Transequatorial VHF Propagation info

VK2ZRH · Post by **VK2ZRH** » Tue Apr 24, 2007 1:05 pm

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 involved 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.

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.

Both TEP types are supported by the ionosphere, but by entirely different mechanisms. Afternoon TEP supports frequencies up to 60-70 MHz over paths of 4000-10,000+ km, while evening TEP supports frequencies up to 432 MHz on paths of 3000-6000+ km.

Up-to-date info on the two TEP modes, authored by yours truly, is now available on the internet.

The article on afternoon-type TEP is online at: http://home.iprimus.com.au/toddemslie/aTEP-Harrison.htm

The article on evening TEP is online at: http://home.iprimus.com.au/toddemslie/eTEP-Harrison.htm

For readers' edification, I joined the IPS Low Latitude Research Section in 1971, working with Dr Leo McNamara on TEP (see http://www.tepov.org) and other propagation research projects. I wrote a review paper on TEP in 1972, published in Amateur Radio (May & June) and VHF Communications. I left IPS in 1977 for another career. However, I have maintained my interests in the ionosphere and propagation over the years since then.

73, Roger Harrison VK2ZRH

VK3SIX · Post by **VK3SIX** » Wed Apr 25, 2007 11:09 am

Informed discussion can only occur between adults.

VK4BKP · Post by **VK4BKP** » Thu Apr 26, 2007 3:08 pm

Thanks very much for the info VK2ZRH. Much appreciated.

VK2ZRH · Post by **VK2ZRH** » Mon Apr 30, 2007 4:24 pm

Thanks Kevin. Hope you can make use of the info and get amongst some juicy DX.

TEP's a big field. Always lots more to discover/learn.

73, Roger Harrison VK2ZRH

VK4QB · Post by **VK4QB** » Fri Nov 09, 2007 8:39 pm

Roger, many years ago I was in New Guinea and was on 6 mteres with an Am rig. We used to work the JAs in the evenings but one night I worked VK8KK in I think Darwin until about 1 am when we were both too tired to continue. I didn't have a S meter on the rig (modified Pye Reporter 3 watts!) but he had a very strong signal and mine evidently was the same. I reasoned that if we could use TE skip across the equator why can't we go along the equator and this contact tended to make me believe you could but there are not many amateurs along the equator. Does this seem right. Re the along the equator skip?
Brian VK4QB

VK2ZRH · Post by **VK2ZRH** » Wed Nov 14, 2007 7:20 am

Hi Brian,

That sounds more like sporadic-E to me!

Ducted-mode, or night time, TEP 'constrains' the signal path to within a few degrees of normal (right angle) to the geomagnetic equator, because the signal is ducted via a field-aligned bubble in the F-layer, which spans the equatorial region. They drift eastward at about 120 metres/second so an individual opening/path lasts tens of minutes, not hours. Of course, successive bubbles drifting past 're-opens' TE paths.

The path from PNG to Darwin is, in any event, well south of the equatorial region in geomagnetic terms.

73, Roger Harrison VK2ZRH

VK4QB · Post by **VK4QB** » Wed Nov 14, 2007 7:45 am

Hi Roger,
I thought Sporadic E was very temporary, not the 5 hours we were on. No dips at all in signals but continuous.He could have been next door, but I checked and he wasn't. Lae was a small town in those days. I would really like to find out what was going
on with the propagation. We tried after that evening but never had any success.
73
Brian
VK4QB

VK2ZRH · Post by **VK2ZRH** » Wed Nov 14, 2007 9:15 am

Hi Brian,

Sporadic-E can be "temporary" (I prefer evanescent!) and it can hang around for many hours, and everything in between.

In 1972, when I worked for IPS Radio & Space Services, I did relief duty at their station on Cocos Island over the 1972-73 summer. Apart from keeping the ionosonde running and doing the daily/weekly ionospheric data reporting, I did a lot of VHF listening. On a number of occasions, I copied the VK8VF Darwin beacon rolling in with good to rock-crushing signal strengths for hours on end. Could I raise anyone on 6m? Nope! One of nature's purposes with sporadic-E is to torment VHF enthusiasts!

Cocos Island is 12 degrees south of the geographic equator and close to 20 degrees south of the geomagnetic equator. The distance Cocos-Darwin is more than one-hop for Es.

73, Roger Harrison VK2ZRH

VK4GHZ · Post by **VK4GHZ** » Wed Nov 14, 2007 9:37 am

: Geomagnetic equator region

Gary, VK4ABW, sent me this recently.
You can see the relationship between geographic equator and magnetic equator.

YS1AG · Post by **YS1AG** » Mon Apr 18, 2011 10:26 am

Hello Mates!
year after year during the Holy Week (begins today) I enjoy having qsos with you guys in VK. This year I haven't heard anything, not even a whisper. As you are the gurus of TE please help me to understand what happens now with TE? this equinox I have heard only briefly some guys from LU, CE, CX and PY, short lasted propagation, with signals never above S7. And only one opening in the evening TE, I could rag chew with my old friend OA4TT. Also in more than 20 years active in 6 mts, NEVER could cross continents in the eastern direction, that is never a single TE qso with Africa, but hundreds of contacts with your area, VK ZL, FK etc etc and South America. Why? I see reports of JA working South America and Europeans working South America, Perhaps the angle of the signal hitting the geomagnetic equator is terribly critical for me?
I am now in vacation because the Holy Week if you also stop working at least on Holy Friday, enjoy the DX hunting!
Cheerios
Andy YS1AG

VK2ZRH · Post by **VK2ZRH** » Sun Apr 24, 2011 4:10 pm

Hi Andres.

My apologies for not answering earlier, but I've been rather busy lately. I've also answered your email to me about this subject.

I think the answer why you experience poor afternoon-type TEP is that I guess you are rather too close to the geomagnetic equator and the northern peak of the equatorial ionospheric anomaly (EIA) to the southeast of you (towards Africa). From what you said (in email to me) about XE, Carribbean and South Florida stations, the propagation's passing over your head! Also, the propagation path angle with the geomagnetic equator will be rather skewed, not to mention very asymmetrical, so propagation is not favoured. However, to the southwest, you are far enough away from the EIA to achieve favourable elevation and azimuth angles.

Perhaps the angle of the signal hitting the geomagnetic equator is terribly critical for me?

In a word - Yes.

If you went mobile/portable up into XE, you'd have more success to Africa

You could try for QSOs 2-4 hours earlier than the general rule-of-thumb (14-19 LMT at mid-path), when the EIA is building over the land mass of Africa.

As for not making any VK QSOs this season, the 7-day solar flux, which generally needs to average 80+, and daily A-index (which needs to be 5 or below) probably haven't been "on your side".

I hope that information helps. Don't stop trying, though

73, Roger Harrison VK2ZRH

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