Category: Antennas

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

Bullseye TCXO LNB for QO-100 33% Off Sale Ending Soon

On September 15 we began our 33% off stock reduction sale for the Bullseye LNB. The Bullseye is an ultra stable LNB for receiving QO-100 and other Ku-Band satellites/applications. We'll be ending this sale on Wednesday, so if you'd like to purchase a unit please order soon to avoid missing out on the sale price. The current sale price is US$19.97 including free worldwide shipping to most countries. 

To order the product, please go to our store, and scroll down until you see the QO-100 Bullseye TCXO LNB heading. Alternatively we also have stock via our Aliexpress store or on eBay.

For more information about the Bullseye and some reviews please see the original sale post.

The Bullseye LNB for QO-100

33% OFF Sale: Ultra Stable Bullseye LNB for QO-100/Es’Hail-2

Back in May we started selling the Bullseye LNB on our store, which is an ultra stable LNB for receiving QO-100 and other Ku-Band satellites/applications. We have recently managed to secure a good deal from the supplier. However, our storage warehouse is now low on space and we are hence running a 33% off stock clearance sale with the unit now priced at only US$19.97 including free worldwide shipping to most countries. 

To order the product, please go to our store, and scroll down until you see the QO-100 Bullseye TCXO LNB heading. Alternatively we also have stock via our Aliexpress store or on eBay.

What is QO-100 and an LNB?

QO-100 / Es'hail-2 is a geostationary satellite at at 25.5°E (covering Africa, Europe, the Middle East, India, eastern Brazil and the west half of Russia/Asia) providing broadcasting services. However, as a bonus it also has the world's first amateur radio repeater in geostationary orbit. Uplink is at 2.4 GHz and downlink is at 10.5 GHz.

Most SDRs do not tune all the way up to 10.5 GHz, so an LNB (low noise block) is typically used, which contains the feed, an LNA, and a downconverter which converts the 10.5 GHz frequency into a much lower one that can be received by most SDRs.

What's special about the Bullseye LNB?

In order to properly monitor signals on QO-100 an LNB with a Temperature Compensated Oscillator (TCXO) or other stabilization method is required. Most LNBs have non-stabilized crystals which will drift significantly over time on the order of 300 PPM with temperature changes.  This means that the narrowband signals used on QO-100 can easily drift out of the receive band or cause distorted reception. Software drift compensation can be used to an extent, but it works best if the LNB is somewhat stable in the first place. It is possible to hand modify a standard Ku-band LNB by soldering on a replacement TCXO or hacking in connections to a GPSDO, but the Bullseye LNB ready to use with a built in 1PPM TCXO and is cheap.

Reviews

In the past Tech Minds has reviewed this product favourably in the video shown below. In a second video he has also shown how the Bullseye can be combined with a transmit helix in order to create a dual feed uplink + downlink capable antenna.

Ultra Stable Bullseye LNB For QO-100 Es Hail2 10 kHz

F4DAV has also reviewed the unit on his website, concluding with the following statement:

As far as I know the BE01 is the first affordable mass-produced Ku-band TCXO LNB. These early tests suggest that it can be a game changer for amateur radio and other narrowband applications in the 10 GHz band. The stability and ability to recalibrate should allow even unsophisticated analog stations to tune to a 5 kHz channel and remain there for hours at a time. For SDR stations with beacon-based frequency correction, the absolute accuracy removes the need to oversample by several hundred kHz or to scan for the initial frequency offset.

There are also several posts on Twitter by customers noting good performance

Official Feature List + Specs

Features

  • Bullseye 10 kHz BE01
  • Universal single output LNB
  • Frequency stability within 10 kHz in normal outdoor environment
  • Phase locked loop with 2 PPM TCXO
  • Factory calibration within 1 kHz utilizing GPS-locked spectrum analyzers
  • Ultra high precision PLL employing proprietary frequency control system (patent pending)
  • Digitally controlled carrier offset with optional programmer
  • 25 MHz output reference available on secondary F-connector (red)

Specifications 

  • Input frequency: 10489 - 12750 MHz
  • LO frequency 9750/10600 MHz
  • LO frequency stability at 23C: +/- 10 kHz
  • LO frequency stability -20 - 60C: +/- 30 kHz
  • Gain: 50 - 66 dB
  • Output frequency: 739 - 1950 MHz (low band) and 1100 - 2150 (high band)
  • Return loss of 8 dB (739 - 1950 MHz) and 10 dB (1100 - 2150 MHz)
  • Noise figure: 0.5 dB

We note that an external bias tee power injector is required to power the LNB as it requires 11.5V - 14V to operate in vertical polarization and 16V - 19V to operate with horizontal polarization. The bias tee on the RTL-SDR Blog V3 outputs 4.5V so it is not suitable.

Comparing Shortwave Antennas with an RTL-SDR and FT8 Monitoring

Eric had an inverted L and T3FD antenna set up in his backyard and he wanted to test both at the same time to see which received HF better overall. Rather than relying on subjective 'by ear' measurements he decided to use the digital FT8 mode as his comparison signal. FT8 is quite useful for this purpose as the decoded data includes a calculated signal-to-noise (SNR) reading which is a non subjective measure that can be used for comparisons. It also contains information about the location of the signal which can be used for determining the DX capability of the antenna. 

To perform the comparison he used two or our RTL-SDR Blog V3 dongles running in direct sampling mode, and also added an additional low pass filter to prevent excessively strong TV and FM signals from overloading the input. Each antenna is connected to it's own RTL-SDR, and a modified version of GQRX with remote UDP control is used to switch between multiple FT8 frequencies so that multiple bands can be covered in the experiment. WSJT-X is used for decoding the FT8 packets.

After logging SNR values for several days he was able to plot and compare the number of packets received by each antenna, the maximum distance received by each antenna. His results showed that his inverted L antenna was best in both regards. He then performed a relative comparison with the SNR readings and found that the inverted L performed best apart from at 14 MHz, where the T3FD performed better.

In further tests he also compared the antennas on which signal headings they were receiving best from. The results showed that Erics inverted L was receiving best from one direction only, whereas the T3FD received signals from more headings.

Eric's post includes full instructions on the software setup and also Python code which can be used to replicate his experiments. We think that this is a great way to objectively compare two types of antennas.

Antenna directionality measurements via FT8 received headings

TechMinds: Decoding GPS with an RTL-SDR

Over on his YouTube channel Tech Minds has uploaded a video showing how it's possible to receive and decode GPS signals with an RTL-SDR. To do this he uses one of our RTL-SDR Blog V3 dongles and a GPS patch antenna which is powered via the bias tee on the dongle.

On the software side he uses GNSS-SDRLIB and RTKLIB to decode the GPS signal. The result of the two programs is your current GPS coordinates which can be plotted on a map. Unfortunately in the video Tech Minds was unable to get the Google Maps display to work, but you can easily type the coordinates into Google maps yourself.

Decoding GPS using an RTL SDR Receiver

 

KerberosSDR: Tracking a Weather Balloon Radiosonde with Radio Direction Finding

The KerberosSDR is our 4-channel phase coherent capable RTL-SDR unit that we previously successfully crowdfunded back in 2018.  With a 4-channel phase coherent RTL-SDR interesting applications like radio direction finding, passive radar and beam forming become possible. It can also be used as 4 separate RTL-SDRs for multichannel monitoring.

KerberosSDR can be purchased from our partner store at https://othernet.is/products/kerberossdr-4x-coherent-rtl-sdr.

In one of our latest tests we've been able to track a weather balloon radiosonde via the direction finding ability of KerberosSDR. These balloons are launched twice daily by meteorological agencies around the world, and the radiosonde carried by the balloon transmits an RS-41 signal continuously throughout it's flight sending back telemetry such as weather information and GPS coordinates. The KerberosSDR tracks the bearing towards the balloon using only the raw signal - it does not decode. Having the actual GPS location from the RS41 data allows us to compare and confirm that the KerberosSDR is indeed tracking the bearing of the balloon.

In this test we used the excellent 4-element dipole array made by Arrow Antennas. In particular we used the 406 MHz element version as the RS-41 signal is broadcast at 403 MHz. The antenna array is mounted on the roof, the KerberosSDR is in the attic connected to a Raspberry Pi 4. Our KerberosSDR Android app is used to plot the bearings. A separate RTL-SDR running on the video recording PC is connected to it's own antenna and is used to receive and decode the RS41 signal. The free software RS41 Tracker is used to decode and map the balloon for location confirmation. 

We are currently using the latest beta code in development (unreleased at the time of this post - it will be released within 1 to 2 months) which handles non-continuous intermittent signals better.

Arrow Antennas 4-Element Dipole Array Mounted on Roof

The short video below shows a timelapse of the RS41 decoder tracking a balloon which circled the south of our KerberosSDR. The red line indicates the zero degree direction of the antenna array, while the blue line indicates the estimated direction of the balloon determined via the MUSIC radio direction finding technique.

The GPS balloon map from RS41 tracker is overlayed on top of the KerberosSDR Android app map for clarity via video editing. We can see that it mostly tracks the balloon to within a few degrees. When the blue bearing line diverges this is due to the balloon's line of sight path to the antennas being obscured by terrain, buildings or trees. When this is the case a multipath signal reflecting off surrounding hills tends to become dominant.

In the second short video below the weather balloon tracked northwards. Towards the north, north west and north east we have antenna obstructions in the form of rising terrain, houses and hills, so the overall accuracy is poorer. However, it still tracks within a few degrees most of the time.

Finally the YouTube video below shows the same as the above, but in the second half includes the full screen including the KerberosSDR DoA graphs and SDR# waterfall showing signal strength.

KerberosSDR Tracking a Weather Balloon Radiosonde with Radio Direction Finding

In the future we hope to test with two or more KerberosSDR units producing multiple bearing lines on RDFMapper, hopefully resulting in cross points that can be used to estimate the actual location of the balloon.