Category: Antennas

Job’s Radio Telescope: Hydrogen Line Northern Sky Survey with RTL-SDR

We've posted about Job Geheniau's RTL-SDR radio telescope a few times in the past [1] [2] [3], and every time his results improve. This time is no exception as he's created his highest resolution radio image of the Milky Way to date. We have uploaded his PDF file explaining the project here.

Job used the same hardware as his previous measurements, a 1.5 meter dish, with 2x LNA's, a band pass filter and an RTL-SDR. Over 72 days he used the drift scan technique to collect data in 5 degree increments. The result is a map of our Milky Way galaxy at the neutral Hydrogen frequency of 1420.405 MHz.

JRT - Northern sky Hydrogen Line Survey with RTL-SDR

This image is quite comparable to an image shown in a previous post which was created by Marcus Leech from CCERA who used a 1.8m dish and Airspy.

If you're interested in exploring our Galaxy with an RTL-SDR via Hydrogen Line reception, we have a simple tutorial available here. The ideas presented in the tutorial could be adapted to create an image similar to the above, although with lower resolution.

JR Magnetics Small Ultra Wide Band 750 MHz to 6 GHz Antenna for SDRs on Kickstarter

John from JR Magnetics has written in and wanted to share his Kickstarter for a US$50 ultra wide band antenna that he has designed. The size is a just little bit bigger than two credit cards and the advertised coverage is from 750 MHz up to 6 GHz with a VSWR of less than 2.0.

John's Kickstarter text reads below:

Flat Ultra Wide Band Antenna Suitable for SDR


I was never satisfied with the commercially available wide band antennas.  They were all too large or did not have suitable VSWR over the frequency range generally required by SDRs.  I read many research papers and ultimately made a omni-directional ultra wide band antenna, but it was too expensive for most people.  Details regarding that antenna can be found at

However,  a bi-directional antenna was good enough for most people, so I have made a flat one.  The antenna I ended up with is 5 inches by 4 inches and about 3 mm thick with an SMA connector.  It is quite definitely not a square patch antenna, which usually has a narrow bandwidth.

This antenna has a VSWR measured to be under 2.00 from around 750 MHz to over 3 GHz.  It simulates to have a VSWR under 2.00 out to over 6 Ghz.  This is enough for most of the available SDRs.  It works very well with WiFi, Bluetooth, Zigbee and other systems within the bandwidth.

Typical Directional Log Antenna

Existing Antennas

The log antenna, Figure 2, has a wide bandwidth, but it is specified as having ranges, because the VSWR rises over 2.00 several times over that range.  The antenna measure sover 40 centimeters long, which is problem for me in a laboratory setting.  It is too large to fit anywhere and wants to be permanently fixed to a pole or something like that.

The other antenna I have is a discone type device, Figure 3.  It is huge.  There is not practical for it to fit on a lab bench around various RF devices.  It is measures around 28 centimeters at its base.  It needs to be elevated above any ground planes, which complicates a laboratory environment with metal bench tops.  I have it sitting on a shelf above the computer monitors on the opposite side of the room away from the lab bench.  This does not work well when I am trying to deal with wireless devices connected to USB hubs on the bench with short range features.

Discone Type Wide Band Antenna

Figure 4 shows the Flat Antenna next to the Log Antenna for a size comparison that illustrates just how much space saving there is with this new device.  This is no small feat.  This Flat Antenna is useful around all manner of RF devices on the bench without causing space issues, getting in the way of instruments and couples well with all of the wireless devices I am using.  It is small enough with a convenient shape for moving it around and keeping it above a metal bench top.  It only needs to be a few centimeters above any ground planes when perpendicular, not horizonal.

Due to its size and shape, near field problems have not been a problem, as with the other antennas.  The antenna is quite directional, which is not much of a problem, since the RF bounces around all over the place.  A Faraday shield is the only way to keep this device from picking out everything in the vicinity.  The neighbors IoT devices create mountains of RF clutter.  This antenna picks up all of it.  If you only want restricted bandwidths, band pass and reject filters can be used.  The load impedance is 50 Ohms across the band making an excellent match for all of the filters I have here.

Our Flat Antenna Size Comparison with the Log Antenna


Figure 5 shows the VSWR as measured by the NanoVNA Version 2.  It only goes out to 3 Ghz.  The device must be calibrated before use, or you will get extraneous results.  I am told the VSWR never goes above 2.00 until after 6 GHz.  This is a remarkable antenna.  I never found anything comparable to it on the Internet.

It can be used for all wireless and SDR applications normally within the 750 MHz to 6 GHz bandwidth.  This is not guess work or speculation.  The network analyzer shows the response clearly.

The antenna is 5 inches long by 4 inches wide by roughly 3 mm thick, not counting the SMA connector.

VSWR of Our Flat Antenna

What You Get

You get one (1) antenna, as shown in Figure 1, for each US$50.  You cannot do this yourself for that price.  Your time alone is worth more than that after you do the calculations, simulations and prototyping.  You also would have to deal with fab shops to get this done correctly, which is not always convenient for many people.

In other words, this is a remarkable Ultra Wide Band Antenna at a remarkable price.


This has already been done.  I have a Masters Degree in RF Engineering.  I also have all of the simulation tools that are not available to most people, with the exception of some university students.


I have sources that I use all the time.  I just put this one into the queue.  We also have a minimum order, which is why we Crowd Fund this operation.


Once in the queue, it takes about two (2) weeks.  After that, we are only concerned with delivery time.  We intend to use ordinaty Postal Service mail, to keep the cost down, so time of delivery may vary depending upon the destination.

Risks and challenges

We already have laboratory results, so there is nothing to risk in performance. The only other thing that could be troublesome is the lead time by the vendor that manufactures the main component or any delays caused by the Postal Service.

AirNav 20% Off ADS-B Hardware Black Friday/Cyber Monday

AirNav is the company behind, a flight data aggregation service similar to sites like and RTL-SDR hardware is typically used to receive ADS-B, and like other providers AirNav have their own custom ADS-B optimized RTL-SDR unit. In addition they sell RTL-SDR's optimized for UAT 978 MHz and the VHF Airband. They also have a range of ADS-B/UAT/VHF airband outdoor antennas as well as filters.

Currently their products are discounted by 20% for Black Friday/Cyber Monday sales. The discount is available on Amazon, as well as directly from their store with coupon GET20.

Searching For Extraterrestrial Intelligence (SETI) with a HackRF

The Search for Extraterrestrial Intelligence (SETI) is an ongoing project that aims to detect radio signals originating from intelligent species somewhere in the universe. Recently Alberto Caballero, a SETI researcher has been proposing a distributed search (project pdf document) with amateur and/or professional radio telescopes. The idea is that multiple stations around the world would monitor a single star for a period of time in order to collect data 24/7. To participate the requirements are a dish 2.1 meters or larger, a motorized mount, and a feed, LNA and radio system able to receive 1 - 4.5 GHz.

An example of a SETI station can be found at SETI Net. Here the owner has a 3M dish on a rotor connected to a HackRF. An LNA and band pass filter are also used at the feed end. SDR Console or SDR# is used to monitor a specific frequency, and the audio is sent into a special automatic SETI analysis program as well as spectrum analysis software. If an interesting signal is detected the software notifies the user, then further analysis can be undertaken.

If you have a suitable radio telescope available and want to participate, you can contact the SETI project via their contact form.

SETI Net Block Diagram

FengYun-2H/G Geostationary Weather Satellite Now Decodable with 120cm Dish (Europe to Australia Coverage)

Hot on the heels of the GOES-13 weather satellite decoder that we posted about a few days ago, @aang254 has just released a new RTL-SDR compatible decoder for the FengYun-2H, 2G and possibly 2E geostationary weather satellites.

The FengYun-2 line of weather satellites are the Chinese equivalents to GOES, and they are positioned to cover parts of Europe, Africa, the Middle East, Asia, Russia, and Australia. So this is another geostationary weather satellite now available to Europeans which broadcasts in the L-Band at 1687.5 MHz. And unlike the weaker GOES-13 L-Band downlink, the FengYun-2 downlink is much stronger which means that reception with a 120cm satellite dish should be possible. We note that it has not yet been confirmed if the typical 90-100 cm WiFi dishes used with GOES-16 and 17 will be big enough to work. @aang254 writes:

Yesterday I successfully decoded the S-VISSR downlink from FengYun-2H thanks to a recording by @MartanBlaho. It is stronger than PDR on EWS-G1 (see Zbychu's signal meaning it should (untested) be doable with a 120cm (or smaller but no confirmation again) dish instead of 180cm.

It covers parts of Europe, Russia and down to Australia. FY-2G and FY-2E (no confirmation for this one yet) are also decodable in the same way. I released an early decoder, that currently is not suitable for automated setups but allows getting images already. A later version (that should come soon-ish) will allow live decoding / autonomous setups in a similar fashion to other satellites.

Also, the res is 2km/px on VIS and 8km/px on IR, so half that of GOES-13 with similar-ish coverage (Europe is less visible though).

(also forgot to say but the bandwidth is under 2Mhz, allowing a rtlsdr to be used)

FengYun 2H (Left) / 2G (Right) Coverage
FengYun-2H Image Courtesy of @ZSztanga and inverted by @petermeteor

Video Tutorial on Debugging RF Emissions on a Circuit Board with an RTL-SDR

Over on the Hackaday YouTube channel a video by Alex Whittemore has been uploaded showing how to do some basic RF emissions debugging. When creating electronic products it's important to ensure that there is no unintentional RF leakage in excess of emissions standards, and there is often a need to debug a circuit board to determine exactly what part or areas are generating excessive RF noise. To do this expensive EMC analyzers and near field probes are typically used.

Alex's tutorial video shows us how we can create a low cost home made EMC probe using an RTL-SDR, LNA and home made near field probe made out of magnet wire. The video starts by explaining RF compliance, demonstrating some higher end equipment, then moves on to showing how to build a probe yourself, before finally demonstrating it being used on some circuit boards. For software, he uses SDRAngel and QSPectrumAnalzyer which are preinstalled on a DragonOS image. 

The project page has the tutorial in text and the video slides can be found here.

In the past we've also seen another post about home made EMC probes, and how to combine this idea with OpenCV to create noise heatmaps of circuit boards.

Basics of RF Emissions Debugging: Alex Whittemore

DF Aggregator: New Software for Networked Radio Direction Finding with KerberosSDR

Over on GitHub Corey (ckoval7) has released a new open source radio direction program called "DF Aggregator". This software is able to receive bearings and locations from multiple remotely networked KerberosSDRs, and display them on a map.

If you weren't already aware KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously crowdfunded back in 2018. With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding (RDF), passive radar and beam forming become possible. It can also be used as four separate RTL-SDRs for multichannel monitoring.

A single KerberosSDR combined with an antenna array is able to determine a bearing towards a signal source. By using multiple KerberosSDR units spread over a large area it is possible to triangulate the location of a transmitter and display it on a map. Corey's software uses a modified branch of our open source KerberosSDR code in order to generate a modified XML page that the mapping software polls for updated data. Some instructions on it's use are available on our forums and on the GitHub.

The image below shows three KerberosSDR stations on the map, and two transmitter locations that have been triangulated using the bearings from the three distributed KerberosSDR units. 

Alternative direction finding mapping software includes our Android App (mostly for mobile vehicular use), and RDF Mapper with our adapter code.

DF Aggregator: KerberosSDR Direction Finding Mapping Software

Frugal Radio: Sharing One Antenna with Fifteen Receivers

In his latest video Frugal Radio shows how he shares one antenna with fifteen SDR and scanner receivers using two splitters/multicouplers. He explains that he uses a low cost $35 second hand 1->8 Electroline TV Drop Amp in combination with a more expensive Commercial 1->8 Strisdberg multicoupler. The splitters both have built in amplifiers which help to avoid splitting losses.

Over on his website there is also a companion blog post which shows all the antennas he uses, as well as the multicouplers and adapters.

Share 1 antenna with 15 receivers - signal splitting in the shack with TV amp & multicoupler