Dual Band Digipeater Project

The Amateur radio community of the Macon and surrounding area is active in many facets of emergency communications. One facet, digital packet communications, has seen a revival of sorts with experiments in packet communications done by several area amateurs. Ralph Howard, WD6BGN; David Krueger, AB0DK; and Matthew Chambers, NR0Q all having done propagation testing with each other and nearby communities using AX.25 packet running both the APRS and Winlink 2K higher level protocols. Those higher level protocols are defined with example usages below.

APRS An amateur AX.25 packet protocol for short tactical and information messaging. Packets are sent in UI or unconnected frames in a broadcast manner. Typical information carried on APRS is short SMS like messages between amateurs, real-time mobile tracking and GPS locating, real-time weather station data, and real-time event and incident status and tracking. APRS operations are conducted nationwide on the 2M amateur frequency of 144.390 MHz.

Winlink 2K An amateur AX.25 packet, Pactor and Winmor communications protocol and network for exchanging standard email formatted messages between amateurs and with users on the Internet. Winlink 2k started as a means for mariners to receive and send email, weather and radio propagation information on the high seas. Usage has since extended to the general amateur community and is used by ARES and EmComm groups for passing of Health and Welfare traffic from a shelter population to their families via traditional email style messages.

APRS and Winlink 2K while both using AX.25 packet as the base communications method are generally not compatible on the same communications channel due to the different types of information and types of stations involved in each. Winlink 2K uses traditional style connected packet sessions with stations rapidly sending and acknowledging to each other. APRS uses unconnected packets originating from typically low power mobile stations being repeated in a ui-flood manner out to typically 2-3 hops.

This proposal is build a dual band digipeater system located at the long time digipeater site behind Macon City Hall in Macon, Missouri.  APRS would be on the national 2M 144.390 MHz frequency. APRS would be on an agreed upon 70CM frequency such as 446.200 MHz.

Operating each on a separate band would decrease interference between the two and also facilitate additional Winlink 2K stations at shelter and EOC locations that wouldn’t set up such operations due to concerns of interference between Winlink 2K and VHF band public safety and 2M amateur stations at those locations.

Much work has already been done to build the needed software to operate such a digipeater system. Ralph Howard, WD6BGN, has built and experimented with a Winlink 2K station operating from a Raspberry Pi with a TNC-X “TNC-Pi” addon board. Matthew Chambers, NR0Q, has also built an APRS digipeater with a Raspberry Pi running APRX connected to a serial TNC. The goal of this project to combine those two separate experiments into a hardened digipeater appliance.

Equipment and Materials

1 Raspberry Pi 3 $40.00 ea
2 TNC-X TNC-Pi 2 $65.00 ea
1 VHF 50W 8Ch FM Transceiver (Icom IC-F5011) $276.80 ea
1 UHF 45W 8Ch FM Transceiver (Icom IC-F6011) $276.80 ea
2 Icom OPC1939, D-SUB 15-Pin ACC Cable $80.75 ea
1 Astron SS25 25A Switching Power Supply $131.60 ea
1 Comet GP-9N 144 / 440 MHz Fiberglass Antenna 8.5 / 11.9 dBi 16ft 9in Tall with N Connector $209.95 ea
110 Times Microwave LMR400 Low Loss Coax $1.00 / foot
1 Comet CF-416 2M / 70CM Diplexer $49.95 ea

Estimated project cost $1,386.60
(does not include equipment and material shipping costs)

Request for comments

Information will not be released to anyone for any reason. Contact information is only if project developers have additional questions about your comments.

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