Category: Antennas

TechMinds: Testing a DC-160 MHz Panadapter Switch

Over on his YouTube channel Tech Minds has uploaded a video where he tests out a cheap US$90 automatic antenna switch with DC-160 MHz range that he purchased from Chinese goods retailer Banggood. An automatic antenna switch like this is required when wanting to use an SDR such as an RTL-SDR as a panadapter with a transmit capable radio. The switch will automatically switch the SDR to ground when transmitting, so that high power does not enter the SDR via the shared antenna and destroy it.

In the video Tech Minds shows how to set the switch connections up and then demonstrates the switch in action with a Yaesu FT-991A and SDRplay SDR. He notes that this cheap Chinese version is actually built better than the MFJ-1708 antenna switch which until recently was the only commercial option available. It is also half the price.

PANADAPTER For Any Radio DC - 160 MHz SDR Antenna Switch

Building an 11.2 GHz Radio Telescope with an Airspy and 1.2m TV Satellite Dish

In the past we've posted several times about how 1.42 GHz Hydrogen Line amateur radio telescopes used with RTL-SDRs or other SDRs for Hydrogen line observations of the galaxy. Recently Hackaday ran a post highlighting a project from "PhysicsOpenLab" describing an 11.2 GHz radio telescope that uses an Airspy SDR as the receiver.

Celestial bodies emit radio waves all across the radio spectrum and typically observations can be made anywhere between 20 MHz to 20 GHz. Choosing an optimal frequency it is a tradeoff between antenna size, directivity and avoiding man made noise. For these reasons, observations at 10-12 GHz are most suitable for amateur radio telescopes.

The posts by PhysicsOpenLab are split into two. The first post highlights the hardware used which includes a 1.2m prime focus dish, and 11.2 GHz TV LNB, a wideband amplifier, a SAW filter, a bias tee, and the Airspy SDR. The LNB converts the 11.2 GHz signal down to 1.4 GHz which can be received by the Airspy. Once at 1.4 GHz it's possible then to use existing commercial filters and amplifiers designed for Hydrogen line observations.

The second post explains the GNU Radio based software implementation and the mathematical equations required to understand the gathered data. Finally in this post they also graph some results gathered during a solar and lunar transit.

Finally they note that even a 1.2m dish is quite small for a radio telescopic, but it may be possible to detect the emissions from the Milky Way and other celestial radio sources such as nebulae like Cassiopeia A, Taurus A and Cygnus A a radio galaxy.

A 11.2 GHz 1.2m Amateur Radio Telescope with GNU Radio and Airspy

FengYun-2G Confirmed to be Receivable with a WiFi Grid Dish

Back in November 2020 we posted about the release of a decoder for the FengYun line of geostationary weather satellites which provide full disk images of the Earth and are positioned to cover parts of Europe, Africa, the Middle East, Asia, Russia, and Australia. Back then only a few people had attempted decoding this, and it was believed that a 120cm satellite dish or larger would be required.

However, today on Reddit user u/Harrison_Clark55 has shown that it is possible to receive FengYun-2G with a typical 90-100cm WiFi grid dish. These WiFi grid dish's have proven to work well for other geostationary weather satellites such as GOES and GK-2A.

We do note that u/Harrison_Clark55's image appears to be missing a few lines of data, and they are based in Australia where the elevation of FY-2G could be quite high depending on what side of the continent they are on. So it's possible that receivers in lower elevations may still require a larger dish size to work.

Full Disk FY-2G image received by u/Harrison_Clark55 (see the Reddit post for full resolution image)

SATRAN: An Affordable Motorized Satellite Antenna Rotator

Recently we came across the SATRAN project by Daniel Nikolajsen, which is an attempt to design, build and sell low cost kits of an automatic motorized satellite antenna rotator for less than US$200. A motorized satellite antenna rotator is useful for pointing high gain directional antennas such as a Yagi or satellite dish at low earth orbit satellites which can move across the sky quickly. This is also an idea used by the well known SATNOGS project which also provides a design for a 3D printed antenna rotator, and runs servers that archive received satellite data.

Compared to the SATNOGS design, the SATRAN design appears to be much simpler and easier to build. Although being a smaller unit it's only design to handle small compact antennas such as a 70cm Yagi. SATRAN is also controllable via a web interface and there is an Android App. The design is capable of rotating 360 degrees, and 110 degrees from zenith, which allows a user to cover the entire sky.

Daniel notes that SATRAN kits should be available for sale from Feburary/March 2021. He also notes that it is possible to 3D print most of the parts and to just purchase the electronics for a lower price.

More technical information about the project is available on it's Hackaday.io blog.

SATRAN 3D render and actual prototype

Explaining the 9A4QV V-Dipole Design for Receiving 137 MHz Weather Satellites

Back in 2017 we posted about Adam 9A4QV's simple V-Dipole antenna design which works very well for receiving NOAA and Meteor weather satellites at 137 MHz. This type of antenna is a lot easier to build compared to a QFH or turnstile, and it results in good performance if built and set up correctly. Over the years he notes that he's received a number of questions asking to clarify the design and so he's uploaded a YouTube video which explains the built and dimensions of the antenna clearly.

137 MHz WX-SAT original 9A4QV V-dipole antenna

Tech Minds tests out the YouLoop HF Passive Loop Antenna

Over on YouTube Tech Minds has uploaded a new video where he unboxes and tests a YouLoop HF Passive Loop Antenna with his Airspy. The YouLoop design is also known as a Möbius loop, or noise cancelling passive loop "NCPL". The passive nature of the antenna means that highly sensitive radios will work best with it, however limited results may still be obtained with other radios. The advantages are extremely low levels of interference pickup and high portability.

In the video Tech Minds explains the specifications of the antenna before demonstrating the antenna receiving the HF bands with an Airspy + SpyVerter. He also tests the loop on VHF, demonstrating its ability to receive a distant 2M beacon.

We note that we sell official YouLoop antennas on our store for $34.95 including free shipping to most countries.

YouLoop HF Passive Loop Antenna

KerberosSDR with DF-Aggregator Direction Finding Attempt

Back in October we first posted about the release of DF-Aggregator, a program by Corey (ckoval7) which can be used to receive and plot data from multiple KerberosSDR direction finding units. 

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.

In one of his latest DragonOS videos, Aaron has been testing out DF-Aggregator. In his test he had two vehicles driving around each with a KerberosSDR and antenna array, with both using a mobile data connection to send data to a remote PC running DF-Aggregator. The results were successful, with the team being able to determine the location of a broadcast FM transmitter to within a few meters after a short drive.

DragonOS Focal KerberosSDR x2 Mobile w/ DF-Aggregator Direction Finding Attempt 2 (Better Results)

Gorizont-RTLSDR Linux Distro Updated to V2.0.3

Gorizont-RTLSDR is an RTL-SDR focussed Linux distribution based on Xubuntu 20.04 LTS. Recently it was updated to V2.0.3. The creator Steve Cox writes: 

New release and upgrade of gorizont linux, v 2.0.3. uploaded to sourceforge. The new AMSynch option in gqrx 2.14.2 works rather well for broadcast stations in direct sampling mode.

  • gqrx 2.14.2 - now with AMSynch mode!
  • SigDigger 0.1.0
  • Universal Radio Hacker 2.9.0
  • gqrx-scan
  • Welle.io 2.2 for all your DAB and DAB+ needs.
  • Baudline
  • fldigi
  • fmsg
  • Due to multiple issues with linux versions of Dream DRM, Dream DRM is now installed as a Win 32 .exe running under wine. It works!
  • w-scan for creating DVB-T/ATSC/etc. scan files for TV viewing using VLC