EZNEC is a popular antenna modelling program created by W7EL which is based on the "Numerical Electromagnetics Code" or NEC. With a NEC based antenna modelling program it is possible to design antennas by modelling their geometry and connections, and then simulating parameters like radiation pattern gain and VSWR. You can also determine the effects of height, roof angles, nearby objects and more.
Originally the pricing was $99 for EZNEC, $149 for EZNEC+, $525 for EZNEC Pro/2 and $675 for EZNEC Pro/4. W7EL is retiring and from Jan 1 2022 EZNEC Pro/2 and EZNEC+ will be made free, and EZNEC Pro/4 will be discontinued. The source code will not be released, and no support will be provided.
If you're after a free NEC based antenna modeler today, 4NEC2 is a similar program that is already free. There is also the recently released and more modern CENOS, which is free for hobbyist use.
Since it's announcement in early 2016 we've posted many times about the KiwiSDR, a 14-bit wideband RX only HF software defined radio created by John Seamons (ZL/KF6VO). The KiwiSDR has up to 32 MHz of bandwidth, so it can receive the entire 10 kHz - 30 MHz VLF/LF/MW/HF spectrum all at once.
Compared to most other SDRs the KiwiSDR is a little different as it is designed to be used as a public web based SDR, meaning that KiwiSDR owners can optionally share their KiwiSDR online with anyone who wants to connect to it. The public functionality allows for some interesting distributed applications, such as TDoA direction finding, which allows users to pinpoint the location of unknown HF transmissions such as numbers stations.
In order to implement this online capability, the KiwiSDR runs custom open source software on a Beaglebone single board computer which connects to your home network. Recently there has been vocal concern about a security flaw in the software which could allow hackers to access the KiwiSDR. The flaw stems from the fact that the KiwiSDR has 'backdoor' remote admin access that allows the KiwiSDR creator to log in to the device and troubleshoot or make configuration changes if required. This backdoor has been public knowledge in the KiwiSDR forums since 2017, although not advertised and explicit consent to have it active and used was not required.
Interesting post on the KiwiSDR forums. Seems to imply the KiwiSDR author has remote access to all KiwiSDRs? Post has since been modified to remove the last paragraph and the thread locked :-/ https://t.co/cAi5dS7J49pic.twitter.com/elqSsaUJ65
The intent of the backdoor is of course not malicious, instead rather intended as an easy way to help the creator help customers with configuration problems. However, as KiwiSDR owner Mark Jessop notes, the KiwiSDR operates in HTTP only, sending the admin master password in the clear. And as KiwiSDR owner and security researcher @xssfox demonstrates, the admin page gives full root console access to the Beaglebone. These flaws could allow a malicious party to take over the Beaglebone, install any software and perhaps work their way onto other networked devices. Another tweet from xssfox implies that the password hashes are crackable, allowing the main admin password to be easily revealed.
Quick video showing how the backdoor on the kiwisdr works.
I've also tested that touch /root/kiwi.config/opt.no_console mitigates the issue
Creator John Seamons has already released a patch to disable the admin access, and as of the time of this article 540 out of 600 public KiwiSDRs have already been auto-updated. Owners of KiwiSDR clones should seek out updates from the cloner.
It is clear that the KiwiSDR is a passion project from John who has dedicated much of his time and energy to consistently improving the technical RF engineering side of the device and software. However we live in an age where malicious hacking of devices is becoming more common, so anyone releasing products and software that network with the internet should be reminded that they have a responsibility to also dedicate time to ensuring security.
John has reached out to us in advance and noted that he currently cannot yet comment publicly on this topic due to legal advice.
Over on YouTube we've seen a good video from channel Ham Radio DX where presenter Hayden shows how to use an RTL-SDR to receive slow scan television (SSTV) images from the International Space Station (ISS). Often the ISS will transmit SSTV images down to earth on the VHF 2 meter bands as part of an event. With an RTL-SDR and simple antenna it's possible to receive those images.
In the video Hayden discusses the SSTV transmission, and demonstrates some SSTV decoding happening in real time as the ISS passes over his location. If you're looking to get started in ISS SSTV reception, this is a good video to get an idea of what's involved. He finishes the video with some useful tips for reception.
Using a RTL SDR Dongle to receive pictures from the ISS! | Software Defined Radio
The company ebcTech who makes AIS Share for Android has recently come out with a new app which is an Android App version of Dump1090. Dump1090 is a popular command line based ADS-B decoder for RTL-SDR dongles which allows you to receive and plot the locations of nearby aircraft on a map.
The app directly accesses the RTL-SDR via a USB OTG connection and provides a list of aircraft with planespotters.net image lookup, and a Google map display. The app is free however there is a message limit on received aircraft which can be unlocked via a low cost in-app purchase.
The author also wrote in and wanted to make a note about a special feature "In the app you can add Airport layers – This consist now 4480 Airports – most of them with corresponding homepage address / or Wikipedia link."
In Rob's latest episode of his excellent aviation communications series on his Frugal Radio YouTube channel he shows how to decode aircraft HF ACARS (HFDL) using a software defined radio. HFDL is short for "high frequency data link", and is a method aircraft use for sending text and data communications to ground stations. It is an alternative to VHF or satellite ACARS communications methods.
In the video he shows how he's been able to receive HFDL from all over the world using a simple HF dipole antenna and an Airspy HF+ Discovery. He goes on to show how to find HFDL signals, and how to decode signals using SDR# and the PC-HFDL software. Finally he shows examples of aircraft received, and how to interpret some of the information being received, including location information.
How to decode HF ACARS (HFDL) free with your SDR - Monitoring Aviation Communications Episode 8
Thank you to Antonio from the Polytechnic University of Madrid, Department of Photonic Technology and Bioengineering for writing in and sharing with us his teams latest research titled "Dual-Comb Spectrometer Based on Gain-Switched Semiconductor Lasers and a Low-Cost Software-Defined Radio". The research involves the use of an RTL-SDR Blog V3 dongle in place of an expensive digital oscilloscope for measuring the output of a dual-comb spectrometer. The abstract of the paper reads as follows:
Dual-comb spectroscopy has become a topic of growing interest in recent years due to the advantages it offers in terms of frequency resolution, accuracy, acquisition speed, and signal-to-noise ratio, with respect to other existing spectroscopic techniques. In addition, its characteristic of mapping the optical frequencies into radio-frequency ranges opens up the possibility of using non-demanding digitizers.
In this paper, we show that a low-cost software defined radio platform can be used as a receiver to obtain such signals accurately using a dual-comb spectrometer based on gain-switched semiconductor lasers.
We compare its performance with that of a real-time digital oscilloscope, finding similar results for both digitizers. We measure an absorption line of a H13C14N cell and obtain that for an integration time of 1 s, the deviation obtained between the experimental data and the Voigt profile fitted to these data is around 0.97% using the low-cost digitizer while it is around 0.84% when using the high-end digitizer.
The use of both technologies, semiconductor lasers and low-cost software defined radio platforms, can pave the way towards the development of cost-efficient dual-comb spectrometers.
Back at home he pulled up the FCC filing for the device, which unveiled that it is OOK-PWM modulated, and operates at 433.92 MHz. The rest of the filing also had information noting that the implant transmits a 59-bit data packet every 12 seconds, and contained a nice breakdown of the packet structure, making it easy for decoding.
With all the information about the device's wireless transmissions now known, James grabbed his RTL-SDR and fired up SDR# to confirm that the signal was indeed transmitting every 12 seconds at 433.92 MHz. Next he was able to decode the data from the device by inputting the protocol information learned from the FCC filing into an rtl_433 command line string.
After a bit of further work James discovered that the pH data was actually two readings in one data string. At this stage he finally had the pH reading, however it was represented as an 8-bit ADC reading with a value between 0 to 255. James plotted the relationship between the 8-bit raw ADC reading, and the pH value shown on the official Medtronic receiver. With this he was able to determine a linear relationship between the ADC reading and real pH reading, but notes that there may be a more accurate calibration curve required for actual medical use.
Decoding pH readings from a stomach implant with an RTL-SDR
Thank you to Viol Tailor for submitting news about the release of his general purpose multimode software defined radio receiver program for Windows called "uSDR" or "microSDR". Viol writes that uSDR is designed as a lightweight binary with a simple and compact user interface and highly optimized DSP to minimize CPU, hence the "micro" part of the name.
The software is compatible with RTL-SDR, Airspy, BladeRF, HackRF and LimeSDR radios. It has features including demodulation, base band and pass band recording, playback, and spectrum and waterfall visualizations.
uSDR aka microSDR. A lightweight SDR receiver program from Windows.
