Mystery signal that slides up and down within frequency ranges

[mr magoo]

I've been DXING and monitoring the HF bands for well over 45 years. I'm also a licensed amateur radio operator. I can identify many signal types on the HF bands but this one has me stumped.

I've been monitoring this strange "mystery" signal that slides up and down within frequency ranges. I first came across this signal back in November of 2014. It was continually moving up and then down in the 5.303 Mhz. to 5.498 Mhz. frequency range. This signal seems to begin around 0330UTC. When it reached the upper and lower limits of this frequency range, it would sit for a few seconds, then change its direction. This pattern always repeats. Lately I've noticed the frequency range seems to change a bit. I've heard it as low as 4.899 Mhz. and as high as 5.512 Mhz. This signal has no regards for any stations operating within these segments. For example RAF VOLMET is always active on 5.505 and this signal will move right through it.

I had been wondering if perhaps this signal was something local to me. I answered that question by going to the WEB SDR site and selected other controllable receivers world wide. I was able to hear it on most of them. This signal is best heard in USB or LSB modes.

I have spectrum and waterfall recordings of this signal along with a mp3 file. You can view these files along with others on my Shortwave MW DX blog here: http://www.w2gjw.com. 

If anyone has any idea what this may be, please leave a message on my site or respond here.

Thank you for your time and help in solving this mystery!

73-

[Token]

I've been monitoring this strange "mystery" signal that slides up and down within frequency ranges. I first came across this signal back in November of 2014. It was continually moving up and then down in the 5.303 Mhz. to 5.498 Mhz. frequency range. This signal seems to begin around 0330UTC. When it reached the upper and lower limits of this frequency range, it would sit for a few seconds, then change its direction. This pattern always repeats. Lately I've noticed the frequency range seems to change a bit. I've heard it as low as 4.899 Mhz. and as high as 5.512 Mhz. This signal has no regards for any stations operating within these segments. For example RAF VOLMET is always active on 5.505 and this signal will move right through it.

I had been wondering if perhaps this signal was something local to me. I answered that question by going to the WEB SDR site and selected other controllable receivers world wide. I was able to hear it on most of them. This signal is best heard in USB or LSB modes.

I have spectrum and waterfall recordings of this signal along with a mp3 file. You can view these files along with others on my Shortwave MW DX blog here: http://www.w2gjw.com.  

If anyone has any idea what this may be, please leave a message on my site or respond here.
 

I have noticed this signal many times in the past few years.  While I do not know what it is, I have always dismissed it as a probable unintentional signal.  A couple of years ago I took a pretty close look at it and never could find what I thought was intelligent data.

While I am certainly open to this being a “real” signal with some use / meaning, there are a lot of things about it that make me think unintentional, however long lived it is.

This signal drifts up and down the band in a roughly sinusoidal pattern, however the end points of each cycle are not fixed and do not typically repeat.  The cycle time is inconsistent, for example last night it was “about” 10 minutes peak to peak, but that varied by quite a bit, 5% or more (30+ seconds) was common over an hour period (~6 cycles).  The width of the cycle changes, there does not appear to be a fixed or consistent swept width.

Here is a 2 hour and 5 minute waterfall image of its action last night.  This is a pretty large image, ~6.5 MB, so if you are on a mobile device you might not want to click the link.  Time UTC is down the left side, freq in kHz across the top.
http://www.pbase.com/token/image/159457911/original.jpg

The source seems to be from the east of my location.  It is typically there after the band starts to open up in the evening and it goes away before local sunup.  It is often receivable all night long.  Last night I did not set down at the gear until some time after 0230 UTC, and it was present, and this morning when I left for work just before 1200 UTC it was still present, but fading.  For me it is often hard to see / hear in the pre-dawn, but that is mostly because the Chinese OTHRs often hit the same range of frequencies, and they are typically strong in the morning here.

As I said, I have no idea what the signal is, but it might be interesting to try and narrow down the source a bit.

T!

[mr magoo]

I have noticed this signal many times in the past few years.  While I do not know what it is, I have always dismissed it as a probable unintentional signal.  A couple of years ago I took a pretty close look at it and never could find what I thought was intelligent data.

While I am certainly open to this being a “real” signal with some use / meaning, there are a lot of things about it that make me think unintentional, however long lived it is.

This signal drifts up and down the band in a roughly sinusoidal pattern, however the end points of each cycle are not fixed and do not typically repeat.  The cycle time is inconsistent, for example last night it was “about” 10 minutes peak to peak, but that varied by quite a bit, 5% or more (30+ seconds) was common over an hour period (~6 cycles).  The width of the cycle changes, there does not appear to be a fixed or consistent swept width.

Here is a 2 hour and 5 minute waterfall image of its action last night.  This is a pretty large image, ~6.5 MB, so if you are on a mobile device you might not want to click the link.  Time UTC is down the left side, freq in kHz across the top.
http://www.pbase.com/token/image/159457911/original.jpg

The source seems to be from the east of my location.  It is typically there after the band starts to open up in the evening and it goes away before local sunup.  It is often receivable all night long.  Last night I did not set down at the gear until some time after 0230 UTC, and it was present, and this morning when I left for work just before 1200 UTC it was still present, but fading.  For me it is often hard to see / hear in the pre-dawn, but that is mostly because the Chinese OTHRs often hit the same range of frequencies, and they are typically strong in the morning here.

As I said, I have no idea what the signal is, but it might be interesting to try and narrow down the source a bit.

T!

Thank you T! for your very informative analysis of this signal. I had no idea this signal has been active for that long.

I have no doubt this is some type of intentional sampling signal, especially since the frequency range is always within the 4.8-5.5Mhz range. You're correct in saying the sweep time does change within the segments it selects. The frequency segments also seem to change as the night progresses. I actually heard the start of the signal last night for the very first time. When the signal began, it sounds very different from what I was accustomed to hearing, but after 10-15 minutes it returned to the "normal" sound I've been experiencing the last several months.

As of now, I'm leaning towards some sort of ionospheric pulse or plasma sampling testing conducted by NASA or the military. I have read several articles describing a signal with similar characteristics as this one and those reports mention a transmitter site in Goose Bay Labrador Canada. However, this is not confirmed.

If you learn any other information regarding this "mystery" signal, please post here again. I really enjoyed studying your waterfall capture as well as reading your detailed analysis of this signal. At least I now know I'm not the only one whose heard this!

Thank you for your reply and for your time. I appreciate it. I will also report any further findings.   

[Token]

As of now, I'm leaning towards some sort of ionospheric pulse or plasma sampling testing conducted by NASA or the military. I have read several articles describing a signal with similar characteristics as this one and those reports mention a transmitter site in Goose Bay Labrador Canada. However, this is not confirmed.
 

The transmitter at Goose Bay you mention, that would not be a node of the DISS (Digital Ionospheric Sounding System) Network, coordinated by the USAF, would it?

T!

[mr magoo]

The transmitter at Goose Bay you mention, that would not be a node of the DISS (Digital Ionospheric Sounding System) Network, coordinated by the USAF, would it?

T!

Yes, correct. If you search online, there are documents which mention sweeping signals within the band segments we've been hearing this signal in. These documents are highly technical and scientific, and they describe techniques well beyond my electrical engineering expertise.

The transmitter site at Goose Bay is described as a 600W transmitter and a dipole antenna arrangement. Again, this is all speculative on my part, but the similarities outlined in these documents are very are interesting.   This article in particular is very informative and can be viewed here:  http://onlinelibrary.wiley.com/doi/10.1029/2001JA005082/pdf

[Token]

The transmitter at Goose Bay you mention, that would not be a node of the DISS (Digital Ionospheric Sounding System) Network, coordinated by the USAF, would it?

T!

Yes, correct. If you search online, there are documents which mention sweeping signals within the band segments we've been hearing this signal in. These documents are highly technical and scientific, and they describe techniques well beyond my electrical engineering expertise.

The transmitter site at Goose Bay is described as a 600W transmitter and a dipole antenna arrangement. Again, this is all speculative on my part, but the similarities outlined in these documents are very are interesting.   This article in particular is very informative and can be viewed here:  http://onlinelibrary.wiley.com/doi/10.1029/2001JA005082/pdf

As I said before, I do not know what this signal is, but I can make some pretty good guesses as to what it is not, and I would bet this signal is not from the DISS at Goose Bay or anyplace else.  The DISS is a Standardized D256 Ionosonde, its waveform is well understood, and does not look like this signal.  But, even if the D256 waveform were not known I think we can make a pretty strong case for this not being a DISS.

Goose Bay is only one of 17 locations using the DISS, there are over a dozen more users of the legacy D-256 Ionosonde, with a waveform very similar to the DISS ( http://umlcar.uml.edu/stationlist_instrument.html ).  With over 30 users  of a “standardized” item, including locations in Colorado, Texas, Florida, Alaska, and Puerto Rico, why do we only see one of these signals?

The “take” from the ionsondes (including Goose Bay) are available online, and it shows results for a much wider frequency range than what this signal is sampling.  The fact is this signal covers far to narrow a range of frequencies to be useful as a traditional ionosonde, most ionosondes cover about 2000 kHz to about 30000 kHz (the frequency range is user selectable, as are any skipped frequencies) in a single pass, and they typically do this very quickly several times an hour.

T!

[mr magoo]

As I said before, I do not know what this signal is, but I can make some pretty good guesses as to what it is not, and I would bet this signal is not from the DISS at Goose Bay or anyplace else.  The DISS is a Standardized D256 Ionosonde, its waveform is well understood, and does not look like this signal.  But, even if the D256 waveform were not known I think we can make a pretty strong case for this not being a DISS.

Goose Bay is only one of 17 locations using the DISS, there are over a dozen more users of the legacy D-256 Ionosonde, with a waveform very similar to the DISS ( http://umlcar.uml.edu/stationlist_instrument.html ).  With over 30 users  of a “standardized” item, including locations in Colorado, Texas, Florida, Alaska, and Puerto Rico, why do we only see one of these signals?

The “take” from the ionsondes (including Goose Bay) are available online, and it shows results for a much wider frequency range than what this signal is sampling.  The fact is this signal covers far to narrow a range of frequencies to be useful as a traditional ionosonde, most ionosondes cover about 2000 kHz to about 30000 kHz (the frequency range is user selectable, as are any skipped frequencies) in a single pass, and they typically do this very quickly several times an hour.

T!

Thank you for the great info. Very educational. I was referring solely to the article in the link I provided, which outlines a sweep range from 5380 to 5440, which may be varied as can the sweep rate of the plasma pulses. See diagram below. Again this is nothing more than a guess, but some of the similarities are interesting never-the-less.

Also I was unable to receive this signal the other night. Perhaps because of the Auroral conditions?