APRS Part 3: Using TEMPn-N Digipeater Paths
By ERIC HENDRICKSON
An APRS station can be heard by a nearby mobile or portable APRS station and still fail to reach a regional digipeater. Now, imagine if those nearby stations could relay your APRS packets to a digipeater while leaving your WIDE path hops intact? TEMPn-N is the extra hop you’re looking for.
By providing a local relay, a properly configured TEMP station relays APRS packets to a digipeater. Further, the TEMPn-N path lets operators request temporary digipeating with or without the assistance of regional digipeaters.
This can be especially helpful during a supported community event like a parade or marathon, search-and-rescue exercises, disaster drills, Field Day, or other portable operations. A TEMP-capable station might be placed on a hill, in a support vehicle, at an aid station, or near an incident command post. Stations in weak locations can request a relay from one of these TEMP helpers.
TEMP is an alias convention, not a feature every APRS radio or software TNC handles automatically. A station must support and be configured for TEMP digipeating. The Kenwood TM-D750 and TH-D75 offer configurable APRS digipeater functions; settings and support differ by model.
How TEMPn-N Works
In a TEMPn-N path, TEMPn identifies the alias and N gives the remaining number of hops. TEMP2-2, for example, requests up to two TEMP digipeater hops. Each successful TEMP relay marks its use and reduces the remaining TEMP count.
A station configured for ordinary WIDE digipeating will not normally repeat a packet addressed to TEMP unless it has also been configured to recognize the TEMP alias. In other words, don’t assume that your TEMP packets won’t be digipeated.
A TEMP-only path can be useful when an event wants packets to use a temporary local relay layer rather than include a WIDE path that engages high-level regional digipeaters. TEMP2-2 does not create a geographic or internet boundary: Other stations and IGates may still hear packets within radio range. The path controls which digipeater aliases are requested and how many hops are available; other receivers can still hear or gateway your packets.
APRS uses shared RF channels. In North America, 144.390 MHz is the national APRS frequency. Each re-transmission occupies airtime, and unnecessary repeats increase channel loading and the chance of collisions. TEMP is useful when it gives an operator a planned local relay, not as a reason to add hops without considering the local network.
If you expect to generate a lot of traffic and don’t need WIDE, best practice may be to select an alternate frequency to avoid crowding 144.390 MHz.
TEMP1-1,WIDE2-2: A Local Relay Before the WIDE Network
A TEMP path can also help a weak station reach the regular APRS network while leaving its WIDE hop allowance intact. Consider TEMP1-1,WIDE2-2. The packet first requests one TEMP relay. After that relay, the path can appear as TEMP1*,WIDE2-2: The TEMP alias is marked used, while WIDE2-2 remains unchanged.
A WIDE digipeater can then process the WIDE2-2 portion. For example, after one WIDE relay the path may appear as TEMP1,W4DJY*,WIDE2-1; after another it may appear as TEMP1,W4DJY,W5DJY*,WIDE2. The TEMP relay does not consume one of the WIDE hops in this path. The WIDE count changes only when a WIDE digipeater processes it.
This can help a station operating inside a school, community center, hospital, emergency operations center, or Field Day site. A handheld or indoor station may not reach a regional digipeater directly, while a mobile parked outside or a nearby station with a better antenna can hear it. If that station is configured as a TEMP digipeater, TEMP1-1,WIDE2-2 requests the local assist first and leaves the WIDE path available afterward.
The helper is not acting as a general-purpose WIDE digipeater. It repeats packets that match its TEMP configuration, and it can remain available for occasional, deliberate use. A TEMP relay can improve access to the wider network when a WIDE path follows it; a TEMP-only path does not provide that wider route.
When APRS TEMP Paths Help
During an emergency, the regular APRS network may be incomplete, overloaded, damaged, or unreachable from a particular location. A temporary station on a hill, in a vehicle, at a shelter, or near an incident command post can add local relay coverage. From there, packets may continue through a temporary TEMP network or enter the regular WIDE network if the path includes WIDE and that network is available.
These path choices serve different purposes:
- TEMP2-2: Requests up to two TEMP relays and includes no WIDE path. It may suit an event that wants a local TEMP relay route, provided the participating stations and digipeaters are configured and the plan accounts for the RF channel.
- TEMP1-1,WIDE2-2: Requests one TEMP relay before the packet proceeds through the WIDE network. It may help a weak or poorly located station that needs a local assist to reach regional infrastructure.
For an event that needs local tactical visibility, a TEMP-only route may be appropriate. For a station that needs to enter the normal network, a TEMP relay followed by a locally recommended WIDE path may be more useful. Terrain, station density, event size, digipeater locations, and the intended coverage all matter.
When coverage is poor, increasing the WIDE hop count is not always a solution. If a packet cannot reach the first useful digipeater, adding hops after that point will not help. A well-placed nearby TEMP station can improve that first link; the regular network can handle later hops if the remaining path and coverage allow it.
Configure and Coordinate Temporary APRS Digipeaters
Kenwood’s TM-D750 offers a standalone APRS digipeater function. On the TH-D75, Kenwood documents UItrace and a UItrace Alias setting that defaults to TEMP; using the alias still requires enabling UItrace and configuring the station deliberately. The exact settings differ by model, so confirm the model’s manual and configuration before relying on it.
A computer running Dire Wolf can also serve as an event digipeater when connected to a suitable radio interface and configured with rules for the intended TEMP path. Dire Wolf’s digipeater rules are user configurable and beyond the scope of this article.
Temporary digipeating should be planned, tested, and coordinated with the local APRS operators. A group might place helpers where they can hear weak stations and reach one another, then tell participants which path to use. Randomly enabling digipeating at many stations can add traffic without necessarily improving coverage.
For routine APRS operation, continue to use the path recommended for the local network. Common North American paths include WIDE2-2 and WIDE1-1,WIDE2-1, but local digipeater configuration and channel conditions determine which path is appropriate. Use TEMP2-2 only where TEMP digipeaters are deployed and the event plan calls for that path. TEMP1-1 may be enough for a small local operation if one configured relay provides the required coverage.
Use the Least Disruptive Path That Works
APRS carries more than position reports. It can also carry objects, messages, weather reports, telemetry, and bulletins that contribute to local situational awareness. On a shared channel, useful coverage depends on both reaching the intended stations and limiting unnecessary retransmissions.
TEMPn-N adds a way to organize temporary relay support for events, exercises, Field Day, emergency work, and portable stations. TEMP2-2 can request up to two TEMP hops; TEMP1-1,WIDE2-2 can request one local TEMP relay before the WIDE path. Each TEMP hop still uses airtime, but in the latter path it is separate from the WIDE hop count. The right choice depends on the local plan and the coverage needed.
Sources and Further Reading
- Kenwood TM-D750E: APRS and Digipeater Features
- Kenwood TH-D75A/E User Manual: UItrace and Alias Settings
- APRS.org: Fixing the 144.39 APRS Network
- Dire Wolf User Guide: Digipeater Configuration
- Bob Bruninga’s Original Vision for TEMPn-N
Original photograph: Bob Wick / Bureau of Land Management, CC BY 2.0.
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