354 km on Meshtastic by tropospheric duct

Summary

In the two openings, 20:36-23:43 and 00:33-04:30, 656 packets from 70 nodes in Bahía Blanca, Monte Hermoso, Coronel Dorrego, Tres Arroyos, Irene, Pigüé and Carhué reached Viedma. There were traceroutes in both directions and a chat between the two cities on the MediumFast channel. The farthest node was ElArroyoMesh, on the El Arroyo farm 15 km north-east of Carhué: at 01:56 it answered a traceroute from MRCO across 416 km, with five nodes in between each way.

Everything came in through PAT1, a SenseCAP Solar P1 with the ROUTER role installed the day before on a tower in Carmen de Patagones. In the previous 31 hours it had heard nothing from that area. Of the 656 packets from the region received by the Viedma gateway, 654 had been relayed last by PAT1.

Map

100 km200 km300 km400 km354 km273 km247 km242 kmPAT1 · tower at PatagonesViedma · 15 nodesBahía Blanca · 41 nodesCoronel Dorrego · 7 nodesN-MH Monte Hermoso3PIC Cerro Tres PicosTres Arroyos · C-3A (90 m tower) and N-3AN-IR IreneGUIA · near PigüéCURA Cura MalalARRO El Arroyo (Carhué) · 416 km from ViedmaPunta AltaCoronel PringlesCoronel SuárezPedro LuroVillalongaStroederSan BlasClaromecóMédanosArgentine Sea

PAT1 Viedma-Patagones Bahía Blanca region Direct hop between networks Other hops seen

Direct hops

Monte Hermoso was the entry used most: 71 readings, with signal up to +2.25 dB. C-3A was the longest and Coronel Dorrego the second.

Path profile PAT1-C-3A

• Normal radio horizon between the two antennas: about 90 km. The 354 km hop is four times longer.
• At mid-path the Earth rises 1,848 m above the straight line between the antennas.
• In free space, with 22 dBm and 3 dBi antennas, the expected SNR would be about −0.6 dB. The best reading was −6.5 dB: only about 6 dB less.

Propagation

After sunset (19:52 at Patagones) the air next to the sea cooled and became humid, while a few hundred metres higher it stayed warm and dry. That inversion forms a duct: a layer 60 to 85 m deep over the water where the signal is trapped and follows the curvature of the Earth. At 915 MHz about 54 m is enough.

The models (ECMWF, GFS and GEM) show a duct over the sea at mid-path from 15:00 on 1 November to 07:00 on 2 November. The first opening came when the land end, at Patagones, cooled after sunset. The second, from 00:33, came with rising pressure (1007 to 1011 hPa at Bahía Blanca), air sinking at about 3,000 m (700 hPa) and the strongest duct around midnight. It closed at 04:30 with the sea still in duct: at that hour ECMWF and GFS weaken both land ends of the Monte Hermoso-PAT1 hop, where the last packet came in. Tropocast.eu and the Hepburn index showed the coastal strip, with the maximum between 01:00 and 06:00: they got the place and the phenomenon right.

Timeline

1. 19:52Sunset at Patagones.
2. 20:36First packet from Bahía Blanca arrives, relayed by PAT1.
3. 20:41The Bahía Blanca BBS announces the route BBS → STMB → 3PIC → C-3A → PAT1 → MRCO → MRCC.
4. 20:41-21:49C-3A ↔ PAT1, 354 km: 16 readings.
5. 20:37-04:30Monte Hermoso ↔ PAT1: 71 readings in both openings, the main entry.
6. 23:40On Telegram, Ptolomeus suggests a ping from Viedma to ElArroyoMesh, near Carhué.
7. 23:43The first opening closes.
8. 00:33The Bahía region comes back, now on 2 November.
9. 01:56MRCO retries a traceroute to ElArroyoMesh with a hop limit of 7 instead of 3, and the answer arrives in 13 seconds: five nodes in between each way, 416 km through the mesh.
10. 02:31C-3A answers a traceroute from MRCO through PAT1, with the direct hop in both directions.
11. 03:29Monte Hermoso answers a position request from the station: the same position SOMesh publishes.
12. 03:32C-3A answers a position request in 3 seconds, encrypted end to end: the station lacks its key and cannot read it.
13. 04:29C-3A answers a NodeInfo request in 6 seconds, also encrypted.
14. 04:30Last packet from the region: N-MH answers a traceroute from MRCO.
15. 04:31From then on, requests to the region go unanswered: 5 traceroutes up to 06:05.

People on both networks

People on the two networks talked to each other, in both directions.

Messages from people on MediumFast

43

29 from the Bahía region and 14 from Viedma, plus 11 reactions

People who wrote

12

5 from the Bahía region and 7 from Viedma

Replies across networks

9

messages answering one from the other network

Messages from MRCO to Bahía

12

5 on the channel and 7 direct to 5 nodes; 2 acknowledged

From MRCO, the station's roof node, 5 messages went to the channel and 7 direct messages to 5 nodes in the Bahía region; 2 came back with the recipient's acknowledgement, one of them from NJK5 in Bahía Blanca. 3 direct messages came from 2 nodes there; the fastest person to answer a direct message from MRCO took about 2 minutes.

Separately, MRCO sent 8 queries to the Bahía Blanca BBS (Sentinel BBS), which answered 6 times automatically. MRCC, on USB at the station, only listened: it recorded everything and sent nothing to the other side.

Data from 20:36 to 06:48. Text messages on the MediumFast channel count as messages from people; reactions (an emoji on a message) are counted apart. The BBS's 6 automatic notices on the channel, the queries to the BBS and its answers are not counted.

On the channel

• 20:40HamLQue bueno que Viedma esta en mediumfast tmb
• 20:42MIKEhay contacto con bahia?
• 20:42HamLLo hay
• 20:43ZEROBienvenidos!
• 20:43plgmEstará entrando por el mar?
• 20:45VDMHola Zero desde Viedma!
• 20:51HamLSerá propa?
• 20:51HamLO es estable?
• 20:55plgmQ está con rol Router
• 21:03BASE¡Saludos a todo Bahía!
• 21:127EEAY quien paga el asado?
• 22:03MRCOQue pasó?? vemos Bahía desde patagones???
• 22:14MRCOMis saludos a todo Bahía Blanca. Estamos entrando por el nodo !b03cbf0c no veo el nombre

Messages as written, in Spanish. Orange: Bahía region; blue: Viedma.

Comparison

PAT1 and C-3A talked in a single hop, with no repeater in between, over 354.3 km: 18 traceroutes record the hop and 4 show it in both directions. That is more than the 331 km of the record listed on the official Meshtastic page for links without balloons or aircraft, and in the sources we reviewed we found no longer direct link confirmed in both directions between fixed stations. In Europe there are reports of direct receptions from 475 to 822 km, at 868 MHz and over the sea, in one direction and without independent verification; one of them, 756 km, also on MediumFast. At 915 MHz the longest documented single hop we found was 254 km, and in South America we found none over 250 km. For ducted LoRa the distance is not unusual: links of almost 600 km have been confirmed.

This one was almost half sea and half land: about 200 km over the sea and the low coast, and the rest over the plain to Tres Arroyos.

Sources: meshtastic.org/docs/overview/range-tests; LoRa Italia; r/meshtastic; Zennaro et al., "TROPPO", arXiv 2004.02802; The Things Network. Open-web search in 14 languages on 02/11/2026.

For the next opening

• The routers of the chain should mark each other as favorites: STMB, 3PIC, N-MH, C-3A, EA01, PAT1 and MRCO. Since firmware 2.7.11 a router does not spend a hop when it relays what a favorite router passes to it. A message from a client in Bahía then reaches Viedma using a single hop of the default limit of 3.
• The antenna height of 3PIC (Cerro Tres Picos) is still missing.
• C-3A's NodeInfo, with its public key, is still missing, so the station can read its answers and confirm its position by radio. meshbox can now request it from the panel during the next opening.
• PAT1 stays as ROUTER on the Patagones tower, and the Viedma station records every opening.