Saturday, August 29, 2009

This blog is dead !

You may have noticed that this blog is dead. Although it may not be definitive, my interest is for the moment attracted elsewhere... However the archives are still here and provide many hours of reading on various topics. A simple way to start is to consult the "best of" which provides a quick summary and list the articles in the right order... Good reading !

Saturday, December 13, 2008

No comment !

No comment... comme ils disent sur euronews !

Friday, December 05, 2008

CQWW CW 2008 - M/S @TM6M - OM8A EU-Leader ?

The OM8A 3830-claimed score did not came as a real surprise, but shows what remains to be done to expect a first European M/S place... a lot !
Once again, the biggest gap is on 80m very weak both in QSO's and mults. 160 and 10m come after, while the results on 15 and 20 are not that bad. 40m is almost competitive, just missing 10~15 multipliers...

Wednesday, December 03, 2008

CQWW CW 2008 - M/S @TM6M - Known M/S claimed scores

This year for the CQWW-CW Nico (F5VIH/SV3SJ) and myself responded to the TM6M (F6KHM) invitation. A long trip by road (2300kms), but a lot of fun ! Following are the first known raw-claimed European results for the M/S HP category. Above are the top known EU-claimed scores. It is quite obvious that the multipliers are our weak point, while the QSO-points is our strong one... Above are the compared EU-M/S 3 known top-scores, by band. Our weaker band is 80m, while our strong band is 15m. In general, our multipliers deficit is stronger on the low bands.

Tuesday, November 25, 2008

Low-band DX'ing: The high-angle mode hypothesis - G0KYA contribution

In my previous post, I gave a few links mentionning the "high angle mode". I found extremely interesting G0KYA's paper "the twilight zone".
This is the introduction: Steve Nichols G0KYA, of the RSGB's Propagation studies Committee, believes that propagation around sunrise and sunset is not fully understood. Here he outlines the mechanisms behind grey line and other twilight propagation modes and a research project to help us understand them.
And a particulary interesting paragraph
Now imagine a radio wave hiting the ionosphere at about 75-85 degrees to the earth - a near vertical incidence wave (NVIS). Below the critical frequency, it would be returned. At some frequency close to fof2 it could be refracted through a large angle and could end up travelling almost parallel to the earth, giving a very long first skip distance. This is the condition for the Pedersen or critical ray, discovered in 1927, characterised as being high angle, long distance and close to and probably above the fof2 frequency. As there would be no intermediate ground hops the signal strength could be very high indeed.

Following this reading, I exchanged a few emails with Steve (one of them, reproduced here with
his authorization)
Hi Patrick, Thank you very much for your e-mail. I have had a quick look at your blog and it is very interesting. Your message was actually very timely as I have been looking at WSPR as a greyline beacon tool, but had put it to one side to concentrate on other things - I will pick it up again! Here are some thoughts and observations that might be useful.
1. VOACAP is not very good at predicting openings below about 5MHZ. It was never intended for this and is usually very pessimistic. W6ELProp is better.

2. You are quite right - it doesn't take into account sunrise enhancements I did some work on signals from VP6DX into the UK on 80m and using VOACAp looked at the number of modes (hops). It showed clearly that there are more modes around sunrise and the radiation angle goes higher. I can send you this if you want. I am therefore convinced that greyline has more to do with higher angle signals due to ionospheric tilting and multiple modes than the old "D layer not illuminated/F layer illuminated" model.
This also explains why you get good greyline openings at right angles to the terminator.

Thanks for thinking of me.
Steve G0KYA
RSGB Propagation Studies Committee
You will find other articles and powerpoint presentations on Steve page, definitely a "must read" for whoever is interested by those phenomenas (the above pictures are from Steve presentations).
Steve's VP6DX presentation is available as a PDF.
By the way, the "high angle mode" has a name: The Pedersen Ray... and nothing new, since it was discovered in 1927...

Saturday, November 22, 2008

Low-band DX'ing: The high-angle mode hypothesis - part 2

Following are the results of a quick test done this morning on K1JT 80m WSPR beacon. As for the previous post, I was using 2 antennas, my K9AY pointed NW and a magn loop, this time oriented NE, so roughly 90 degrees away from Joe's direction. The magn loop pattern at 90 degrees is particulary interesting because its response at low angle is minimum.
Following is the plot of the measured SNR's around sunrise.
Although the mag-loop is 90 degrees away from the TX-direction, it still takes the advantage just after sunrise (SR at 0645z). (you may click on the plots to enlarge them). The above plot is for the SNR's measured on K1JT WSPR-beacon on 2 antennas , a K9AY oriented NW and a mag-loop oriented NE. Despite the limited number of points, and the mag-loop orientation, the trend is clear: Just after sunrise the mag-loop provides slightly better SNR's than the K9AY, which is likely to confirm the "high-angle propagation mode hypothesis".
This plot shows the pattern of the magnetic-loop, for various elevation angles. The front to side ratio goes from 12dB at 5degrees elevation (red pattern) to 1dB at 60 degrees elevation (blue pattern). The orange pattern is for 20 degrees, while the purple is for 40 degrees.
This plot shows the compared patterns of the K9AY and the magn-loop turned 90 degrees away from the transmitter direction. In blue the magn loop pattern a 60 degrees, in light blue at 20 degrees. In red the K9AY pattern at 60 degrees, in purple at 20 degrees. The respective max gains being almost equal, the 2 patterns cross at an elevation angle of approximately 60degrees. Below 60 degrees, the K9AY should provide better SNR's while the Magn-loop takes the advantage at angles higher than 60 degrees.

IMHO, those plots clearly show that a high angle propagation mode appears at sunrise. It would seem, still for this particular path at this particular moment, that the take-off angle is at least 60 degrees, or higher. This explains why stations using low horizontal antennas, get "better than expected" results on a few DX-paths, although a low horizontal antenna
(below 1/4 wl) has a poor efficiency due to important ground losses. The little difference shown in the earlier published plot of DG0OPK signal (using a G5RV at 5m) vs mine (using a 1/2 wave vertical over a good soil), as received by VK7KRW on 40m long-path, may also have an explanation when looking at the "high angle mode" hypothesis.

For information I also looked at the SNR's measured on WA6MTZ (CA) 80m signal. On this particular 9300 kms path, there is no obvious benefit provided by the magn-loop. However as I have only a few spots, it might be too early to make definitive conclusions... so, more to follow !

Addendum: I experienced the same phenomena on YA/T61AA signal at sunset..
If you are interested by the topic, I found 4 online articles which mention the phenomena: By ZL1BPU, by G3CWI, by G0KYA and from antennex by ON5AU

Thursday, November 20, 2008

Low-band DX'ing: The high-angle mode hypothesis

Following the publication on this blog, of the VOACAP articles and the comments received from AB7E and OH6BG, my friend Seb F8CMF pointed me an old K3LR post on the "top-band reflector". Here is the post (reproduced with Tim's authorization).
Topband: Low RX Dipole
*To*: >
*Subject*: Topband: Low RX Dipole
*From*: k3lr at (Tim Duffy K3LR)
*Date*: Mon May 5 20:52:53 2003
Hi Gale!
It all depends on what other antennas you have. I have had up a 14 ft
high 1/2 wave dipole on 160 for many years. It has always impressed me
as a high angle antenna which limits its prime effectiveness to gray
line use. I also use it in tandem with other antennas and the MFJ
receive antenna noise canceling W8JI magic box (also an effective
antenna phasing unit). My low dipole's claimed fame was a sunrise QSO
with KH2. No other antenna (1100' beverage, vertical array, etc.) could
hear the KH2, but he was 569 on the low dipole.
Tim K3LR

Remembering that I received ZL1RS only on the magn-loop, this post interested me very much. Taking the opportunity of the "WSPR 80m Special Activity Day" I quickly setup a diversity receive test, using 2 receivers, one connected to the K9AY loop, oriented NW and one to the magn-loop (roughly E/W).

The compared patterns of the K9AY and the magnetic loop. Considering RX antennas, it should be made abstraction of the respective Gains and focus on the RDF. According to K7TJR tables, the RDF of the K9AY considered at 20degrees elevation is 7.2dB, vs 4dB for the magnetic loop, thus a 3.2dB advantage for the K9AY. Of course considering a higher angle, the difference will turn to the magn-loop advantage, as it exhibits a pattern more favorable to NVIS.

The plot shows the SNR's measured on 80m from 9 NA-stations during 2 nights on 2 RX-antennas. Over 500 spots, were used. By distance order VE1VDM (5205kms), W1BW, W1XP, K1JT, WD4KPD, W8LIW, KI4MTI, vE5MU, K4MF(7572 kms). In the middle of the night, the K9AY provides some 5dB average better SNR than the Magnetic-loop wich suggests an elevation angle lower than 20degrees.

The same as above, but focusing on the morning. The fact that the magn-loop takes the advantage near sunrise seems to be a confirmation that some "high angle" mode occurs at this particular moment and not only on paths following the grey-line. The respective antenna patterns suggest an vertical angle >45 degrees. A more "radical" NVIS antenna (like the "cizirf-special") has to be tried to confirm this hypothesis.
Last but not least: for the path F6IRF to W8LIW, VOACAP suggest a vertical angle of 8 degrees, with a peak at 15 degrees in the middle of the night. Once again the VOACAP-model is obviously far away from the above observations. As Dave AB7E mentionned "
It (voacap) is especially weak in predicting the effects of takeoff angles /// I'm convinced that much of gray line propagation is chordal hop, which is supported by the comments from K3LR and others (as well as my own observations) that high angle antennas often work better for such openings. When you draw a picture of the earth showing an F2 gradient at sunrise/sunset it is easy to see why that would be true."
What seems to show the above, is that "the high angle mode" does not only concern long DX-paths along the grey-line (such as F<>ZL) but also shorter distances DX paths.

Tuesday, November 18, 2008

The VOACAP mystic, an interesting comment...

I received the following emails from Dave AB7E (reproduced here with his authorization). Think he is saying interesting things...Hi, Pat. Wow ... what a rigorous and interesting analysis. Very impressive.
My first reaction, though, is that an antipodal path (ZL-F) is possibly not the most valid for comparing VOACAP predictions to real life propagation. VOACAP assumes a single direct path (either SP or LP), whereas the actual path for an antipodal target could be almost any direction. VOACAP might render its calculation based upon a path over Asia while the actual signal might not take that route at all.
As a real life example, my Optibeam OB16-3 has a pretty narrow beam width on 20m (I can easily hear the difference in 20 degrees of beam heading), yet when working VQ9RD recently (close to antipodal for me), it was almost impossible to find a "best" beam heading within about a 70 degree spread. VOACAP, of course, is based upon heaps of experimental observations taken decades ago, with extrapolations based upon theoretical models of the ionosphere. It doesn't even come close to being a valid predictor of real-time conditions, a fact that the authors were very quick to point out but which hams have conveniently ignored.
It is especially weak in predicting the effects of takeoff angles, which can have a large impact. So overall I'm not surprised that your analysis would find large discrepancies between predicted and actual SNRs, but I suspect that the results would have been closer for a non-polar path of roughly 1/3 the circumference of the earth instead of 1/2.
73, Dave AB7E

pat_f6irf wrote:
Yes David agree... I think Jari that OH6BG summarized it very well in the part 4. The purpose of this article was to draw the attention of contesters and DX-men, on the fact that VOACAP is not suitable at all for low-band DX'ing... What the designers accept, but most hams ignore (including me b4 looking at it !); see
Even the 10degrees vertical angle forecast may be wrong...

Hi again, Pat.
Yes, I think VOACAP is quite poor for low band use, especially since so much of it is gray line dependent. I'm convinced that much of gray line propagation is chordal hop, which is supported by the comments from K3LR and others (as well as my own observations) that high angle antennas often work better for such openings. When you draw a picture of the earth showing an F2 gradient at sunrise/sunset it is easy to see why that would be true. I don't think that VOACAP even considers chordal hop propagation mechanisms at all. I certainly hope you keep up the excellent work, and I think the diversity experiments should be very interesting as well. 73, Dave AB7E

Thanks Dave...
Your email reminded me that already ZL at long path (audio recording) was something for my "Cizirf-special" antenna, which was not designed to be a DX antenna.
Promised, I'll come back with the same type of analysis for shorter distance paths

By the way, I have updated the blog "best of" , an easy way to find articles...

Monday, November 17, 2008

The VOACAP mystic, a summary...

Why "the VOACAP mystic" ?
I would recommend to read this as a starter

Once done and for those who may have missed the early posts. Following is a summary of all the posts published on the a/m topic. It will allow to read them in the right order...

- VOACAP vs WSPR reports part 1 (study of a 30m transatlantic path)
- VOACAP vs WSPR reports part 2 (study of a 30m transatlantic path)
- VOACAP, the end of the myth ? part 1 ( study of a F<>ZL 40m path)
- VOACAP, the end of the myth ? part 2 ( continuation of the study of the F<>ZL 40m path)
- VOACAP, the end of the myth ? part 3 (study of a 40m long path F to VK7 + my temporary conclusions)
- VOACAP, the end of the myth ? part 4 (back to F<>ZL short/long path, OH6BG calculations and opinion)

May not be complete: I am still consolidating data on 80m F<>ZL path, which may lead to strange conclusions on the required take-off angle. Now that I have improved my knowledge of Voacap, I may also come back later on shorter distance paths. So, stay tuned !

Please note: So far these articles, exist only as "blog posts" (I like the spontaneous day to day blog form). Of course they may be made available for publication in a more conventionnal support, or public presentations if some interest is expressed. In any case, please contact me for any adaptation/translation...