Category: Antennas

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 Hacakday.io 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

A 3D Printed Automatically Adjusting Linear Antenna Array for KerberosSDR Radio Direction Finding

Over on GitLab Josh Conway has released a design for an automatically adjusting antenna array which can be used with radio direction finding capable SDRs like our KerberosSDR. KerberosSDR is a SDR consisting of four RTL-SDRs connected to the same oscillator, a USB hub, a built in noise source and calibration hardware which allows software to use the four RTL-SDRs coherently. Coherent operation of SDRs enables interesting applications such as radio direction finding, passive radar and beam forming.  

With coherent antenna array based direction finding, the optimal spacing between the antenna elements is proportional to the wavelength of the frequency being received. If you want to do RF direction finding on different frequencies, either multiple antenna arrays with different element spacings, or manually adjusting the antenna array with each frequency change is required.

Josh's design automates this problem with an antenna array that can adjust the spacing automatically. The design puts the antennas on an extending pantograph arm whose length is controlled via a threaded rod connected to a stepper motor. An Arduino microcontroller controls the stepper, thus allowing the spacing to be adjusted automatically. 

A Pantograph Antenna Array for Direction Finding

A full description of the build is provided in the document on GitLab titled "provisional_patent_application.pdf". From Twitter it appears that Josh (@CrankyLinuxUser) was unable to secure a patent for this design, so he has released the design for free under AGLP3. Most of the parts are 3D printed, and the CAD stl files all appear to be available on the GitLab. The Arduino microcontroller firmware is also available.

Thank you to Josh for releasing this design!

Pantograph Antenna Array for Direction Finding

New GOES Weather Satellite Bundle from NooElec

NooElec have recently released for sale a GOES geostationary weather satellite reception bundle which includes a parabolic grid dish, feed, GOES LNA and RTL-SDR dongle. The bundle should be usable for the GK-2A satellite, as well as HRIT from polar orbiting satellites, although for HRIT you'll need some way to motorize or hand track the satellites.

Typically to receive GOES a 2.4 GHz WiFi grid dish has been used in the past. While the mismatch between 2.4 GHz and the 1.7 GHz used by GOES doesn't cause too much trouble, the dish provided by NooElec has a feed optimized for the 1.7 GHz which should make receiving the signal easier. The bundle also comes with their SAWbird+ GOES LNA, one of their always ON bias tee E4000 tuner based RTL-SDR dongles and a roll of 10m LMR400 cable.

The bundle is currently available on Amazon USA priced at US$179.95. Canadian customers can also order from Amazon.ca for CDN$259.95. Amazon shipping is free within the USA, however shipping this overseas will cost at least US$100 extra due to the weight + additional import fees. That said, the coverage area of GOES is mostly only for the USA, Canada and South America.

If you're interested in GOES or GK-2A satellite reception we have a tutorial written here.

NooElec GOES DIsh
NooElec GOES Bundle Data

Easy-SDR: Open Source Designs for SDR Accessories

Back in 2018 we posted about Igor Yatsevich's Easy-SDR project which consisted of open source designs for a Mini-Whip antenna and upconverter. Igor has now added several new open source designs to the project including a bias tee, LNA, LNA with filtering, attenuator and SPDT antenna switch. On his Reddit post he notes:

The most interesting thing I've added so far:

  1. Most of the devices are now prepared for installation in a metal case measuring 80 x 50 x 20 millimeters.
  2. Completely redesigned LNA design. Now, Bias Tee powered amplifiers are housed in a 50 x 25 x 25mm metal case and have N-type connectors.
  3. Added an amplifier based on the PGA-103 microcircuit.
  4. Added the ability to install filters in final amplifiers (a separate printed circuit board, depending on the filter used).
  5. Added a new device - SPDT antenna switch for receiving antennas.
  6. The UP converter has been redesigned. Added intermediate buffer stage between crystal generator and mixer.
  7. RF lines in all devices were recalculated to correspond to the characteristic wave impedance of 50 Ohm.
  8. Reduced size of PI attenuator PCB.

In this project, I focused on the simplicity of self-assembly devices, which you can make at home. In the repository, you can find detailed assembly instructions, a list of necessary components for assembly, and GERBER files.

SPDT Antenna Switch from the Open Source Easy-SDR Project

Notes on Observing Pulsars with an SDR from CCERA

A pulsar is a rotating neutron star that emits a beam of electromagnetic radiation. If this beam points towards the earth, it can then be observed with a large dish or directional antenna and a software defined radio. In the past we've posted a few times about Pulsars, and how the HawkRAO amateur radio telescope run by Steve Olney in Australia has observed Pulsar "Glitches" with his RTL-SDR based radio telescope.

Over in Canada, Marcus Leech has also set up a Pulsar radio telescope at the Canadian Centre for Experimental Radio Astronomy (CCERA). Marcus has been featured several times on this blog for his various amateur radio experiments involving SDRs like the RTL-SDR. In one of his latest memos Marcus documents his Pulsar observing capabilities at CCERA (pdf). His memo describes what Pulsars are and how observations are performed, explaining important concepts for observation like de-dispersion and epoch folding.

The rest of the memo shows the antenna dish and feed, the SDR hardware which is a USRP B210 SDR, the reference clock which is a laboratory 0.01PPB rubidium atomic clock and the GNU Radio software created called "stupid_simple_pulsar". The software DSP process is then explained in greater detail. If you're thinking about getting involved in more advanced amateur radio astronomy this document is a good starting point.

Dish Antenna + Feed used for receiving Pulsars

Conference Talk on PICTOR A Free-to-Use Open Source Radio Telescope based on RTL-SDR

At this years FOSDEM 2020 conference Apostolos Spanakis-Misirlis has presented a talk on his PICTOR open source radio telescope project. We have posted about PICTOR in the past [1, 2] as it makes use of an RTL-SDR dongle for the radio observations. The PICTOR website and GitHub page provide all the information you need to build your own Hydrogen line radio telescope, and you can also access their free to use observation platform, where you can make an observation using Apostolos' own 3.2m dish radio telescope in Greece.

The PICTOR radio telescope allows a user to measure hydrogen line emissions from our galaxy. Neutral Hydrogen atoms randomly emit photons at a wavelength of 21cm (1420.4058 MHz). The emissions themselves are very rare, but since our galaxy is full of hydrogen atoms the aggregate effect is that a radio telescope can detect a power spike at 21cm. If the telescope points to within the plane of our galaxy (the milky way), the spike becomes significantly more powerful since our galaxy contains more hydrogen than the space between galaxies. Radio astronomers are able to use this information to determine the shape and rotational speed of our own galaxy.

PICTOR: A free-to-use open source radio telescope