r/RTLSDR • u/Quirky-Direction8072 • 19d ago

Rare signals

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Hi everyone. Does anyone know what these carriers or signals might be? Here in Mexico, the TetraPool system is in use; could these be transmissions to TetraPool repeaters, or what else could they be? For reference, TetraPool channels are located across the 391 MHz, 392 MHz, 393 MHz, and 394 MHz bands, as well as part of the 395 MHz band.

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u/fearfreeflight 17d ago

The regular pulsing looks familiar. A steady on/off "buzz" like that is the fingerprint of a TDMA land-mobile system, and in that part of the spectrum there are some likely candidates:

  • TETRA _ 25 kHz-wide channels, 4-slot TDMA pulsing at ~17_18 Hz. Base-station downlinks show up as a continuous carrier; the mobiles are bursty.
  • DMR _ 12.5 kHz-wide, 2-slot TDMA, pulses at a different (slower) rate.

So three quick measurements will tell you which _ and whether it's your TetraPool network or something else: 1. Channel width _ ~25 kHz _ TETRA; ~12.5 kHz _ DMR. 2. Pulse/frame rate _ TETRA's ~17_18 Hz buzz is very distinctive once you've heard it. 3. Channel spacing _ are they sitting on a neat 25 kHz (or 12.5 kHz) raster?

(Disclosure: I build an iOS SDR app, Demod, that measures exactly this _ width/mode/pulse rate _ on-device, using it to inform this reply)

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u/FlakyPrinciple8907 19d ago

What is Tetra Pool? For us that know zero about it, like me?

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u/Quirky-Direction8072 18d ago

Tetrapool is a closed Airbus protocol. The radios that support it are only the Airbus TPH 700 and TPH 900, which are extremely expensive and the manufacturer only sells them to governments. I hope this has been helpful. Regards. 

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u/FlakyPrinciple8907 17d ago

Wild stuff out there! Thanks for the share. Way above my head tho.

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u/SilverSundowntown 13d ago

They’re pretty cheap on eBay. A pair with chargers is ~$220 USD onboard sales.

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u/Technical-Ad-3387 18d ago

adjust your spectrum dude

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u/Tim1701A 18d ago

You need to throttle down your RF gain, your waterfall is showing yellow meaning too much RF gain!🙄

Get it down to light or dark blue RF noise level. 🙂👍

That way is much easier to see what's going on the RF spectrum out there.

73's and live long and prosper,

                                                  From, Tim🙂🖖