. Marcia March 5, 2021 / 2:00 PM

    Impressive entry, Bill! To be perfectly honest, your technical terminology lost me quite early, but I enjoyed reading about the entire process. I don’t know how you know what you’re doing and what you need to do throughout each step!! The photos remind me of movies when scientists are trying to save society from evil forces.


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