Akos of the rtlsdr4everyone blog has recently written up a comparison of the RTL-SDR and SDRplay. The SDRplay is a $149 USD software defined radio with a 100 kHz to 2 GHz frequency range, a 12-bit ADC, and up to 8 MHz of bandwidth. It now competes heavily with the $99 Airspy Mini which is a similarly specced SDR.
Akos compares the two units and comes to the conclusion that the RTL-SDR is still the best choice for beginners, but that the SDRplay is definitely a good choice if you have good antennas in place and if the receiver is the major bottleneck in your setup.
In his review he goes over several points covering the costs involved, aesthetics, customer support, PC hardware requirements, setup, operation and finally reviews the performance of the SDRplay. His results show that the SDRplay generally receives much better than the RTL-SDR, but has some problems with broadcast FM imaging.
The SDRplay team have been hard at work during the last few weeks. First they announced beta support for Android via SDRtouch, then they announced an improved ADS-B decoder, and finally they have just announced their acquisition of Studio1.
The SDRplay is a 12-bit software defined radio with tuning range between 100kHz – 2 GHz. Many consider it along with the Airspy to be the next stage up from an RTL-SDR dongle.
Android Support
The author of SDRTouch on Android recently announced support for the SDRplay. SDRTouch is a Android program similar in operation to PC based software like SDR#. To access the beta you can sign up at this link. Currently there is support for up to 2 MHz of bandwidth.
SDR Touch demo on Android device using SDRplay RSP
Improved ADS-B Decoder
Back in March the SDRplay team released ADS-B decoder software for their SDR with the promise of improving its performance in the near future.
Recently the SDRplay team released an updated version of their ADS-B decoder for the Raspberry Pi which now fully utilizes the full 12-bits of the ADC and takes advantage of the full 8 MHz bandwidth. Jon, the head of marketing at SDRplay writes the following:
We now have an updated beta version of ADS-B for both the Raspberry Pi 2 and 3. This is based upon the 16bit Mutability version of dump1090 developed by Oliver Jowett and unlocks the full 12 bit performance of the RSP1. People should see a significant performance improvement over the dump1090_sdrplus version, which was based upon 8 bit code. The latest beta version can be downloaded in binary form from http://www.sdrplay.com/rpi_adsb.html . Should anyone have questions or feedback, please contact [email protected]
We plan to eventually compare the SDRplay with the Airspy and RTL-SDR on ADS-B performance. If you are interested we previously did a review of the SDRplay, Airspy and HackRF here, but as the SDRplay did not have ADS-B back then, that particular test was not done.
Acquisition of Studio1 SDR Software
The last major piece of news is that SDRplay have now acquired the Studio1 SDR software. Studio1 is a paid SDR program, similar in nature to SDR#/HDSDR/SDR-Console. Like HDSDR, Studio1 is a spinoff from the old WinRad software. Their press release reads:
SDRplay Limited has today announced that it has reached an agreement with Sandro Sfregola, (formerly CEO of SDR Applications S.a.s.) to acquire all Rights, Title and Interest in Studio 1 a leading software package for Software Defined Radio applications.
Jon Hudson, SDRplay Marketing Director said: “We are delighted to have reached this agreement with Sandro to acquire Studio 1. Studio 1 is the perfect complement to our SDR hardware products and gives us the ideal platform to deliver a complete class leading SDR solution for our customers. We look forward to working with Sandro and further developing Studio 1 to unlock the full capability of our current and future products”.
Hudson added: “Studio1 has established a strong customer base with users of many other SDR hardware products. Studio 1 will continue to be available as a stand-alone product from WoodBoxRadio http://www.woodboxradio.com/studio1.html for the foreseeable future , but we also look forward to further developing Studio 1 to specifically benefit present and future owners of our products”
Sandro Sfregola added: “I am very pleased to have reached this agreement with SDRplay. The long term future for SDR lies in complete end to end solutions and I feel the SDRplay RSP combined with Studio 1 software gives users an outstanding combination of performance and affordability”.
About Studio 1:
Studio1 was developed in Italy by SDR Applications S.a.s. and has hundreds of happy customers around the world.Studio 1 is known for its user friendly stylish GUI, CPU efficiency and advanced DSP capabilities, including features notavailable on other SDR software packages.
www.sdrapplications.it
About SDRplay:
SDRplay limited is a UK company and consists of a small group of engineers with strong connections to the UK Wireless semiconductor industry. SDRplay announced its first product, the RSP1 in August 2014
www.sdrplay.com
We believe that this is a good move for SDRplay, as one of the major issues with the RSP SDR was the lack of decently supported software.
Over on YouTube user London Shortwave has uploaded a video showing a comparison of the FunCube Dongle Pro+, Airspy with SpyVerter upconverter and SDRplay on shortwave reception. The Funcube, Airspy and SDRplay are all $150 – $250 USD software defined radios that have much higher performance compared to the RTL-SDR.
In the video he tests the reception of Radio New Zealand International (RNZI) at 9400 kHz using a 6m copper wire dipole and 9:1 matching balun raised 2m off the ground. He did not use any external antenna preselectors. The RNZI station is weak and appears to be almost blocked by a stronger station so reception of the station is difficult.
In his results it appears that the FunCube and Airspy/SpyVerter are able to clearly receive the RNZI station, but the SDRplay has trouble with images of other stations mixing into the signal.
A new ADS-B decoder for the SDRplay RSP has recently been released by the SDRplay programmers. The SDRplay is a $149 USD software defined radio with a 0.1 – 2000 MHz range, 12-bit ADC and up to 8 MHz of bandwidth. In a previous review we compared it against the Airspy and HackRF.
The SDRplay team have based their new decoder on the multi-platform compatible dump1090 code, which is an ADS-B decoder that was originally written for the RTL-SDR. The Windows version can be be downloaded from http://www.sdrplay.com/windows.html, and the code for other platforms can be downloaded from https://github.com/SDRplay.
To help with the installation procedure the SDRplay has also provided a manual (pdf) which shows exactly how to download and set up the required ADS-B software on a Windows system. They also write that the software is fairly new and is still being optimized for best performance.
In the future after the software is further optimized we hope to compare the RSP against the RTL-SDR and Airspy on ADS-B reception.
The SDRplay compatible version of dump1090 deceiving ADS-B data.
The SDRplay RSP is a $149 USD software defined radio that many consider as a next step upgrade from the RTL-SDR. See our recent review for a comparison between the Airspy, SDRplay RSP and HackRF.
One problem with the SDRplay RSP is that it comes in an unshielded plastic enclosure. This means that strong interfering signals can pass through the enclosure and cause interference, making any filtering done on the antenna less effective. Recently Tom Naumovski wrote in to us to let us know that he has been experimenting with a simple fix that involves shielding his RSP with adhesive copper tape. (Tom carefully notes that doing this may void the warranty). Tom simply wraps the plastic enclosure with conductive copper tape, making sure that electrical contact is made between the copper shielding and RSP ground (e.g. making sure the RSP USB and SMA ports make electrical contact with the copper tape)
Copper tape shielding for the RSP.
After shielding the RSP, Tom tested the shielding effectiveness by using his shielded RSP with no antenna connected to try and pick up an interfering tone transmitted by his HackRF SDR. He collected the results in a pdf file. The results clearly show that the shielded RSP does not pick up, or significantly reduces the power of the HackRF’s interfering tone.
IMPORTANT NOTE: Please note that this review is now out of date as the SDRplay RSP line has received significant improvements to their hardware and Airspy have brought out a new SDR that is much better at HF.
Overall it is now difficult to pick a winner between Airspy and SDRplay products. However, our preference is the Airspy HF+ Discovery for HF signals, and the SDRplay RSP1A for generic wideband wide frequency range receiving.
When people consider upgrading from the RTL-SDR, there are three mid priced software defined radios that come to most peoples minds: The Airspy (store), the SDRplay RSP (store) and the HackRF (store). These three are all in the price range of $150 to $300 USD. In this post we will review the Airspy, review the SDRplay RSP and review the HackRF and compare them against each other on various tests.
Note that this is a very long review. If you don't want to read all of this very long post then just scroll down to the conclusions at the end.
What makes a good SDR?
In this review we will only consider RX performance. So first we will review some terminology, features and specifications that are required for a good RX SDR.
SNR - When receiving a signal the main metric we want to measure is the "Signal to Noise" (SNR) ratio. This is the peak signal strength minus the noise floor strength.
Bandwidth - A larger bandwidth means more signals on the screen at once, and more software decimation (better SNR). The downside is that greater CPU power is needed for higher bandwidths.
Alias Free Bandwidth - The bandwidth on SDR displays tends to roll off at the edges, and also display aliased or images of other signals. The alias free bandwidth is the actual usable bandwidth and is usually smaller than the advertised bandwidth.
Sensitivity - More sensitive radios will be able to hear weaker stations easier, and produce high SNR values.
ADC - Analogue to digital converter. The main component in an SDR. It samples an analogue signal and turns it into digital bits. The higher the bit size of the ADC the more accurate it can be when sampling.
Overloading - Overloading occurs when a signal is too strong and saturates the ADC, leaving no space for weak signals to be measured. When overloading occurs you'll see effects like severely reduced sensitivity and signal images.
Dynamic Range - This is directly related to ADC bit size, but is also affected by DSP software processing. Dynamic range is the ability of an SDR to receive weak signals when strong signals are nearby. The need for high dynamic range can be alleviated by using RF filtering. Overloading occurs when a strong signal starts to saturate the ADC because the dynamic range was not high enough.
Images/Aliasing - Bad SDRs are more likely to overload and show images of strong signals at frequencies that they should not be at. This can be fixed with filtering or by using a higher dynamic range/higher bit receiver.
Noise/Interference - Good SDRs should not receive anything without an antenna attached. If they receive signals without an antenna, then interfering signals may be entering directly through the circuit board, making it impossible to filter them out. Good SDRs will also cope well with things like USB interference.
RF Filtering/Preselection - A high performance SDR will have multiple preselector filters that switch in depending on the frequency you are listening to.
Center DC Spike - A good SDR should have the I/Q parts balanced so that there is no DC spike in the center.
Phase Noise - Phase noise performance is determined by the quality of the crystal oscillators used. Lower phase noise oscillators means better SNR for narrowband signals and less reciprocal mixing. Reciprocal mixing is when high phase noise causes a weak signal to be lost in the phase noise of a nearby strong signal.
Frequency Stability - We should expect the receiver to stay on frequency and not drift when the temperature changes. To achieve this a TCXO or similar stable oscillator should be used.
RF Design - The overall design of the system. For example, how many lossy components such as switches are used in the RF path. As the design complexity increases usually more components are added to the RF path which can reduce RX performance.
Software - The hardware is only half of an SDR. The software the unit is compatible with can make or break an SDRs usefulness.
Next we will introduce each device and its advertised specifications and features:
Device Introduction and Advertised Specifications & Features
As of April 2016, the Airspy Mini is now also for sale at $99 USD.
$149 USD + shipping ($20-$30 world, free shipping in the USA)
£99 + VAT + ~£10 shipping for EU.
$299 USD + shipping
Freq. Range (MHz)
24 - 1800
0 - 1800 (with Spyverter addon)
0.1 - 2000
0.1 - 6000
ADC Bits
12 (10.4 ENOB)
12 (10.4 ENOB)
8
Bandwidth (MHz)
10 (9 MHz usable)
6 MHz (5 MHz usable) (AS Mini)
8 (7 MHz usable) (10 MHz in SDRuno/~9 MHz usable)
20
TX
No
No
Yes (half duplex)
Dynamic Range (Claimed)(dB)
80
67
~48
Clock Precision (PPM)
0.5 PPM low phase noise TCXO
10 PPM XO
30 PPM XO
Frontend Filters
Front end tracking IF filter on the R820T2 chip.
8 switched preselection filters + switchable IF filter on MSI001 chip
Two very wide preselection filters - 2.3 GHz LPF, 2.7 GHz HPF
ADC, Frontend Chips
LPC4370 ARM, R820T2
MSi2500, MSi001
MAX5864, RFFC5071
Additional Features
4.5v bias tee, external clock input, expansion headers.
LNA on the front end
5v bias tee, LNA on front end, external clock input, expansion headers.
Notes
The Airspy is designed by Benjamin Vernoux & Youssef Touil who is also the author of the popular SDR# software.
Of note is that there has been a misconception going around that the Airspy is an RTL-SDR/RTL2832U device. This is not true; there are no RTL2832U chips in the Airspy. The confusion may come from the fact that they both use the R820T2 tuner. The RTL2832U chip is the main bottleneck in RTL-SDR devices, not the R820T2. When coupled with a better ADC, the R820T2 works well and can be used to its full potential.
The Airspy team write that they sell units mostly to universities, governments and professional RF users. However, they also have a sizable number of amateur users.
Update: As of April 2016 the Airspy Mini is now for sale for $99 USD. The main difference is a 6 MHz bandwidth and fewer expansion headers, but all other specs appear to be the same.
The SDR Play Radio Spectrum Processor (RSP) is designed by UK based engineers who appear to be affiliated with Mirics, a UK based producer of SDR RF microchips.
The chips used in the SDRplay RSP are dedicated SDR chips which were designed for a wide variety of applications such as DVB-T tuners. The RSP uses these chips and improves on their front end capabilities by adding an LNA and filters in order to create a device capable of general SDR use.
Initially when writing this review we had deep problems with the imaging of strong signals on the RSP. However, a recent Dec 22 update to the drivers has fixed this imaging problem tremendously.
The HackRF is designed by Micheal Ossmann a computer security researcher who was given a development grant from DARPA. His company is called "Great Scott Gadgets".
The HackRF's most unique feature when compared to the other two SDR's is that it is capable of both receiving and transmitting.
There is also a clone called the HackRF Blue out on the market which is about $100 cheaper, but they don't seem to have stock or be producing these any more.
From the specs it is clear from the ADC sizes that both the Airspy and SDRplay RSP are in a different class of RX performance when compared to the HackRF. However, people always compare the Airspy and SDRplay with the HackRF due to their similar price range, so we will continue to compare the three here in our review, but with more of a focus on comparing the Airspy and SDRplay RSP.
In order to use the Airspy on HF (0 - 30 MHz) frequencies a $50 add on called the Spyverter is required. This is an upconverter that is designed for use with the Airspy's high dynamic range and bias tee power port. However, one hassle is that the Spyverter must be connected/disconnected each time you want to switch between HF and VHF/UHF reception as it does not have VHF/UHF passthrough. The RSP and HackRF on the other hand can receive HF to UHF without the need of an upconverter or the need to change ports. A single port for HF to UHF can be very useful if you have a remote antenna switcher.
Post continues. Note that this is a long post with many images.
The SDRplay team have recently released a major update to their API and drivers. The new version is 1.8.0 and they write that it should remove the DC offset, reduce in band images from strong signals, and lower the noise floor. The SDRplay is a software defined receiver that costs $149 USD. They write:
We are pleased to announce release 1.8.0 of the API for the RSP. This is a major upgrade to the API with new features and an improved gain map which should result in improved performance over a key portion of the gain control range. Currently this API is available for Windows only, but versions for Linux and Mac OS and Android will follow shortly.
The API now incorporates automatic post tuner DC offset correction and I/Q compensation. This will almost completely eliminate the DC centre spike that was previously present in zero IF mode and also correct for amplitude and phase errors in the I/Q signal paths that can lead to in-band images when strong signals are present.
There is a new gain map for the RSP which should help improve the receiver noise floor for gain reduction settings in the range of 59-78 dB. To achieve this, the IF gain control range has been increased from 59 to 78 dB. In addition, the user can now turn the LNA on or off at any point within the IF gain control range. This means that the LNA can remain on for gain reduction settings of up to 78 dB, whereas previously the maximum gain reduction that could be attained whilst the LNA was on was only 59 dB. Being able to leave the LNA on will result in improvements in the receiver noise performance for gain reductions in the range of 59 to 78 dB. The upper 19 dB of the IF gain control range have now been disabled. In practice this part of the gain control range was useless as trying to operate within this region always lead to receiver overload even when signals were very weak.
To fully exploit the features of this new API release, we have also issued release 3.5 of the ExtIO plugin. This plugin will work with HDSDR, SDR sharp (releases 1361 or earlier) and Studio 1. Automatic I/Q compensation and DC offset correction will work with later versions of SDR sharp, but we will need to update the native plugin for users of these later versions to be access the new gain map.
Similarly, users of SDR Console will gain the benefit of automatic DC offset compensation and I/Q correction, but will not yet be able to access the new gain map. We hope that a version of SDR console that unlocks this feature will become available in the near future.
Until a new release of SDR-Console is available, you can copy the API into the SDR-Console installation directory…
from C:\Program Files\MiricsSDR\API\x64\mir_sdr_api.dll to C:\Program Files\SDR-RADIO-PRO.com\mir_sdr_api.dll
The API installer has also contains an extra certificate to be more user friendly for Windows XP, Vista and Windows 7 users.
As they write that in band images from strong signals are reduced in this version we decided to do a quick before and after test using our own RSP receiver. We tuned into some TETRA signals that had exhibited images in the past on our RSP (you can see them as the yellow signals in the before image). In the new driver the images are completely gone.
Akos of the rtlsdr4everyone blog has recently written up a comparison of the RTL-SDR and SDRplay. The SDRplay is a $149 USD software defined radio with a 100 kHz to 2 GHz frequency range, a 12-bit ADC, and up to 8 MHz of bandwidth. It now competes heavily with the $99 Airspy Mini which is a similarly specced SDR.
Akos compares the two units and comes to the conclusion that the RTL-SDR is still the best choice for beginners, but that the SDRplay is definitely a good choice if you have good antennas in place and if the receiver is the major bottleneck in your setup.
In his review he goes over several points covering the costs involved, aesthetics, customer support, PC hardware requirements, setup, operation and finally reviews the performance of the SDRplay. His results show that the SDRplay generally receives much better than the RTL-SDR, but has some problems with broadcast FM imaging.
The SDRplay team have been hard at work during the last few weeks. First they announced beta support for Android via SDRtouch, then they announced an improved ADS-B decoder, and finally they have just announced their acquisition of Studio1.
The SDRplay is a 12-bit software defined radio with tuning range between 100kHz – 2 GHz. Many consider it along with the Airspy to be the next stage up from an RTL-SDR dongle.
Android Support
The author of SDRTouch on Android recently announced support for the SDRplay. SDRTouch is a Android program similar in operation to PC based software like SDR#. To access the beta you can sign up at this link. Currently there is support for up to 2 MHz of bandwidth.
SDR Touch demo on Android device using SDRplay RSP
Improved ADS-B Decoder
Back in March the SDRplay team released ADS-B decoder software for their SDR with the promise of improving its performance in the near future.
Recently the SDRplay team released an updated version of their ADS-B decoder for the Raspberry Pi which now fully utilizes the full 12-bits of the ADC and takes advantage of the full 8 MHz bandwidth. Jon, the head of marketing at SDRplay writes the following:
We now have an updated beta version of ADS-B for both the Raspberry Pi 2 and 3. This is based upon the 16bit Mutability version of dump1090 developed by Oliver Jowett and unlocks the full 12 bit performance of the RSP1. People should see a significant performance improvement over the dump1090_sdrplus version, which was based upon 8 bit code. The latest beta version can be downloaded in binary form from http://www.sdrplay.com/rpi_adsb.html . Should anyone have questions or feedback, please contact [email protected]
We plan to eventually compare the SDRplay with the Airspy and RTL-SDR on ADS-B performance. If you are interested we previously did a review of the SDRplay, Airspy and HackRF here, but as the SDRplay did not have ADS-B back then, that particular test was not done.
Acquisition of Studio1 SDR Software
The last major piece of news is that SDRplay have now acquired the Studio1 SDR software. Studio1 is a paid SDR program, similar in nature to SDR#/HDSDR/SDR-Console. Like HDSDR, Studio1 is a spinoff from the old WinRad software. Their press release reads:
SDRplay Limited has today announced that it has reached an agreement with Sandro Sfregola, (formerly CEO of SDR Applications S.a.s.) to acquire all Rights, Title and Interest in Studio 1 a leading software package for Software Defined Radio applications.
Jon Hudson, SDRplay Marketing Director said: “We are delighted to have reached this agreement with Sandro to acquire Studio 1. Studio 1 is the perfect complement to our SDR hardware products and gives us the ideal platform to deliver a complete class leading SDR solution for our customers. We look forward to working with Sandro and further developing Studio 1 to unlock the full capability of our current and future products”.
Hudson added: “Studio1 has established a strong customer base with users of many other SDR hardware products. Studio 1 will continue to be available as a stand-alone product from WoodBoxRadio http://www.woodboxradio.com/studio1.html for the foreseeable future , but we also look forward to further developing Studio 1 to specifically benefit present and future owners of our products”
Sandro Sfregola added: “I am very pleased to have reached this agreement with SDRplay. The long term future for SDR lies in complete end to end solutions and I feel the SDRplay RSP combined with Studio 1 software gives users an outstanding combination of performance and affordability”.
About Studio 1:
Studio1 was developed in Italy by SDR Applications S.a.s. and has hundreds of happy customers around the world.Studio 1 is known for its user friendly stylish GUI, CPU efficiency and advanced DSP capabilities, including features notavailable on other SDR software packages.
www.sdrapplications.it
About SDRplay:
SDRplay limited is a UK company and consists of a small group of engineers with strong connections to the UK Wireless semiconductor industry. SDRplay announced its first product, the RSP1 in August 2014
www.sdrplay.com
We believe that this is a good move for SDRplay, as one of the major issues with the RSP SDR was the lack of decently supported software.
Over on YouTube user London Shortwave has uploaded a video showing a comparison of the FunCube Dongle Pro+, Airspy with SpyVerter upconverter and SDRplay on shortwave reception. The Funcube, Airspy and SDRplay are all $150 – $250 USD software defined radios that have much higher performance compared to the RTL-SDR.
In the video he tests the reception of Radio New Zealand International (RNZI) at 9400 kHz using a 6m copper wire dipole and 9:1 matching balun raised 2m off the ground. He did not use any external antenna preselectors. The RNZI station is weak and appears to be almost blocked by a stronger station so reception of the station is difficult.
In his results it appears that the FunCube and Airspy/SpyVerter are able to clearly receive the RNZI station, but the SDRplay has trouble with images of other stations mixing into the signal.
A new ADS-B decoder for the SDRplay RSP has recently been released by the SDRplay programmers. The SDRplay is a $149 USD software defined radio with a 0.1 – 2000 MHz range, 12-bit ADC and up to 8 MHz of bandwidth. In a previous review we compared it against the Airspy and HackRF.
The SDRplay team have based their new decoder on the multi-platform compatible dump1090 code, which is an ADS-B decoder that was originally written for the RTL-SDR. The Windows version can be be downloaded from http://www.sdrplay.com/windows.html, and the code for other platforms can be downloaded from https://github.com/SDRplay.
To help with the installation procedure the SDRplay has also provided a manual (pdf) which shows exactly how to download and set up the required ADS-B software on a Windows system. They also write that the software is fairly new and is still being optimized for best performance.
In the future after the software is further optimized we hope to compare the RSP against the RTL-SDR and Airspy on ADS-B reception.
The SDRplay compatible version of dump1090 deceiving ADS-B data.
The SDRplay RSP is a $149 USD software defined radio that many consider as a next step upgrade from the RTL-SDR. See our recent review for a comparison between the Airspy, SDRplay RSP and HackRF.
One problem with the SDRplay RSP is that it comes in an unshielded plastic enclosure. This means that strong interfering signals can pass through the enclosure and cause interference, making any filtering done on the antenna less effective. Recently Tom Naumovski wrote in to us to let us know that he has been experimenting with a simple fix that involves shielding his RSP with adhesive copper tape. (Tom carefully notes that doing this may void the warranty). Tom simply wraps the plastic enclosure with conductive copper tape, making sure that electrical contact is made between the copper shielding and RSP ground (e.g. making sure the RSP USB and SMA ports make electrical contact with the copper tape)
Copper tape shielding for the RSP.
After shielding the RSP, Tom tested the shielding effectiveness by using his shielded RSP with no antenna connected to try and pick up an interfering tone transmitted by his HackRF SDR. He collected the results in a pdf file. The results clearly show that the shielded RSP does not pick up, or significantly reduces the power of the HackRF’s interfering tone.
IMPORTANT NOTE: Please note that this review is now out of date as the SDRplay RSP line has received significant improvements to their hardware and Airspy have brought out a new SDR that is much better at HF.
Overall it is now difficult to pick a winner between Airspy and SDRplay products. However, our preference is the Airspy HF+ Discovery for HF signals, and the SDRplay RSP1A for generic wideband wide frequency range receiving.
When people consider upgrading from the RTL-SDR, there are three mid priced software defined radios that come to most peoples minds: The Airspy (store), the SDRplay RSP (store) and the HackRF (store). These three are all in the price range of $150 to $300 USD. In this post we will review the Airspy, review the SDRplay RSP and review the HackRF and compare them against each other on various tests.
Note that this is a very long review. If you don't want to read all of this very long post then just scroll down to the conclusions at the end.
What makes a good SDR?
In this review we will only consider RX performance. So first we will review some terminology, features and specifications that are required for a good RX SDR.
SNR - When receiving a signal the main metric we want to measure is the "Signal to Noise" (SNR) ratio. This is the peak signal strength minus the noise floor strength.
Bandwidth - A larger bandwidth means more signals on the screen at once, and more software decimation (better SNR). The downside is that greater CPU power is needed for higher bandwidths.
Alias Free Bandwidth - The bandwidth on SDR displays tends to roll off at the edges, and also display aliased or images of other signals. The alias free bandwidth is the actual usable bandwidth and is usually smaller than the advertised bandwidth.
Sensitivity - More sensitive radios will be able to hear weaker stations easier, and produce high SNR values.
ADC - Analogue to digital converter. The main component in an SDR. It samples an analogue signal and turns it into digital bits. The higher the bit size of the ADC the more accurate it can be when sampling.
Overloading - Overloading occurs when a signal is too strong and saturates the ADC, leaving no space for weak signals to be measured. When overloading occurs you'll see effects like severely reduced sensitivity and signal images.
Dynamic Range - This is directly related to ADC bit size, but is also affected by DSP software processing. Dynamic range is the ability of an SDR to receive weak signals when strong signals are nearby. The need for high dynamic range can be alleviated by using RF filtering. Overloading occurs when a strong signal starts to saturate the ADC because the dynamic range was not high enough.
Images/Aliasing - Bad SDRs are more likely to overload and show images of strong signals at frequencies that they should not be at. This can be fixed with filtering or by using a higher dynamic range/higher bit receiver.
Noise/Interference - Good SDRs should not receive anything without an antenna attached. If they receive signals without an antenna, then interfering signals may be entering directly through the circuit board, making it impossible to filter them out. Good SDRs will also cope well with things like USB interference.
RF Filtering/Preselection - A high performance SDR will have multiple preselector filters that switch in depending on the frequency you are listening to.
Center DC Spike - A good SDR should have the I/Q parts balanced so that there is no DC spike in the center.
Phase Noise - Phase noise performance is determined by the quality of the crystal oscillators used. Lower phase noise oscillators means better SNR for narrowband signals and less reciprocal mixing. Reciprocal mixing is when high phase noise causes a weak signal to be lost in the phase noise of a nearby strong signal.
Frequency Stability - We should expect the receiver to stay on frequency and not drift when the temperature changes. To achieve this a TCXO or similar stable oscillator should be used.
RF Design - The overall design of the system. For example, how many lossy components such as switches are used in the RF path. As the design complexity increases usually more components are added to the RF path which can reduce RX performance.
Software - The hardware is only half of an SDR. The software the unit is compatible with can make or break an SDRs usefulness.
Next we will introduce each device and its advertised specifications and features:
Device Introduction and Advertised Specifications & Features
As of April 2016, the Airspy Mini is now also for sale at $99 USD.
$149 USD + shipping ($20-$30 world, free shipping in the USA)
£99 + VAT + ~£10 shipping for EU.
$299 USD + shipping
Freq. Range (MHz)
24 - 1800
0 - 1800 (with Spyverter addon)
0.1 - 2000
0.1 - 6000
ADC Bits
12 (10.4 ENOB)
12 (10.4 ENOB)
8
Bandwidth (MHz)
10 (9 MHz usable)
6 MHz (5 MHz usable) (AS Mini)
8 (7 MHz usable) (10 MHz in SDRuno/~9 MHz usable)
20
TX
No
No
Yes (half duplex)
Dynamic Range (Claimed)(dB)
80
67
~48
Clock Precision (PPM)
0.5 PPM low phase noise TCXO
10 PPM XO
30 PPM XO
Frontend Filters
Front end tracking IF filter on the R820T2 chip.
8 switched preselection filters + switchable IF filter on MSI001 chip
Two very wide preselection filters - 2.3 GHz LPF, 2.7 GHz HPF
ADC, Frontend Chips
LPC4370 ARM, R820T2
MSi2500, MSi001
MAX5864, RFFC5071
Additional Features
4.5v bias tee, external clock input, expansion headers.
LNA on the front end
5v bias tee, LNA on front end, external clock input, expansion headers.
Notes
The Airspy is designed by Benjamin Vernoux & Youssef Touil who is also the author of the popular SDR# software.
Of note is that there has been a misconception going around that the Airspy is an RTL-SDR/RTL2832U device. This is not true; there are no RTL2832U chips in the Airspy. The confusion may come from the fact that they both use the R820T2 tuner. The RTL2832U chip is the main bottleneck in RTL-SDR devices, not the R820T2. When coupled with a better ADC, the R820T2 works well and can be used to its full potential.
The Airspy team write that they sell units mostly to universities, governments and professional RF users. However, they also have a sizable number of amateur users.
Update: As of April 2016 the Airspy Mini is now for sale for $99 USD. The main difference is a 6 MHz bandwidth and fewer expansion headers, but all other specs appear to be the same.
The SDR Play Radio Spectrum Processor (RSP) is designed by UK based engineers who appear to be affiliated with Mirics, a UK based producer of SDR RF microchips.
The chips used in the SDRplay RSP are dedicated SDR chips which were designed for a wide variety of applications such as DVB-T tuners. The RSP uses these chips and improves on their front end capabilities by adding an LNA and filters in order to create a device capable of general SDR use.
Initially when writing this review we had deep problems with the imaging of strong signals on the RSP. However, a recent Dec 22 update to the drivers has fixed this imaging problem tremendously.
The HackRF is designed by Micheal Ossmann a computer security researcher who was given a development grant from DARPA. His company is called "Great Scott Gadgets".
The HackRF's most unique feature when compared to the other two SDR's is that it is capable of both receiving and transmitting.
There is also a clone called the HackRF Blue out on the market which is about $100 cheaper, but they don't seem to have stock or be producing these any more.
From the specs it is clear from the ADC sizes that both the Airspy and SDRplay RSP are in a different class of RX performance when compared to the HackRF. However, people always compare the Airspy and SDRplay with the HackRF due to their similar price range, so we will continue to compare the three here in our review, but with more of a focus on comparing the Airspy and SDRplay RSP.
In order to use the Airspy on HF (0 - 30 MHz) frequencies a $50 add on called the Spyverter is required. This is an upconverter that is designed for use with the Airspy's high dynamic range and bias tee power port. However, one hassle is that the Spyverter must be connected/disconnected each time you want to switch between HF and VHF/UHF reception as it does not have VHF/UHF passthrough. The RSP and HackRF on the other hand can receive HF to UHF without the need of an upconverter or the need to change ports. A single port for HF to UHF can be very useful if you have a remote antenna switcher.
Post continues. Note that this is a long post with many images.
The SDRplay team have recently released a major update to their API and drivers. The new version is 1.8.0 and they write that it should remove the DC offset, reduce in band images from strong signals, and lower the noise floor. The SDRplay is a software defined receiver that costs $149 USD. They write:
We are pleased to announce release 1.8.0 of the API for the RSP. This is a major upgrade to the API with new features and an improved gain map which should result in improved performance over a key portion of the gain control range. Currently this API is available for Windows only, but versions for Linux and Mac OS and Android will follow shortly.
The API now incorporates automatic post tuner DC offset correction and I/Q compensation. This will almost completely eliminate the DC centre spike that was previously present in zero IF mode and also correct for amplitude and phase errors in the I/Q signal paths that can lead to in-band images when strong signals are present.
There is a new gain map for the RSP which should help improve the receiver noise floor for gain reduction settings in the range of 59-78 dB. To achieve this, the IF gain control range has been increased from 59 to 78 dB. In addition, the user can now turn the LNA on or off at any point within the IF gain control range. This means that the LNA can remain on for gain reduction settings of up to 78 dB, whereas previously the maximum gain reduction that could be attained whilst the LNA was on was only 59 dB. Being able to leave the LNA on will result in improvements in the receiver noise performance for gain reductions in the range of 59 to 78 dB. The upper 19 dB of the IF gain control range have now been disabled. In practice this part of the gain control range was useless as trying to operate within this region always lead to receiver overload even when signals were very weak.
To fully exploit the features of this new API release, we have also issued release 3.5 of the ExtIO plugin. This plugin will work with HDSDR, SDR sharp (releases 1361 or earlier) and Studio 1. Automatic I/Q compensation and DC offset correction will work with later versions of SDR sharp, but we will need to update the native plugin for users of these later versions to be access the new gain map.
Similarly, users of SDR Console will gain the benefit of automatic DC offset compensation and I/Q correction, but will not yet be able to access the new gain map. We hope that a version of SDR console that unlocks this feature will become available in the near future.
Until a new release of SDR-Console is available, you can copy the API into the SDR-Console installation directory…
from C:\Program Files\MiricsSDR\API\x64\mir_sdr_api.dll to C:\Program Files\SDR-RADIO-PRO.com\mir_sdr_api.dll
The API installer has also contains an extra certificate to be more user friendly for Windows XP, Vista and Windows 7 users.
As they write that in band images from strong signals are reduced in this version we decided to do a quick before and after test using our own RSP receiver. We tuned into some TETRA signals that had exhibited images in the past on our RSP (you can see them as the yellow signals in the before image). In the new driver the images are completely gone.
ATSC is the digital HD TV standard used within the United States and Canada. It is 6 MHz wide so the RTL-SDR with its maximum bandwidth of about 2.8 MHz cannot decode this signal. However, higher end SDR’s such as the SDRplay, Airspy and HackRF have larger bandwidths that can easy cover 6 MHz.
The process the author used was to first record a RAW IQ WAV file in HDSDR in Windows, making sure that any DC spike correction is applied. The WAV file is then opened in a premade GNU Radio flow graph in Linux and processed into an MPEG file. The process is not real time. The authors article shows a step by step tutorial on how its done.
In an update post to his results the author also notes that to successfully do a recording at the maximum SDRplay bandwidth of 8 MHz a RAM disk or perhaps SSD is required so that samples are not dropped.
An ATSC signal shown in HDSDR received with an SDRplay
