Briefly, their build consists of a horn antenna and reflector designed for the 1,420.4 MHz Hydrogen line frequency. The horn is built out of a few pieces of lumbar, metallic house wall insulation sheets and aluminum tape. The feed is made from a tin can and piece of wire. In terms of radio hardware, they used an Airspy SDR, GPIO labs Hydrogen Line Filter + LNA, and 2x Uputronics Wide band preamps, and a Minicircuits VBF-1445+ filter. For software processing, they used a GNU Radio flowgraph to integrate and record the spectrum.
The results show that they were able to achieve a good hydrogen line peak detection, and they were able to measure the galactic rotation curve doppler shift, and tangent points which prove that we do in fact live in a spiral galaxy.
The Finished Hydrogen Line SDR Based Horn Radio Telescope Antenna
Over the last several months we've been working on a versatile active L-band patch antenna that can cover Inmarsat to Iridium satellite frequencies. That antenna is now almost ready, and should be able to ship out from our Chinese storage warehouse by week 1 or 2 of October NOTE: Due to an unfortunate Typhoon near the factory in Taiwan, and the Chinese National Week long holidays and Taiwan National day we are expecting them to ship out in week 3 or 4 of October now. Apologies for the delays. No other components like filters or amplifiers are required to be able to use this antenna, as it is an all in one system.
The expected price will be US$39.95, but right now we're releasing it for a discounted PREORDER price of US$34.95 incl. free shipping.
Preorder sale has ended. Please see our store to order.
Your preorder will ship out as soon as it's stocked in the warehouse in China. If you prefer to wait we'll also have this product on Amazon (at retail $39.95) about 2-3 weeks after it is stocked in our Chinese warehouse.
The antenna is based on the active (low noise amplified with built in filter) ceramic patch design that was used by Othernet (aka Outernet), back when they had their L-band service active. We've asked them to modify the antenna to cover a wider range of frequencies, and include an enclosure that allows for easier mounting.
The antenna is 3.3 - 5V bias tee powered, so you will need a bias tee capable RTL-SDR like our RTL-SDR Blog V3, or a 5V external bias tee. It draws about 20-30mA of current, so it is compatible with other SDRs like the SDRplay, HackRF and Airspy too.
With this antenna we've paid close attention to the mounting solutions. One major difficulty with these patch antennas is finding a convenient place to mount them. The patch is designed with a built in 1/4" camera screw hole, so any standard camera mount can be used. In the kit we're including a window suction cup, a flexible tripod and 2 meters of RG174 cabling to help with mounting. Your own longer coax cabling can be used, however we'd recommend using lower loss cabling like RG59/58 or RG6 for anything longer than 3 meters.
The patch is also fully enclosed in an IP67 weather proof plastic case, so it can be kept mounted outdoors in the rain.
The RTL-SDR Blog L-Band Satellite Patch Antenna SetWays to mount the patch antenna
Performance
With the patch receiving AERO, STD-C and GPS should be a breeze. Simply point up at the sky, or towards the Inmarsat antenna, apply bias tee power and receive. Below are some sample screenshots showing reception.
The patch is designed to be used with a 1m+ length of coax cable. It may perform poorly if the RTL-SDR is placed right at the antenna due to interference.
If receiving Inmarsat, the patch antenna should ideally be angled to face the satellite.
Rotate the patch until the signal strength is maximized. Rotating the patch optimizes the polarization of the antenna for the satellite and your location. NOTE: Using the wrong orientation could result in 20 dB attenuation, so please do experiment with the rotation.
You can also use the patch on a flat surface for Inmarsat (and rotate for best reception), but signal strength may be a little reduced. Depending on your location and the satellites elevation it should still be sufficient for decoding.
For receiving Iridium and GPS signals you can use the antenna flat, pointing straight up towards the sky. Try to get it seeing a clear view of the sky horizon to horizon to maximize the satellites that it can see.
If you happen to have a very marginal signal, you can clamp on a flat sheet of metal behind the patch antenna for improved performance.
AERO C-Channel: C-Channel transmissions are at 1647-1652 MHz which are outside of the advertised range of this antenna. However, the filter cut off is not that sharp, and you may be able to get results, although we cannot guarantee this. (If you want to test this for us and can demonstrate that you can receive C-Channel already, please contact us at [email protected] for a sample)
To keep them away from humid air Scott uses "PrintDry" plastic vacuum canisters. Unfortunately he found that the vacuum sealing system wasn't perfect, and that some canisters would lose their vacuum after a few days. In order to ensure that the canisters were properly sealed he decided to add some active monitoring with pressure and humidity sensors and a wireless transmitter.
His monitoring system consists of a cheap 315 MHz ISM band transmitter, ATTINY85 microcontroller and pressure + humidity sensor. To receive and monitor the data he uses an RTL-SDR that runs the rtl_433 software, which is a program that is capable of decoding many different types of wireless ISM band sensors.
DIY Wireless Temp/Humid/Pressure sensors for measuring vacuum sealed 3d printed filament containers
Canadian based researchers from the "Open Privacy Research Society" recently rang the alarm on Vancouver based hospitals who have been broadcasting patient data in the clear over wireless pagers for several years. These days almost all radio enthusiasts know that with a cheap RTL-SDR, or any other radio, it is possible to receive pager signals, and decode them using a program called PDW. Pager signals are completely unencrypted, so anyone can read the messages being sent, and they often contain sensitive pager data.
Open Privacy staff disclosed their findings in 2018, but after no action was taken for over a year they took their findings to a journalist.
Encryption is available for pagers, but upgrading the network and pagers to support it can be costly. Pagers are also becoming less common in the age of mobile phones, but they are still commonly used in hospitals in some countries due to their higher reliability and range.
In the past we've seen several similar stories, such as this previous post where patient data was being exposed over the pager network in Kansas City, USA. There was also an art installation in New York called Holypager, that continuously printed out all pager messages that were received with a HackRF for gallery patrons to read.
HolyPager Art Installation. HackRF One, Antenna and Raspberry Pi seen under the shelf.
Over on YouTube user JellyImages has uploaded a video demonstrating his Windows based ARESrcvr software. ARES is a railway control communications protocol used by some trains in the USA. His code connects to an RTL-SDR dongle, and demodulates the ARES protocol, providing decoded packets to ATSCMon via UDP on localhost.
ATSCMon allows you to view train telemetry data, and see on a rail map where that control indication came from. It appears that ATSCMon actually already supports ARES decoding via audio piping, but the decoder by JellyImages is a cleaner solution that doesn't require audio piping. In the past we've posted about one other YouTube user whose uploaded videos on using ATSCMon to monitor trains [Post 1][Post 2].
JellyImages also notes that his software only supports the ARES protocol which is used mostly around former Burlington Northern (BN) territory in the USA.
Over on YouTube Black Hills Information Security (aka Paul Clark) has uploaded a one hour long presentation that shows how to use a software defined radio to reverse engineer digital signals using GNU Radio.
One of the most common uses of Software Defined Radio in the InfoSec world is to take apart a radio signal and extract its underlying digital data. The resulting information is often used to build a transmitter that can compromise the original system. In this webcast, you'll walk through a live demo that illustrates the basic steps in the RF reverse engineering process, including:
- tuning - demodulation - decoding - determining bit function - building your own transmitter - and much, much more!
The NanoVNA is an open source VNA project by @edy555 and ttrftech that has recently become extremely affordable at less than US$50 for a fully assembled unit thanks to Chinese manufacturing (or a little more if you order it via Amazon).
Ohan Smit had recently been playing with the NanoVNA and came across a software package from Rune B. Broberg (5Q5R) called NanoVNASaver. NanoVNASaver is an open source program that can be used to read and plot data from the NanoVNA. It has some nice features like the ability to display multiple charts, increase the resolution up to 10k points, measure cable length via TDR calculations, save Touchstone files and more.
Testing our RTL-SDR.COM BCFM Bandstop filter with a NanoVNA and the NanoVNASaver Software.
Later in the same post Ohan also includes an update about his experiments with some new experimental NanoVNA firmware that extends the maximum frequency range from the previous maximum of 900 MHz up to 1500 MHz. Results show that while it can work up to 1500 MHz, accuracy rapidly degrades above 900 MHz.
Recently Chinese manufacturers have begun producing a low cost wide band (100 kHz - 30 MHz) magnetic loop HF antenna known as the MLA-30. The loop can be found on eBay for under US$45 with free shipping. In the past wide band HF loop antennas have not been cheap, normally costing $300+ dollars from manufacturers like Wellbrook.
RF signals are electromagnetic waves that consist of an electric and magnetic component. A magnetic loop antenna mostly receives the magnetic portion of the wave. This is useful as most unwanted interference from modern electronic devices is generated in the electric component only. So, a magnetic loop antenna may be preferable in city and suburban environments over other antennas like wires and miniwhips. Magnetic loops are also directional, and can be rotated to avoid interference.
One of the biggest costs to a magnetic loop antenna is the shipping, because a large hula hoop sized piece of metal needs to be sent. The MLA-30 cuts costs on shipping by providing a folded up thin loop wire and no physical support for the loop. You are expected to provide your own support, or simply hang the loop wire on something. If you like you can also replace the included loop wire with a larger loop.
The MLA-30 comes with 10m of RG174 coax, is bias tee powered, and comes as a set with a bias tee injector that is powered over 5V USB. We tested our own unit with the RTL-SDR Blog V3, Airspy and SDRplay bias tee's and found that they all worked well instead of the included bias tee. So if you have one of those SDRs using the loop is as simple and neat as plugging it in and turning on the bias tee.
In terms of build quality, the unit is sturdy and the PCB is fully potted and protected against rain/weather. It is yet to be seen how the external screw terminals holding on the loop will age over a longer period of time however.
So how does the very cheap MLA-30 compare to higher end magnetic loop antennas? Below are some reviews by various hams and SWLs. The general consensus is that it works well for the price, but as you'd expect, falters on handling very strong signals and produces a higher noise floor compared to the more expensive loops, especially in the higher HF bands. But overall we'd say that it's probably still better than using a miniwhip, especially in suburban/city environments, and is probably the best compact HF antenna that you can get on a budget.
What's included in the MLA-30 set. Photo from David Day's Review.
MLA-30 Magnetic Loop Antenna Review and Comparison by David Day (N1DAY)
In this review David compares the MLA-30 against a 30-ft ground loop and a Wellbrook ALA1530-LF. His results show that while the loop is capable of receiving the same signals that the two comparison loops can, the SNR is much lower. He also notes that the much thinner loop wire used on the MLA-30 seems to result in a much deeper null, and that IMD was a problem for him.
Inside the MLA-30 Active Loop Antenna by Matt (M0LMK)
This post is a complete teardown of the antenna. As the PCB is fully potted Matt had to boil down the epoxy in order to get to the actual PCB. He notes that the PCB is a simple single amplifier design with the exposed pot working as a gain control.
Cheap Chinese Magnetic Loop Antenna (MegaLoop aka MAGALoop) MLA-30 by John
First hour battle of the antennas W6LVP loop VS MLA 30 loop test by OfficialSWLchannel
This is a YouTube video where OfficialSWLchannel compares his MLA-30 against a W6LVP loop. He notes that his initial testing shows that the MLA-30 performs as well as the W6LVP loop.
First hour battle of the antennas W6LVP loop VS MLA 30 loop test
MLA-30 Loop vs 80M EFHW by Matthew Payne
In this YouTube video Matthew compares his MLA-30 against a 80M end fed halfwave antenna with an SDRplay RSP1a.
MLA-30 Magnetic Loop Modifications by Scanner and Sdr Radio
In this video the Scanner and Sdr Radio YouTube channel uses an RSPduo to compare the MLA-30 against a Wellbrook loop. His results show that the MLA-30 definitely has a higher noise floor compared to the Wellbrook, but still receives signals decently although chasing weak signals it's not good enough. He also shows how to improve the MLA-30 by replacing the cheap coax that it comes with, noting that the modification reduced his noise.
