Unusual Signal on 138.3 MHz

spongella

SatelliteGuys Pro
Original poster
May 12, 2012
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Central NJ
Found this unusual transmission around 8pm tonight, consisted of a repeating transmission of 3 different tones as following:

3 tones at 600 Hertz
3 tones at 450 Hertz
3 tones at 350 Hertz.

This pattern was transmitted over and over until about 8:15 pm when it stopped. Attached is a screenshot. Some of the tones were at different volume levels. Haven't the slightest idea what this is. If you have ever taken a hearing test, that is how it sounded.
 

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Perhaps some sort of beacon in testing.
 
Yes, might be a beacon. I think we can rule out any kind of spurious signal from an appliance. This is the portion of the band where satellites can be found. Did not notice any Doppler effect though, it just stopped abruptly. Next time will make a recording.

Can we attach sound files or are they too large a file?
 
Signal is back this morning. Using same three tones at 325, 450, 600 Hz but with a different repeating sequence than last night, it now is thus:
450/325/600/325, 325/450/600/325, 600/450/325/600, 450/600/325/450, 325/450/600/325. Wondering if it is some kind of tone-paging system. If anyone hears this in their area, please post, thanks.
 

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Yes, might be a beacon. I think we can rule out any kind of spurious signal from an appliance. This is the portion of the band where satellites can be found. Did not notice any Doppler effect though, it just stopped abruptly. Next time will make a recording.

Can we attach sound files or are they too large a file?
Yes you can attach a sound file and no it should not be too large unless you record for hours and in a Super High Q format, but that is not needed for this.
 
According to Google and the UFO crowd, that's a Military Surveillance frequency. You aren't near a base anywhere are you?
;)
 
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Ft. Dix is a few counties South, probably too far to receive from here. Nothing on the FCC database except some Alaskan stations. Could also be an unlicensed low power station like a wireless microphone.

But, you've given me an idea, I can hook up my OTA antenna and rotate it to find what direction the signal is coming from.

Will also program it into my RS scanner and while mobile will see how the signal is a different locations.

Thanks for the comments all.
 
Last edited:
Found this unusual transmission around 8pm tonight, consisted of a repeating transmission of 3 different tones as following:

3 tones at 600 Hertz
3 tones at 450 Hertz
3 tones at 350 Hertz.

This pattern was transmitted over and over until about 8:15 pm when it stopped. Attached is a screenshot. Some of the tones were at different volume levels. Haven't the slightest idea what this is. If you have ever taken a hearing test, that is how it sounded.

Transmissions from the Joint Land Attack Cruise Missile Defense Elevated Netted Sensor System (JLENS) radar at Aberdeen, MD occur centered on 138.3125 and 149.4375 MHz. As this tethered aerostat (blimp) can be at altitudes like 10,000 feet, the transmissions are easily heard at distances overt 100 miles. Due to the high pulse repetition rate, these have a bandwidth over 100 kHz (about 100 kHz @ -10 dB, 150 kHz @ -20 dB, and easily seen over a 400 kHz bandwidth). They can be heard in AM, FM, or WFM modes, but are best heard in AM mode. As the pulses are very short, when received this way, the audio will contain harmonics of the pulse repetition rates.

The transmission uses intervals with pulse repetition rates of 360.23 Hz, 460.40 Hz, and 599.52 Hz that follow repeat a pattern for long periods of time.

Let the following represent the the different pulse repetition rate intervals on the two frequencies:
"a" 360.23 Hz on 138.3125 "A" 360.23 Hz on 149.4375 (780 ms)
"b" 460.40 Hz on 138.3125 "B" 460.40 Hz on 149.4375 (610 ms)
"c" 599.52 Hz on 138.3125 "C" 599.52 Hz on 149.4375 (469 ms)
[Interval time lengths are first to last pulse. In each case, the result is 282 pulses are transmitted during an interval of each pulse repetition rate. Multiplying by 282/281=1.0036 to convert to full cycle lengths obtains 783, 612, and 471 ms, respectively.]

An example transmission pattern heard is abcaBCABcabcABCAbcabCABC and then that repeats.
Another heard transmission pattern heard is aBCaBcaBcABcAbcAbCAbCabC. Note that each pattern always contains 4 intervals of each radio frequency pulse rate combination. This gives 4 x 3(PRR) x 2 (radio frequencies) = 24 intervals which takes typically about 16 or 17 seconds to transmit (the times between the frequency pulse rate intervals do not seem precisely controlled but is often roughly 57 ms).

In the above cases, the pulse repetition patterns did not change, only the radio frequency pattern changed.

There are occasional skips and rarer slight overlaps. The transmissions sometimes go off the air for a while.

The transmissions interfere with a trunked LTR system at Dahlgren, VA which uses 149.3000 and 149.4500 among its frequencies; but most users around the 138.3125 area (several DC area EDACS trunks) moved out several years ago.

*The pulse rates 360.23, 460.40, and 599.52 Hz correspond to times between pulses of 2.776, 2.172, and 1.668 ms, respectively.
 
Thanks David L. wilson for the ID on that station. Checked out Raytheon's website regarding this type of radar, very interesting. Glad to see that blimps are still being used today for sophisticated applications such as homeland security. Did not hear any signals yesterday though. Feel much safer when it is around. And welcome to the forum!
 
Got the JLENS xmission today on 149.448 MHz. My dongle frequency readout is a bit off though.
 

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Thanks, I wondered that earlier today when I heard about it breaking free.
 
Thanks, I wondered that earlier today when I heard about it breaking free.
 
Hi fellas' yes, the cable was dragging along the ground and it caused some damage. Kinda' miss it's signal these days. Hope they can get it back in shape.
 
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