Category: Airspy

Several new Airspy HF+ Reviews

The new Airspy HF+ SDR receiver has now been shipped to multiple customers and reviewers, and new reviews are coming online fast. If you weren't already aware, the Airspy HF+ was a hotly anticipated low cost, but high performance HF speciality SDR receiver. The claims are that it can compete with the high end $500 US+ units. We have our own review of an early model here. Below are some new reviews that we are aware of.

Nils DK8OK's photo of the Airspy HF+.
Nils DK8OK's photo of the Airspy HF+.

Nils Schiffhauer - DK8OK

On his blog Nils presents us with a comprehensive set of audio recordings comparing the $525 US Elad FDM-S2 with the $199 US Airspy HF+. He compares the two receivers on various shortwave broadcast stations, time stations, and an airport VOLMET. The recordings are identical, with the two radios recording the same signals simultaneously via a splitter.

Both receivers produce excellent results so you will probably need headphones and keen ears to be able to tell the difference.

Mile Kokotov

In this review YouTube video Mile Kokotov presents a comparison of the Airspy HF+ vs. the ColibriNANO, a similarly specced SDR dongle. He writes:

In this video I am comparing two high quality SDR Receivers: Airspy HF+ and ColibriNANO. They both have 16 bit Analog-to-Digital Converter. Comparison was made with the same overall conditions.

For example, both receivers was set with equal size spectrum windows, with the same amount of decibels in their scale, and the same high of the spectrum windows.
ColibriNANO has LNA gain slider which was set to maximum SNR.

Airspy HF+, on the other hand, has no LNA gain control.
The SV2HQL/Beacon was chosen as a test signal on 3579.32 kHz (on 80m band)

Antenna is half-wave resonant Dipole (40 meters long) for 80m band.

In the second part of the video I was inserted 27 dB external Attenuator on both receivers. ColibriNANO automatically increased the LNA gain and sets itself to maximum SNR. With this amount of attenuation, The Airspy HF+ noise floor level was at about the same place in spectrum window like ColibriNANO, Unlike in the first part of the video, when no external attenuator was used.

Both SDR-receivers are very good! Which is better? I leave on you to judge...

Mile also does a second test with his HF+ and an active Mini-Whip antenna. He writes:

Airspy HF+ is superb High-Dynamic HF and VHF SDR-receiver and I am impressed with it. In order to minimize possible negative effect on signal path from antenna connector to tuner input, Airspy HF+ has no internal attenuator. Developers takes in account that this SDR-receiver has enough dynamic range that is very difficult to overload it. Actually it is true for most cases. But, if we want to use some type of active antenna (with internal amplification) like Mini-Whip Active Antenna for example, it is good idea to add an external attenuator between antenna and receiver HF-input connector, in order to have opportunity to lower the signal level from the active antenna, and to avoid possible overload issues. In this video I am presented some scenario (receiving MW AM band) when my homemade external step-attenuator is more than welcome! By the way, the external step-attenuator is very easy to made in almost no money. All you need is 9 resistors, three switches and one metal box) I have 5.5 dB switch, 10.5 dB switch and 22 dB switch. It can be set for 8 various combinations: 0, -5.5 dB, -10.5 dB, -16 dB, -22 dB, -27.5 dB, -32.5 dB and -38 dB.

You can see on this video that the AM Broadcast signal from Macedonian Radio on 810 kHz is very strong. The Antenna is about 30 km from my house. It is self standing huge 185 meters high vertical antenna, radiating enormous RF-power, so I have to use my homemade attenuator I mentioned it before.

The SWLing Post Blog

Here Thomas of the SWLing post blog has posted a brief review of his HF+ unit. He notes how the HF+ is very compact, with a durable enclosure and how easy it was to set up with it being completely plug and play. So far Thomas hasn't fully evaluated the performance, but his first impressions are good.

Adam 9A4QV

In his two videos Adam doesn't directly review the Airspy HF+, but he does show some pretty impressive reception with his Skyloop antenna.

RadioHobbyist (Update: 8 Dec 2017)

This review by RadioHobbyist just came online shortly after this post went out. It compares the HF+ against the expensive $1449 US NetSDR using sound samples from both radios. The difference between the two radios is almost undetectable.

TempestSDR: An SDR tool for Eavesdropping on Computer Screens via Unintentionally Radiated RF

Thanks to reader 'flatflyfish' for submitting information on how to get Martin Marinov's TempestSDR up and running on a Windows system. If you didn't already know by definition "TEMPEST" refers to techniques used by some spy agencies to eavesdrop on electronic equipment via their unintentional radio emissions (as well as via sounds and vibrations). All electronics emit some sort of unintentional RF signals, and by capturing and processing those signals some data can be recovered. For example the unintentional signals from a computer screen could be captured, and converted back into a live image of what the screen is displaying.

TempestSDR is an open source tool that allows you to use any SDR that has a supporting ExtIO (such as RTL-SDR, Airspy, SDRplay, HackRF) to receive the unintentional signal radiation from a screen, and turn that signal back into a live image. This can let you view what is on a screen without any physical connections. If a high gain directional antenna is used then it may be possible to receive images from several meters away as well.

TempestSDR showing what's on the screen via unintentional RF radiation from the monitor.
TempestSDR showing what's on the screen via unintentional RF radiation from the monitor.

Although TempestSDR has been released now for a number of years it hasn't worked properly in Windows with ExtIO interfaces. In his email flatflyfish showed us how to compile a new version that does work.

1. You need to install a 32-bit version of the Java runtime. The 64-bit version won't work with extio's possibly because they are all 32-bit. Also install the JDK.

2. You need to install MingW32 and MSYS and put their bin folders in your Windows PATH.

3. Then when compiling I was seeing a lot of CC command unknown errors. To fix that I just added CC=gcc to the top of all makefiles. I also removed the Mirics compilation line from the JavaGUI makefile to make things easier as we're not using that sdr.

4. Originally my JDK folder was in Program Files. The makefile didn't like the spaces in the folder, so I moved it to a folder without spaces and it fixed the errors.

5. Lastly to compile it you need to specify the ARCHNAME as x86 eg "make all JAVA_HOME=F:/Java/jdk1.7.0_45 ARCHNAME=X86"

After doing all that it compiled and I had a working JAR file. The extio's that are used normally with HDSDR work fine now and I get some images from my test monitor with an rtlsdr.

We tested compilation ourselves and were successful at getting a working program. To help others we've just uploaded a fork of the code with the makefile changes done, as well as a precompiled release ZIP available on the releases page so no compilation should be required to just use it. Note that to use the precompiled JAR you still need to install MingW32, and also don't forget to install the MingW /bin and msys /1.0/bin folders into the Windows PATH. You also do need to have the 32-bit Java runtime installed as the 64-bit version doesn't seem to work. On at least one Win 10 machine we also had to manually add a 'Prefs' folder to the Java path in the registry.

We've tested the software with the ExtIO for RTL-SDRs (available on the HDSDR downloads page) and confirmed that it works. Images from one of our older DELL monitors using DVI are received nicely, although they are a bit blurry. We also tried using an Airspy or SDRplay unit and this significantly improved the quality of the images a lot due to the larger bandwidth. The quality was good enough to make out large text on the screens. ExtIO's for the Airspy are available on this page, and for the SDRplay on the official SDRplay website. Note that for the SDRplay we were unable to go above 6 MHz, and on the RTL-SDR 2.8 MHz was the limit - anything higher on these SDRs did not produce an image possibly due to dropped samples.

To use the software you should ideally know the resolution and refresh rate of your target monitor. But if you don't there are auto-correlation graphs which actually help to predict the detected resolution and frame rate. Just click on the peaks. Also, you will need to know the frequency that your monitor unintentionally emits at. If you don't know you can browse around in SDR# looking for interference peaks that change depending on what the image of the screen is showing. For example in the image below we show what the interference might look like. A tip to improving images is to increase the "Lpass" option and to watch that the auto FPS search doesn't deviate too far from your expected frame rate. If it goes too far, reset it by re-selecting your screen resolution.

Unintentionally radiated RF signal from computer screen shown in SDR#
Unintentionally radiated RF signal from computer screen shown in SDR#

The best results were had with the Airspy listening to an older 19" DELL monitor connected via DVI. A newer Phillips 1080p monitor connected via HDMI had much weaker unintentional signals but images were still able to be recovered. A third AOC 1080p monitor produced no emissions that we could find.

Clear images were obtained with an antenna used in the same room as the monitor. In a neighboring room the images on the DELL monitor could still be received, but they were too blurry to make anything out. Possibly a higher gain directional antenna could improve that.

An example set up with RTL-SDR antenna and monitors
An example set up with RTL-SDR antenna and monitors

Below we've uploaded a video to YouTube showing our results with TempestSDR.

If you want to learn more about TEMPEST and TempestSDR Martin Marinovs dissertation on this software might be a good read (pdf).

Airspy Black Friday Deal – 15% off Airspy Mini/R2

Airspy have just tweeted a Black Friday deal for their products sold on iTead Studio. Simply use the coupon "AIRSPYBLACK" when checking out. It looks like the coupon is giving 15% off the Airspy Mini and Airspy R2. No discounts yet for the Airspy HF+ or SpyVerters.

Airspy HF+ Released!

The much anticipated Airspy HF+ has just been released for sale. The cost is $199 USD plus shipping from the manufacturer iTead in China which costs about $6 for a registered air mail parcel or $19 for DHL express delivery to the USA. There was a coupon available via this tweet, but it ran out within hours.

The HF+ is also available for preorder for US/Canada customers over at the reseller. Currently there is a last chance $50 coupon available for US/Canada residents purchasing from by using the code provided in the link. We don't know how long that coupon will last though.

Note that we believe that these are preorders, with shipping expected to commence in early December.

If you didn't know already the Airspy HF+ is a HF/VHF RX only SDR which has extremely high dynamic range and excellent sensitivity. The high dynamic range means that the SDR is unlikely to ever overload on strong signals meaning that no external filtering which can reduce SNR/sensitivity is required. The minimum discernible signal (MDS) measurements are also excellent meaning that sensitivity to weak signals is excellent too. With high dynamic range, great sensitivity and low cost combined, this SDR blows most of the current offerings out of the water by being able to 'just work' without the need to fiddle around with gain sliders, filters or attenuation.

Airspy HF+: Why Linearity Matters
Airspy HF+: Why Linearity Matters

The only disadvantage to similar offerings like the Airspy R2/Mini or SDRplay is the reduced frequency range and bandwidth specs. On the HF+ the frequency range tops out at 260 MHz and the bandwidth at 680 kHz. The Airspy R2/mini/SDRplay units have frequency ranges that go up to 1.8 - 2 GHz, and have bandwidths of up to 10 MHz. But this is an SDR designed for DXing or pulling in those weak signals, so wideband operation is not a major concern for that application.

We have a review of a prototype version of the Airspy HF+ that we received earlier in the year available here. It's one of the most impressive low cost SDRs that we've seen to date. (We consider sub $300 USD as low cost, and $20 RTL-SDRs as ultra-low cost). You can also freely test some publicly available Airspy HF+ units that were provided to reviewers and developers over the internet.

Technical specifications

  • HF coverage between 9 kHz .. 31 MHz
  • VHF coverage between 60 .. 260 MHz
  • -140.0 dBm (0.02 µV / 50 ohms at 15MHz) MDS Typ. at 500Hz bandwidth in HF
  • -141.5 dBm MDS Typ. at 500 Hz bandwidth in FM Broadcast Band (60 – 108 MHz)
  • -142.5 dBm MDS Typ. at 500 Hz bandwidth in VHF Aviation Band (118 – 136 MHz)
  • -140.5 dBm MDS Typ. at 500 Hz bandwidth in VHF Commercial Band (136 – 174 MHz)
  • -140.0 dBm MDS Typ. at 500 Hz bandwidth in the upper VHF Band (> 174 MHz)
  • +15 dBm IIP3 on HF at maximum gain
  • +13 dBm IIP3 on VHF at maximum gain
  • 110 dB blocking dynamic range (BDR) in HF
  • 95 dB blocking dynamic range (BDR) in VHF
  • 150+ dB combined selectivity (hardware + software)
  • 120 dB Image Rejection (software)
  • Up to 660 kHz alias and image free output for 768 ksps IQ
  • 18 bit Embedded Digital Down Converter (DDC)
  • 22 bit! Resolution at 3 kHz channel using State of the Art DDC (SDR# and SDR-Console)
  • +10 dBm Maximum RF input
  • 0.5 ppm high precision, low phase noise clock
  • 1 PPB! frequency adjustment capability
  • Very low phase noise PLL (-110 dBc/Hz @ 1kHz separation @ 100 MHz)
  • Best Noise reduction of the market using state of the art algorithms
  • 2 x High Dynamic Range Sigma Delta ADCs @ up to 36 MSPS
  • No Silicon RF switch to introduce IMD in the HF path
  • Routable RF inputs with simple modification
  • Wide Band RF filter bank
  • Tracking RF filters
  • Sharp IF filters with 0.1 dB ripple
  • Smart AGC with real time optimization of the gain distribution
  • All RF inputs are matched to 50 ohms
  • 4 x Programmable GPIO’s
  • No drivers required! 100% Plug-and-play on Windows Vista, Seven, 8, 8.1 and 10
  • Industrial Operating Temperature: -45°C to 85°C
  • Full details at
The Airspy HF+
The Airspy HF+

Testing Public Airspy HF+ SpyServers over the Internet

SpyServer is a streaming server for SDR# which allows you to use Airspy and RTL-SDR radios remotely over a network connection. There is now a list of publicly available SpyServers that you can connect to over on the website.

The servers that are currently online include some streaming from Airspy HF+ devices, which is the hotly anticipated but as of yet unreleased HF receiver from Airspy. Over the last few months and weeks a number of prototype devices went out to testers and programmers and some have now put them online with a SpyServer. There are also some Airspy One/Mini and RTL-SDR devices available for streaming too.

To connect to one of the servers simply download the latest version of SDR# from, and then in SDR# select SpyServer from the Source menu. Enter the URL from the list into the box and press the play button up the top. Note that you must ensure that there are no spaces after entering the URL in SDR#.

Most servers are locked to a particular frequency band, but some allow for free tuning. But if more than one person is connected to the server free tuning will be locked until there is only one person connected again. Currently streaming from most servers seems smooth, but it's possible that some may struggle if many users are connected at once.

If you want to set up your own SpyServer then we recently put up a tutorial which is available here.

The current list of SpyServers
The current list of SpyServers

Alternative streaming SDR lists for other non-Airspy SDR hardware include and, but those stream compressed audio instead of IQ data.

RTL-SDR Tutorial: Setting up and using the SpyServer Remote Streaming Server with an RTL-SDR

A number of people have asked how to use SDR#'s SpyServer with an RTL-SDR. In this tutorial we will show how to set up SpyServer on both Windows and Linux systems. We try to assume as little knowledge as possible, but we do assume that you have decent experience with computers. Also for the Linux/Raspberry Pi setup we need to assume that you have some basic experience with Linux and setting up Raspberry Pi's.

What is SpyServer?

SpyServer is a free RTL-SDR compatible SDR server that is designed to work with the popular SDR# software. It is actually designed for the Airspy range of products, but the author has also made it compatible with RTL-SDR dongles. Running a SpyServer allows you to connect to and use a remotely positioned RTL-SDR over a network connection (such as a local LAN/WiFi or the Internet). Once connected, using the dongle is the same as if the dongle was directly connected to the users PC.

An example SpyServer Overview
An example SpyServer Overview (Can use an RTL-SDR instead of the Airspy HF+)

Remote servers are useful as you may want to set up an antenna in a remote location (such as up on your roof or shack), and don't want to run a long lossy coax cable down to the PC. Instead you could run Ethernet cable, or avoid cables by using WiFi. All you'd need is power for a remote computing device like a Raspberry Pi 3. Perhaps you also have a great antenna location at a friends house, or other property and want to access that antenna remotely. Or maybe you want to use your radio while travelling.

SpyServer is similar to another tool that you may already be familiar with called rtl_tcp. However, SpyServer is regarded as superior because it is signficantly more efficient at network usage. Instead of sending the entire raw data like rtl_tcp does, SpyServer only sends the IQ data of the currently tuned in signal. Waterfall data is processed on the server and sent in compressed form. There is one disadvantage to SpyServer in that it requires slightly more powerful computing hardware like a Pi 2 or Pi 3, whereas rtl_tcp can run on the lowest end hardware.

Network usage when streaming with SpyServer will be about 120 KB/s when listening to WFM and about 38 KB/s when listening to narrow band modes for one client being connected. Multiple clients can connect to the SpyServer and share the same currently tuned bandwidth.

Continue reading

SpyServer Updated: Very Efficient Network Usage with 8-Bit PCM Mode

Over the last month SDRSharp's SpyServer has been updated several times. SpyServer is a streaming server for SDR# which allows you to use Airspy and RTL-SDR radios remotely over a network connection.

The updates brought improvements such as IQ PCM compression at various bit depths including an efficient 8-bit mode, removing the DC spike residual in the 8-bit streaming mode, and recently improving the 8-bit mode to work like lossy compression for strong signals. 

We tested the new 8-bit PCM streaming mode and found it to be extremely efficient with network usage. When streaming at 2 MHz with an RTL-SDR a WFM signal on the older SpyServer versions used to use about 1.2 MB/s without any compression modes, and now with 8-bit compression active it only uses 322 KB/s. A NFM signal used to require 120 KB/s, now only requiring about 38 KB/s. No DC spike is present and no degradation in reception quality is noticeable unless the signal requires over 70 dB of dynamic range, which is unlikely for most signals.

If you've had trouble with SpyServer or rtl_tcp not working well on your slow network connection, then the new updated SpyServer may be the solution for you.

Prog, the author of SDR# and SpySever writes about the update on the Airspy group:

This new development allows you to stream large signals over 8bit and reduce the network bandwidth.

The server will try to pack the useful signals into whatever bit depth you select ensuring optimal SNR for the transport. No manual scaling required.

SpyServer with 8-Bit PCM IQ Compression
SpyServer with 8-Bit PCM IQ Compression

Airspy HF+ Real World Performance Examples by the Author of GQRX up on YouTube & Twitter

Alexander Csete (OZ9AEC) is the programmer behind the popular GQRX software. Recently Alexander has received a review sample of the upcoming Airspy HF+ and has been uploading videos showing it in action to his YouTube channel.

The Airspy HF+ is a soon to be released low cost (expected price $149 USD) yet high performance HF/VHF receiver designed for DXing with exceptional performance in the presence of strong overloading signals. If you are interested we also have our own review of the HF+ available here.

In the video below Alexander demonstrates the HF+ on SSB and CW modes in his GQRX software. See his YouTube channel for the rest of the videos. Currently there are about 7 videos demonstrating the HF+ on his channel.

Over on his Twitter account @csete Alex has also been uploading several images of the HF+ in action as well as some screenshots of it being compared against the RFSpace Cloud-IQ which is a $629 USD SDR. So far his impressions of the HF+ seem very high.