rtl_tcp SDR vs smartDF
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
rtl_tcp SDR
This app acts as a software-defined radio receiver for iOS devices, allowing you to listen to various radio signals and view RF spectrum data. It connects to external SDR peripherals via a network protocol, requiring a separate server setup.
- Listen to AM, FM, SSB, CW signals
- View RF spectrum and waterfall
- Connect to networked RTL-SDR peripherals
- Supports Airspy HF+, SDRPlay, LimeSDR Mini
- Direct connection to Hermes Lite 2
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An RTL-SDR Software Defined Radio receiver app for iOS devices. Listen to AM, FM, SSB and CW radio signals. View an RF spectrum and waterfall. Connect, via the rtl_tcp network protocol, to networked RTL-SDR USB peripherals. This app requires an external rtl_tcp server. iOS devices do not currently support the direct connection of USB peripherals such as an RTL-SDR. Thus, the use of this app requires network access to a server, such as a Raspberry Pi (or Mac), with an RTL-SDR unit plugged into its USB port, and running the rtl_tcp protocol at an TCP/IP network address accessible from your iOS device. This allows a Raspberry Pi (or Mac) to act, essentially, as the USB port adapter for your iOS device. The rtl_tcp SDR app can also connect to hfp_tcp for the Airspy HF+, rsp_tcp for SDRPlay devices, and lmm_tcp for the LimeSDR Mini; see GitHub for server source code. This app can also connect to a Hermes Lite 2 QRP transceiver directly, if it has a known IP address, or through an hl2_tcp server. No support is provided for installing any of the rtl_tcp or other tcp software needed to use this app (with a Raspberry Pi, or otherwise). Please do not download this app unless you are already familiar with Software Defined Radio, have an RTL-SDR or equivalent USB SDR peripheral, and have already installed and tested rtl_tcp on your Raspberry Pi, Mac, or other server. Note that this app requires a very high bandwidth network connection in order to receive streams of real-time RF samples from an RTL-SDR. It is recommended that your rtl_tcp server be on a wired connection rather than on the same WiFi as your iOS device.
smartDF
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iPadOS application designed in cooperation between certified developer Carlos Lago and Rhotheta International Inc - www.rhothetaint.com - for the remote control and monitoring of Rhotheta radio direction finders via Bluetooth (BLE) or Wi-Fi. A modern UI for direction finder (DF) products increases crew productivity and enhances mission awareness during search-and-rescue, law enforcement, and special missions. DF sensor data is conveniently displayed over maps with state-of-the-art graphics.
Screenshots
Verdict
The clearest difference is price: smartDF at Free against rtl_tcp SDR's $12.99. smartDF also leads on update cadence (weekly vs every 4 months). On ads, in-app purchases, device support and iOS requirement 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
smartDF is free to download; rtl_tcp SDR costs $12.99 up front. Neither carries in-app purchases, so what you see is what you pay.
rtl_tcp SDR ships an update every 4 months, smartDF weekly. The most recent releases landed on October 23, 2026 and October 25, 2026 respectively.
| Parameter | rtl_tcp SDR | smartDF |
|---|---|---|
| Price | $12.99 | Free — better |
| Rating | 3.9 (32 ratings) — better | — |
| Positive reviews | 40.0% of reviews | — |
| Number of ratings | 32 — better | — |
| Update frequency | Every 4 months | Weekly — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Paid | — |
| Devices | iPhone, iPad — better | iPad |
| Requires iOS | 16.6 | 15.4 — better |
| Further details — not scored | ||
| Size | 3 MB | 59 MB |
| Age rating | 4+ | 4+ |
| Developer | HotPaw Productions | Carlos Yordanis Lago Gonzalez |
In-app purchases
rtl_tcp SDR
No in-app purchases
smartDF
No in-app purchases









