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I have noticed a common theme regarding propagation on the 10 meter band. There is a wide perception that when the band goes quiet and worldwide DX dries up in June or July, the solar cycle must be diving such that the frequencies become useless. Having written the propagation column in CQ Amateur Radio magazine since 2001, I have done much research into this topic.

The reality is that while the 11 year solar cycle certainly dictates overall band health, the dramatic differences we see between seasons on 10 meters are driven by complex changes in the Earth’s atmospheric chemistry and magnetic field.

The F2 Layer and the Winter Anomaly

During the autumn and spring months, 10 meters comes alive for long range global communication. To understand why this changes with the seasons, we have to look at the F2 layer of the ionosphere.

Complex Propagation Modes

The seasonal shift in thermospheric winds and the resulting chemical changes in the F2 layer are the true drivers of what we experience on the radio. This phenomenon is known in physics as the Winter Anomaly.

• The Summer Fade: During the summer months, intense solar heating creates upwelling wind patterns in the thermosphere. These winds pull heavier molecular gases, specifically molecular nitrogen (N₂) and molecular oxygen (O₂), higher into the F2 region. This drastically increases the recombination rate of ions. The extra nitrogen acts like a sponge, rapidly absorbing the free electrons we need to reflect 28 MHz signals. Because the electron loss is so high, the overall electron density drops, and transoceanic skip fades away.

• The Winter Peak: The opposite happens during the cooler seasons. As we move away from summer, the thermospheric winds shift and the heavy nitrogen settles back down. The F2 layer becomes dominated by atomic oxygen (O). Without the nitrogen there to absorb the electrons, the recombination rate slows down significantly. This allows a highly dense F2 layer to build up, reaching peak electron densities around November and February. This atomic oxygen rich environment creates the perfect reflective environment for global 10 meter communication.

Summer’s Silver Lining: Sporadic E

When summer arrives and the F2 layer thins out, the band brings its own unique conditions with the prevalence of Sporadic E propagation.

These intense, highly localized clouds of ionization form in the lower E layer of the ionosphere. Sporadic E provides incredibly strong short skip contacts. These openings typically range from a few hundred to a couple of thousand miles, temporarily replacing the global propagation we enjoy during the spring and fall. Most folks scrolling through social media just want a basic understanding of why they are suddenly making loud contacts into neighboring states instead of talking across the ocean, and Sporadic E is the answer.

Global Reach: TEP and Chordal Hop

For North American operators looking to communicate with places like Brazil or Australia, different propagation mechanics come into play.

For communication down into South America, you are dipping into a fascinating phenomenon called Transequatorial Propagation (TEP). TEP is deeply tied to the F2 layer conditions, but it is heavily driven by the structure of the Earth’s magnetic field near the equator.

Around the geomagnetic equator, the magnetic field lines run exactly parallel to the surface of the Earth. This causes the free electrons in the F2 layer to be pushed outward and downward, creating two massive, highly dense bands of ionization located about 15 to 20 degrees north and south of the magnetic equator. We call this the equatorial anomaly, and it is the engine for TEP.

When you transmit from North America down toward Brazil, your 10 meter signal hits that northern dense band. Instead of reflecting back down to the ground or ocean, the signal deflects horizontally across the equator high in the ionosphere. It then hits the southern dense band and reflects down into deep South America. Because the signal stays entirely in the upper atmosphere and avoids a lossy bounce off the Earth’s surface in the middle, the signals can be incredibly strong and clear. TEP is most reliable during the spring and autumn equinoxes, usually peaking in the late afternoon and early evening hours.

Talking to Australia from North America is slightly different because the path does not cross the magnetic equator at the perfect right angle needed for textbook TEP. However, working Australia often relies on a very similar principle called chordal hop propagation. Instead of bouncing between the ionosphere and the ocean all the way across the Pacific, the signal enters the F2 layer and skips along the underside of the ionosphere for thousands of miles. It stays trapped high up where there is very little absorption, eventually dropping down to receivers in Australia with surprising signal strength.

Regional Variances

Radio wave propagation is never a one size fits all experience. Your location on Earth plays a massive role in what you hear on 10 meters.

• The Coasts versus the Midwest: If you live on the East Coast of the United States, your signals have a relatively unobstructed single hop path over the highly reflective saltwater of the Atlantic Ocean to reach Europe. The West Coast enjoys a similar geographic advantage when working Japan and the Pacific Rim. In the Midwest and central USA, your signals must often make an extra hop over land. Because land absorbs radio waves much more than saltwater does, central USA operators might find global F2 paths a bit more challenging. However, Midwest operators are perfectly positioned to work both coasts simultaneously when intense summer Sporadic E clouds form over the continent.

• Equatorial Advantage: Operators located closer to the equator experience less of the severe Winter Anomaly shift. Because they sit under the equatorial anomaly, they enjoy much more consistent F2 and TEP openings year round compared to mid-latitude stations.

• High Latitude Challenges: Operators in high northern or southern latitudes, such as Alaska or northern Europe, must contend with auroral absorption. During periods of high geomagnetic activity, the auroral oval expands and can severely degrade or completely absorb 10 meter signals, shutting down paths that cross the polar regions.

If 10 meters feels like a completely different band right now, do not blame the sunspot numbers. It is simply the natural seasonal shift in atmospheric chemistry and radio wave propagation at work. Enjoy the loud Sporadic E contacts while they last, and get ready for the worldwide skip to return when the seasons change.

Addendum: From the Southern Hemisphere

I was asked how this looks, from the land of Down Under.

Thank you for bringing the Southern Hemisphere perspective into the conversation! You hit the nail on the head regarding the inclination of the Earth’s axis, and it is the perfect starting point to explain why our experiences are mirrored.

Because the Earth is tilted on its axis by 23.5 degrees, the hemispheres take turns leaning toward the Sun as we orbit. Right now, the Northern Hemisphere is tilted toward the Sun, giving us summer. The Southern Hemisphere is tilted away, resulting in your winter. This means the ionospheric effects we experience are exactly reversed on the calendar.

When you mention that the high bands shut down after dark during your current winter, you are experiencing the harsh reality of wintertime solar geometry. During the winter months in the Southern Hemisphere, the Sun is much lower in the sky and the daylight hours are significantly shorter. While the Winter Anomaly we discussed earlier means your daytime F2 layer can actually become quite dense and highly supportive of 10 meter skip during the daylight hours, that ionization is entirely dependent on active sunlight. The moment the Sun sets at 5:30 PM, the source of ionization disappears. Because the winter night is so long, the F2 layer rapidly depletes, shutting the band down until the Sun rises again the next morning.

Conversely, when you head into your summer months of November and December, two major things happen. First, your daylight hours increase dramatically, which keeps the ionosphere charged much later into the evening and extends your operating time. Second, just as the Northern Hemisphere experiences a massive peak in Sporadic E propagation during our summer, the Southern Hemisphere experiences its own Sporadic E season during your summer. This provides those loud, reliable regional contacts. Finally, as you move into mid autumn around March and April, the Earth reaches the equinox. During the equinoxes, the Sun is directly over the equator, providing optimal and balanced F2 layer ionization for both hemispheres. This is why global, long haul propagation is at its absolute peak for everyone at the same time.

Regarding your question about East to West paths: yes, communication between Australia and South America is fundamentally very similar to the path between North America and Europe. Both are mid latitude transoceanic paths that rely on multi hop F2 propagation.

However, the Southern Hemisphere actually has a distinct geographic advantage for these contacts. Radio waves lose a small amount of energy every time they reflect off the Earth’s surface between ionospheric hops. Saltwater is an excellent, highly efficient reflector of radio waves, while landmasses absorb much more of the signal. Because the path between Australia and South America is almost entirely over the highly reflective saltwater of the Pacific Ocean, your multi hop signals suffer far less ground absorption compared to Northern Hemisphere paths that must often cross large expanses of land. This makes those Southern East to West paths incredibly efficient when the F2 layer is cooperating!

I started in the ham radio and shortwave listening hobby in 1972. By 1975, this was my first real receiver. It heard very well, and ignited my lifelong passion for radio.

The R-366/TRR-5 military receiver.

This old radio, the R-366/TRR-5, which is clearly identified on the faceplate in this picture of the military rig, had great ears. It was what I used to hone my Morse code copying skills and to get the hang of how amateur radio operators conducted communications with each other, with CW, AM, or SSB. I hope someday to own one once again.

The R-366

The R-366/TRR-5 is a significant piece of military history manufactured for the Navy Department Bureau of Ships by the Espey Manufacturing Company. Built during an era when the United States Navy required absolute reliability for ship to shore and ship to ship communications, the unit is a testament to the rugged industrial design of the mid-twentieth century. Often referred to as part of the TRR-5 receiving set, this equipment frequently incorporated high quality components and precision engineering including the gold standard Collins Radio Company designs of that period. These internal components were vital in providing the remarkable stability and selectivity needed to pull weak signals out of the dense electronic noise environment found on a crowded naval vessel. It did have heterodyne squeals on a select few frequencies, which any old tube receiver was prone to have, but those did not detract from the excellent capability of the radio.

The Service

For the sailors and radio operators serving aboard ships in the 1950s and 1960s these receivers were far more than just tools for duty. In the often cramped and isolated conditions of life at sea these radios served as a critical psychological anchor. Access to the bands meant hearing the familiar sounds of home or tuning into MARS stations where amateur radio operators facilitated phone patches that reconnected sailors with their families. This bridge to the outside world was essential for maintaining morale and supporting the mental health of military personnel who were otherwise cut off from the rhythms of civilian life for months at a time. Sitting in the radio shack and slowly tuning that large central dial while listening to the crackle of the ionosphere was a meditative escape from the constant hum of shipboard operations. Many ships would pipe ball games and news shows, or music programs, over the ships intercomms, providing health and morale to the personnel.

Operating the Radio

The tactile experience of operating this specific receiver remains vivid in my memory. The layout with its distinct knobs for selectivity phasing and BFO control was designed for the hands of a professional radio operator who needed to manipulate the signal in real time. It required a disciplined ear and a steady hand to copy Morse code through heavy atmospheric conditions but that struggle made every successful reception feel deeply rewarding. It taught me the patience and technical appreciation that have defined my amateur radio hobby for decades. Owning and using a piece of history like this represented a connection to the generations of operators who stood the watch before me.

Traveling the World…

With this historic military receiver, I discovered an entire world as a child in the mid 1970s. I spent countless nights in the quiet darkness of my room with only the warm orange and yellow glow from the vacuum tubes leaking out of the back and top grills and slots of the radio enclosure, as those hot tubes cast soft light on the ceiling and walls. That radio allowed me to travel the globe from my listening position often sitting cross-legged on the floor in front of this big rig. Those late night listening sessions, when I should have been sleeping, ignited a lifelong passion for understanding the vast and interconnected world of shortwave radio as well as medium-wave DXing. I heard International Shortwave Broadcast stations as well as AM broadcast stations from Europe, Asia, the South Pacific, the Atlantic regions, South America, Central America, and North America–all over the world! I listened to amateur radio operators on Morse code, SSB, and AM modes. Ships at sea, aircraft doing transoceanic flights, fishing vessels comms where fishing captains would chat with other boat captains, and even military communications were all at my fingertips on the dial of the radio as I listened to these exotic places by headphones. I even picked up a station from Peru, South America late one night, on the mediumwave broadcast band. That is how great that receiver could hear. Of course, I had a very excellent outdoor dipole antenna that was cut for 160 meters.

What Receiver Was Your First?

What was your first major receiver? Was it just a receiver, or was it a transceiver? When was that? What did you hear that captured your imagination? Do you still have that radio?
I hope to someday have this R-366/TRR-5, once again.

~ Happy DX!
NW7US

Senator Ted Cruz, in this pre-Memorial-Day message, thanks amateur (ham) radio volunteers who serve the public through emergency communications, readiness to meet public communications needs, and are ever-ready technical assets.

Senator Ted Cruz Highlights Amateur Radio Public Service (Memorial Weekend 2026)

Sen. Cruz highlights the role these amateur radio FCC-licensed volunteers have in providing essential communications when violent storms knock out communications in local and regional areas, when power is out, cellular communications limited or overwhelmed, and communications services are stressed beyond capacity. Senator Cruz notes that these ham radio operators step forward to provide first-response communications in many situations, and gives examples of such in recent years, such as the 2017 Hurricane Harvey emergency when the catastrophic flooding across Texas took so many lives, and ham radio was there providing critical emergency communications. This was again demonstrated in the horrible Camp Mystic floods. He emphasized that as the United States of America prepares for yet another Summer Season, ham radio volunteers are ready to step up and provide these essential amateur emergency communications services. His comments also reflect growing Congressional recognition of the value Amateur Radio Operators bring to communities across the country.

Senator Cruz is Chairman of the Senate Committee on Commerce, Science, and Transportation. His comments align with the ARRL’s ongoing efforts to strengthen and protect Amateur Radio’s role in emergency preparedness and public service communications. As a member of ARRL, I applaud the Senator’s acknowledgement of the service we amateur radio operators provide our communities.

This livestream recording is from September 1, 2024 – the NW7US Radio Communications Channel Livestream.  We do this livestream every Sunday at 21:15 UTC.  Here is the link to the livestream from this past Sunday:

The livestream list is here:

https://www.youtube.com/@nw7us/streams

I hope to see you in our livestream live chat, during the next session on Sunday, at 21:15 UTC.  See you there!

This is a video of the German Weather Broadcast from DWD, Hamburg, on shortwave (HF), using teletype (RTTY). I demonstrate two decoding software options: JWcomm32 (older), and, FLdigi. Note the in FLdigi, the “Reverse” feather is selected to properly decode the signal (in either USB or LSB, you still need to select, “Reverse”).

The radio used to receive these weather bulletins is an Icom IC-7610, using an antenna designed for 160 Meters.

RTTY is a system for broadcasting text over radio. The technology dates back to the late 1950s and seems somewhat anachronistic. Speeds are slow, even slower than NAVTEX. A similar service is the USCG service, SITOR (Simplex Teletype Over Radio) providing offshore and coastal forecasts over very wide and remote areas from the tropics to the polar regions.

There is dedicated equipment to receive RTTY and SITOR but we can receive both using a standard HF/SSB receiver with software packages such as TRUETTY and SEATTY to decode the signals.

The main advantage of RTTY/SITOR is the reception of information over an entire ocean area. The USCG also shares frequencies across multiple transmitters according to a schedule, rather like NAVTEX. The system is available over the Atlantic and Pacific including polar regions not served. For more about SITOR see the Monitoring Times link or the USCG site.

Around Western Europe and the Mediterranean, the Deutscher Wetterdienst (DWD) , the German Weather Service has accepted the responsibility to broadcast weather information for mariners on RTTY. Frequencies are in the table on the webpage at:
https://weather.mailasail.com/Franks-Weather/Radio-Teletype-Weather-Broadcasts

This video captures the RTTY transmission on 14467.3 kHz (with adjustment in the passband to center on Mark and Space as seen in the video).

DWD (Hamburg) Broadcast Content:

Some broadcasts are of raw weather observations in a WMO coded form. Otherwise, for the broadcasts include,

• Strong wind, gale and storm warnings for German Bight, Western and Southern Baltic Sea, German North Sea and Baltic Sea coast
• Weather forecast for the North Sea and Baltic Sea, Weather situation, forecast valid for 12 hours and outlook valid for another 12 hours
• Weather report German North Sea and Baltic Sea coast, Weather situation and forecast valid for 12 hours.
• Navigational warnings for North Sea, Baltic Sea and German coast
• Weather report Norwegian Sea and Baltic Sea Route North Cape – Shetlands, The Quark – Gulf of Finland. Weather situation and time series forecast for 2 days
• Weather report North Atlantic. Route Pentlands – Southwest Greenland. Weather situation and time series forecast for 2 days
• Station reports North Sea and Baltic Sea
• Weather report Western European Sea. Route Southern Ireland – Area Canarias. Weather situation and time series forecast for 2 days
• Medium range weather report North Sea, Weather situation and time series forecast for 5 days
• For the Mediterranean there are Station reports Mediterranean Sea
• Weather report Mediterranean Sea (in German), Weather situation and forecast valid for 24 hours.
• Alborán – Tunis. Weather situation and time series forecast for 2 days
• Weather report Eastern Mediterranean Sea (in German). Route Eastern Tunis – Rhodes/Cyprus. Weather situation and time series forecast for 2 days
• Medium range weather report Mediterranean Sea (in English), Weather situation and time series forecast for 5 days
• Around the North Sea and the Baltic this service is a useful supplement to NAVTEX. Particularly so are the 5 day outlooks, These give wind forecast every 12 hours for the 5 day period. The values are straight from the DWD NWP model at a few grid points although these are sufficient to give an overall view and much quicker to receive than synoptic charts on radio fax.

In the Mediterranean, most valuable is the 5 day forecast which seems to be used and very highly regarded by the majority of serious cruising yachtsmen. It is a most valuable service for predicting the major strong wind systems such as Mistrals, Libeccios, Tramontanes, etc. Such winds are usually well predicted 4 and often 5 days ahead. Conversely, I have never found the 24 hour forecast to be much use. For this period, the French, Spanish and even the Italian NAVTEX broadcasts are to be preferred.

There is a new book from a fellow Morse code amateur radio operator, Chris Rutkowski (NW6V), about “Learning, Living, and Loving Morse Code (in a Digital World).” NICE!

Title: “The CW Way of Life“
link: https://amzn.to/3Tm3KfD

I received a new book! Here it is, at my radio shack operations desk, at NW7US radio station.

Already, I think it rivals any other book on the topic, including “The Art and Skill of…,” or, “The Zen of…”

It is not, however, meant to replace, but to augment, what is available. But, it is a complete guide, including a “work book” section (nearly half of the book?) on how to improve your skill. Really good stuff, but I’m only in one day.

73 de NW7US dit dit
https://nw7us.us

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