1. Getting started
SDRSowa turns an RTL-SDR receiver into a radio on your phone. The app does the work on the phone: it shows the spectrum, plays the audio, scans bands and reads text signals.
What you need
- Either a network receiver: an RTL-SDR that another computer shares with rtl_tcp, for example a PC running SDRSowa for Windows. No USB adapter is needed.
- Or an RTL-SDR stick on the phone: the stick, a USB-C (OTG) adapter and the separate SDR driver app from Google Play. The driver app opens the stick for SDRSowa. Without it, only a network receiver works.
- An antenna. Stick and antenna are not part of the app.
The first start
- Licence. A welcome notice asks you to accept the SDRSowa licence (I agree) or leave the app (Exit). You can read the full licence from the notice.
- Connect a receiver. Open Settings and connect a network receiver or plug in your stick. See Receivers.
- Explore. More > Explore answers the question "What can I receive?" with a list of cards: what is on the air, on which frequencies, how hard it is, which antenna helps, and a button to listen or scan.
- Antenna location (optional). You can set the place of your antenna in Settings > Receiver. It stays on the phone. Explore asks for it so it can tell what is used in your region.
- First recording. The first time you record, a notice reminds you that you are responsible for what you record and how you use it. You have to agree before the recording starts.
The pages
The bottom bar has five pages (on a tablet or a phone turned sideways, the same pages are in a side menu).
| Page | What it is for |
|---|---|
| Home | Tune, listen, record. The spectrum and the waterfall, the receiver controls and the decoder cards. |
| Scan | Sweep ranges or your saved stations and stop where there is a signal or speech. |
| Library | Recordings, favourites, stations, reminders, history, muted and blocked channels. |
| More | Explore, DAB+, Bands and profiles, the full-screen Spectrum. |
| Settings | Receiver, correction, antenna location, appearance, privacy and notices. |
2. Receivers
A network receiver
Open Settings > Receiver > Network receiver. The receiver can be a PC running SDRSowa for Windows (which shares its stick from Settings > Receiver > Share this receiver on the network), or any computer that serves an RTL-SDR with rtl_tcp.
| Control | What it does |
|---|---|
| Address | The address of the receiver, for example 192.168.1.10. The last address you used is remembered. |
| Connect | Connects to that address. The line under the field shows the state: connecting, connected, or the reason it failed. |
| Disconnect | Appears while connected. Lets go of the receiver. |
| Find on network | Looks once for receivers on the networks your phone is on. It does this only when you tap it, and nothing runs in the background. Each result has Add (puts the address in the field) and Use now (puts it in the field and connects). If nothing is found, it says so and you can type the address. |
On the newest Android versions the phone first asks for permission to reach devices on your local network ("Nearby devices"). Allow it, or the app cannot reach the receiver.
An RTL-SDR stick on the phone
Plug the stick into the phone with a USB-C (OTG) adapter. In this version of the app the stick is opened by the separate SDR driver app, not by SDRSowa itself. Settings > Receiver shows whether the driver app is installed. If it is not, the card says so and has a Get the SDR driver app button.
| Control | What it does |
|---|---|
| Stick name and state | Shows the stick found on the USB port and whether it is connected. Tap the stick's name to connect to it. |
| Refresh devices | Looks at the USB port again. |
| Disconnect | Lets go of the stick. |
| Why no sound? | Opens a short check of the stick, the antenna and the sound output. |
The receiver bar
At the top of the app, the receiver bar shows the receiver's name, its state and the sample rate. The dot is green when connected, amber while connecting or retrying and red when there is no receiver. Tap the bar to open the receiver settings. The power button in the bar is Disconnect while you are connected and Connect after you let the receiver go. While the receiver is busy (listening, scanning, tuning DAB+), a line there says what it is doing and has a Stop button. The receiver does one thing at a time.
Gain
On Home, Gain has an Auto box. With Auto on, the receiver sets the gain itself and the app shows an amber hint when the signal is too strong or too weak. Clear the box to set the gain with the slider (the value shows in dB).
- Optimise tries up to 12 gain settings on the station you are listening to, about 3 seconds each, and keeps the one with the best signal over noise. Press Play on a station first. Stop ends the test and puts the gain back.
- Undo returns to the gain you had before Optimise.
The sample rate is shown in the receiver bar. This guide does not describe a control for changing it.
3. Home
Home is the radio. At the top is the frequency, then the play controls, the spectrum with the waterfall under it, and the receiver controls. On a phone the controls sit in a card under the spectrum. When the phone is turned sideways, they slide in from the right with the Controls handle.
Frequency, favourites and play
| Control | What it does |
|---|---|
| Frequency (MHz) | Tap the number and type a frequency in MHz. The whole value is selected, so typing replaces it. |
| Star | Saves the station you are on. It asks for a name (optional; empty saves it under its frequency). A filled star means it is saved; tap it to remove the station. |
| Arrow next to the star | Opens Favourites: a list with search, a delete button on every row, Import list (from SDR#, SDR++, CHIRP or a CSV file) and Export CSV. |
| Previous / Next station | Seeks to the previous or next station. Held down, it steps channel by channel until you let go. |
| Play / Stop | Starts and stops the live reception. Play needs a connected receiver. |
| Record | Records what you hear. While recording the button becomes Stop recording and the elapsed time shows. Recordings go to the Library. |
Spectrum and waterfall
The spectrum shows how strong the signals are at each frequency. The waterfall under it shows the same over time, newest at the top. Tap or drag on the spectrum to tune. The frequency scale between the two turns the receiver like a dial. Pinch to zoom (Full view returns to the whole span).
A long press on the spectrum opens a menu for that frequency:
| Item | What it does |
|---|---|
| Tune here | Tunes to the frequency you pressed. |
| Save as station | Saves it as a favourite. |
| Copy frequency | Copies it to the clipboard. |
| Add marker / Clear markers | Up to two markers (M1, M2). With both set, the app shows the difference between them in kHz. |
| Add notch, Remove this notch, Remove all notches, Notches on | A notch cuts one narrow frequency out of the sound. It works in AM, SSB and CW. You can choose the notch width in Hz. |
| Band labels, Saved stations | Show or hide the band names and your saved stations on the spectrum. |
| Mark signals that come and go | Marks signals that appear and disappear. |
| 3D spectrum, 3D settings | Shows the last traces as a landscape. 3D settings has three sliders: Floor (how far under the noise the surface starts), Height (how high the signals rise) and Width (at 100 the far rows are as wide as the near ones, lower they narrow). |
| Waterfall: signals only, Waterfall: time lines, Spectrum: peak line, Show the UTC clock | Look of the waterfall and spectrum. Signals only keeps the noise dark. Time lines add UTC times. The peak line shows the highest level of each frequency. The clock shows UTC; tap it for local time. |
Receiver controls
| Control | What it does |
|---|---|
| Mode | AM, SAM (AM with a detector locked to the carrier, which sounds steadier when the signal fades), NFM (narrow FM: walkie-talkies, amateur radio, marine), WFM (wide FM: broadcast radio), USB and LSB (single sideband), CW (Morse) and CWR (CW on the other sideband). |
| Band | Jump to a band. The list also has a marine DSC entry and Manage profiles, which opens Bands and profiles. |
| Step | The tuning step. Auto follows the band. You can also pick a fixed step from 1 Hz to 100 kHz. |
| Squelch | Keeps the speaker quiet when there is no signal. With Auto on, it opens 6 dB over the noise next to the channel. Clear Auto to use the slider (the value is in dB, or Open for fully open). |
| Volume | 0 to 200 percent. 100 is unchanged. |
| Stereo (WFM only) | Switches stereo on or off. Under the frequency, a line says Stereo locked or Mono signal. |
| DSP | Opens Receiver audio: the filters. See Receiver audio filters. |
| SNR meter | A dial that shows how many dB the signal stands over the noise, measured on the channel you listen to. |
Station name and text
On broadcast FM (WFM), the app shows the station name and the radio text when the station sends them (RDS). The text scrolls under the frequency.
If the sound is paused by the system but the receiver is still running, a bar says Sound paused. Still receiving. and has a Resume button.
4. Receiver audio filters
Press DSP on Home or on Scan to open Receiver audio. These settings change only what you hear. Recordings and decoders use the original sound. Some settings work only in some modes and are greyed out in the others.
| Setting | What it does |
|---|---|
| Filter width | The width of the channel you hear, from Auto to 25 kHz. A narrow filter keeps a nearby station out. (Not on Scan, where each range sets its own width, and not in WFM.) |
| Passband shift | Moves the filter's passband up or down in steps of 10 Hz, to get away from a neighbour. Shown with the width. |
| Quiet until | A second squelch that listens to the signal itself. Off: Squelch slider only; A station transmits (like a handheld radio: silent until a carrier quiets the hiss, open through the pauses of an over); Someone speaks (only speech is heard; carriers, data and noise stay silent). A station transmits needs the NFM filter at Auto or 12.5 kHz and wider. |
| AGC | Automatic gain control, which keeps the volume even. Fast, Medium or Slow. |
| FM de-emphasis | Broadcast FM is sent with boosted highs. This undoes it. 50 µs: Europe, Asia, Africa. 75 µs: the Americas, South Korea. |
| Mute the buzz (digital voice) | Quiets the buzzing sound of digital voice signals, which the app does not decode into speech. |
| Clear voice (AM, SSB) | Makes speech easier to understand. |
| Remove hum | Takes out the steady hum of the mains and its tones. Works in AM, SSB and CW. |
| Noise reduction | One at a time: Off; Spectral (AM, SSB and CW); AI, light (little processing, works well on FM); AI, strong (more processing). The AI ones run on your phone. With a method on, Strength sets how much (0 to 100 percent) and Hold to compare plays the sound without noise reduction while you hold it. In CW, AI noise reduction stays off because it would take out the Morse tones. |
| Auto notch (ANF) | Finds a steady whistle or carrier tone in the signal and removes it. AM, SSB and CW. |
| Noise blanker (NB) | Cuts short clicks and pulses, such as ignition or power line noise. |
| Decode RTTY (USB / LSB) | Turns on the RTTY decoder. See Decoders. |
| Decode PSK31 (USB / LSB) | Turns on the PSK31 decoder. |
In FM, use the AI noise reduction: Clear voice, Remove hum, Spectral noise reduction and Auto notch work in AM, SSB and CW only.
5. Scan
The scanner sweeps a set of channels and stops where something is on the air. The page is called Frequency Scanner. Start Scan starts it and becomes Stop while it runs. DSP and Volume sit beside it.
What it scans
| Choice | What it does |
|---|---|
| Ranges | Scans the scan ranges you selected. |
| Favourites | Watches the stations you saved. It has its own timing (see below). With Favourites you can choose Listen or Watch silently. |
While it runs
Three tabs show what the scanner does.
| Tab | What it shows |
|---|---|
| Live | The sweep: the spectrum of the range and the channels the scanner holds. |
| Activity | Every transmission the scanner stopped on in this session, marked Voice or Signal. The bin clears the session's list. Library > History keeps them all. |
| Channels | The channels found in this session. |
Scan Ranges
The ranges are grouped by service (for example PMR446, the 2 m and 70 cm bands and their repeaters). Ranges for other countries are hidden unless you show all; your antenna location sets the country. Tap a heading to open a group. Each range shows its colour bar, name, mode and channels.
| Action | What it does |
|---|---|
| Tap a range | Selects it (green). |
| Press and hold a range | Excludes it (red): its channels are never scanned. |
| Section title | Selects or clears all ranges of that section. |
| Edit (pencil on a range) | Opens the range to change it. |
| Add a range (plus) | Makes a range of your own. |
| Import ranges / Export ranges | Reads or writes your list of ranges as a file. |
| Search and selected only | Find a range by name, or show only those you selected. |
A range that is outside what your receiver can reach is greyed out and is not scanned.
Scanner controls
The card collapses to a one-line summary. You can move a slider or type the number.
| Control | What it does |
|---|---|
| Squelch | How many dB a signal must stand over the band noise before the scanner stops (3 to 30). |
| Skip | Lets a channel go after this many seconds (3 to 30), so the scan moves on. A box turns it on or off. |
| VFOs | How many channels you hear at once, from 1 to 3, within the span the receiver sees at a time. |
| Hang | How long the scanner keeps a channel after its signal ends (0.2 to 10 seconds), so a reply is not missed. SSB and CW wait 1.5 seconds longer, because their pauses carry no signal. |
| Stop only on speech | Passes channels with no speech, such as data or a bare carrier. |
| Split channels left / right | With several VFOs, one channel plays on each speaker and a third quietly on both. |
With Favourites chosen, the controls above that do not apply are greyed out and three others appear: Look (seconds on each group of nearby saved stations), Check all (while you listen, a quick look at all the others this often, which is a short break in the sound) and Move on (seconds the station you hear may be quiet before the scan goes on).
6. Library
The Library keeps what you made and what you heard. It has tabs; the tabs scroll sideways on a phone.
| Tab | What it holds |
|---|---|
| Recorded | Your recordings. Each row shows the frequency and mode, the station if you saved it, a waveform, the date, the length and the size. Tap a row (or the play button) to play. The three dots menu has Tune to... (sends Home to that frequency), Make playable on other devices and Delete. Use the search box to find a recording by frequency, mode or name. The bin, or a long press, lets you tick several to delete; it asks first. |
| Favorites | The stations you saved with the star. |
| Stations | A list of shortwave stations from a public schedule. It shows what is planned, not what comes in. The clock button adds a reminder. |
| Reminders | Your reminders for stations. |
| History | What you heard: scanner stops, Home, DAB+, NAVTEX and weather fax. You can search all of it (a name, a frequency, or a time such as "last night") and save the list as CSV, JSON or ADIF. |
| Muted | Channels you muted. They are detected but silent. |
| Blocked | Channels you blocked. The scanner skips them. |
Recordings are protected
Recordings stay encrypted, so only SDRSowa can open them. A setting in Settings > Privacy ("Recordings can be played on other devices with SDRSowa", on by default) lets SDRSowa on your other devices play them too, for example a recording you copy to a friend. The ID of the device that made a recording stays in the file either way, so a copy can be traced.
History is kept on the phone only. In Settings > Privacy you can switch it off, choose how long it is kept (7 or 30 days at most) and clear it. Recordings are not deleted when you clear the history.
7. More
More holds the pages that are not in the bottom bar.
| Card | What it does |
|---|---|
| Explore | "What can I receive?" A list of what is on the air, grouped by kind (broadcast, aviation, marine, amateur, two-way radio and more). Each card says the frequencies, an easy or hard rating, the range you can expect, the best time, an antenna that works, and whether your receiver can do it ("Your receiver can", "Needs HF" or "Outside your receiver's range"). The button is Listen (tunes there), Scan (starts a scan of that range), Open (opens a page) or Learn more. Cards for pages that are not in this version say "Coming soon". |
| DAB+ | Digital radio in Band III. Press Scan and the app finds the ensembles itself. Then pick a station from the list (with a search box). The page shows the station, its programme text and the slideshow picture, the block, signal and FIC quality, and a Record button. You need a receiver that reaches Band III. |
| Bands & profiles | The setup of what Scan sweeps: the ranges (profiles) and the per-range timing, with an editor for a range. |
| Spectrum | The spectrum full screen, with the frame rate (frames a second; fewer saves battery), a Waterfall switch and a Smoothing switch. It needs a live spectrum: start listening on Home first. |
8. Decoders you can read
Decoders turn a signal into text. They work from the audio you are listening to, so tune to the signal first. The results are also in the History.
| Decoder | How to use it |
|---|---|
| Morse code | Choose the CW mode. A Morse strip shows the text ("Tune a Morse station: its text shows here"). Tune so the tone sits at about 700 Hz, where the decoder and the narrow filters expect it. |
| NAVTEX | Maritime safety messages on 518 kHz and nearby, in USB or LSB. The NAVTEX card shows the messages when a station sends; each station sends in its own time slot, every 4 hours. Needs a receiver that reaches HF. |
| RTTY | In USB or LSB, tick Decode RTTY in Receiver audio. A card shows the text. |
| PSK31 | In USB or LSB, tick Decode PSK31 in Receiver audio. A card shows the text. |
| Weather fax | Weather charts from coast stations, drawn line by line in USB. The card appears while a fax station is in the audio. Charts take 10 to 20 minutes; if you tuned in during one, press Start now. Save now saves the chart so far. Needs HF. |
| DSC calls | Digital calls between ships on marine channel 70 (156.525 MHz, NFM). Choose it from the Band list. The card lists the calls; distress and urgency calls also raise an alert. |
| Digital voice: who is talking | It is on by default; the switch is in the Settings card Digital voice: who is talking (Decode DMR, dPMR, NXDN, P25, M17, YSF and D-STAR calls in NFM). It needs no internet and no website. In NFM, a list shows who calls whom on DMR, dPMR, NXDN, P25 and other digital voice systems, with talk group or callsign and similar details. It never plays the voice. |
HF decoders (NAVTEX, weather fax, RTTY, PSK31, most Morse) need a receiver that can tune below about 24 MHz, such as an RTL-SDR Blog V4. Explore says "Needs HF" where this applies.
9. Settings
Open Settings from the bottom bar or the cog in the top bar.
Receiver
| Card | What it does |
|---|---|
| Network receiver | See Receivers. |
| USB receiver | The stick and the SDR driver app. See Receivers. |
| Correction and antenna power | Frequency correction (PPM) in steps of 0.1: 0 for the RTL-SDR Blog V4; older sticks may need about 20 to 80 either way. Measure with DAB+ measures how far off your receiver is, using a DAB+ station, and Apply sets it. It works best after the stick has run for 10 minutes. Follow the warm-up while a DAB+ station plays moves the correction by at most 0.1 ppm a minute, only on a clear signal. Bias-T gives the antenna 5 V: switch it on only for an LNA or active antenna that needs power; on a stick plugged into the phone, the phone's battery powers it. RTL AGC (digital gain) can help strong AM and FM stations; leave it off for weak signals. |
| Up- or down-converter | For a converter in front of the stick: enter its oscillator frequency (LO) in MHz and its correction in ppm. The app then shows the real frequency. |
| One receiver | "Ask before switching what the receiver is doing": asks before a new action stops the one that is running. Off, the new action starts at once. |
| Digital voice: who is talking | See Decoders. A second switch, Digital voice decoder output, sends the raw NFM signal to a decoder app of your own on the phone (TCP 127.0.0.1, port 7355, 48 kHz, 16-bit mono). |
| Antenna location | Set your place by searching for a city or town, by typing latitude and longitude, or on a map you tap (the location icon on the map uses where you are). The map is saved only when you press Use this place. Clear removes it. It stays on the phone. Map pictures are loaded only while the map is open. |
Appearance
Choose the colours (SDRSowa, Dark, Light, or the phone's own setting) and the spectrum speed in frames a second. The same page has the spectrum look switches (3D spectrum, signals-only waterfall, time lines, peak line, UTC clock). On a tablet you can also shrink the side menu to icons.
Recordings, storage and data
- Check a recording tells which device made a recording, from its sealed details or the hidden watermark in a copy.
- Storage shows what the app keeps on the phone and the offline data (station lists and similar), with an update button for each.
- Data source: Automatic (the default) downloads the offline data when it is due. Offline only: nothing goes online, with no downloads or lookups. Everything on the phone keeps working.
Privacy
Diagnostics and tools
- Write a diagnostic log keeps receiver, tuning and audio events, one file per day, for 7 days. It holds no audio and no personal data. Share today's log and Diagnostic report let you send it yourself.
- Hardware compatibility test checks which features work with your receiver. You decide whether to share the report.
- Copy your settings: Export settings and Import settings save and load your settings, favourites, scan ranges, saved channels and reminders as one file.
- Reset all settings puts every setting back to how it was when the app was new. Your recordings, favourites, scan ranges and reminders stay.
About and notices
About shows the version, the licence (Read the licence) and the third-party licences. The licence and the recording notice are shown by the app when they are needed, and the choice is yours.
10. Privacy and your data
- No account, no ads, no analytics. Not in the app and not on this website.
- Audio, recordings, decoded messages and the frequencies you listen to stay on your phone.
- The app sends nothing by itself. After a crash, the app saves a short text without names or addresses. Under Settings > Privacy you can e-mail it to the developer (your mail app opens and you press Send) or share the file. Nothing is sent unless you do it.
- The only things that go online are the offline data downloads (station lists and similar), and only in Automatic data mode. Offline only stops them.
- The antenna location and the history stay on the phone.
The full text is in the privacy policy.
11. Troubleshooting
| What you see | What to try |
|---|---|
| "No receiver connected", or Play is greyed out | Connect a receiver in Settings > Receiver: a network receiver by its address, or a stick through the driver app. |
| The stick does not open | Install the separate SDR driver app and open it once. Allow it to use the USB device when the phone asks. Push the stick fully into the adapter and the adapter into the phone, then press Refresh devices. Some phones need an OTG adapter that is known to work. If the stick still does not open, the driver app shows the reason. |
| A network receiver is not found | The phone and the receiver must be on the same network. On the receiver, sharing must be on and its program must be running (only one program can use a stick at a time). Press Find on network; if nothing is found, type the address. On newer Android versions, allow the Nearby devices permission. |
| No sound | Press Why no sound? in Settings. Check the volume (Home, Volume), the phone's media volume, that Squelch is not closed (try Auto), and that Quiet until is Off. For FM, use WFM. Check that the station is really on the frequency by looking at the spectrum. |
| Weak or no stations, only noise | Check the antenna is screwed on and put it by a window, as high as you can. A short whip indoors hears little. Try Optimise for the gain. |
| Distorted or clipping sound, a lot of false signals | The signal is too strong. Lower the gain (clear Auto and use the slider), or use Optimise. Switch RTL AGC off. |
| Too quiet | Raise Volume (up to 200 percent). Raise the gain if the amber hint says the signal is weak. Narrow the filter width for a weak signal. |
| The frequency is a little off, or DAB+ does not lock | Set the frequency correction: Settings > Receiver > Measure with DAB+ if you have a DAB+ station, after the stick has warmed up for 10 minutes. |
| The sound stops when the app is in the background | The bar "Sound paused. Still receiving." has a Resume button. |
| The receiver is busy | The receiver does one thing at a time. Press Stop in the receiver bar, or choose whether the app asks before switching in Settings > Receiver > One receiver. |
What Find on network does. It makes one bounded look at the networks your phone is on and lists the receivers that answer. It runs only when you tap it, it ends by itself, and it does not look at anything outside your own network.
Still stuck? Write to [email protected]. A diagnostic report from Settings helps, and it is yours to share or not.
12. Glossary
- AGC
- Automatic gain control. Keeps the volume even when a signal gets stronger or weaker. Fast, Medium and Slow set how quickly it reacts.
- Bias-T
- A 5 V supply sent up the antenna cable to power an LNA or an active antenna.
- CW
- Continuous wave: Morse code sent by switching a carrier on and off. You hear it as beeps.
- De-emphasis
- Broadcast FM boosts the high tones before it is sent. De-emphasis lowers them again at the receiver. It is 50 µs in Europe and 75 µs in the Americas.
- LNA
- Low-noise amplifier. A small amplifier next to the antenna that helps weak signals.
- NFM, WFM
- Narrow FM (a channel about 12.5 kHz wide, used for walkie-talkies, marine and amateur radio) and wide FM (about 180 kHz, broadcast radio).
- Notch
- A very narrow filter that removes one frequency, such as a whistle.
- ppm
- Parts per million. How much a stick's clock is off. Fix it with the frequency correction.
- RDS
- The data sent with a broadcast FM station: its name and a line of text.
- rtl_tcp
- A way to share an RTL-SDR over the network. A computer with a stick runs it; SDRSowa on your phone connects to it.
- SAM
- Synchronous AM. AM with a detector locked to the carrier, which sounds steadier when the signal fades.
- SNR
- Signal-to-noise ratio, in dB. How far the signal stands over the noise. More is better.
- Spectrum, waterfall
- The spectrum shows how strong signals are at each frequency. The waterfall shows the same over time, newest at the top.
- SSB (USB, LSB)
- Single sideband. A voice mode used by radio amateurs and on shortwave. USB is the upper sideband, LSB the lower one.
- Squelch
- Keeps the speaker quiet until a signal is strong enough.
- VFO
- Variable frequency oscillator. In the scanner, one VFO is one channel you hear. SDRSowa can hold up to 3 at the same time.