This is a mode that I have heard VK8 operators talking about, but unwittingly dismissed it,
thinking it was just a mode that was only available to VK8 operators, the studies into this
mode disprove that idea, so I have now created this page to encourage and promote this mode
of operation in the Oceania region, as there are two opportunities during each year to make
use of it, both at times outside the generic "Summer" VHF season. DX propagation occurs all
throughout the year, it is a case of go and find it, instead of waiting for it to come to you.

See below for more information on the subject of TEP:

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TEP article from Roger Harrison, VK2ZRH



VHF TRANSEQUATORIAL PROPAGATION: AFTERNOON-TYPE


VHF transequatorial propagation (TEP) is so called because it involves the reception of VHF signals,
or the making of VHF contacts, over very long paths that cross the geomagnetic equator.

The frequencies are well above those supported by the familar F-layer propagation at HF, and signal
strengths are often much higher than would be expected for the distances involved. In addition,
the paths involved are not those commonly experienced with VHF sporadic-E propagation, in length,
geography and seasonal characteristics.

There are two types, or modes, of TEP: afternoon-type TEP (aTEP) and evening-type TEP (eTEP),
based on the hours they occur during a day.

Here's an outline of AFTERNOON TEP:

PATHS

Paths cross the geomagnetic equator and range from 4000 to 10,000 km in length, but longer paths
have been recorded (perhaps extended by other propagation modes).

The paths most often observed cross the geomagnetic equator at angles within 30 degrees of orthogonal,
but can be at quite oblique angles (think VK to XE).

Path terminals generally lie in a zone between 32 and 62 degrees dip angle (roughly 20 to 40 degrees
geomagnetic latitude).

This map aTEP_paths(PacSec) of the Pacific sector shows the general terminal zones (hatched areas)
and the propagation paths between them (grey arrows).
The oblique paths are S-shaped because that's the shape of a great-circle path on a Mercator projection map.

FREQUENCIES

Maximum observed frequencies (MOFs) for afternoon TEP are typically 40-55 MHz, and occasionally
extend to the 60-70 MHz region.

On the 5870 km Townsville-Yamagawa (Japan) path, for example, the MOFs observed are 15-20 MHz greater
than the normal two-hop F-layer maximum usable frequency (MUF).

TIMES/SEASONS

For paths oriented generally north-south (eg. VK - JA/HL), afternoon TEP generally occurs between
1400 and 1900 local mean time (LMT), occasionally extending as early as 1200 and as late as 2100 LMT.
On oblique paths where the terminals lie in different time zones, times at the path terminals can
be determined from the LMT at the path midpoint. For example, the time difference between eastern
Australia and Central America (ignoring the international date line) is eight hours. So, from Brisbane
you�d be looking for aTEP to Costa Rica or Mexico from 12 noon (1400 LMT in the mid-Pacific), or earlier.

Afternoon TEP is generally experienced during the equinoctial months of March-April and September-October
(whereas sporadic-E peaks in the summer months, with a minor winter peak and minimum at the equinoxes).
However, it has been observed as early as two months before and after the equinoctial months (ie. January
and May for the March 20-21 equinox, July and November for the September 22-23 equinox).

Solar maximum years brings more afternoon TEP openings, but openings never disappear during solar minimum.

SIGNALS

Signal strengths observed for afternoon TEP range from weak to very strong. Path loss can be significantly
less than free-space loss because of signal focussing that occurs in the path through the ionosphere
(see the section on propagation mode).

The signal fading rate experienced is generally slow, with shallow fades every few seconds, occasional
deep fades of 20-30 dB and often sustained periods of very strong signals. Doppler shift/spread is
generally small, generally in the range 1-5 Hz and varying slowly.

Here is a chart recording  aTEPchart_S_Hz  I made of the JA1IGY beacon on 52.5 MHz received in
Townsville on 26 April 1972. It shows some 45 seconds of Doppler shift and signal strength of the
received signal. The signal strength, fading and Doppler shift characteristics are typical of afternoon TEP.
The Doppler recording is a linear scale, centred on chart line 7, while signal strength is a logarithmic
scale from chart line 0.

PROPAGATION MODE

The propagation mode of afternoon TEP is 'chordal hop', having two F-layer reflections without an
intervening ground reflection. The reflection points occur within two zones of enhanced ionisation
either side of the geomagnetic equator known as the 'equatorial anomaly'. This diagram aTEP100
shows the general chordal-hop geometry of afternoon TEP, now known as "super-mode" propagation.

Solar radiation causes ionisation over the equatorial region to rise during the morning hours, which
then flows north and south along the Earth's magnetic field lines, away from the magnetic dip equator,
in a complex process called the 'Fountain Effect'. The ionisation accumulates in the equatorial
anomaly zones, becoming more dense as the day progresses.

A VHF signal from a suitable area will encounter the nearest equatorial anomaly at a very shallow angle
and be refracted such that its path is above the ground over the equatorial region. When the signal
reaches the other anomaly region it is then refracted through a small angle towards the Earth.
Over a small range of angles, the signal ray paths from a transmitter in one hemisphere will converge
in the opposite hemisphere, as illustrated in the diagram. This signal focussing phenomena can yield
very high signal strengths and narrow 'footprints' on the ground � sometimes, signals heard strongly by
one station can't be heard by others nearby; after a while, the situation can be reversed!

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VHF TRANSEQUATORIAL PROPAGATION: EVENING-TYPE   by Roger Harrison VK2ZRH

VHF TRANSEQUATORIAL PROPAGATION: EVENING-TYPE



INTRODUCTION

VHF transequatorial propagation (TEP) is so called because it involves the reception of
VHF signals, or the making of VHF contacts, over very long paths that cross the geomagnetic
equator. The frequencies are well above those supported by the familiar F-layer propagation
at HF, and signal strengths are often much higher than would be expected for the distances
involved. In addition, the paths involved are not those commonly experienced with VHF
sporadic-E propagation, in length, geography and seasonal characteristics.

There are two types, or modes, of TEP: afternoon-type TEP (aTEP) and evening-type TEP (eTEP),
 based on the hours they occur during a day. This article covers evening-type TEP.

eTEP PATHS

Paths cross the geomagnetic equator and range from 3000 to 6000 km in length, but longer
paths have been recorded, e.g. a 144 MHz contact between I4EAT, Northern Italy (JN54VG),
and ZS3B, Namibia (JG73), about 7800 km; observation of a 144 MHz ZE2 beacon (Zimbabwe)
by DC3MF (South Munich, Germany), about 8000 km.

The paths most regularly observed cross
the geomagnetic equator within a small range of angles close to 90 degrees, and very nearly
symmetrically spaced about the geomagnetic equator. Paths having an obliquity of 15 degrees
or more experience considerably fewer occurrences, particularly in the bands above 50 MHz.

Path terminals are generally situated in a zone between 30 and 55 degrees magnetic dip
angle north and south of the geomagnetic dip equator. However, a station in one hemisphere
will most often contact stations in a zone close to its geomagnetic conjugate in the opposite
hemisphere.

This map of the Asian-Australian sector eTEP_paths(AsiaAus) shows examples of the paths
observed (contacts made and signals heard).

The short-dash line running from Singapore to the Darwin-Southern Japan path indicates an
observation made by a Defence Science Establishment (now DSTO) scientist who received and
recorded Darwin VHF beacons in Singapore one evening using a handheld antenna pointing
skyward. The intriguing reason for this is explained later.

Given that paths to 8000 km have been established in the African-European sector, evening
TEP contacts on at least 50 MHz, and conceivably 144 MHz, over such distances could be
achieved between Australia and Japan, e.g. from Coffs Harbour (or Armidale) in Northern
NSW, or Woomera in South Australia, to JA7 on the northern coast of Honshu, Japan.

FREQUENCIES

Maximum observed frequencies (MOFs) for evening TEP extend to at least 432 MHz.
No upper limit has been established.


Since TEP was first reported in 1947 (Ed Tilton, World Above 50 MHz, QST, May and October 1947),
MOFs for evening TEP climbed ever higher during each decade. Over the 1950s and 1960s,
Australian amateurs and DX listeners observed VHF signals in the evening at frequencies up to
70+ MHz. In the late 1960s, Stuart Kingan ZK1AA on Raratonga, Cook Islands in the South Pacific,
observed TV signals (NTSC chA2-A6) from Hawaii on frequencies up to 90 MHz.

Until the mid-1970s, the highest frequency observed was the 102.7 MHz Defence Science beacon
in Darwin recorded in Yamagawa, Japan.

On 8 November 1976, around 0040 UTC, YV5ZZ in Venezuela noticed Mode A downlink signals from
Argentina via Oscar 7 some 10 minutes earlier than normal AOS. On listening to the 2m uplink
frequency, YV5ZZ heard LU7DJZ direct, over a 5000 km path (reported in World Above 50 MHz,
QST, January 1977). Then, on 29 October 1977, YV5ZZ contacted LU1DUA on 144 MHz, a 5044 km path.

Subsequently, on 24 February 1978, VK8GB in Darwin, Northern Australia exchanged reports on
144 MHz with JH6TEW in Kyushu, Japan, a path of 4950 km. On 28 April 1978, ZE2JV in Rhodesia
(now Zimbabwe) worked 5B4WR on Cyprus on 144 MHz, a path of 6300 km.

It appears the first recorded instance of evening TEP on 432 MHz was the reception of the
ZE2JV beacon by SV1DH in Greece, on 20 March 1979, a path of 6300 km.

TIMES/SEASONS

Evening TEP has a peak diurnal occurrence between 2000-2300 LMT (at the midpath, where it
crosses the geomagnetic equator). It may open a little earlier, and extend past midnight on
the lower frequencies, but openings on the higher frequencies rarely extend past 2300 local
time.

Openings peak around the equinoctial months of March-April and September-October, particularly
for the higher frequencies.  All this is clearly apparent in this diagram eTEP_times-seasons showing the
diurnal and seasonal characteristics of evening TEP.

On the lower frequencies, openings may still occur through the solstitial months.

Evening TEP openings are more frequent during high sunspot years, although never disappear
during solar minima years. Researchers have noted that the requirement of path symmetry about
the magnetic equator is more important during solar minimum than at solar maximum.

SIGNAL STRENGTHS

Observed signal strengths for evening TEP can range from weak to very strong, although signals
of weak to fair strength are more usual. Path loss can, at times, be substantially less than
the free-space path loss for the distances involved, but is generally 20 dB to 50 dB greater
than that. For a 6400 km path, for example, free-space path loss is about 150 dB. Signals as
strong as -66 dBm (S9 being -73 dBm) have been observed (e.g. in the South American sector),
while signals in the range -85 dBm to -110 dBm seem to be typical in the JA-VK sector.

Signals rise in strength rapidly from the start of an opening, typically reaching a peak within
15-20 minutes, after which they plateau for a period before declining slowly.

For a given opening, signals are generally of higher strength at the lower frequencies.

Evening TEP exhibits a characteristic 'fluttter' fade at rates up to 15 Hz on 50 MHz and
rather faster fade rates on higher frequencies, often giving 144 MHz signals a 'raspy' quality.
The fading can also be 'choppy', fading out completely for fractions of a second.

This set of chart recordings eTEPchart_Sx4_vkvhf of the Australian Defence Science beacons at Darwin, on
48, 72, 88 and 102 MHz, as received in Yamagawa, southern Japan, over 16-17 October 1970,
illustrate many of the general signal characteristics of evening TEP. The time axis proceeds
from right to left; the vertical markers are at 10 minute intervals. Note the steep rise
as the path opens, the lower frequencies opening earlier than the higher frequencies, and
the lower frequencies continuing after midnight, while the higher frequencies decline
after 2300. Note also the rapid fading of about 5-10 dB, ranging up to about 15 dB, and the
longer period fades of about 40 minutes to an hour between peaks (Kuriki et al, Journal of
Radio Research Labs, Japan, Vol. 19, 1972).

Doppler shifts of 20 to 50 Hz on 50 MHz are observed, and similar Doppler 'smearing' or
spreading of signals.

On 144 MHz, Doppler shifts vary from +50 Hz ranging up to -350 Hz have been recorded,
generally averaging around -100 Hz. However, Doppler spreading of more than 1 KHz has been
recorded, giving rise to remarks that the signals "sound like auroral or moonbounce" reception.
This diagram eTEP_Doppler_SV1DH shows the pattern of Doppler shift on the 144 MHz signal
of ZE2JV in Harare (Zimbabwe) recorded by SV1DH in Greece for two eTEP openings during October 1980.

EVENING TEP PROPAGATION MODE

The propagation mode of evening TEP is via 'ducting' or 'guiding' through field-aligned
'bubbles' of depleted ionisation which thread the equatorial ionosphere and extend symmetrically
north-south across the geomagnetic equator. The general details are illustrated in this diagram
eTEP_vkvhf

Ionisation inside the bubbles can be very sparse - a 10th to a 1000th less than the surrounding
F layer, while the bubble wall has a sharp boundary, where the ion (and electron) density changes
rapidly between the inside and the outside of the bubble.

A signal from a VHF transmitter at a favourable location in one hemisphere enters the end of
the bubble at a grazing angle to the magnetic field at that point and then skids around the top
wall until it exits the bubble in the opposite hemisphere where a station at a favourable location
can receive the signal.

These equatorial plasma bubbles ('EPBs') appear in the base of the equatorial ionosphere about
an hour after the sun has set at that height (around 250-350 km). They rise up and extend rapidly
along the curved magnetic field lines, drifting eastward at speeds of 25-125 metres/second.
Their upward motion is typically 125-350 metres/second; some have been measured rising at
supersonic speeds of more than 2 km/sec! They rise to peak heights of 1500 km or more at the
geomagnetic equator and their ends can extend to more than 40 degrees dip angle; i.e. south of
Darwin and north of Yamagawa in southern Japan.

The reason for the observed flutter fading and the Doppler shift and spreading is now abundantly
clear!

The general development of the EPBs and the consequent influence on signal elevation angles and
path lengths are illustrated in this diagram eTEP_geometry

The bubbles may be 40-350 km in diameter and successive bubbles may be 40-100 km apart. The
walls are not smooth, except for the early phase of their development, are often bifurcated
(e.g. like looking up an elephant's trunk), and sometimes remain open at the bottom. When this
latter feature is present, the propagation can 'leak' to locations below and to the side of
the bubble.

Indeed, there have been reports of such events. For example, as mentioned in Part 1, I saw a
presentation given by Doug Fyfe, a Defence Science Establishment (now DSTO) scientist, who
received and recorded Darwin VHF beacons in Singapore one evening using a handheld antenna
pointing skyward.

EPBs have diurnal and seasonal characteristics that match those of evening TEP, which is why
eTEP is observed to behave as it does. The diurnal characteristics of eTEP at 44-48 MHz and
144 MHz over the JA-VK path are compared to that for EPBs (global average of satellite
measurements) in this diagram eTEP_diurnal_vs_EPBs

ARE THERE BUBBLES THERE YET?

To tell when eTEP propagation is likely on any given evening, you can look for the precursors,
or the 'signatures' of equatorial plasma bubbles. There's the time-hounoured method of monitoring
upper-HF and/or lower-VHF signals from suitable locations. For example, monitoring the JA2IGY
NCDXF/IARU time-share 5-band HF beacon in Japan from around 1900 LMT
(see http://www.ncdxf.org/beacons.html).

Developing EPBs will cause multipath and and off-great circle propagation on the 21 MHz and
28 MHz beacon signals (or whatever else you're monitoring). Look out for characteristic sudden,
deep fading patterns and phase distortion. When flutter fading arrives, you know there may
be bubbles in the equatorial ionosphere. Fortunately, the IPS Radio and Space Services vertical
incidence ionosonde at Vanimo, on the north coast of Papua New Guinea, is ideally placed to
detect the presence of EPBs. They produce characteristic range-spreading, or 'spread-F', on
ionograms. Extra 'traces' appear suddenly on the ionogram, as shown in the examples in this
set of images eTEP_Vanimo_spread-F. The presence of spread-F on Vanimo ionograms
is a necessary, but not sufficient condition of itself for VHF evening TEP.

The two left-hand ionograms show typical night time F-layer traces, while the two right hand
ionograms show the start of spread-F five minutes later. In the upper right hand ionogram,
a weak extra trace at the lower frequency end of the first F-layer reflection is just visible.
In the lower right hand ionogram, the range-spreading is very obvious. The IPS ionogram
viewer is online at: http://www.ips.gov.au/HF_Systems/1/3


---------------------------------------------------------------------------------------------------------

For those interested in further information, try these references:

GENERAL


"Transequatorial Radio Propagation", John Kennewell & Phil Wilkinson, IPS Radio & Space Services

"Transequatorial VHF Propagation", Roger Harrison (VK2ZTB), Amateur Radio, April & May 1972;
also published in VHF Communications (UKW Bewrichte), 90-108 1972.

EVENING TEP
"Transequatorial VHF Propagation and Equatorial Plasma Bubbles", M L Heron, Physics
Department, James Cook University of North Queensland, Australia, Proceedings of the 1979
symposium on Future Amateur Communications Techniques, NSW VHF & TV Group.

"Investigations of Long-Distance VHF/UHF Amateur Contacts Across the Geomagnetic Equator",
Roger Harrison VK2ZTB, Proceedings of the 1979
symposium on Future Amateur Communications Techniques.

"On transequatorial VHF propagation paths", M L Heron, Physics Department, James Cook
University of North Queensland, Australia, Journal of Atmospheric and Terrestrial Physics,
Vol. 43, No. 8, 1981.

Posted in the interests of sharing useful information.

73, Roger Harrison VK2ZRH








---------------------------------------------------------------

Extract from vk-vhf mailing list 4th July 2006

Author: Tony Mann

Has anyone read the account by Wolfgang Schippke, DC3MF (reference
below) of the numerous  2m TEP openings (from ZE) into southern
Germany in 1979-1980?

Signal recordings of ZE2JV's 2m beacon by DC3MF can be found on the
EA6VQ TEP website.

The magnetic latitude at DC3MF's QTH is similar to Sydney or Perth.
And the angle of the path is about 14 degrees off perpendicular to
the geomagnetic equator, compared to only 10 degrees for Sydney-Tokyo.

Given these results you might expect some JA 2m evening TEP signals
to be detectable in SE VK, at least in solar cycles as strong as 21
and 22.

Food for thought.
regards,
Tony

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144 MHz TEP report from VHF mail list,  on 4th October 2007

Author: Roger Harrrison

Andr� PY5EW reports he had 144 MHz QSOs via Ducted (evening-type)
TEP with stations in Trinidad & Tobago on Monday 1 October from 0059 UTC.

He worked 9Z4FZ, 9Z4GU and 9Z4DMA with signals 5x5.

Andr� is in Londrina, South Brazil, and runs an FT-857D (170W) to
a 15-element horizontal Yagi.

Solar activity - Low. 10.7 cm Flux - 65.

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