Winter 2007 Issue

HSMM

Building an Amateur Radio Digital Network
New Opportunities for Radio Amateurs


By John Champa, K8OCL
This month’s HSMM column is guest authored by Paul Toth, NA4AR.

Anyone who has ever linked two or more analog voice repeaters together knows you need several key ingredients to build a network. You need spectrum diversity for the repeaters and the linking fabric, vertical real estate to mount the antennas, security to control how the links and repeaters are managed, and RF (radio frequency) systems. Building a broadband, HS (high-speed) digital network requires those same ingredients, as well as a working knowledge of a number of industry-standard networking protocols.

Now you can start building your RF network with no particular purpose or goal in mind other than maybe the experimentation factor and what I will call “pure nerd enjoyment.” However, I would recommend some thought be given, up front, to how the network could or will be used once it is built. Unlike the analog voice repeater network, a digital broadband network can carry many different kinds of traffic simultaneously. You might have live data streams originating from weather sensors operating in your area. As good as APRS (Automatic Position Reporting System) on 144.39 MHz is, the bandwidth available at 1200 baud HD (half duplex) limits the amount of data you can collect and transmit. Collecting live weather data from a network of sensors every minute at 1200 baud is not practical. However, tie those sensors to a broadband RF system capable of transmission rates measured in Mbps (megabits per second) and collecting that data every minute is practical.

You might want your network to serve as a transport for live streaming video, web services, e-mail (SMTP, or Simple Mail Transport Protocol) messaging, and IM (instant messaging) chat. You might want to build this network to provide the backbone for a conventional or digital voice repeater system. Or, you might want your network to do all these things and more. IT (information technology) professionals will tell you the best way to build a network is to develop a utilization plan up front. That way, you will not be committing endless time and resources engineering and re-engineering your network.

Once you have some idea of how your completed network will be used, you can start planning your network design. Radio amateurs have long held in their back pocket a number of key, licensed spectrum allocations upon which to build a viable digital network. These include:

• 902–928 MHz (33 cm)*
• 1240–1300 MHz (23 cm)
• 2390–2450 MHz (13-cm or 2.4-GHz band)*
• 3300–3500 MHz (9 cm)
• 5650–5925 MHz (5 cm or 5.8 GHz)*
• 10.0–10.05 GHz band.
*Shared with overlapping Part 15 allocations.

Selecting the right frequency mix is important, particularly if you are planning a digital backbone and end-user WAPs (Wireless Access Points) into the network. The 902-MHz and 2.4-GHz bands are very popular, with a wide range of low-cost end-user equipment available. Be mindful that in many geographic areas both bands are heavily populated with Part 15 operators.

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