Over on our forums poster hotpaw2 has released news about his new RTL-SDR app for iOS (iPhones/iPads). If we're not mistaken, this will be the first app that enables RTL-SDR usage on iOS. However, as iOS devices don't allow RTL-SDRs (or any arbitrary USB device) to connect directly to devices, you still need to use a Raspberry Pi or other network connected computing device as an rtl_tcp server. So the RTL-SDR does not plug directly into the iOS device. Currently he is looking for beta testers to help test a pre-release of the software. Hotpaw2 writes:
Hi. A first version of my iOS SDR app is nearing completion. So I'm interested finding a few users who would like to beta test a pre-release of the app, and provide some feedback. The beta test requirements are having a 64-bit iOS device (iPhone or iPad) running iOS 11.2.x or newer, having Apple's TestFlight app installed, having a Mac, PC, Raspberry Pi (or other Linux box) that already has rtl_tcp installed and ready to run. (And an RTL-SDR obviously.) The rtl_tcp server must be on a fast WiFi network reachable by your iOS device. Note that iOS TestFlight app distributions do have an expiration date.
iOS does not recognize arbitrary USB devices such as an RTL-SDR. This is even true when using Apple's Lightning Camera Connection kit to provide an iPhone with a wired USB port. So an adapter must be used. I use a headless Raspberry Pi 3 running rtl_tcp as the USB adapter to provide raw IQ samples from the RTL-SDR to the iOS app. A Raspberry Pi Zero W would also work. I then connect to the server either over WiFi, or via wired ethernet.
This iOS SDR app is fairly simple. I've been experimenting with developing low-level DSP code in Swift. So this SDR app was written from scratch in the Swift programming language. Because the app is targeted for the iOS App store, it uses none of the existing SDR C++ code base.
The app currently demodulates AM, N-FM, and mono W-FM. It also displays a spectrum and rudimentary waterfall, and allows one to swipe-to-tune. There are not a lot of controls, as screen real-estate on an iPhone is quite limited. But I can walk around the house and, from my iPhone, monitor if my RTL-SDR or AirSpy HF+ are picking up any interesting signals.
QRadioLink is a Linux and Android compatible radio app that can run on smartphones. It can be used to receive and transmit digital radio signals with a compatible SDR such as an RTL-SDR (RX only), or a LimeSDR Mini (TX and RX). The following video by Adrian M shows QRadioLink running on an Android phone with a LimeSDR Mini connected to it. An external battery pack is also connected to maintain power levels over a longer time.
In the video Adrian shows how this combination can be used as a fully portable radio transceiver. The video first shows him receiving broadcast FM, digital amateur radio voice (Codec2 & Opus is supported), narrowband FM and SSB signals. Later in the video he transmits a digital voice signal using the microphone on his Android phone. He notes that an external amplifier would still be needed if you wanted more transmission power.
Portable SDR transceiver: LimeSDR-mini, mobile phone and QRadioLink
Over on YouTube user Osama SH has uploaded a video briefly showing the steps needed to use an RTL-SDR dongle to sniff some SMS text messages and voice calls made from his own phone. This can be done if some encryption data is known about the phone sending the messages, so it cannot be used to listen in on any phone – just ones you have access to. In the video he uses Airprobe and Wireshark to initially sniff the data, and find the information needed to decode the text message. Once through the process he is able to recover the SMS message and some voice audio files.
Now a new software package called gr-gsm has been released on GitHub which seems to be a newer and improved version of Airprobe. The gr-gsm software is also much easier to install, uses the newer GNU Radio 3.7 and seems to decode the system data with much less trouble than Airprobe did. We will soon update our tutorial to use gr-gsm, but the instructions on the GitHub are already quite good. The author of gr-gsm also appears to be actively adding new features to the software as well. The video below shows gr-gsm in action.
Sniffing GSM data with gr-gsm and cheap RTL-SDR receivers
SDR Touch, the popular Android based software defined radio software for the RTL-SDR has been updated to version 2.0. This new version is a complete rewrite with many optimizations listed below.
100% rewritten from scratch
Improved reception sensitivity and quality
GUI overhaul (Landscape mode, more flexible)
16 bit audio
The author also writes that the rewrite allows for new features coming out in the future such as adjustable bandwidth, FFT size, plugins and a separate GUI for in-car use. SDR Touch is available from the Android Play store.
With its 100 kHz to 1.7 GHz receiving range, the XiOne has a similar tuning range to the standard RTL-SDR dongles when an upconverter or the direct sampling mod is used. What makes the XiOne different is that it will have a built in MIPS processor, an internal rechargeable battery for portability and it will connect directly through WiFi to a smart device. They are also developing SDR GUI software for mobile devices including decoders for things like ADS-B, AIS and NOAA Satellites.
The IndieGoGo backer price for a XiOne is $179 USD, but if you act fast there are 100 units available at the promotional price of $139 USD. At the moment they have a working prototype with completed firmware, portable Java based SDR GUI, iPhone demodulation software, a MacOS ADS-B receiver, an iPad AIS receiver and an iPad spectrum analyzer. The fundraiser is to help them begin serial production.
TD-LTE is a mobile phone standard acronym for Time Division Long Term Evolution. It is one of two variants of LTE technology, with the other being FD-LTE (Frequency Division LTE).
Over in China where TD-LTE is commonly used, Jiao Xianjun discovered that the current LTE-Cell-Scanner Linux program did not support TD-LTE, so he made a fork which does support TD-LTE. LTE-Cell-Scanner is a program which can decode LTE cell tower data which contains information like the cell ID, transmit frequency and transmit strength. With his modified LTE-Cell-Scanner, some MATLAB scripts he wrote and an RTL-SDR, Jiao was able to decode the cell information from 10 TD-LTE signals and 2 FD-LTE signals. He has uploaded a video showing this too.
TD-LTE, LTE FDD, scanning/demodulation results in Beijing, China
To use the app, you will need an Android device that supports USB OTG, which most Android devices on Android 4.0+ should support. You will also need a USB OTG cable, and an RTL-SDR dongle. You may want to consider a USB OTG cable that has a second port for external charging capabilities, as the RTL-SDR can drain the battery quickly.
The app is cheaply priced at under $2, so give it a try!