The Sporadic-E (Es) Doughnut Effect

[Clark L. Stewart]

There was a discussion on the FrontRan...@groups.io email reflector about why K6VHF/HR9 on 6-M was not making contacts in a particular part of the country.  The reason is described below by NØJK as the "Sporadic-E Doughnut Effect."  Below is a PSKMap showing where he was working and the Green ellipse indicates the "Doughnut Hole" where it was difficult if not impossible to work him.

This can be really frustrating when you hear people all around you working the DX and you can't make a contact.  Probably there is nothing wrong with your radio or antenna, it's just "Propagation."




Here is how Jon, NØJK, describes the issue:

The PSK repoter map you sent graphically shows your Es skip zones.

First hop from HR9 to W4 and W5.

Second hop to W1, W2, W3, W7, W8, W9 and northern W0. 

NOTE  — Kansas, Missouri and Nebraska were in the "Es doughnut hole" from HR9. This is the zone between first and second Es hop. It can be a difficult distance to 

work via sporadic-E.

The “doughnut effect” in sporadic-E (Es) propagation is a well‑known phenomenon in amateur radio where certain distances are much harder to make than others. 

Short paths (< ~400 km) are rare because the required E‑layer ionization is too low to support a single hop at HF frequencies.

Longer paths (up to ~2300 km) are the most common because they fall within the typical single‑hop range for Es, with an average E‑layer height of ~105 km.

Around 2300–2800 km, there’s a sharp drop in success rate — this is the “hole” in the doughnut. Why?

At 50 MHz, a 2,400 km path would require two hops of ~1,200 km each.

1,200 km hops need a high MUF (around 100 MHz) to be supported, which are much less common than lower‑MUF hops.

Finding two Es patches with the right geometry and MUFs to complete such a path is rare.

https://uksmg.org/content/doughnut.htm

"Cloud to cloud" Es can extend the single hop Es range into the "doughnut hole" as well. 

Cloud-to-cloud sporadic-E (Es) propagation occurs when a radio signal is reflected off two separate Es “clouds” in sequence, rather than a single cloud. This is a form of double-hop Es that can extend communication distances far beyond the typical single-hop range.

• Jon N0JK

73, Clark, W8TN