Radio Signal Identification Guide

A guide to help you identify some amateur and utility digital radio signals and sounds which you may find on the frequency spectrum. I will be slowly adding more to this list over time. If you enable stereo mix and pass the sample audio to an appropriate decoding program the sample audio should be decodable for most samples.

If you would like to suggest a modification or contribute a sample, please send a sample, waterfall image and information about the signal to rtlsdrblog@gmail.com, or post in the comments.

More sites with sample audio can be found at this list on dxzone.com. A very nice overview video of the HF spectrum by balint can be found here. There are also two paperback books: Technical Handbook for Radio Monitoring VHF/UHF (PDF Excerpt) & Technical Handbook for Radio Monitoring HF (PDF Excerpt) which have a very comprehensive list, description and images of many signals.

ACARS

Sample Audio:

Typical Frequency: 131.550 MHz

Mode: AM

Bandwidth: 5000-8000 Hz

Description: Aircraft Communications Addressing and Reporting System (ACARS). Short messages sent to and from aircraft.

Decoding Software: PlanePlotter, ACARSD

Video Examples: [1], [2]

ACARS Packets

P25 Phase 1 (C4FM Modulation) (Encrypted)

Sample Audio:  

Typical Frequency: ~860 MHz, ~500 MHz + others

Mode: NFM

Bandwidth: 10000 Hz

Description: P25 encrypted digital voice signal with C4FM modulation.

Decoding Software: Digital Speech Decoder (DSD). Note, only unencrypted can be decoded.

Video Examples:  [1], [2][3]

P25 Waterfall Example

DMR/MotoTRBO

Sample Audio:  

Typical Frequency: ~860 MHz

Mode: NFM

Bandwidth: 10000 Hz

Description: Motorola digital voice signal known as MotoTRBO (pronouced Moto-Turbo).

Decoding Software: Digital Speech Decoder (DSD). Note, only unencrypted can be decoded.

Video Examples: [1], [2]

DMR/MOTOTRBO Signal Waterfall

POCSAG/FLEX-A

Sample Audio:

Typical Frequency: ~151 MHz, ~900-950 MHz

Mode: NFM

Bandwidth: 10000 Hz

Description: Pager digital signal known as POCSAG. An acronym of Post Office Code Standardization Advisory Group.

Decoding Software: PDW

Video Examples: [1], [2]

 POCSAG/FLEX Pager Waterfall Image

Weather Balloon (Radiosonde) Vaisala RS92SGP

Sample Audio: 

Typical Frequency: ~400 MHz

Mode: NFM

Bandwidth: ~5500 Hz

Description: Weather balloon (Radiosonde) telemetry data. Only transmits during a weather balloon launch.

Decoding Software: SondeMonitor

Video Examples: [1], [2]

  RS92SGP Radiosonde Waterfall Image

TETRA Downlink

Sample Audio: 

Typical Frequency: 380 – 430 MHz

Mode: -

Bandwidth: 25000 Hz

Description: Terrestrial Trunked Radio (TETRA), also know as Trans-European Trunked Radio is a professional mobile radio and two-way transceiver (walkie-talkie) specification. Modulated with π/4 DQPSK. Audio sample recorded in NFM mode.

Thanks to Jenda for the submission.

Decoding Software: osmocomTETRA

Video Examples: [1], [2]

TETRA Downlink

Trunking Control MPT1327

Sample Audio: 

Typical Frequency: ~420 MHz

Mode: NFM

Bandwidth: 10000 Hz

Description: Radio trunking control channel.

Decoding Software: Trunkview, UniTrunker

Video Examples: [1]

MPT1327 Waterfall Image

Trunking Control Motorola Type II Smartnet

Sample Audio: 

Typical Frequency: ~860 MHz

Mode: NFM

Bandwidth: 8000 Hz

Description: Radio trunking control channel.

Decoding Software: UniTrunker

Video Examples:

Motoroal 2F1D Trunking Channel

Trunking Control EDACS96

Sample Audio: 

Typical Frequency: ~860 MHz

Mode: NFM

Bandwidth: 10000 Hz

Description: Radio trunking control channel.

Decoding Software: UniTrunker

Video Examples:

EDACS96 Trunking Channel

Trunking Control APCO P25

Sample Audio: 

Typical Frequency: ~860MHz

Mode: NFM

Bandwidth: 12500 Hz

Description: Radio trunking control channel.

Decoding Software: UniTrunker

Video Examples:

APCO P25 Trunking Channel

AFSK1200

Sample Audio: 

Typical Frequency: ~144 MHz

Mode: NFM

Bandwidth: 10000 Hz

Description: Audio frequency-shift keying (AFSK). Used by amateur radio hams for packet radio, Automatic Packet Reporting System (APRS) and telemetry.

Decoding Software: QTMM

Video Examples: [1]

AFSK1200

AIS

Sample Audio: 

Typical Frequency:

Marine Channel 87 – 161.975 MHz
Marine Channel 88 – 162.025 MHz

Mode: NFM

Bandwidth: 12500 Hz OR 25000 Hz

Description: Automatic Identification System (AIS). Used by ships to broadcast position and vessel information. Uses 9.6 kbit GMSK modulation.

Decoding Software: ShipPlotter, AISMon (In the Files Section of the Yahoo Group)

Video Examples: [1], [2]

AIS Waterfall

NOAA Weather Satellite (APT)

Sample Audio: 

Typical Frequency:

NOAA 15 137.620
NOAA 18 137.9125
NOAA 19 137.100

Mode: WFM

Bandwidth: 30000 Hz

Description: NOAA Automatic Picture Transmission (APT) signal. Used to by the NOAA weather satellites to transmit satellite weather photos.

Only transmits at certain times throughout the day when the satellite passes overhead at your location.

Decoding Software: WXtoImg

Video Examples: [1], [2], [3]

 NOAA APT Waterfall Screenshot

Stereo Wideband FM (WFM)

Sample Audio: -

Typical Frequency:

Common – 87.5 to 108.0 MHz
OIRT – 65 to 74 MHz
Japan – 76 to 90 MHz
Consumer Wireless Devices – ~860 MHz

Mode: WFM

Bandwidth: 30000 Hz

Description: Stereo Wideband FM signal. Used for typical broadcast radio, and in some wireless headsets and speakers. This particular signal is from an AKG headset.

Top signal is WFM transmitted with low amplification. Bottom signal is WFM transmitted with high amplification.

Thanks to Tobby for the submission.

Decoding Software: Unencoded

Video Examples: [1], [2]

 WFM

Amplitude Modulation (AM)

Sample Audio: -

Typical Frequency:

Long wave – 153 to 279 kHz
Medium wave – 531 to 1,611 kHz in ITU regions 1 and 3 and 540 to 1610 kHz in ITU region 2.
Short wave – 2.3 to 26.1 MHz

Aircraft - 108 to 137 MHz

Mode: AM

Bandwidth: 10000 Hz

Description: Amplitude Modulation broadcast audio radio station.

Thanks to rtlsdr_is_fun for the submission.

Decoding Software: Unencoded

Video Examples: [1], [2]

 AM Waterfall

Weatherfax (HFFAX)

Sample Audio: 

Typical Frequency: HF ~3 to 16 KHz. Location dependant.

Mode: Upper side band (USB)

Bandwidth: ~1900 KHz

Description: HF Weatherfax. Used by boats for weather reports. Also Kyodo News, a Japanese newspaper transmits entire pages via HFFAX.

Decoding Software: FLDIGI

Video Examples: [1], [2]

 WeatherfaxWaterfall

Upper Side Band Voice (USB)

Sample Audio: 

Typical Frequency: All HF band.

Mode: USB

Bandwidth: ~1900 Hz

Description: Single side band, specifically upper side band. Used in the HF band by amateur radio hams and aircraft weather reports. Single side band saves bandwidth.

Decoding Software: Unecoded

Video Examples: [1], [2]

 UpperSideBandWaterfall

Over the Horizon (OTH) Radar

Sample Audio: 

Typical Frequency: All over HF Band

Mode: -

Bandwidth: -

Description: Over the horizon radar. Used by governments for very long range radar systems.

Decoding Software: Unencoded

 OTHRadar

Analogue PAL TV

Sample Audio: -

Typical Frequency: Multiple

Mode: PAL TV

Bandwidth: 5 MHz

Description: Analogue PAL TV. Color TV signal.

Decoding Software: TVSharp

Video Examples: [1]

 Analogue PAL TV

Digital Audio Broadcast (DAB+)

Sample Audio: No Audible Sound Produced

Typical Frequency: 

Multiple channels.
Block 13F – 239.200 MHz

Mode: DAB

Bandwidth: 1,537 KHz

Description: Digital Audio Broadcast (DAB+). A type of digital broadcast radio signal, containing multiple digital radio stations in the signal.

Decoding Software: SDR-J

Video Examples: [1]

 DAB+ Digital Audio Broadcast

Baby Monitor (NFM)

Sample Audio: -

Typical Frequency: ~40 MHz, 49.5 – 50 MHz

Mode: NFM

Bandwidth: < 15 KHz

Description: NFM signal from a baby monitor. Periodically bursts signal when no audio is detected. Thanks to Dean for some extra info.

Decoding Software: Unencoded

Video Examples: [1]

 BabyMonitorNFMSpikes

Digital Radio Mondiale (DRM)

Sample Audio:

Typical Frequency: Below 30 MHz on HF, near other shortwave radio stations.

Mode: USB

Bandwidth: 10000 Hz

Description: Digital Radio Mondiale (DRM). A form of international digital shortwave radio. Replaces AM shortwave radio.

Thanks to Will P. for the contribution.

Decoding Software: DREAM, SODIRA

Video Examples: [1], [2]

 Digital Radio Monodiale Waterfall Digital Radio Monodiale Waterfall

STANAG 4285

Sample Audio:

Typical Frequency: All over HF.

Mode: USB

Bandwidth: 2500 Hz

Description: Standardization Agreement (STANAG) 4285. NATO standard for HF communication.

Decoding Software: Sorcerer (Waring: Potential Virus Alert), Sigmira

Video Examples: [1]

 STANAG 4285 Waterfall Example

GSM Downlink (Non-Hopping)

Sample Audio:

Typical Frequency: 900 MHz and 1800 MHz Band OR 850 MHz and 1900 MHz Band

Mode: -

Bandwidth: 200 KHz

Description: GSM Cell Phone Downlink (Non Hopping Signal). Audio sample used NFM mode.

Decoding Software: Airprobe

 GSM Non Hopping Waterfall Image

GSM Uplink

Sample Audio: No Audible Sound Produced.

Typical Frequency: ~890 MHz

Mode: -

Bandwidth: 200 KHz

Description: Initial connection GSM signal sent from a cellphone.

Decoding Software: -

 GSMUplinkFrequencyHopping

GSM Downlink (Hopping)

Sample Audio: No Audible Sound Produced

Typical Frequency: 900 MHz and 1800 MHz Band OR 850 MHz and 1900 MHz Band

Mode: -

Bandwidth: Each channel 200 KHz

Description: GSM cell phone hopping.

Decoding Software: -

 GSM Hopping Waterfall

“Japanese Slot Machine” (XSL)

Sample Audio:

Typical Frequency: Between 4 MHz and 9 MHz

Mode: USB?

Bandwidth: -

Description: Known as the Japanese Slot Machine. Thought to be data originating from the Japanese Navy.

Decoding Software: Sigmira (But Cannot Decrypt)

Video Examples: [1], [2]

 Japanese Slot Machine Waterfall

Automatic Dependent Surveillance-Broadcast (ADS-B)

Sample Audio: No Audible Sound Produced

Typical Frequency: 1090 MHz

Mode: -

Bandwidth: 2 MHz

Description: Automatic Dependent Surveillance-Broadcast (ADS-B). Used by aircraft to broadcast their latitude, longitude and altitude.

Decoding Software: ADSB#, Dump1090, RTL1090

Video Examples: [1], [2], [3]

 ADSBWaterfallScreenShot

Cuban Numbers Station HM01

Sample Audio: 

Typical Frequency: 11.530 MHz.

Mode: AM

Bandwidth: -

Description: (Previously Unidentified Signal 5). Numbers stations are thought to transmit encoded information for various spy agencies around the world. They are recognized by a voice reading a sequence of numbers or words. This is a Cuban Numbers Station which has a data portion and a voice portion. Sound sample recorded in AM mode.

Thanks to Andrew from the comments section for the ID.

Decoding Software: Information Here

Video Examples: [1], [2], [3], [4], [5]

UnknownSignalWaterfall_5

High Frequency Data Link (HFDL)

Sample Audio: 

Typical Frequency:  HF Band

Mode: USB (1440 Hz below center)

Bandwidth: ~2800 Hz

Description:  (Previously Unidentified Signal 2). An Aircraft Communications Addressing and Reporting System (ACARS) data link that aircraft use to communicate short messages over long distances using HF signals.

Thanks to Andrew from the comments section for the ID.

Decoding Software: PC-HFDL

Video Examples: [1], [2], [3]

UnknownSignalWaterfall_1

Binary Phase Shift Keying (BPSK31)

Sample Audio: 

Typical Frequency:  HF Amateur Band

Mode: SSB

Bandwidth: ~31 Hz

Description:  A digital amateur radio mode based on Phase Shift Keying (PSK) modulation

Thanks to Patrick for the submission.

Decoding Software: Fldigi, MixW, HRD Digital Master 780, MultiPSK

Video Examples: [1], [2][3]

BPSK Waterfall Example

AFSK Paging Link

Sample Audio: 

Typical Frequency: 72-76 MHz

Description: (Previously unidentified signal 10). Identified in the comments section by Ronen as an Asynchronous Frequency Shift Keying (AFSK) pager link. It is easier to transmit the FSK pager signal to the transmitter site as AFSK.

unknown_10_waterfall

Pulse Code Modulated (PCM) RC Toy Signal

Sample Audio: 

Typical Frequency: 27.145 MHz, 72 MHz

Description: (Previously unidentified signal 9). Identified in the comments section by W1BMW as a Pulse-code modulated (PCM) signal used for remote control (RC) Toys. Link to IQ file http://i.nyx.cz/files/00/00/09/99/999880_c640d91142db39ee7d57.zip?name=SDRSharp_20130613_113322Z_27186kHz_IQ.zip. Sample audio recorded in USB mode.

UnknownSigna_9

Overlapping RTTY Signals

Sample Audio: 

Typical Frequency: HF band

Description: Previously unidentified signal (11). Identified in the comments by various contributors as multiple overlapping RTTY signals sent by ham radios.

Unknown CW #3

Voice Frequency Telegraph

Sample Audio: 

Typical Frequency: 7453.50 KHz USB

Description: Previously unidentified signal (13). VFT or Voice Frequency Telegraph is one of several systems for sending multiple RTTY signals over one voice-bandwidth radio channel.

74535khzusb

Portable Traffic Lights

Sample Audio: 

Found Frequency: 154.463 MHz

Description: Previously unidentified signal (17). Identified by Peter via email as being signals sent from portable traffic lights that are often used at roadworks.

unid17

X2 on iDEN

Sample Audio: -

Found Frequency: 154.463 MHz

Description: iDEN is an acronym for Integrated Digital Enhanced Network and is a technology developed by Motorola. It is a type of trunked radio with cellular phone benefits.

Link to RR identification discussion from submission email.

Thanks to Mike (VE3HER) for the submission.

x2 on iden

Funcube-1 Satellite

Sample Audio:

Found Frequency: 145.950 – 145.970 MHz

Mode: USB

Bandwidth: ~2 kHz

Description: The Funcube-1 is a Cubesat amateur radio satellite.

Decoding Software: Funcube Telemetry Dashboard

funcube-1_waterfall

Swedish Pocsag Minicall

Sample Audio:

Typical Frequency: ~161 MHz

Mode: NFM

Bandwidth: 20 kHz

Description: A short Pocsag 1200 signal used in electric plants and remote transformer and insulation stations.

Thanks to Joni for the submission.

Decoding Software: PDW

Video Examples: [1], [2]

swedish_minicall_pocsag

Unidentified Signals

If you know what any of these signals are please write in the comments. You can also submit any unidentified signals you would like to be added to rtlsdrblog@gmail.com.

(1)

Sample Audio: 

Found Frequency: 171.3 MHz

Description: Recognized by DSD as a NXDN96 signal, but is disputed in the comments section. (Possibly a bug in DSD).

QPSK2

(3) – ALE?

Sample Audio: 

Found Frequency:  HF Band

Description: Sound sample recorded in USB mode. Potentially some sort of 2G ALE signal. Similar signal shown in balints HF tour video. Possible a weather map transmitted from Tokyo as noted in the comments section by Syd, or 4xFSK from China as identified by K2RCN in the comments.

UnknownSignalWaterfall_2

(4)

Sample Audio: 

Found Frequency: HF Band

Description: Periodic pulses. Sound sample recorded in USB mode. Possibly a GlobeWireless signal as identified in the comments section by K2RCN.

 UnknownSignalWaterfall_4

(6)

Sample Audio: 

Found Frequency: 152.652 MHz

Description: Continuous signal. Audio sample recorded in NFM.

UnknownSignal_6

(7)

Sample Audio: 

Found Frequency: 162.863 MHz

Description: Continuous bursts. Audio sample recorded in NFM.

UnknownSignal_7

(8)

Sample Audio: 

Found Frequency: 457.168 MHz

Description: Audio sample recorded in NFM.

UnknownSignal_8

(10)

Sample Audio: 

Found Frequency: 452.325 Mhz

Description: Sent in over email. Sounds like Motorola Type II smartnet, but Unitrunker does not recognize.

unid_10

(12)

Sample Audio: 

Found Frequency: 154.646 MHz

Description: Sent in over email. Repeats every minute.

154646

(14)

Sample Audio: 

Found Frequency: 433 MHz

Description: Sent in over email.

Hello! I was listening in the 433MHz band and saw this blip (about 1-2sec) on the waterfall on 433.873 (Millville, MA). It repeats about every 30-50 seconds, though doesn’t seem to be the same every time. Maybe a wireless instrument of some type (weather or something?). The only clear sound of it I could get was with AM, about a 4.2kHz wide filter (rtl-sdr, gqrx linux). Any ideas? Thanks!

(15)

Sample Audio: 

Found Frequency: 455 MHz

Description: Sent in over email.

unid15

(16)

Sample Audio: 

Found Frequency: 173.262 MHz

Description: Sent in over email.

unid16

(18)

Sample Audio: None

Found Frequency: ~856 MHz

Description: Sent in over email.

The antenna has a Yagi pointed to West from 23.5° South latitude, 47.46° West longitude.
The signal can be local or from the sky. The signal is horizontal polarized.

uid16

(19)

Sample Audio: 

Found Frequency: ~409.6 MHz

Description: Sent in over email. Recorded in NFM mode.

screen

65 comments

  1. Pingback: Radio Signal Identification Guide - rtl-sdr.com | Blog @ nomanshah.com
  2. Lzq3425

    Talking about Osmocom TETRA for Windows.. I have found a site that contains the working version for windows, but does anyone have a password for it? http://bitdrop.co.uk/5Nu0eB

    If anyone knows the password, I would be very grateful if you could share it here..

    Loz Q

    • Marodian

      Mike, Im pretty sure thats Over the Horizon Radar. The Australian JORN network. We hear it heaps all over the HF spectrum. It moves around quite a lot. Im not sure if its an actual radar pulse or some soft of frequency probe. We had a HF radio base setup not far from the Stonehenge JORN site and that signal was incredibly strong and frequent.

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  5. Acuario

    If you slow #13 down substantially then you will find it is almost certainly high speed mores sent using frequency shift keying (fsk).

  6. MrBudson

    great web page keep up the good work.
    a question have you recorded the data tracking for wild life coyotes and other wild life. there is a tracking area locally and would like to see it being tested, they will not talk to me about any tec stuff .
    MRBUDSON

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  8. K2RCN

    (3) is a 4xFSK from China if I recall.
    (4) is GlobeWireless, a now defunct system.
    (11) is RTTY overlapping in ham bands.
    HM01 is a mode called RDFT, now only used by Cuba, formerly a ham mode.

  9. Tom

    #4 – Japanese Navy fax transmissions for newspaper pages and weather maps for ships at sea.
    I remember reading about them in Popular Communications about 20 years ago. Tuned in the published freqs and there they were. Each pulse is a line/carriage return

    • Ken - WB0OCV

      What a great and useful web site. I agree that #11 is not Olivia. I think it is four separate RTTY signals offset from each other by a few hundred Hertz. The left-most one appears to be the strongest, the second from left weaker, the third strong, and fourth weak. If you listen on the amateur “ham” bands during a RTTY contest where several signals are within a couple of kHz, it sounds similar.

      • KC3APN

        You are correct. It is RTTY. Several signals are show at once in the screen capture. You can decode RTTY and many other digital modes with free software such as Digital Master which is part of the Ham Radio Deluxe package. Version 5 is free but may be harder to find now.

    • Bob H.

      The recording is in NFM and I tested and it is not internal but it is really strong even with the small MCX antenna that came with the dongle.

  10. Pingback: Poursuite radar : ADS-B & Pi | Chakram AirlinesChakram Airlines
      • Mateus

        You can include 72MHz also for the RC transmitters. They use FM from 72~73 which channels are separated by 10Khz. I could read my transmitter with NFM at 10Khz band. Although the image looks a little bit different than this one in the guide, not sure if PCM or PPM. I’ll come up with a sample shortly.

  11. Robbi

    Just a typo hint: It is Radio “Mondiale” and not “Monodiale”.
    And BPSK31 has a bandwidth of 31Hz, not kHz.

    Great website anyways!

  12. Ronen

    Audio #10 is a Pager link to the pager transmitter (since Pager use FSK it is much simple to transfer the FSK signal as AFSK to the transmitter site ) as for the pager itself i dont know if it is Pocsag or other one (Flex) i can check if neccessary

  13. Smokey Behr

    Samples 6-8 are all the same type of signal. They seem to be some kind of SCADA type data. If you look up the frequency in the FCC database (if in the US) you can tell who the licensee is, and see what information is on the license.

    • ea5idn

      Agree, we’ve tracked many of these signals in my city and they are all emitted from electrical substations, water smart valves/meters and that kind of stuff

    • admin

      Thanks, I think you’re right again. I’m going to try test it later tonight with PC-HFDL. EDIT: Yup, was HFDL, got some decoded using PC-HFDL.

  14. Tobby

    (6), I belive 152mhz is widely used for Radio tracking of animals.
    Not sure about the protocol used.

  15. Marodian

    I think (3) could be JORN – Over the horizon radar. I hear this a lot usually along with something very similar to the OTH recording yo already have, normally very early in the mornings.

      • Marodian

        Id have to agree that is close to 2G ALE.
        We run a HF network in remote Australia for a few weeks every year and this is a common signal early in the morning before sunrise, and slowly disappears as the MUF increases. A quick search on RF map for our allocated frequencies (plus or minus a bit) returns a few sites that could be using ALE on their network including the RFDS and Dept of Community Safety, and a Tug operator in Brisbane. This makes sense as we quite often get voice interference from trawlers off the Qld coast around the same time.

  16. radiosification

    No unfortunately I don’t have any around me either but I can tell you for sure that this isn’t it. Voice carrying signals would not have breaks like this one does. This is some kind of digital that only carries data and no voice, unless its a trunking control channel, but I doubt it. The information that it is used for taxis is also incorrect so maybe the best idea is to leave it blank until a more reliable source provides a sample. Good luck with the project though its a good start.

    • admin

      Okay, thanks for the help. I’ll cross it out and mark it as disputed for now, and probably start an Unknown Signals list soon.

  17. Radiosification

    I don’t think the NXDN96 one is correct. NXDN is not a data transfer standard, it is primarily for voice not taxi data transfer. And that doesn’t even sound like NXDN! DSD decodes voice so would not decode this standard either.

    • admin

      You might be right, but DSD does recognize it as NXDN96 when I pass it the example audio, no audio decodes though. Could be a bug. Do you have an NXDN example I can see? I don’t personally have any NXDN signals around me.

    • Tobby

      If you select inverted NXDN96 you will get tons of data packages. (more than voice in normal mode)
      It’s a continues stream and according to local frequency listings it belongs to a taxi company.

      But i have no other reference for nxdn96 than Dsd so it might be wrong. Tried to run the taxi decoder on it, nothing.

      • admin

        I think it must be a NXDN96 control channel, as it sounds pretty similar to other control channels.
        EDIT: I think it is a NXDN96 data channel.

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