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
Leif (SM5BSZ) is fairly well known in the SDR community for doing very indepth technical tests of various SDR receivers over on his YouTube channel. Recently he's released part two of a series where he compares the new Airspy HF+ Discovery against various other SDRs such as the Perseus, SDRplay RSP1, Airpsy HF+ Dual, Airspy + SpyVerter and AFEDRI SDR-Net. In the first video he studied the blocking and second order intermodulation effects of each SDR using signal generators. We summarized those results in this previous post.
In the new video Leif compares the dynamic range of each SDR using real HF antenna signals at 7.2 MHz. In order to create a fair test of dynamic range, appropriate attenuation is added to each receiver in order to make their noise figures equivalent, so that the incoming signal strength is the same for each SDR.
The first set of dynamic range results is summarized at time 08:14, and these results show the dynamic range comparisons for strong night time signals. Again like in the other videos the Perseus is used as the reference SDR since it is always the best. The tests show that the HF+ Discovery trails behind the Perseus by only -3dB, followed by the HF+ Dual at -10dB, AFEDRI at -15dB, Airspy+SpyVerter at -18dB and finally the RSP1 at -23dB.
The second set of results is summarized at 17:47 and this includes a day time dynamic range test. The rankings are very similar to the night time test.
Over on YouTube TechMinds has uploaded a video showing how to use the Iridium Toolkit software to receive data and audio from Iridium satellites with an Airspy. Iridium is a global satellite service that provides various services such as global paging, satellite phones, tracking and fleet management services, as well as services for emergency, aircraft, maritime and covert operations too. It consists of multiple low earth orbit satellites where there is at least one visible in the sky at any point in time, at most locations on the Earth.
The frequencies used by the older generation Iridium satellites are in the L-band, and the data is completely unencrypted. That allows anyone with an RTL-SDR or other SDR radio to decode the data with the open source Iridium Toolkit. If you're interested in how Iridium Toolkit was developed, see this previous post about Stefan "Sec" Zehl and Schneider's 2016 talk.
In the video Tech Minds shows decoding of various data, including an audio call and the satellite tracks and heat map of Iridium satellites.
Thank you to Nils Schiffhauer (DK8OK) for submitting an article documenting his tests on the Airspy HF+ Discovery (pdf mirror). Spurred on by discussions on the SDR-Console mailing list, Nils went looking for issues with spurious signals generated by the HF+ itself. In the end he finds some minor spurious signals, but notes that they have absolutely no adverse effects once an antenna is connected.
Youssef Touil (developer of the Airspy HF+ line of products) has also noted that the minimum discernible signal (MDS) of the HF+ is so low that it's become normal for very weak spurs to now be visible without an antenna connected. However, once an antenna is connected the natural atmospheric noise floor which is much higher than the MDS hides these spurs, and so the spurs have no consequence on reception.
In Nils' first test he uses a very high end Winradio W65DDC SDR to detect the spurs coming from an Airspy HF+, Airspy HF+ with preselector retrofit, and the Airspy HF+ Discovery. The results are quoted below:
[With the Airspy HF+] you indeed see a very few spurious signals, all well below -140 dBm/Hz.
With the Airspy HF+ Preselector connected, the number of spurious signal is very much reduced, as is their maximum level.
This picture still further improves with the Airspy HF+ Discovery connected: all visible seven spurious signals are measured to well below -150 dBm/Hz.
The first result is clear:
Airspy has improved also the spurious signals from model to model, landing at a stunning reduction with their matchbox-like Discovery.
The spurious signals were significantly reduced in both numbers and level.
Together with sensitivity and dynamic range, the performance of these SDRs is exceptionally good. If you see their price tag, they are a real bargain.
Overall: they deliver professional performance in every important aspect at an incredible low price.
In the second test Nils tunes to the center of a spur, then tested with a dummy load and then antenna connected. His results showed that all spurs disappeared once an antenna was connected. He summarizes below:
Yes, there are a very few and low-level spurious signals at all Airspy’s receivers – as they are found [much] worse at some competing SDRs.
By development, even this has been significantly improved from model to model with the new Discovery leading the gang.
All spurious signals disappear with an antenna connected.
There has been found no case where, in practice, any spurious signal even remotely touched or even limited reception of the most miniscule signals.To complain about “spurious signals” simply is “Much Ado about Nothing” in an Ivory Tower, far away from any practical application.
Nils also tested 7300 kHz reception and the co-existance of weak amateur radio signals with strong broadcast signals.
Last week we posted about Oona Räisänen's ([Windytan] and @windyoona) project to capture live video from her 1985 Nintendo Entertainment System (NES) using an Airspy SDR. In order to avoid expensive Video Capture cards which didn't work on her Mac, she used an Airspy SDR to decode the PAL composite video output of the NES. Last week she had black and white video working.
This week she has full color working, and has on her blog posted a write up about her project with the Airspy and her experiences with trying to find a suitable capture solution. She also goes into some detail about the CPU performance considerations of this solution, noting that there are some performance bottlenecks. She's also uploaded a video showing the results in action.
The Airspy HF+ Discovery is a new US$169 software defined radio that recently began shipping. On HF it can tune from 0.5 kHz to 31 MHz, and on VHF from 60 to 260 MHz.
It is advertised as having extremely high dynamic range and sensitivity, comparable to high end (and much more expensive) SDRs. High dynamic range means that extremely strong powerhouse stations will not block weaker stations from being received. On lower end SDRs strong stations can cause an SDR to overload, resulting in poor reception.
The HF+ Discovery is an improvement over the original HF+ (now known as the HF+ Dual Port). Back in 2017 we reviewed the original HF+ and found it's performance to be excellent. However, a number of people found that by using low loss preselectors the performance could improve the performance even further.
Originally Youssef (the developer of Airspy products) began designing a low cost preselector add on for the HF+ Dual Port, in order to increase the already great dynamic range. However, it was deemed too difficult for users to retrofit their devices. The result was the creation of the HF+ Discovery, which combines these preselectors with the already excellent HF+ SDR circuitry. Compared to the HF+ Dual, the Discovery is much smaller, and comes in a plastic case rather than a metal one. Instead of the split HF/VHF dual ports seen on the HF+ Dual, the Discovery only has one port that covers both bands. Overall performance with the preselectors is increased, and the price is even lower than the HF+ Dual Port.
Over the past few weeks a number of reviews and comparison videos have come out. Below we list a few that we found interesting.
In this video, the Techminds YouTube channel gives an overview on what the HF+ discovery is, and then gives a quick demo. If you haven't heard of the HF+ Discovery before then this is a good introduction.
Airspy HF+ Discovery - Overview & Brief Testing
The following video by Leif (sm5bsz) is the most technical, as he performs sensitivity and dynamic range lab tests on multiple SDRs including the Microtelecom Perseus, Airspy HF+ Dual Port, Airspy HF+ Discovery, Airspy Spyverter plus Airspy, SDRplay RSP1 and AFEDRI SDR-Net.
If you want to skip the testing procedures, a summary of the results are presented at 16:20, 31:06, 38:19, and 53:55 video time. In most tests the HF+ Discovery is the second best, after the Perseus.
The first in a series of videos that compare the dynamic range of six receivers: Microtelecom Perseus, Airspy HF+ Dual Port,, Airspy HF+ Discovery, Airspy Spyverter plus Airspy, SDRplay RSP1 and AFEDRI SDR-Net. Here blocking and second order intermodulation is studied with signal generators. Attenuators are used to make the noise figure 26 dB of all radios at the output of the 6 port Wilkingson splitter. This video is for dynamic range on 7.2 MHz. The Discovery is a pre-production unit and the noise figure is a little higher than that of regular production units for unknown reasons.
rx7compare-part1
In this article over on the SWLing Blog guest poster Guy Atkins submits a comparison video between the Airspy HF+ Discovery and an Elad FDM-DUOr ($899). Results appear to show that the HF+ has close to identical performance.
Over on YouTube icholakov has posted two comparison videos. In the first he compares the HF+ Discovery to the HF+ Original. In the second video he compares the HF+ Discovery against an SDRplay RSP1A.
Airspy HF+ Discovery SDR vs. HF+ Original SDR - Blind Test
Airspy HF+ Discovery vs. SDRPlay RSP-1A on Medum Wave and Short Wave
In this post, Arctic DX measures the sensitivty of the HF+ Discovery, providing a very useful sensitivity comparison table against multiple other SDRs. The HF+ Discovery comes in with excellent numbers.
Over on Twitter there has been a lot of activity too. In the following Tweet, Simon Brown, author of the popular SDR-Console V3 application notes that the HF+ Discovery is virtually immune to strong signals.
Airspy HF+ Discovery performing sterling service on Band II FM - as always, it's France Musique. The Discovery virtually immune to strong signals. (This time with the correct image.) pic.twitter.com/UlqOUMjXm2
We've also seen how the HF+ Discovery's LF performance is so good that it's possible to simply connect a photodiode and see the light spectrum produced by CFLs.
The new @airspy_com Airspy HF+ Discovery works so well in LF that you can just attach it a photodiode to see the light spectrum of noise produced by some low energy bulbs. I see a future in optical communications @lambdaprogpic.twitter.com/bYYNLaS2PI
GOES 16/17 and GK-2A are geosynchronous weather satellites that transmit high resolution weather images and data. In particular they are far enough away from the earth to be able to take beautiful 'full disk' images which show the entirety of one side of the Earth. As these satellites are in a geosynchronous orbit, they can be counted on to be in the same position in the sky at all times, so no tracking hardware is required and images can be pulled down constantly throughout the day without having to wait for a polar orbiting satellite to pass over like you would with the NOAA APT or Russian Meteor satellites.
With a low cost WiFi grid dish antenna, LNA and RTL-SDR dongle, any home user within the footprint of one of these weather satellites can receive and decode live images directly from the sky. Setting up a station is overall not too difficult, but it can be a bit fiddly with a number of steps to complete. Below is our comprehensive guide. We'll show how to set up a self contained Raspberry Pi based system with goestools (free), as well as a guide for the Windows PC software XRIT decoder (US$125).
We've attempted to make the tutorial as newbie friendly as possible, but we do need to assume basic RF knowledge (know what antennas, SDRs, coaxial, adapters etc are), basic Linux competency for the goestools tutorial (using the terminal, using nano text editor), and basic Windows competency for the XRIT decoder tutorial (unzipping, editing text files, running programs).
A full disk false color image received directly from the GOES-17 satellite with an RTL-SDR. Click for the full size image (14MB).
There are two fourth generation NOAA GOES satellites that are currently active, GOES-16 and GOES-17. These transmit HRIT signals, and also transmit shared data from the older third generation GOES 15, and Japanese Himiwari8 satellites. At the moment GOES-16 and GOES-17 are producing full disk images every 30 minutes, and close up "mesoscale" shots of the USA every ~15 minutes. GOES-16 (aka GOES-R) and GOES-17 (aka GOES-S) are also known as GOES-EAST and GOES-WEST respectively. At least one of these satellites can be received from North/South America, Canada, Alaska/Hawaii, New Zealand, Eastern Australia and some pacific islands.
There is also the older generation GOES-15 and GOES-14 which have been placed in standby orbits. These transmit LRIT signals which provide images at a slower rate.
GOES 16/East and GOES 17/West Signal Footprint
There is also the Korean GK-2A (GEO-KOMPSAT-2A) satellite which is very similar to the GOES satellites. GK-2A covers countries like India, Asia, Australia, New Zealand and parts of Russia. Note that you may have previously heard of the COMS-1 satellite which used to cover this area. Since July 2019 COMS-1 was replaced by GK-2A. Unlike GOES, GK-2A images are encrypted. However it has been found that "sample" encryption keys found online in demo code work just fine.
GK-2A contains both LRIT and HRIT channels, but at the moment only the LRIT channel can be decoded with the currently available software. The LRIT channel sends full disk IR images every 10 minutes in 2200 x 2200 resolution. Compared to the 5424 x 5424 resolution GOES full disk images, this is smaller, but still large enough to be interesting.
Note that even if HRIT decoding is added by the current software, you would require an Airspy or other wideband SDR as the GK-2A HRIT signal bandwidth is 5 MHz. Also since the HRIT bandwidth is so wide, the signal strength is reduced, meaning that you'll need a larger dish. People who have received the HRIT signal note that a 3M+ sized dish seems to be required.
GK-21 (GEO-KOMPSAT-2A) Footprint
You might ask why bother receiving these satellite images directly, when you can get the exact same images from NOAA at https://www.star.nesdis.noaa.gov/GOES/index.php. Well, you might want to set up your own station to be independent from the internet, or you live in a remote location without internet, or maybe just for the fun and learning of it.
To set up a receiver for GOES 16/17 HRIT or GK-2A LRIT you'll need to purchase a dish antenna such as a cheap 2.4 GHz WiFi antenna, an RTL-SDR, GOES LNA, and a Raspberry Pi if using goestools, otherwise a Windows PC can be used. The total cost could be anywhere from $150 - $200 depending on what pieces you already have available.
Before we start the tutorial, you might want to use an augmented reality Android app like "Satellite-AR" to get a rough idea of where either GOES 16/17 or GK-2A (GEO-KOMPSAT-2A) is in your sky, and if receiving them is even feasible for your location. You'll need to find an area on your land where you can mount a small satellite dish with an unobstructed line of sight view to the satellite (no trees or buildings can be blocking the signal path). If the satellite is low on the horizon (below 25 deg elevation), then things get a little more difficult as you have more obstructions and a weaker signal. But it can still be done, and we're able to routinely get good results at 24.5 deg elevation.
Note that for Europe and Africa, unfortunately there are no satellites that can be received easily with an SDR and LNA. But you might instead be interested in the EUMETCAST service, which can be received from EUTELSAT 10A (Ku band), Eutelsat 5 WEST A (C Band) and SES-6 (C Band) . To receive this service you'll need a DVB-S2 receiver and a satellite dish with appropriate band LNB. You also need a license keys and software which all together cost €100. EUMETCAST reception is not covered in this tutorial, instead see this video.
Oona (also known as [Windytan] and @windyoona) was recently looking for a way to capture PAL composite video from her old 1980’s Nintendo Entertainment System (NES) without spending a bunch of money on what are often poor video capture cards. As she already owned an Airspy SDR she decided to receive the PAL signal with the Airspy and modify some software to act as a PAL decoder.
SDR-based PAL decoder is still black & white, but after a notch filter on the audio the picture quality is getting a lot better. pic.twitter.com/SUoBlnBZF3
PAL decoding was handled via some modifications to her private Tempest software. Normally Tempest type programs like TempestSDR that we covered in a [previous article] are used to spy on computer/TV monitors from signals that are unintentionally emitted in the surrounding area.
Oona has made the connection from the composite output directly to the SDR antenna input so it’s not unexpected that you’d have a strong signal. However, I have to admit that’s an incredibly clear image for a video being demodulated via a software radio.
What makes this an even more amazing feat is that the latency is low enough that it’s nearly playable using a computer and SDR in place of a television set.
I’ve been looking for ways to capture NES video on my Mac. No easy+cheap solutions, but with some changes to my Tempest tool I can use the Airspy to receive the analog video carrier. The latency is almost good enough for playing, though it’s not my goal 🙂 pic.twitter.com/B6x44NEuvK
