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Author Topic: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i  (Read 2421 times)

Offline Dag

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Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« on: December 13, 2015, 2056 UTC »
I am hearing 3 strong carriers on 6993 KHz:

6993.017 KHz, another up ~10 Hz, and a third down ~10 Hz from the 6993.017 KHz "center" carrier.  It sounds as if is some faint modulation of two of the three carriers, perhaps a fraction of a Hz.

 Very strong in central Florida: S8-9. I've not heard this before.

What could it be?   
« Last Edit: December 13, 2015, 2129 UTC by Dag »
Seminole county, Florida, USA, Earth, Solar System, Universe.
TS440s + attic dipole.

Offline Skipmuck

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #1 on: December 13, 2015, 2225 UTC »
I don't know what it is, but have been hearing this for the last week or so. I thought it was some kind of internally generated birdie or maybe a spur of some kind. It can get quite loud here! Another mystery.....
2225 UTC Just barely audible atm....
« Last Edit: December 13, 2015, 2229 UTC by Skipmuck »
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Offline Dag

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #2 on: November 06, 2016, 2220 UTC »
Update: It's hard to believe I've been monitoring (from time to time) the warbling carrier on 6993 KHz since my initial post and never heard anything of note, but here are some observations:

-The carrier is easily heard during daylight hours from my Florida location and can be nearly S9. It's solid S7-S8 without any fading as I write this.

-I rarely hear it at late at night.  Perhaps it's within a single hop of daytime propagation from me and skips over me at night?

- Today I put the receiver on 6993.000 KHz, zerobeating the carrier while I did some paperwork nearby.
 At 2145 UTC (4:45 pm EST), I was startled by approximately 15 seconds of what sounded like a STANAG 4481 (?) signal. I can't be certain of the mode, but it was very similar to STANAG 4481 and strong.

Except for the carrier, the frequency was quiet again for 30 seconds after that short 15 second signal. Another 15 second ?STANAG?  signal followed.   I've been listening now for nearly 25 minutes after those two 15 episodes without any other intelligence and the 6993 KHz carrier persists.

Could the constant carrier on 6993 KHz be a guard-signal? What other information is available for this signal?

Dag
Seminole county, Florida, USA, Earth, Solar System, Universe.
TS440s + attic dipole.

Offline ChrisSmolinski

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #3 on: November 06, 2016, 2226 UTC »
I've noticed 6993 for some time as well.
Chris Smolinski
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Offline refmo

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #4 on: November 06, 2016, 2257 UTC »
I have been hearing this most days (actually local nights) for the last 3 or 4 years here.
« Last Edit: November 06, 2016, 2301 UTC by refmo »
central Kentucky
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Offline Josh

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #5 on: November 06, 2016, 2337 UTC »
Anyone get recordings?
Conveniently located near Vincennes Indiana.

Offline aurora

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #6 on: November 06, 2016, 2338 UTC »
I have been hearing this as well for some time now. Signal is typically no more than S5 on most days.
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Offline Dag

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #7 on: October 19, 2017, 0028 UTC »
Update:  the 6993 kHz has a parallel transmission on 4443 kHz  (heard Oct 145 2017 @ 2300z.)

Note: I can usually hear the 6993 kHz signal best in daylight hours, suggesting it's somewhere in the southeast USA or in the Caribbean.

 What is this signal for?

Dag
Seminole county, Florida, USA, Earth, Solar System, Universe.
TS440s + attic dipole.

Offline Chuck A

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #8 on: November 06, 2017, 2226 UTC »
Hearing it here in NC, at S3~S5 daytime, and as strong as S9 from about SUNSET-1hr until SUNSET+2hrs, so I'm definitely hearing it via NVIS skywave, because when ~7Mhz 'goes long' at night its signal level drops back down to the S1~S3 range.  I can't remember when I first heard it, but it's at least 2 years ago.

Sometimes the carrier is steady and unmodulated, but other times it definitely has a PSK (or maybe MinFSK) modulation on it.  I haven't taken a shot at trying to decode it so far... 

Offline Dag

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #9 on: May 06, 2018, 1518 UTC »
Update for May 6 2018:

Yesterday I discovered something I find interesting about these 3 carriers which are about 10 Hz apart on 6993 KHz.


I was watching the three signals on the waterfall and found that two of the three carriers showed an equal and stable signal strength over perhaps 3 minutes of viewing.

However, the third carrier, in this case the lowest frequency carrier, showed obvious fading from moment to moment and at one point faded out. It soon returned to perhaps 2/3 signal strength as compared to the other two, but the signal fading continued.  I recall seeing this selective fading of one carrier in the past but paid no attention to it. Keep in mind these 3 carriers are only 10 Hertz apart.


Atmospheric fading of constant carriers  is easily seen on the waterfall, but two of the three carriers seemed pretty much in lockstep with signal strength: only the third showed obvious fading.

I submit these possibilities:

   The signals are emmitted from one source but with different antenna patterns

   The signals are of different power

   The signals are eminating from different locations

   A combination of the possibilites above.


The 6993 KHz signal is clearly readable during daylight hours her in Florida and with the current lack of decent HF propagation, I venture to guess the antenna is in the Southeast USA, Caribbean, Central America, or perhaps less likely South America north of the equator.
   
The source and function of these carriers is still a mystery. With nearly 5 years of casual monitoring of these signals, not much has come to light about their reason for being. 
   
The 4993 KHz sister-signal is still readable here, but only at night.

Dag



Seminole county, Florida, USA, Earth, Solar System, Universe.
TS440s + attic dipole.

Offline Josh

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Re: Three carriers: 6993.015 KHz +/- 10 Hz Dec 13 2014z i
« Reply #10 on: May 06, 2018, 1600 UTC »
Not too long ago there was a US mil (think it was USN) rtty freq that had bad spurs, this may be a similar case. However, whoever the intended receiver is, they're not paying attention apparently.
Conveniently located near Vincennes Indiana.