Every station in a Terrestrial Amateur Radio Packet Network consists of a Raspberry PI, a TNC, a radio, and an antenna.
A station with only one radio and TNC is called a Terminal.
Some TARPN stations will have more than one TNC, radio and antenna.
An important point is that the Raspberry PI TARPN architecture is expandable. You can start with one port, and add more later if the need arises.
The drawing below represents a three port node, with three sets of TNC + radio + feedline + antenna. The drawing also shows only mobile radios and on 3 separate ham bands. It shows the TNCs connected using Insulation Displacement Connectors and ribbon cable to the Raspberry PI. These TNCs are TNC-PI and are available from Coastal Chipworks for $40 each. The Raspberry PI and memory card cost about $50 from Amazon or other vendors. See Node Shopping List.
Why multiple radios? Why multiple bands?Each station can have one or more links, one link per neighbor. TARPN nodes use dedicated point to point links to neighbors to overcome congestion and collision problems.
See Networking on Purpose for the why of dedicated links.
Each link runs asynchronous to each other link and so you could have inbound traffic on one link while transmitting a message on another. While it is possible to receive on a radio while transmitting on another on the same band without blocking the receiving radio, it is much easier to do that when on different bands. It may seem difficult or complex to do multiple bands. It is easier to do multiple bands than to do two radios on the same band.
The antennas shown include a separate antenna for each radio. You could use a multi-band vertical. Or a mag-mount.
The only required part of the node is that it uses a Raspberry PI. Everything else is dependent on the situation the node/switch is being built for.
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