Category: Airspy

OpenWebRX now Supports the Airspy HF+

Thanks to Stefan Dambeck for letting us know that there is now a fork of libairspyhf made by DL9RDZ which contains an adapted version of airspyhf_rx (the raw IQ generator). This enables the Airspy HF+ to be easily integrated into OpenWebRX.

If you weren't aware, OpenWebRX is a browser based SDR interface and server software that allows an SDR to be used by multiple people at the same time over the internet. It performs audio demodulation and compression on the server side allowing for very low and efficient network usage.  In this way it is different to Airspy official server solution SpyServer which sends the IQ data over the network. So an OpenWebRX server uses significantly less network bandwidth and might be more suitable for those on slower or capped internet connections.

At the moment we're not seeing any public HF+ servers available on the OpenWebRX database at sdr.hu, but this may change in the future.

Airspy HF+ Running on the OpenWebRX Web Browser Interface
Airspy HF+ Running on the OpenWebRX Web Browser Interface

Using an Airspy SDR for Optical FM Spectroscopy

Spectroscopy is the study of how electromagnetic radiation interacts with matter and it can be used to study the internal structure of matter. At the DLR Institute for Technical Physics in Stutgart Germany, Peter Mahnke has been using an Airspy software defined radio as a "lock-in amplifier" in a FM spectroscopy setup. A lock-in amplifier is simply a type of amplifier that can extract a signal from a known carrier in an extremely noisy environment. 

In the experiment a laser is fiber optically coupled to an eletro-optic phase modulator, which modulates a 400 MHz FM signal onto the light. The light is then passed into a Carbon monoxide absorption cell with a photodiode used to take the spectroscopic measurements. The signal from the photodiode is passed into a LNA and then into the Airspy where the signal can then be processed on the PC.

The paper is very technical, but describes the setup, and how they characterized and calibrated the Airspy for their measurements. They conclude with the following:

A successful demonstration of a commercially available software defined radio as a lock-in amplifier was performed. For this purpose, the tuner front end and back end were characterized. The sensitivity and non-linearity of the receiver circuit was measured and analyzed. Acquisition of a CO spectral line was demonstrated using FM-spectroscopy with a repetition rate of 1 kHz. This proves the usability of an off-the-shelf SDR as a cheap but powerful lock-in amplifier by adding PLL driven frequency generators. The drawback of the arbitrary initial phase of the used phase locked loops can be either solved by software or hardware measures.

This experiment is somewhat similar to one we posted about earlier in the month where an RTL-SDR was used in an optical interferometer lab experiment.

FM Spectroscopy with an Airspy Software Defined Radio.
FM Spectroscopy with an Airspy Software Defined Radio.

Leif Compares the Airspy HF+ with the Airspy+Spyverter Combo

Over on YouTube Leif (sm5bsz) has uploaded a video where he compares the Airspy HF+ with the Airspy+Spyverter combination. In the test he compares the two radios at 7 MHz. The signals come in from an antenna, are amplified and then passed into a notch filter which notches at 7.198 MHz. The antenna signal is then passed into an attenuator, and then through a directional coupler and then split into the two radios. A signal generator is used to inject a signal via the directional coupler at the notch frequency, and this signal is used to compare the two radios. This method stops antenna noise from appearing at the notch frequency and so any non-linearities appearing in the notch must be a problem with the radio.

The results that Leif finds are quoted below. They show that although the Airspy HF+ has good linearity, it can still be significantly improved in tough environments by adding a front end filter for the band of interest.

The Airspy HF+ and the Airspy+Spyverter are compared on 7 MHz with and without a band pass filter on the input. Without the filter the HF+ is a little better than the Airspy+Spyverter combo, but when the filter is inserted, the HF+ is MUCH better than the combo.

In an earlier video Leif also compares the two Airspy units on FM broadcast and the 2 meter band. Again he shows that the Airspy HF+ is better than the standard Airspy, but adding a filter to block out the broadcast FM can still help fairly significantly when trying to listen to the 2M band on the HF+.

Video Comparing the Airspy HF+ and KiwiSDR

Over on YouTube user icholakov has uploaded a video comparing the Airspy HF+ with the KiwiSDR. The Airspy HF+ and KiwiSDR are both high performance yet low cost SDR platforms. The differences are that the Airspy HF+ is normally connected directly to a PC (but can be run remotely too) whereas the KiwiSDR is designed to be run remotely only, and so can only be accessed through a browser platform. In addition the HF+ only has maximum live bandwidth of 660 kHz whereas the KiwiSDR samples the entire 30 MHz of the HF band. Both are very sensitive and fairly resistant to overloading, but the HF+ should be better in both regards.

In his video icholakov does side by side comparisons with each radio. He writes

Comparing short wave and medium wave reception from Airspy HF+ SDR Console 3 and KiwiSDR with its built in web server. Using the same 80m dipole antenna. No special noise cancelling on the Airspy HF Plus.

Airspy HF+ vs. Kiwisdr SDR Radio comparison

Testing the Airspy HF+ Against the FDM-S2 on the Medium and Long Wave Bands

Over on the swling.com blog (short wave listening) contributor Guy Atkins has posted about his comparisons of the Airspy HF+ and the Elad FDM-S2 SDRs on the Medium Wave band. In the test he connected the two SDRs to the same ALA1530S+ Welbrook loop antenna via a splitter and recorded some audio comparisons.

It appears that the Airspy HF+ even outperforms the FDM-S2 on one particular test where he tries to listen to 1540 kHz which is just 10 kHz away from a strong signal at 1550 kHz. He also writes:

It became apparent quickly that the upstart HF+ provides strong competition to the Elad SDR. Clearly, the AirSpy’s trade-off is bandwidth for raw performance at lower cost–approx. 660 kHz alias-free coverage versus about 6 MHz maximum for the Elad.

Also in a later post on the swling.com blog Guy makes an addendum where he swaps out his ALA1530S+ Wellbrook loop antenna for the ALA1530LN Pro which overloads his receivers less. He notes that with the new antenna 6 dB of attenuation is required for the FSM-S2 in order to prevent overloading. With the HF+ very little overloading apart from a weak image could be found, and that was removed by adding 3 dB of attenuation.

He also tests longwave reception with the two receivers, and this time finds that the HF+ seems to have additional MW spurs in the LW band, compared with the FDM-S2.

The Airspy HF+ and Elad FDM-S2.
The Airspy HF+ and Elad FDM-S2.

Airspy HF+ Can Receive L-Band 1.2 GHz to 1.67 GHz

The Airspy HF+ is a much anticipated and recently released software defined radio that specializes in HF and VHF reception. However, one little known and not often advertised feature is that it can actually be used for L-band reception between 1.2 and 1.67 GHz as well. This means that it could be used for signals such as AERO, STD-C, Iridium, the 23cm amateur radio band and more.

Over on YouTube Adam 9A4QV has uploaded a video that tests the HF+ with Alphasat AERO signals at about 1.545 GHz. He notes that the sensitivity is quite good as it is able to receive the satellite signals directly with only the antenna connected and no external LNA used. Of course adding in an external low noise figure LNA and filter would improve the signal even further. Adam notes that reception on the 23cm amateur band (1240 MHz to 1300 MHz) is also quite good with sensitivity reaching about -130 dBm.

Airspy HF+ L-band satcom test

Video Comparison of the Airspy HF+ and SDRplay RSP1A on the FM Broadcast Band

Frequent reviewer of SDR products Mile Kokotov has just uploaded on his YouTube channel a new video where he compares the Airspy HF+ against the SDRplay RSP1A on FM broadcast reception.

At first Mile compares the two against strong broadcast stations, and then later compares them on weak DX stations surrounded in amongst other strong stations. With the strong stations a difference between the two radios is impossible to detect. But with the weaker stations that are surrounded by strong signals the Airspy HF+ has the edge with it's higher dynamic range and sensitivity.

Mile writes:

In this video I am comparing two popular SDR-Receivers (Airspy HF+ and SDRplay RSP1A) on FM Broadcast Band.

I have made few recordings with every receiver with the same antenna trying to set the best SNR = signal-to-noise ratio.

My intention was to ensure the same conditions for both SDR`s in order to make as fair as possible comparison.

No DSP enhancing on the SDR`s was used.

Antenna was Vertical Dipole.

When receiving signals are strong enough, You should not expect the difference between most receivers to be very obvious!

If you compare one average transceiver (which cost about $ 1000 USD) and top class transceiver which cost ten times more, the difference in receiving average signals will be very small too. Almost negligible! But when you have difficult conditions, the very weak signal between many strong signals, than the better receiver will receive the weak signal readable enough, but cheaper receiver will not. Today it is not a problem to design and produce the sensitive receiver, but it is far more difficult to design and produce high dynamic receiver for reasonable price! The Airspy HF+ and RSP1A are very very good SDR-receivers. They have different customers target and have strong and weak sides. For examle Airspy HF+ has better dynamics in frequency range where it is designed for, but RSP1A, on the other hand, has broadband coverage...

Airspy HF+ vs SDRplay RSP1A Comparison on FM Broadcast Band

Video Comparison of the Airspy HF+, SDRplay RSP1A and ColibriNANO on VLF to MF

Over on his YouTube Channel Mile Kokotov has uploaded a video that compares three mid priced SDRs: the Airspy HF+, the SDRplay RSP1A and the ColibriNANO. Each SDR is compared on several ALPHA and NBD morse code stations which exist in his tests from between 14 kHz to 474 kHz. He writes:

In this video I am comparing three SDR-Receivers. I have made few recordings with every receiver with the same antenna and choose the best one (one with the best SNR = signal-to-noise ratio). My intention was to ensure the same conditions for all three SDR`s in order to make as fair as possible comparison. For example, I was set the frequency span displayed on the window to be as same as possible for all three receivers. The vertical axis for the signal stregth, was set to be equal (in decibels) too.Airspy HF+ and ColibriNANO was set to their minimum sample rate (48 kHz). RSP1A was set to minimum sample rate (2 MHz and 8 decimation).

No DSP enhancing on the SDR`s was used except APF (Audio peak filter) on ColibriNANO (I forgot to swith off).

The differences between each receiver as very difficult to detect as only really challenging signal conditions will really set them apart. Mile also added in a comment:

You should not expect the difference to be very obvious! If you compare one average transceiver (which cost about $ 1000 USD) and top class transceiver which cost ten times more, the difference in the receiving the average signals will be very small too. Almost negligible! But when you have difficult conditions, the very weak signal between many strong signals, than the better receiver will receive the weak signal readable enough, but cheaper receiver will not. Today it is not a problem to design and produce the sensitive receiver, but it is very difficult to design and produce high dynamic receiver for reasonable price! The Airspy HF+ and RSP1A are very very good SDR-receivers. They have different customers target and have strong and weak sides. For example Airspy HF+ has better dynamics in frequency range where it is designed for, but RSP1A, on the other hand, has broadband coverage...

SDR Receivers Comparison on VLF, LW and NDB band