If we listen to a transmission on the VHF or UHF bands from a distance greater than what a direct line-of-sight ray provides, we are experiencing sporadic propagation. But has it occurred in the troposphere or in the ionosphere's E-layer?
Differences in Appearance
If it is Sporadic-E (Es): The signal bursts in suddenly but is highly unstable. It will sound perfectly clear for 2 or 3 minutes, after which it will begin to distort deeply and then disappear completely. The phenomenon usually lasts from a few minutes to a couple of hours at most, vanishing without a trace.
If it is Tropospheric: The signal is much more stable and progressive. Stations start to be heard with background noise early in the morning or at sunset, gradually increasing in intensity. The signal remains stable on the dial for hours (sometimes entire days) without sudden fading.
Geographic Distance
If it is Sporadic-E: The skip distance is usually between 800 km and a maximum of 2200 km.
If it is Tropospheric: The maximum range rarely exceeds 400 or 500 km.
Geographic Areas
If it is Sporadic-E: Signals are received from stations across a very wide geographical area.
If it is Tropospheric: It is much more localized.
Example 1
On Friday, I was traveling by car, and while scanning the FM band, an Italian station came in (the minimum distance is 795 km) => Sporadic-E.
Example 2
On the afternoon of the 29th, my MeshCore client (868 MHz) located in Valencia received signals coming from central Catalonia between 17:57 and 20:05. (A specific area, a distance of around 300 km, and a prolonged opening—the three textbook characteristics of a tropo opening).
Detailed breakdown of the tropospheric opening on Monday, June 29, 2026, including times (17:57 - 22:11) and distances (256 - 327 km).
Map generated with
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| General overview of the tropospheric opening on Monday, June 29, 2026, on 868 MHz. Generated with |
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| Note the difference in propagation (distance and times) of the tropospheric openings toward the south. |
See also:
- La propagación ionosférica: capa esporárica E
- Comunicaciones troposfericas esporádicas por conductos (ducting)
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