Posts Tagged ‘Unusual Propagation’

FT8 anomaly or long delayed echo?

My friend Alf, LA2NTA, has sent med these screenshots from when he has been operating FT8. The first image is when operating 10 meters and took place early in November.

Two of LA2NTA CQs being received by himself on 10 meter (in red)

It shows how his own CQ comes back to him at 10.54.00 and at 11.00.00 and is decoded in his own receiver.

The second example is from 20 meters and took place just a few days ago.

LA2NTA CQ being received by himself on 20 meter (in red)

For the first example he also took an image of the spectral display. It shows lots of repeated noise burst all over the FT8 band.
FT8 band on 10 meters showing some form of noise all over the band
It is hard to explain this, but my hunch is that it is something local and not a propagation phenomenon, but who knows?

Magnetospherically ducted echoes in the San Francisco area

On 7. November 2015, several radio amateurs in northern California heard echoes in the 80 meter band. I was made aware of it by Jack, W6FB in Santa Clara, who recorded signals from K6YT some 25 miles away. According to W6FB, the echo effect was also heard north of Sonoma (several hundred miles north of him, reported by N6ZFO).

KM6I, Gordon, in Palo Alto also heard echoes of his own signals and recorded them. In his blog he analyzed the delay from the output of his transceiver and found 157 ms. He found that to be so close to the round-the-world time for signals of 138 ms, that he assumed that to be the cause.

I don’t agree, so I took the location of W6FB at locator CM97ah (Santa Clara) as a starting point for computing delay. This is latitude 37.31 and longitude -121.96 and gives a geomagnetic latitude of about 42.5 degrees. Then I put it into my program for computing path length along geomagnetic field lines assuming a height of the reflecting ionosphere on the opposite side of 100 km. The result is shown in the figure and predicts a delay time of 126 ms. My estimate of uncertainty is +/-5 ms.

The delay value is slightly less than 138 ms and easy to confuse with a round-the-world path. The challenge with estimating delays like this from the signal is that amateur transceivers may have an unspecified delay between start of transmission and start of sidetone. Measuring on the audio output as done here, measures the sidetone, not the actual RF.

I discussed this source of error in my 2009 QST article “Magnetospheric ducting as an explanation for delayed 3.5 MHz signals.” Therefore the measurement shown above may fit with 138 ms just as well as with 126 ms, it depends on the actual transceiver’s delay.

Other properties of the echo, such as the amplitude of the echo which according to W6Fat times was louder than the direct signal, also point to the duct theory as the explanation.

Others have heard such echoes also:

Other posts on the theme: Magnetospherically Ducted Echoes or Medium Delayed Echoes

Nice, watery CW signals from Alaska

 Great circle path between Anchorage and Oslo

Here’s what a transpolar signal sounds like (click here to listen) and looks like (below). This one has traveled from Anchorage, Alaska to Oslo, Norway.

The characteristic sound of a CW signal that has passed over a moderate geomagnetic disturbance (Kp = 2) isn’t too hard to recognize with a little practice. There is also some static on this short recording as we had a local thunderstorm coming in with the first summer days here.

The great circle distance between the two cities (actually their two airports) is 6446 km as illustrated by GPSVisualizer. Anchorage and Oslo are about at the same latitude, 61° N and 60° N, respectively. As they are at longitudes 149° W and 10° E, there is a difference of 159 ° – almost 180 ° – and this means that the signal almost passes directly over the North Pole, although a bit hard to see on the projection used in the map.

 “TU KL7SB UP“, 1550 UTC, 19 May 2014, 18 MHz

There is rapid fading, or flutter, as seen e.g. from the large level difference between the two initial dots in “U”. Also the dah-dih-dah pattern of the “K” has more or less merged into each other in the image, but not in the audio, as this is caused by a static crash.

It was recorded just after my contact with KL7SB on 18 MHz today from my Elecraft K3 using Audacity® which is a free, open source, cross-platform software for recording and editing sounds.

Long Delayed Echo on VOA Chinese Service

Thierry, F4EOB from Paris is still hearing strange echoes on the VOA Chinese service broadcasts. There isn’t really any good explanation for this phenomenon.

Now during winter he is hearing it both on 13650 kHz from 9 to 12 UTC and on 21590 kHz from 9 to 11 UTC. The 21590 kHz transmission has been heard by him for a long time and I mentioned it here last year also. As then the echo is about 2 seconds. Thierry also made a youtube video of it with a recording.

The transmitter locations are in Asia. The 19 m band site is on the Mariana Island (Tinian) and the 13 m band transmitter is in Tinang in the Philipines.

In my blog last year I discussed possible explanations such as multiple transmitters or multiple round-the-world travel. But since the delay is so consistent and has had the same delay for such a long time, the probability that it is man-made is rather large.

Thierry tells me that this LDE can easily be heard with the WebSDR at the University of Twente in the Netherlands also. I would be curious to hear from people outside Europe who could compare the Dutch WebSDR with their own local reception and see if the same echoes are heard everywhere.

The most interesting contact in the CQ WW Contest

Sometimes looking up remote stations on or other sites gives a glimpse of the person behind the callsign. I did this for the Chinese station BY5CD which I contacted on 40 m during the CQ Worldwide contest this weekend.

It turned out to be a club station called “YinZhou Middle School Amateur Radio Club Station” which is located just south of Shanghai.

It is interesting to consider the age of the operators as one can see from the picture. More pictures and some information can be found on their website. With this many young people entering ham radio in China, maybe we will see more stations there in the future. The number of stations is unreasonably low compared to the enormous population of China.

And the most interesting signal was that of GM5X on 21 MHz at 1207 UTC on 25. November. It had a distinct echo which seems to indicate that the signal travelled both on the direct path of about 800 km and the long path of about 39200 km.

The image shows “GM5X GM5X Test”. The long path signal seems to fade in and out as there is much less of it in the last part, the word “test”, than in the second “GM5X”.

F/LA3ZA on Long Delayed Echoes

Laurent, F6GOX, who is one of the primary forces behind the ARP, Radio-Club de Paris, has written a nice little French-language presentation of me since I am a former member of the club. It also includes my interest in Long Delayed Echos (LDE).

Here he also talks about the presentation I gave for the Paris club of radio amateurs on 18 March 2009 on this subject during my year-long stay in Paris. That was a very nice evening which I remember with pleasure.

I also talked then about the interest that the French general Gustave Ferrié (1868 – 1932) took in this phenomenon (The link is in French, but read about Ferrié here in the English Wikipedia). There were French studies of LDEs in Indochina, Senegal, and Mauretania, French territories at the time, which he played a major role in.

Merci Laurent!

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