Unravelling the Mysteries of Trans-Equatorial Propagation: A 2024 Perspective

Introduction

The Science and Mathematics Behind TEP

The ionosphere, a layer of the Earth’s atmosphere that is ionized by solar and cosmic radiation, plays a crucial role in TEP. The ionosphere is often modelled as a series of horizontal layers that vary with time, location, and sunspot activity. However, the real ionosphere, particularly in equatorial and polar regions, is much more complex.

One of the key features of the equatorial ionosphere that gives rise to TEP is the equatorial anomaly. This is where a high electron concentration is found on each side of the magnetic equator, usually seen in the region of 10 to 20 degrees latitude. The afternoon TEP is believed to occur when a signal is reflected first by an anomaly on one side of the equator and then again by another anomaly on the other side.

Evening TEP is less well understood but is believed to rely on “ionospheric bubbles” – areas of high ionization density off which signals are reflected. Other features of the ionosphere that give rise to these unusual modes include sporadic-E, the equatorial ionization enhancements, ionospheric tilts at twilight, and ionospheric irregularities such as equatorial spread-F.

The mathematical modelling of TEP involves understanding the behaviour of radio waves as they interact with these ionospheric layers. This is typically done using the principles of electromagnetic wave propagation, which are governed by Maxwell’s equations. The propagation of signals in TEP is often modelled using ray tracing techniques, which involve solving a set of differential equations that describe the path of the radio wave as it travels through the ionosphere. These equations consider the varying electron density in the ionosphere, as well as the frequency of the radio wave.

Web-Based Radio Systems Studying TEP

With the advancement of technology, web-based radio systems have become a valuable tool in studying phenomena like TEP. These systems allow for real-time monitoring and data collection from various locations around the world, providing a wealth of information for researchers. They can track changes in signal strength, propagation times, and frequencies of occurrence, contributing to our understanding of TEP¹.

Recent Breakthroughs in TEP Research

There have been several recent breakthroughs in TEP research. A study by Keisuke Hosokawa and his team investigated the feasibility of monitoring equatorial plasma bubbles (EPBs) using VHF radio waves used for aeronautical navigation systems. This study represents a significant step forward in the use of existing infrastructure for the wide-area monitoring of EPBs².

A comprehensive overview of TEP was provided, detailing its historical context, occurrence times, and the characteristics of afternoon and evening TEP. This resource serves as a valuable reference for both newcomers and experienced researchers in the field¹.

How Can Radio Amateurs Contribute?

Radio amateurs can contribute to the study and understanding of TEP in several ways. By operating on the VHF and UHF bands, particularly around the equinoxes when TEP is most prevalent, radio amateurs can collect valuable data on signal strength, propagation times, and frequencies of occurrence. Sharing these observations with the scientific community can provide real-world data to support theoretical models and predictions¹.

Amateurs can also conduct their own experiments to test theories and hypotheses about TEP. This could involve varying the frequency, time of day, or antenna configuration to see how these factors influence TEP¹.

Practical Examples of TEP Observations

TEP was first noticed in the 1940s by both military and amateur operators who discovered that it is possible to communicate in the VHF band over intercontinental distances during times of high sunspot activity. The first organized and therefore relatively large scale TEP communications occurred during 1957-1958 in the peak of sunspot cycle 19¹.

There are two distinctly different types of TEP that could occur. The first type occurs during the late afternoon and early evening hours and is generally limited to distances under 6000 km. Signals propagated by this mode are limited to the low VHF band (<60 MHz), are of high signal strength and suffer moderate distortion (due to multipath). The second type occurs around 2000 to 2300 local time and is more frequent around the equinoxes and especially at times of high sunspot activity. Signals may have doppler spread, are subject to rapid fading and strong distortion, and path lengths are usually between 3000 and 8000 kilometers¹.

TEP can also occur in the late morning hours, allowing for radio communication between southern UK and Southern Europe (Greece, Malta, Spain) and South Africa. During these times, the ionospheric conditions can align in such a way that VHF signals are able to travel over the equator, allowing for communication between these regions. In some cases, as per personal experiences and observations, these distances can extend up to at least 8900 km.

While VHF TEP is more commonly discussed, UHF TEP also occurs, albeit less frequently. In the article “Transequatorial Propagation, TEP: Everything You Need to Know”, it is mentioned that workable contacts have been made on 144MHz (2 meters) and sometimes on 432MHz (70 centimetres), which falls in the UHF band¹. This shows that while UHF TEP is less common than VHF TEP, it is indeed possible and has been observed by radio operators.

Ongoing Research

The International Telecommunication Union (ITU) is actively involved in ongoing research on TEP. They have published a recommendation on the method for calculating sporadic-E field strength, which is relevant to TEP. The ITU Journal has also called for papers on propagation modelling for advanced future radio systems, which includes TEP. Furthermore, a study on monitoring equatorial plasma bubbles using aeronautical navigation systems is a recent development in this field².

A Radio Amateur can contribute a great deal into the study of the propagation and its characteristics helping to provide essential detail on observations. The first step in the analysis process is always to collect sufficient data and the radio amateur community is well placed to make such a sizable contribution, either through the PropNet or BeaconSpot networks.

Observations are quite easy to make once there is an idea of what and where signals are. The amateur radio community benefits from fixed frequencies for computer-generated modulation schemes, generically called MGM and currently consisting mainly of FT8, FT4, and WSPR modes. WSPR signals monitored by radio amateurs can be automatically logged to the WSPRNet servers, and FT4/FT8 reports can be logged to psk reporter, on 28MHz, 40MHz, and 50MHz [7] (https://pskreporter.info/pskmap.html).

In addition, there are a set of highly reliable transmitters beaconing their callsign details continuously so that, provided someone is listening, if a propagation path occurs there is a great chance the occurrence will be logged.

The allocation at 40Mhz has a small number of beacons running and these are very good indications for possible TEP and other anomalous propagation modes.

The beacons can be found from this table:

Beacon	Frequency	Locator	MGM	Last QRG	ODX (km)	Status
ZS6WAB	40.675	KG46rb	FT8	40.6748	12469	On
GB3MCB	40.050	IO70oj	FT8	40.0500	6781	On
EI1KNH	40.013	IO63ve	FT8	40.0130	4539	On
OZ7IGY	40.0702	JO55wn	PI4	40.0710	9479	On
S55ZMS	40.670	JN86cr	PI4	40.6750	8378	On
EI1CAH	40.016	IO53ck	PI4	40.0160	7585	On
ZS6OB	40.680	KG44de	A1A	40.6800	0	On
WM2XCS	40.685	FN20wv	A1A	40.6850	7106	On
WM2XCW	40.680	CN88lx	–	40.6800	2941	unkn
ZL2WHO	40.687	RE79tp	–	40.6870	0	Off

From this location in south-east England ZS6WAB is currently received (early April 2024) at good strength for about 15-20minutes late morning (between 10:30 – 11:30utc). About an hour after first onset a very week signal returns again for about 15-20minutes before fading out slowly after 30 -45 minutes.

The characteristic observation is that the signal at 40MHz suddenly appears and increase in strength then its strength reduces slowly until it disappears after about 30 – 45 minutes. Then an hour or so later a much weaker signal appears with the same fast onset and slow decay profile before fading out completely for the day. This phenomenon seems to have been also observed by other observing stations.

The signals itself is usually T9, i.e. shows no sign of dispersion (no Doppler spread). Signal amplitude varies but can usually be classed and medium fading.

A Closer Look at ZS6WAB on 40MHz

For some reason yet to be determined parallel reception of ZS6WAB on 28MHz and 50Mhz has yet to be noted at this reception location.

At present there is limited data available so that the current observation windows is restricted from late March to the first week of April 2024.

This is best illustrated in this data table: –

Date	Time	Beacon	Frequency	RPT	Dist(km)	Spotter
05/04/2024	12:13	ZS6WAB	40.6748	539	8187	F4CXO
05/04/2024	10:58	ZS6WAB	40.6748	519	8187	F4CXO
05/04/2024	10:59	ZS6WAB	40.6750	519	8303	F6ACU
05/04/2024	11:32	ZS6WAB	40.6747	569	8836	G0API
05/04/2024	11:20	ZS6WAB	40.6748	549	8783	G4OGI
04/04/2024	12:05	ZS6WAB	40.6748	529	7824	9A5CW
04/04/2024	11:35	ZS6WAB	40.6748	539	8187	F4CXO
04/04/2024	11:21	ZS6WAB	40.6750	419	8303	F6ACU
04/04/2024	11:39	ZS6WAB	40.6748	559	8784	G4OGI
03/04/2024	11:09	ZS6WAB	40.6748	539	8187	F4CXO
03/04/2024	13:11	ZS6WAB	40.6750	529	7485	IK0OKY
03/04/2024	11:23	ZS6WAB	40.6750	51	9341	OH7PS
03/04/2024	13:07	ZS6WAB	40.6746	559	7841	S59GS
02/04/2024	10:43	ZS6WAB	40.6750	51	7824	9A5CW
02/04/2024	13:18	ZS6WAB	40.6750	559	7819	EA3ERE
02/04/2024	10:50	ZS6WAB	40.6748	529	8187	F4CXO
02/04/2024	10:51	ZS6WAB	40.6748	559	8249	F4FRQ
02/04/2024	11:08	ZS6WAB	40.6750	539	8303	F6ACU
02/04/2024	10:39	ZS6WAB	40.6748	549	8783	G4OGI
02/04/2024	13:15	ZS6WAB	40.6746	559	7841	S59GS
01/04/2024	11:44	ZS6WAB	40.6750		8622	DH6JL
01/04/2024	11:54	ZS6WAB	40.6748	579	8187	F4CXO
01/04/2024	10:26	ZS6WAB	40.6748	519	8187	F4CXO
01/04/2024	11:33	ZS6WAB	40.6750	579	8303	F6ACU
01/04/2024	11:30	ZS6WAB	40.6748	549	8784	G4OGI
01/04/2024	12:33	ZS6WAB	40.6750	559	7485	IK0OKY
01/04/2024	12:06	ZS6WAB	40.6750	529	7485	IK0OKY
31/03/2024	11:28	ZS6WAB	40.6750	559	7819	EA3ERE
31/03/2024	10:40	ZS6WAB	40.6748	539	8187	F4CXO
31/03/2024	11:45	ZS6WAB	40.6750	549	8303	F6ACU
31/03/2024	11:14	ZS6WAB	40.6745	579	7841	S59GS
30/03/2024	10:47	ZS6WAB	40.6750	559	7819	EA3ERE
30/03/2024	10:21	ZS6WAB	40.6750	529		EI7HBB
30/03/2024	10:27	ZS6WAB	40.6748	559	8187	F4CXO
30/03/2024	09:38	ZS6WAB	40.6748	539	8187	F4CXO
30/03/2024	09:31	ZS6WAB	40.6748	519	8187	F4CXO
30/03/2024	10:25	ZS6WAB	40.6750	539	8303	F6ACU
30/03/2024	10:30	ZS6WAB	40.6747	559	8836	G0API
30/03/2024	10:46	ZS6WAB	40.6750	599	8647	OR7T
29/03/2024	09:15	ZS6WAB	40.6750	539	7819	EA3ERE
29/03/2024	12:15	ZS6WAB	40.6750	559	9167	EI2IP
29/03/2024	11:32	ZS6WAB	40.6748	549	8187	F4CXO
29/03/2024	10:32	ZS6WAB	40.6750	519	8303	F6ACU
29/03/2024	11:05	ZS6WAB	40.6748	559	8836	G0API
28/03/2024	11:44	ZS6WAB	40.6750	559	7819	EA3ERE
28/03/2024	11:11	ZS6WAB	40.6748	529	8187	F4CXO
28/03/2024	12:26	ZS6WAB	40.6748	539	8249	F4FRQ
28/03/2024	12:08	ZS6WAB	40.6750	219	8303	F6ACU
28/03/2024	11:19	ZS6WAB	40.6748	529	8836	G0API
27/03/2024	12:33	ZS6WAB	40.6750	559	7819	EA3ERE
27/03/2024	10:39	ZS6WAB	40.6748	579	8836	G0API

A general trend showing the expected late morning propagation is clear. Observing stations have either horizontal or vertical polarisation, suggest “simple” antennas in use and reported signal strengths appears to be very similar from southern to northern European observers.

Signals also appear to be described as having “T9” note with some fading.

Conclusion

The study of TEP is a fascinating area of research that continues to challenge and engage the scientific community. While we have made significant strides in our understanding of this phenomenon, there is still much to learn. Through continued research and collaboration between scientists and radio amateurs, we can continue to unravel the mysteries of TEP and enhance our understanding of this complex and intriguing phenomenon. The ongoing research in this field is testament to the complexity and intrigue of TEP. It’s a fascinating area of study that continues to challenge and engage the scientific community. The practical examples and observations of TEP provide valuable insights into this phenomenon and contribute to our understanding of this fascinating area of science. As radio amateurs, we have a unique opportunity to contribute to this field and help advance our understanding of the world around us.

Let’s continue to explore, observe, and share our findings with the world.

References

1. Unknown Author. (n.d.). Transequatorial Propagation, TEP: Everything You Need to Know¹.
2. Hosokawa, K., Saito, S., Nakata, H., Lin, C. H., Lin, J. T., Supnithi, P., Tomizawa, I., Sakai, J., Takahashi, T., Tsugawa, T., Nishioka, M., & Ishii, M. (2023). Monitoring of equatorial plasma bubbles using aeronautical navigation systems: a feasibility study².
3. Unknown Author. (n.d.). Trans-Equatorial Propagation – Amateur Radio Wiki.
4. ITU. (n.d.). P Series Radiowave propagation.
5. ITU Journal. (n.d.). Special Issue Propagation modelling for advanced future radio systems.
6. WSPRNet⁶ (https://www.wsprnet.org )

1. Thanks for the UKSMG mention, and the link to the report that Ray Cracknell, G2AHU (former PSC member) wrote in Six News and on which I was a co-author. Unfortunately, it describes a study into troposcatter signals, NOT TEP.

Ray, who died in 2008, was indeed an early pioneer of TEP studies along with Costas, SV1DH, but you’ll need a different reference. I can dig one out if there’s time to change it – let me know and I’ll find it today

1. Sources

1. Transequatorial Propagation, TEP: Everything You Need to Know

2. Definition and Theory of Transmission Network Planning

3.Beaconspot