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This interesting dialogue took place in an exchange of e-mails in late December 2000 and early January 2001, initially responding to the paper `Six-Metre Scatter DX' by Emil Pocock W3EP which was published in Six News issue 66, pp 51-54.

From W7GJ to W3EP, copy to K2RTH, K6MIO/KH6 and others

Hello Emil,

I just read your F2 propagation paper again, at the prompting of seeing it on the UKSMG page announcing recent publications. Having spent more time listening to white noise (while jumping around from website to website, watching postings, checking condx, monitoring satellites, etc. etc.), this all is becoming a bit clearer to me than when I started a few years ago.

One of the most baffling things to me has been why I almost NEVER seem to get an opening up here, despite the fact that stations on both coasts are working DX like mad. Of course, distance to the point of high MUF has something to do with it, and there is no doubt that the `ridges' of high MUF always seem to follow the geomagnetic field lines as they rotate around the world, which pushes them down around the western USA - usually just out of reach from Montana.

But there appears to be more to it than that. If the MUF were higher, I am sure that reflections would take place. W7HAH has told me early-on that we need to have solar flux numbers above 210 before any reliable sorts of F2 openings will happen up here, and I fully agree with his empirical `rule of thumb' -we have had ALMOST NO DAYS of 210 solar flux this cycle (other than last summer),and it appears that a higher solar flux is required for a `clean simple bounce' off the F2 layer. We have only had JUST A FEW transcontinental openings, which were (as far as I can tell) that type of propagation.

What I would like to propose for your consideration is the following explanation, which is based on endless hours of watching the Real Time MUF maps. If you watch those through the day, you will notice that most of the propagation reports are from signals being reflected ALONG the ridges of high MUF. I have NEVER seen a 50 MHz MUF line within reach of this QTH, and usually it is only 37+ MHz MUF ridges that result in propagation, although the propagation is ALONG THE RIDGES.

I believe what is happening is cloud-to-cloud, similar to the TE propagation. Although the MUF might not be strong enough to do a single `clean bounce' back down to the earth, it IS enough to gently bend the signals and prevent them from going off into space (or even to scatter them back). If the MUF is similarly high further `down the path', the signals can be slightly bent again, and this time come down to earth. Thus, even though the MUF was below 50 MHz, signals were bent down through MULITPLE refractions, due to the favourable length of the `MUF ridge'.

If you look at the favoured opening paths on the Real Time MUF map, virtually all of them follow along such ridges, providing opportunity for multiple reflections. My dilemma out here is that it is rare to have such ridges of MUF either 1) within reach for the first reflection and/or 2) properly pointed anywhere. Bounces ACROSS the ridges only work when the MUF really is at 50 MHz, which has almost never happened this cycle (at least in my part of the world).

One direction where there HAS been such an MUF ridge from here is toward Japan, which is 5100 miles from here. You might say that is double-hop, but there has been only a single, elongated ridge of MUF shown on the Real Time MUF maps. What I think is really happening is that if the high MUF is within 1300 miles or so, I can reach it. The refraction takes place, and bends the signals so it travels 2600 miles along the path, then hitting the F2 layer again. The MUF there is not above 50 MHz either, but is high enough to slightly bend it so the signal, coming in at a very high angle anyway, is bent enough to go down to the ground 1300 miles away. Voila -one of my JA contacts!

If one thinks of the ionosphere as BENDING the signals below the MUF (rather than reflecting them), then much of the mystery about propagation on the `Magic Band' is removed. No wonder I cannot work along the same ridge down to the Caribbean after you guys use it to work all over Europe - I am trying to bounce ACROSS an MUF below50 MHz on a single hop! My signals are just going off into space and never touching down anywhere, not even with Es or meteor links. Yours, however, were very neatly captured by the extended "MUF ridge" lined up with Europe, so all kind of opportunities presented themselves.

Take a look at the ridges of MUF extending out along the geomagnetic equator all day and night from Brazil, for example. It is very easy to see how such propagation makes hopping around the world from there a cinch! Probably even has propagation along F2 ridges on both sides of the equator at the same time! ;-)

Perhaps if the MUF ever really got up to 50 MHz in the F2 layer, things would work more like what I am used to from here - clean sporadic-E skip. Single little isolated blobs of ionisation that will cleanly reflect a signal in any direction. With Es, it is very obvious that the rules are quite different - when I see someone working from DM65 to EN47, I KNOW I have propagation into EM57. I just get on and point that direction and BAM!

This cycle has not provided such propagation, however. When MUF ridges above 37 MHz were within 1300 miles, they almost always were aligned crosswise to me ;-( And that won't change - it is just a matter of the way the earth is laid out and oriented. The only thing that brings such ridges to life is higher solar flux and MUF. So much for life with the TRAGIC BAND from Montana this cycle!

Happy New Year to you and Anne!

Vy 73, Lance Collister, W7GJ

From K2RTH:

Hi Lance et al:

I think what have said about your QTH is very correct and I think as you get progressively closer to the magnetic north pole you will get deteriorating conditions. The magnetic north pole is close to due north in northern Canada from your location, and while this certainly does not rule out F2 at your QTH it does mean that their are fewer and fewer openings. A good check for this would probably be talk to VE6TA and ask Grant how many openings he has had to things like JA or transcon. He has a better shot at transcontinental paths than you but probably has less openings.

I think this mode of cloud-to-cloud propagation is more responsible for real six-metre DX then anything else. What you forget to mention is that there is a critical angle associated with all `bounced' propagation modes, whether it be F2 or Es or any combinations thereof. This is what the ionosondes are measuring when we look at their data. They give us both Es & F2 critical angles, what they unfortunately do not give us is data in the places that we want, places where our first bounce on F2 & Es actually takes place. What a station should do is with a map of the world draw a set of circles that for Es would be 300 & 700 miles distance from your QTH. Then draw a set for F2 at 900 miles and 1500 miles from your respective QTH. One could then lightly colour these two doughnut shaped areas on a map and it would help you to visualise how things sometimes happen.

I think there are many more Es-F2 openings from poor QTHs, those with magnetically deformed locations caused by the position of the magnetic north pole, than true F2-F2 openings. For a true F2-F2 opening at the present levels of flux and your location I think disturbed conditions or an Es first hop are almost essential. The disturbed conditions tend to effectively shift the position of the magnetic north pole. While the magnetic north pole may not significantly move, it will provide hot spots that are formed in the auroral zone and shift these spots, sometimes almost instanteously, to more favourable positions. I think you have noticed this effect with your few SA openings following an abrupt decline in an active aurora.

More to the point, Es openings provide a much higher, faster rising, MUF than F2 and provide a great propagation mode
that would not exist EVEN if you were within range of the F2 cloud directly. This effect is not baffling at all when one graphs the F2 critical angles for cloud-to-cloud angles versus those for a ground based reflection F2 angle.

The angle that comes off a cloud-to-cloud Es-F2 is much less than a direct F2 ground reflection. While your F2 direct angle may provide a MUF of perhaps 40 MHz it would be much higher for a cloud-to-cloud reflection from an Es cloud perhaps reaching 50MHz. In addition, this first-hop Es cloud can more importantly put you within range of higher MUF F2 clouds in the first place.

You do not have to hear the Es for their to be an opening, do not forget that both refraction and reflection are taking place. Your first hop Es (orF2) due to refraction will never reach the ground, but may provide a good Es-F2(or F2-F2) link. In addition your Es-F2-F2-Es (or combination thereof) may never reach the ground except for the last link. Therefore, you may be able to work a YB/VK station and never hear Japan or Hawaii or other in between points. One just never knows until one gets on the air from one of these less densely-populated points and starts working stations that such propagation even exists.

For example on Dec 10th, 2000 I worked VK3SIX & VK3OT in a brief ten-minute opening on an otherwise dead band. The key to the opening was noting that at the same time Es was being heard weakly between Oklahoma and Mexico, there was no Es propagation noted from Miami at all. This was my clue to start calling toward VK/ZL across the midpoint of the observed Es opening. On December 27th 2000, KH6/K6MIO was in for an hour; at the time there was a very intense F2 opening from W1/VE1 to W6/7/VE7 and also a weak opening from Miami to VE7. About 1/2 hour after the start of the KH6 opening I started hearing strong Es from N5WS and copied both sides of his QSO with the KH6.

To me this means that my entire one-hour opening to KH6 is probably due to an Es-F2 link rather than F2-F2, and the distances involved seem to bear this out, even though Es was never heard for the first half hour of the opening. Again the critical angle for the Es cloud probably easily exceeded 50 MHz for the first hop Es and then Es-F2 (or some combination thereof), no other signals were heard. The mode of propagation probably never came back to the earth except for the last hop, but this an assumption of course. I know that you are always in there calling when you hear Es, and trying for a possible link, it is just you are that much further from a link than most and consequently this link never gets the F2 cloud within reach of you. I know there are plenty of Es links to W0 that are just 400-500miles short of you to the F2 cloud and you get zip.

One should look at the flux and other possible mechanisms for your JA opening. I don't think you can rule out some type of Es playing a role depending on flux values, date of opening etc. Was there Es between KL7 & W6/7?

In summation, I only suggest that Es under lower flux numbers plays a vitally important role in F2 openings greater then single-hop distances, than has heretofore been suggested. In addition, this role of Es can easily be seen when one examines the critical angles of the propagation involved. This role of Es is noticed much more often at a poor location than a good location, but probably exists both at the good and bad locations. However one must always pay attention to critical angles and look for F2-F2-F2 openings that just do not come down at any point in between.

73, Bruce K2RTH

From K6MIO/KH6:

Lance (and Bruce):

I think each of you is saying a number of things that are certainly correct.

Near Real-time MUF Map

Before going on though, I would like to comment of the Near Real-time MUF Map. I bring up that web page too. It's interesting to watch, but I think you have to take it with a BIG grain of salt. There is nothing wrong with it, but you can't take it too literally. I am not familiar with details of that particular program, but I am morally certain that it is NOT a map of the real-time MUF, but rather a map of the MUF as PREDICTED in near real time by some computer model, based on the time of year, time of day, various solar inputs, historical patterns, and so forth.

A true real time MUF map would be stitched together (by a computer) using current measurements from a vast, worldwide array of ionosonde stations - and making no assumptions, except about how to connect the dots in between stations. Even if real time ionosonde data were used, the number of ionosonde sites on the planet (especially at sea) isn't enough to produce the detail necessary to be of use to six-metre folk.

For example, despite several KH6 to US mainland F2 openings this fall, some of which were clearly double hop (I was hearing W6/W7 and W1/W2/W3/W4 all simultaneously), I never saw the MUF Map show anything nearly high enough for even the first hop. All it showed is a single 45-47 MHz blob 30 deg south of the direct path, south of W6, and just north of the (geographic) equator. The direct path showed more like 35 MHz on the map.

Now, that blob IS often there; I hear it backscattering the KH6HI beacon on Oahu (I can't hear KH6HI any other way, due to 250 miles and intervening rock). And we understand WHY the blob is there. It has to do with the `afternoon fountain' effect, the geomagnetic equator, and so forth (there is a discussion of this in Jim's paper in `Six News' 69).

My point is that the best that the Near Realtime Map can do is produce an educated guess at the general large-scale average structure of the ionosphere, based on 3000 km paths. It isn't showing you what is actually out there, and certainly not showing anything in great detail. Don't assume that the shapes shown are actually current.

Black Holes and Geometry

If one restricts the discussion to F2, based purely on geometry and geography, the worst place in the world for six-meter DX is:

1. in the middle of a continent where the whole continent is too close for 3000/4000 km skip, 2. more than 2000 km north of +20 deg geomagnetic latitude.


ALL F2 propagation is the result of refraction. Talking about it as a reflection is just shorthand for a simpler mental picture. The F-layer is spread out over a very large vertical extent. The electron density increases gradually. The upcoming wave encounters the electrons long before the density is high enough to `reflect' it. But it immediately begins to bend. Any wave going into a region of increasing electron density at an angle will be bent towards the general direction of the earth.

Can two separated clouds bend a signal back to earth when one alone could not? Sure, under the right conditions! As Lance noted, it would be like the TEP skips, but perhaps with a different cloud formation process. (Again there was some discussion of this in the earlier paper). It seems to play a critical role in the six-metre long-path circuits we see from here. Can an elongated cloud stretched out in the direction of the signal path produce a higher MUF for that path than it would for signals traversing the cloud across the short dimension? You bet it would! Are your field-aligned paths like W7 - JA likely to be better than north-south? Yes, on average I'm sure they will be, for the reasons you suggest.

Other Weird Stuff

Bruce mentioned the 27th December opening from KH6 to W4/W5. That particular phenomenon seems to be fairly common during the fall. I've seen it quite a number of times. I can't swear that there was no Es involved, but I think the Es that Bruce encountered was coincidental. I'm sure it has more to do with the `big blob' of ionisation that the models and backscatter say often hangs out over the Pacific, southwest of Central America, and north of the equator.

I think it is really enhanced F scatter from irregularities in that blob. These openings are all south of the direct path for all players. They all involve weak to very marginal signals that may be present for tens of minutes to an hour. The blob in question is MORE than one F-hop away from me, BUT my heading for it is right along the northern cusp of the geomagnetic equatorial bulge. My guess is that the signals get from KH6 to the north flank of the blob by way of the `ridge' mode you mentioned (this is basically a form of TEP in my case) and then scatter off the blob for about one F-hop over wide semicircle from southern California to the Caribbean.

During the 27th December opening I worked stations in Florida, Texas, New Mexico, Mexico City, and was heard in Aruba (the semicircle effect). I have sometimes worked KP4s and southern W6s on this kind of propagation. It's a big boys' game usually. N5JVH, W5UN, K2RTH, N6XQ - power and big antennas. On several occasions it suddenly turned into a normal F2 opening in a heartbeat, with big signals, direct paths, etc. usually to W6/W7/W5, and not obviously related to the blob. On other occasions it becomes an F2 opening to Central or South America, apparently skipping off the blob. On the 27th, I later worked several PYs.

73 and Happy New Year, Jim

From K6MIO/KH6:


Thanks for the reference to Emil's paper. I must have just missed it yesterday.

Needless to say, everything he says is completely consistent with both my experience and understanding, including the conclusion that the side scatter paths result from scattering in the ionosphere, rather than the Earth's surface like backscatter. His description of the Scand-inavian path is almost word for word my description of the KH6 to southern tier US/Caribbean path.

I also agree with you that the detailed geometry of the ionisation structures themselves often plays a crucial role in producing band openings (or not) under marginal conditions. I also can give many examples.

One such is the contacts between the mainland and V73AT a couple of weeks ago. Despite the fact that Tim is one F-hop west (and frequently boils in here) and W6/7 is one hop east, and I am close to the path midpoint, I didn't hear either side of the conversation. A chordal hop is one possible explanation.

Exactly the same thing happens when W6s are working ZLs. I should at least hear the W6s, but I don't (ever, so far as I can recall). That could be Es to the TEP zone, or it could be a slow, stretched out F-refraction to the same area - over my head in either case.

Six is a wonderful laboratory for exploring propagation modes!

73's Jim

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