Posts Tagged ‘Long Delayed Echo’
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) |
FT8 band on 10 meters showing some form of noise all over the band |
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 W6FB at times was louder than the direct signal. This points to the duct theory as the explanation.
Others have heard such echoes also:
- 210-220 ms, G3PLX, November 2006, 160 m. Listen to the signal here.
- 165-168 ms, K4MOG, February 2006, 80 m. Listen to the signal here.
- 214-219 ms, W2PA, February 2008, 80 m.
- 237 ms, OZ4UN, January 2009, 80m, Listen to audio file where also OZ7BQ very close by heard the echoes.
Other posts on the theme: Magnetospherically Ducted Echoes or Medium Delayed Echoes
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 W6FB at times was louder than the direct signal, also point to the duct theory as the explanation.
Others have heard such echoes also:
- 165-168 ms, K4MOG, February 2006, 80 m. Listen to the signal here. This event is also the object of the analysis in my QST article referenced above.
- 210-220 ms, G3PLX, November 2006, 160 m. Listen to the signal here.
- 214-219 ms, W2PA, February 2008, 80 m.
- 237 ms, OZ4UN, January 2009, 80m, Listen to audio file where also OZ7BQ very close by heard the echoes.
- About 200 ms, G3ZRJ, January 2012, 80m. Also heard by GW3OQK, 100 km apart.
Other posts on the theme: Magnetospherically Ducted Echoes or Medium Delayed Echoes
Radio Ghosts Have Haunted the Airwaves for Nearly a Century
“The starship hypothesis is a very interesting one, and the one which seems to be the most popular one on the internet,” said Sverre Holm, a professor of signal processing at the University of Oslo. “Such theories always excite our imagination, but it builds on a very poor data set. Unfortunately I believe it says more about human imagination than anything else.”
Although scientists have yet to settle on a final explanation for these mysterious echoes, Holm believes this is has less to do with a lack of scientific knowledge than a lack of willpower.
“I think that with today’s satellites and sensors, the mystery of Long Delayed Echoes (LDEs) could probably be solved,” he said. “What’s holding us back is most likely the problem is not considered important enough—it doesn’t occur often enough and doesn’t affect important enough forms of communications.”
These are excerpts from an interview in an article entitled “Radio Ghosts Have Haunted the Airwaves for Nearly a Century” on Motherboard Vice written by Daniel Oberhaus.
Radio Ghosts Have Haunted the Airwaves for Nearly a Century
“The starship hypothesis is a very interesting one, and the one which seems to be the most popular one on the internet,” said Sverre Holm, a professor of signal processing at the University of Oslo. “Such theories always excite our imagination, but it builds on a very poor data set. Unfortunately I believe it says more about human imagination than anything else.”
Although scientists have yet to settle on a final explanation for these mysterious echoes, Holm believes this is has less to do with a lack of scientific knowledge than a lack of willpower.
“I think that with today’s satellites and sensors, the mystery of Long Delayed Echoes (LDEs) could probably be solved,” he said. “What’s holding us back is most likely the problem is not considered important enough—it doesn’t occur often enough and doesn’t affect important enough forms of communications.”
These are excerpts from an interview in an article entitled “Radio Ghosts Have Haunted the Airwaves for Nearly a Century” on Motherboard Vice written by Daniel Oberhaus. It builds on a web page that I created some years ago after having spent days studying the archives from the 20’s of professor Carl Størmer at the National Library in Oslo.
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.
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!