The Annual Golden Packet Event

Bob Bruninga, WB4APR

On 24 July 2011 from Maine to Georgia, we came the closest yet to achieving the Golden Packet award. The award (now obsolete) comes from the Amateur Radio Research and Development group (AMRAD)[1], which back in the early 80’s,first developed the AX.25 specification. At the time it seemed apparent that a national network for packet radio would develop. To recognize the exponential growth of packet in those early days,it seemed appropriate to offer a Golden Packet award to incentivize the first packet network to go cross country. But soon industrious amateurs found all kinds of shortcuts, worm holes, gateways, and eventually the internet for linking cross country traffic and this spelled the end to long haul VHF RF networking ideas.

But the goal of RF-only networking still has value at the local and regional level in worst-case scenarios and so the idea of demonstrating a long haul packet link seemed like a neat thing to do. Since packet radios“don’t get no respect” at Field Day anyway, in 2009 we began our own packet Field Day event and call it the Annual Golden Packet event.

Figure 1. The 14 RF links from Georgia to Maine cover the entire 2000 mile length of the Appalachian Trail. Each temporary link is on the order of about 100 miles or so line-of-sight.

The objective is to get packet shack potatoes out into the fresh air on top of hills and mountains all across the country to set up temporary links not only to demonstrate the capability but to just have a good refreshing ad-hoc packet operating event. In 2009 we attempted the first Appalachian Trail (AT) event[2] and by 2011, the Pacific Crest Trail (PCT) began organizing[3]. Maybe the Continental Divide Trail (CDT) will be next? Or even the Lewis and Clark National Historic Trail. There are over 50,000 miles of long linear trails and parks in the USA which are excellent venues for experiencing the great outdoors and ham radio

On the AT this year there were 14 teams on mountains from Maine to Georgia with APRS packet radios as shown in figure 1. The typical set up was a TM-D700, or D710 mobile radio or the new TH-D72 APRS HT because these radios can act not only as APRS communicators but also as digipeaters. In addition, hikers anywhere along the trail or the end stations could also use the VX-8R series of HT or the FTM-350 APRS mobile for communicating. All of these APRS radios are dual band so not only could they operate on the special event APRS VHF channel, but also on the 445.925 UHF voice coordination frequency simultaneously. A typical set up is shown in figure 2.

Figure 2. The typical portable digipeater consists of a D700/D710 or D72 with their internal TNC configured for digipeating. The Antenna and power source suitable for about 6 hours of operations are the biggest challenge.

Normally, APRS packets radiate outward in all directions only 2 hops using a digipeater path of WIDE2-2. Any more than 2 hops causes exponential growth in duplicate packets and QRM. For this event, and in order to get the full 14 hops necessary to go end-to-end, the two-field digipeater path of HOP7-7,HOP7-7 was used. For those not familiar with APRS paths, the ending SSID of the digipeater field is decremented at each hop. After the 7th hop the first field is decremented to zero (HOP7-0,HOP7-7) and the next hop begins decrementing the second field. After the full 14 hops, the packet will arrive at the last station as HOP7-0,HOP7-0. By convention in packet radio, the “-0” is not shown so the actual arrival would be displayed as HOP7,HOP7* showing it went 14 hops and there are no more. The asterisk shows that the digipeater field is completely used up and is only shown on the last field.

To make it easier to visualize the long linear path at a glance, the SSID’s of each station from Georgia to Maine were assigned in order, 1 through 15. This way the SSID’s are useful in recognizing the geometry of each link. The graphic in Figure 3 attempts to summarize the equipment, people and results of the 24 July 2011 event. The vertical lines on the left edge show the greatest distance packets relayed. Note also the NetCon shack-potato in Florida designatedto coordinate among the sites by all means available.

Figure 3. This graphic attempts to summarize the capabilities and manning at each site. The ideal site had the APRS digipeater on the event frequency, a separate APRS radio on the national channel for coordination, and group messaging, and other radios for voice coordination and Echolinks.

Normally, the national APRS network uses the digipeater UITRACE command to make all WIDEn-N packets fully traceable, meaning that the callsign of each digi is inserted into the packet along the way as the path SSID (n-N) is decremented. But this would make packets for this event impossibly long. To keep packet length manageable, only the last digipeater callsign is inserted. This lets operators see how each packet arrives at their site. To make this happen, digipeaters use the UIFLOOD command enabled to support HOPn-N packets. Typical packets might arrive as shown below.

SPRNGR>APRS,GDHILL-8,HOP7,SUGRLF-14,HOP7*: Hi there! (packet North)

KATHDN>APRS,GDHILL-8,HOP7,CLNGMN-2,HOP7*: Still here! (packet South)

In the above examples, the station at GDHILL is the 7th hop from either end, so it is the last callsign inserted as the initial HOP7-7 is decremented to zero. From then on, the last digipeater along the way continues to overwrite the next to last position until it arrives at the end. In that case, the digi callsign of the last adjacent node is visible.

Figure 4. Using Google Earth, you can visit the site in advance and draw line-of-sight lines to the adjacent sites to find the best links.

Planning the event was almost as much fun as doing it. With the tools available on the internet such as Google Earth, it was possible to zoom in on satellite views and see exactly what the site was like, even down to the best rock to set up on, or the best parking place for the drive-up sites. The pathtool could draw line-of-sight lines from point to point to see if there was a good path (figure 4). But this tool does not take into account the 4/3rds Earth propagation concept which allows longer ranges. For detail RF analysis, John Huggins KX4O used the online RF tool called Radio Mobile by VE2DBE[4]. This tool produces accurate predictions of link margins including reliability predictions as shown in figure 5.

Figure 5. K4XO did all of the RF planning using the free VE2DBE Radio Mobile software downloadable from the net. It displays not only the 4/3rds Earth path and Fresnel zones but also calculates the probabilities of success and fade margins.

It was obvious from the beginning that the best way to provide APRS coverage for hikers along the Appalachian trail was not to place digipeaters along the trail, but on adjacent mountains across valleys where the height above average terrain (HAAT) was in thousands of feet instead of routing the path along the ridges of the trail where HAAT was only in hundreds of feet if not zero or negative in some places. This is why the RF path seems to zig-zag relative to the trail as shown in figure 6.

Figure 6. To get the longest range with the best height above average terrain (HAAT) it is best to zig-zag across adjacent valleys to distant mountain ranges. Although these sites are far from the Trail, they provide the best broadside coverage to hikers along the trail. This image is also provided by K4XO and matches the link shown in Figure 4.

The main AT-Golden Packet web page has individual web pages for each site[2]. They list the 45 brave souls and individual heroes at each location. But the two individuals that climbed nearly a mile straight up the side of Mt.Katahdin in Maine at the end of the trail deserve special recognition. Tim KA1YBS and his mule pack brother-in-law Steve ????lugged all their equipment to the spectacular operating position and view shown in Figure 7.

Figure 7. Tim KA1YBS and brother-in-law Steve (inset) operate from the top of Mt Katahdin in Maine with a beam pointed back to Sugarloaf Mountain and Mt Washington in New Hampshire.

There is no reason why these mountain tops cannot be manned during all VHF contesting events, not just this event. The ARRL rules allow all VHF stations to operate APRS on an ad-hoc VHF channel (with no permanent infrastructure) so they can see the location of all other stations in range. Only the single-op stations are prohibited from digipeating their position to extend their visibility. All multi-op stations, or any other station that will not be submitting scores can operate not only through all other station digipeaters, but can also enable their own digipeater to extend the range of all others. The frequency chosen for this ad-hoc use of APRS is the HamIM frequency of 147.585 MHz to be as far as possible from the lower weak-signal end of theband. There is no permanent packet infrastructure on this frequency and it is only used temporarily during events[5].

A final mention should also be made of the Summits-on-the-Air (SOTA) action which frequently brings all kinds of VHF and HF operators to mountain tops and hills all over the world[6]. These teams should also consider activating their APRS beacon while operating so they can see where everyone else is located and coordinate their operations.

Although we were one digipeater short of the full 15 hop length of the Trail, the operator on Sugarloaf Mountain in Maine did have a D7 APRS radio that he could manually send and receive packets in both directions demonstrating the full packet connectivity from Georgia to Maine. The paths are proven. Everyone is convinced that next year we will achieve the Golden Packet! From then on, we hope to add to the event by inviting additional hikers on the trail to join in the fun.

See you from the Mountain Top.

Bob, WB4APR

[1] AMRAD -

[2] Golden Packet -

[3] Pacific Crest -

[4] Radio Mobile Software -

[5] HamIM -

[6] SOTA -