As we prepare EmergencyHam Network (EHN) for its first alpha trials, we’re also looking ahead at additional communications systems that could become part of the network.
One of the most interesting is APRS — the Automatic Packet Reporting System.
APRS is already widely used by amateur radio operators for position reporting, short messages and other information. For EHN, however, APRS could potentially serve two quite different purposes: giving amateur operators access to EHN and providing radio links between EHN basestations.
APRS as an EHN access point
An EHN basestation equipped with an APRS gateway could have its own amateur callsign and SSID, for example:
N2DH-10An amateur operator wouldn’t necessarily need to be a previously registered EHN member to contact it.
A message might be as simple as:
&NEWARK Need information on shelter statusThe & identifies an EHN group. The APRS gateway receives the message, records the sending callsign and passes the message into EHN.
Because the station is operating through amateur radio, EHN could automatically create a limited provisional user record associated with that callsign. Registration or verification could take place later if the operator wanted full EHN membership.
An unregistered operator could initially be restricted to published groups, while someone who already knows another member’s EHN ID could potentially send a direct message using the normal @user-id format.
This gives amateur operators a simple way into EHN without requiring special EHN radio equipment.
VHF APRS — local and regional communications
We see VHF APRS primarily as an access and regional communications system.
A local EHN basestation could receive messages from individual amateur operators and connect them with EHN users on completely different networks.
For example:
VHF APRS → EHN → MeshCore
or:
VHF APRS → EHN → SMS/RCS
VHF APRS could also connect nearby EHN basestations, particularly where an existing APRS network provides coverage between communities.
That means APRS isn’t simply another endpoint like a phone number or mesh node. It can also become a path through which EHN stations exchange traffic.
HF APRS — a different role
HF APRS introduces another possibility.
Rather than concentrating on local user access, its most interesting EHN role may be as a long-distance, infrastructure-independent link between EHN basestations.
Imagine two EHN stations separated by hundreds of miles. Under normal conditions they may communicate over the Internet. If that connection disappears, an HF APRS path could provide an alternative for important EHN traffic.
Conceptually:
EHN Basestation
│
APRS Gateway
│
HF RF
│
APRS Gateway
│
Remote EHN BasestationThe originating station doesn’t need to know how the final recipient can be reached.
It only needs to get the message to another EHN basestation. The remote station can then use its own directory and available gateways to complete delivery by MeshCore, Meshtastic, SMS/RCS or another available network.
Making better use of limited bandwidth
HF radio is a scarce communications resource, so EHN shouldn’t try to move everything across it.
This is where EHN’s store-and-forward architecture becomes particularly useful.
If normal Internet connectivity is available, EHN can exchange messages, directory information and operational data freely.
If only VHF APRS remains, the system could reduce that traffic to information appropriate for the available capacity.
And if an HF APRS link becomes the only path between two areas, EHN could become more selective still — carrying priority messages, essential routing information, acknowledgements and important operational updates while less important traffic remains queued.
The user doesn’t have to choose the transport. EHN’s routing system can make that decision based on what paths are available and the priority of the message.
Access or trunk — VHF or HF
We don’t intend to define VHF and HF too rigidly.
A VHF APRS connection could carry basestation-to-basestation traffic, and an individual operator could potentially reach EHN over HF.
Instead, we’re looking at APRS in terms of two independent roles:
Access Mode connects individual amateur stations with EHN.
Trunk Mode connects one EHN basestation with another.
Either could potentially operate over VHF or HF, with VHF naturally favoring local and regional access and HF becoming particularly valuable for longer-distance resilient links.
Another piece of the EHN puzzle
The goal of EHN isn’t to replace APRS, MeshCore, Meshtastic, cellular messaging or any of the other communications systems people already use.
It is to connect them.
APRS is particularly interesting because it could give EHN both a readily accessible amateur-radio interface and an infrastructure-independent way for EHN basestations to communicate with one another.
It’s still an area we’re exploring rather than part of the initial September alpha trials, but it demonstrates where the EHN architecture can take us.
