iSDR vs RST Decoder
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
iSDR
This app allows experimenters and amateur radio enthusiasts to build a portable software-defined radio receiver using their iOS device. It processes radio signals using the device's processor and offers various display and filtering modes. Additional hardware is required for live signal reception.
- Six receive mode settings (USB, LSB, CW, AM, FM, Binaural)
- Selectable bandwidth settings
- 120 dB dynamic range signal strength meter
- Three AGC settings (fast, slow, off)
- Spectrum, Waterfall, and Oscilloscope display modes
- Supports downloaded audio-format spectrum files via iTunes
- Embed center frequency in file names for automatic display
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PLEASE READ THE ENTIRE DESCRIPTION BEFORE PURCHASING. iSDR is the first and only software-defined radio application compatible with the Apple iPhone®, iPod touch® and iPad™. iSDR is for experimenters and amateur radio enthusiasts looking to construct a truly portable software-defined radio receiver. Additional hardware is required to receive live signals. Currently, iOS devices will not work with RTL-SDR USB dongles, and they are not supported by iSDR. PLEASE NOTE: Receiving live on-air signals using iSDR requires purchasing or constructing a "quadrature sampling detector (QSD)" RF front-end device, and connecting it between an antenna and the microphone input jack. Alternatively, iSDR can be used to implement a panadapter for use with a compatible radio receiver. Without a QSD RF front-end or a connected radio, iSDR will only play I/Q recordings of actual radio signals. Additional recordings can be loaded into the app using iTunes file sharing - some recordings are available free to download from the Internet. Visit the support web site for more information. iSDR includes a sample I/Q recording featuring 30 seconds of a ham radio contest. This is for demonstration purposes only. It is not meant to fool you! It is to allow you to experience how the app works without having to do anything yourself: just turn it on. You can download and play your own files if you like. Please see the support page for details. AND PLEASE contact us directly if you experience any issues with using this app. We will respond promptly when provided with details. When iSDR is used to receive live radio signals, receiver performance will depend largely on the quadrature sampling detector and antenna that you use. iSDR is a software-defined receiver application for use on mobile handset devices and iPad. Despite its extreme portability, the app utilizes the same digital signal processing techniques found in PC-based SDR receivers. It does frequency domain filtering using a theoretical "brick wall" sinc filter algorithm to provide steep and deep bandpass filtering. iSDR doesn't utilize any DSP hardware but instead uses the iOS device's processor to implement DSP algorithms. Features o Six receive mode settings: USB, LSB, CW, AM, FM* and Binaural. o Selectable bandwidth settings for each mode. o Signal strength meter covering 120 dB of dynamic range with peak and average power indication. o Three AGC settings: fast, slow, and off. o Three display modes: Spectrum, Waterfall and Oscilloscope. o File sharing** supports downloaded audio-format spectrum files synced using iTunes. o Most PCM file formats are supported, including .wav and .caf. o Embed the center frequency in your file names and iSDR will automatically display the correct frequency! o Tune quickly using a single touch to the display screen, or tune precisely using the rainbow tune bar. o Change radio settings with a simple double-tap action to the red cursor, mode text, AGC indicator or signal grid! o Up to 44.1 kHz of available spectrum bandwidth. o Dimmable semi-log or linear spectrum grid (native Settings app only). o Adjustable CW offset (native Settings app only). o Monaural microphone input automatically adjusts the display to 22 kHz bandwidth. o Automatically detects if external audio is available for receiving live signals (menu selectable). o Reverse I/Q stereo input logic (menu selectable). *FM mode is not supported for monaural signals, and will not appear as a mode selection unless stereo audio (live or recorded) is available. Narrowband FM only: 16 kHz or 11.2 kHz bandwidth. Please contact Digital Confections with your questions and suggestions!
RST Decoder
This application decodes Morse code from your microphone, acting as a practice tool to verify your keying accuracy. It offers advanced features like BPF and FFT decoders with automatic frequency and gain control, allowing for fine-tuning of reception parameters.
- Microphone Morse code decoding
- Morse practice and keying check
- BPF and FFT decoder options
- Auto Frequency Detector (AFD)
- Auto Gain Control (AGC)
- Real-time CW signal display
- Input signal recording/playback
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This is an App that decodes Morse code input from the microphone. It is a Morse practice App that you can use to check if you are keying the correct code. Signals with good S/N can be decoded correctly, but signals with bad S/N cannot be decoded correctly. Also, the performance will be degraded for extremely slow or fast signals. Usually about 5 to 10 characters are required for speed synchronization of Morse Code. Adjust the input signal so that the peak value changes from level 6 to level 7. Make fine adjustments to each parameter according to the reception status. [Additional Functions] -In addition to the decoder using BPF, a new decoder using FFT has been added so that it can be switched according to the usage. -AFD (Auto Frequency Detector) function has been added to the decoder using BPF, and BPF can be set automatically by pressing the AFD button. -The decoder using FFT automatically follows the strongest signal in the band by AFD (Auto Frequency Detector) and AGC (Auto Gain Control). You can also hold the AFD / AGC parameters by pressing the Lock button. * There will be a time lag of about 1 to 2 seconds for AFD tracking. [Control parameters] 1. Audio Input Level 2.BPF ON/OFF 3.BPF of Center Frequency 4.BPF of Band Width 5.CW Speed Control ON/OFF 6.CW Speed Control Low, Mid1, Mid2 or High 7.Delete All Decoded Text 8.Realtime CW Signal Display 9.Input signal recording / playback function *Japanese/KANA text is not supported. [Note] Since the signal after BPF is output to the audio output, it can also be used as an AF-CW filter. [URL of this App working example video] https://youtu.be/Pwp7W4m-m34
Screenshots
Verdict
The clearest difference is price: RST Decoder at Free against iSDR's $0.99. RST Decoder also leads on rating (5.0 vs 2.5) and in-app purchases (none vs 1). iSDR's advantage is ads (none vs shown) and device support (3 vs 1). On ratings volume and update cadence there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
RST Decoder is free to download; iSDR costs $0.99 up front. iSDR sells 1 one-off in-app purchase. RST Decoder asks for nothing beyond the download.
RST Decoder holds the better App Store score, 5.0 against 2.5. Both are backed by a comparable volume of ratings — 11 and 7 respectively. Written reviews point the same way: 52% of iSDR's written reviews are positive against 67% of RST Decoder's.
iSDR ships an update every 3 months, RST Decoder every 2 months. The most recent releases landed on October 4, 2026 and October 6, 2026 respectively.
| Parameter | iSDR | RST Decoder |
|---|---|---|
| Price | $0.99 | Free — better |
| Rating | 2.5 (11 ratings) | 5.0 (7 ratings) — better |
| Positive reviews | 51.7% of reviews | 66.7% of reviews — better |
| Number of ratings | 11 — better | 7 |
| Update frequency | Every 3 months | Every 2 months — better |
| Ads | No — better | Yes |
| In-app purchases | Yes | No — better |
| Monetization | Paid | Ad-supported — better |
| Devices | iPhone, iPad, iPod — better | iPhone |
| Requires iOS | 9.0 — better | 17.0 |
| Further details — not scored | ||
| Size | 36 MB | 6 MB |
| Age rating | 4+ | 17+ |
| Developer | Digital Confections LLC | koji kamogawa |
Customer experience
iSDR
RST Decoder
In-app purchases
iSDR
- Wi-Fi Radio ControlFree
RST Decoder
No in-app purchases








