But what of this SDR’s performance? In a nutshell: as of today, I’d contend that the RSP1A will simply be the best SDR value on the market. End of story. There is nothing I know in the $99 price bracket that can beat it.
Over on YouTube user Laboenligne.ca (aka Pascal Villeneuve VA2PV) has uploaded an interview that he did with Jon Hudson of SDRplay. The interview discusses the RSP1A product as well as the development around it.
Yesterday the SDRplay team released the $99 US RSP1A, which is a revision of the RSP1A. In this post we present a review comparing its performance against the older RSP1 and the currently selling $169.95 US RSP2. We aim to mainly show demonstrations of improvements that we've found on the RSP1A in areas where we discovered problems on the RSP1 or RSP2.
Discussion of Improvements
First we present a discussion on the improvements made.
TCXO: The first noticeable improvement is that the RSP1A now comes with a 0.5PPM TCXO. This was one of the main criticisms of the RSP1 as the RSP1 only came with a standard oscillator which can drift as the temperature changes. But as mentioned in our previous review that included the RSP1, the drift was fairly small after warmup due to the good heat dissipation of the large PCB, and the relatively low power usage and thus less heating of the Mirics chips used on RSP units. Nevertheless, a TCXO is a good upgrade and brings it back in line with most low cost SDRs on the market now.
Enhanced RF Preselectors + Notches: Strong out of band signals can overload an SDR causing problems like imaging and reduced sensitivity. Preselectors are RF filters which help to filter out unwanted signals for the band that you are listening to.
The RSP1 had 8 preselector bands and the RSP1A brings this number up to 12, which is even more than the 10 preselectors on the RSP2.
In testing we found that the new preselectors certainly do help out a lot. The new 2 MHz low pass and 2 - 12 MHz certainly help to reduce interference from the MW broadcast AM band. Changes in the VHF filters reduce problems from strong broadcast FM and DAB stations. The filters have also been sharpened considerably making the existing filters even more effective. The RSP-1 in some cases suffered quite severely from out of band signal interference, and the RSP-2 made it a bit better, but the RSP-1A solves the interference problem much more.
The new FM/AM and DAB notch filters also do a good job at notching out these often problematic very strong signals.
Improved LNA Architecture: In the RSP1 the front end LNA could only be turned on or off. Turning it on reduces the noise figure and improves performance, especially at UHF frequencies. The single gain step was problematic as often the LNA could overload on strong signals if turned on. The RSP1A introduces a gain control block which allows the LNA to have variable gain steps.
This new architecture helps to maximise the dynamic range of the RSP1A, thus reducing overloading.
Extended frequency coverage down to 1kHz: The lower limit of the RSP1 was 10 kHz, so really low LF reception is now available on the RSP1A.
Bias-T: Just like with the RSP2, the bias-t allows you to power external devices over the coax cable. Such as remote LNAs, switches etc. Running a good LNA next to the antenna is optimal, as this helps push signals through the coax cable losses.
RF Shielding: Like the RSP2 the plastic case is now spray painted with metallic paint on the inside. This works almost as well as a full metal case to shield from unwanted signals entering directly through the PCB, instead of through the antenna. We do still notice some leakage making its way in through the coax shield, but it is relatively minor with the shielding.
ADC Resolution Increased to 14-bits: The RSP1A uses the same ADC chip as the RSP1, but now has unlocked 14-bit ADC capability for bandwidths below 6 MHz thanks to onboard decimation and oversampling. So now 14-bit data comes directly into the PC if using a bandwidth below 6 MHz. Further decimation can still be achieved within software like SDRuno.
A higher bit ADC can improve dynamic range, meaning that strong signals are less likely to overload the SDR.
We asked SDRplay how 14-bits was achieved with the same chips used by the RSP1 and they explained that it is through oversampling and decimation onboard the chip. They also wrote the following technical reply which is a very good read (collapsed as the reply is quite long, click on "Read the Reply" to expand):
READ THE REPLY
The ADCs on the MSi2500 use a sigma-delta topology where a highly oversampled multi-bit ADC uses decimation filtering to provide the desired resolution. As the original spec for the MSi2500 called for 12 bit resolution, the fact that the converter was capable of delivering 14 bits for final sample rates of less than 6.048 MHz was ignored. Working with the Mirics team, we have been able to unlock the extra two bits of resolution that the MSi2500 was always capable of delivering. Using sample rates above 6.048 MHz, the ADC defaults back to 12 bit resolution.
They also explained:
If we take an 8 bit ADC for example, we can expect around 48 dB of instantaneous dynamic range. This will most likely be far lower than that achievable from the RF front end whose dynamic range will be influenced by factors such as noise figure, intermodualtion, cross modulation and synthesizer phase noise (reciprocal mixing). A decent tuner front end should be capable of delivering 65-70 dB of instantaneous dynamic range, which is also roughly what you can expect from a 12 bit ADC. In other words, we believe that in the RSP1, the instantaneous dynamic range of the tuner and ADCs were approximately the same. The limitation that the RSP1 had was because of the single gain step in the LNA, it was not always possible to utilise the available dynamic range in the most effective way. The RSP1A gives much greater (and finer) control over the RF gain and this allows for better alignment of the signal level into the tuner to better exploit the available dynamic range. In our tests in the broadcast FM band, we believe that the RSP1A gives around 10 dB more ‘usable’ dynamic range than the RSP1. In other words, if we combine multiple controlled modulated signals (for RF signal generators), with real weak off-air signals, the RSP1A is capable of handling interferers that are around 10 dB greater than the RSP1. Benchmarking against other products, in our tests, the RSP1A seems to give better performance now than anything else in the same price range, both in terms of sensitivity and in terms of in-band overload performance.
The RSP1 always gave very good sensitivity but in optimising it in this way, we gave up some performance in terms of in-band overload performance. Our objective with the RSP1A was to address this without sacrificing sensitivity.
Now, going back to the issue of 14 bits vs 12 bits and instantaneous dynamic range. If we increase the ADC dynamic range from 12 to 14 bits, then the ADC dynamic range should no longer influence the performance of the receiver. Indeed, it is our view, that for any receiver that needs to use a tuner as part of the front end (and any receiver that operates across the frequency range of the RSP will have to use a tuner for the foreseeable future), there is little benefit to be gained with ADC resolutions in excess of 14 bits, as to utilise the extra dynamic range that a higher resolution ADC can give, a much higher performance tuner would be required. Tuner technology has come a very long way in the last 10-15 years and the performance of modern integrated devices is actually very good. To get 12 dB of better dynamic range from a tuner is extremely difficult and can really only be achieved by using very much greater levels of power and esoteric semiconductor technologies. One possible area where you might see better performance is where you have multiple strong interfering signals to the extent that the RF gain needs to be turned down to such a level that the ADC quantisation noise effectively limits the noise floor of the receiver. In this case, you ought to see improved performance in 14 bit mode when compared to 12 bit mode, but please note that the improvement may only be a few dBs in the weak signal reception. If the noise floor of the receiver is still limited by the external LNA, then improved ADC dynamic range will give no perceptible improvement whatsoever.
A direct sampling receiver that does not use a tuner should in principle allow greater dynamic range than one that does, but in practice any direct sampling ADC needs some form of external low noise amplification to ensure a reasonable noise figure and the dynamic range (noise, intermodulation performance etc) of this external amplification block becomes a limiting factor. This is certainly true at VHF and above. At HF, as you will be well aware, the receiver noise figure is not really very important because the atmospheric noise floor is so high. In principle, you might therefore think that our best approach would be to bypass the tuner and use the decimated 16 bit performance of our ADCs. This would still give an effective receiver bandwidth of 375 kHz with 16 bit performance. The reality though is that the real dynamic range of signals coming into the antenna is limited by propagation conditions and atmospheric noise. It is rare to find signals that are above the atmospheric noise floor that vary by more than 60 dB. In practical terms, we believe that equivalent performance can be achieved, simply by the addition of RF pre-selection and AM-band notch filters and in this way we avoid some of the other compromises of direct sampling systems.
So, in a nutshell, when transitioning from 12bit mode to 14 bit mode, don’t expect to see 12 dB more dynamic range. In the real world, it doesn’t work this way. This is why 12 bit devices can give quite favourable performance to higher end 16 bit SDRs such as the Elad FDM-S2, particularly when you consider the difference in cost. We fully expect the Elad to be better, but the difference will not be 24 dB or anything close to it.
Without wishing to labour the point about myths and misunderstandings, it is worth adding a bit of clarification regarding the term ‘dynamic range’. This is a much misunderstood term which can mean very different things depending upon the circumstances and type of signal being received. There is also a difference between ‘dynamic range’ and ‘instantaneous dynamic range’. If you ask 10 different radio engineers what they mean by the term dynamic range, you are sure to get more than one different answer! Another important point to note is that ADC dynamic range is NOT the same as receiver dynamic range. When referring to ADCs, the term dynamic range generally refers to the Spurious Free Dynamic Range (SFDR). This is measured using a CW tone and refers to the ratio between the maximum RMS signal that the ADC can handle and the largest spur or level or quantisation noise within the ADC bandwidth. This is a measure of both noise and linearity of an ADC. As a case in point, it is worth noting that a 16 bit ADC may not necessarily have a higher SFDR than a 12 bit ADC despite having a greater resolution. The greater resolution will generally result in a lower level of quantisation noise, but not necessarily a lower level of harmonic distortion and spurs. In a multi-channel/multi-signal SDR system a lower level of quantisation noise is generally helpful, even if the SFDR is not better, but is not guaranteed to give better performance if the weak signal of interest happens to fall on top of an ADC spur. Where a single signal occupies the entire ADC bandwidth, it is ONLY the SFDR that matters and not the resolution or quantisation noise. Sometimes you will hear people refer to the Effective Number Of Bits ENOB. ENOB is related to the SFDR in that it is a measure of the maximum SINAD that can be attained with an ADC at a give sample rate and so is also a measure of both linearity and noise performance. ENOB is actually = (SINAD – 1.76)/6.02 In the ADC subsystem used in the RSP, whilst the ADCs are 12 bit at 8 MHz sampling the ENOB is 10.4 (for both I and Q). At lower sample rates, the ENOB improves and gets closer to the idealised performance of the converter.
In a receiver system as a whole, the term dynamic range will generally be interpreted to mean the difference (in dB) between the minimum discernible signal and the maximum level of signal that can be handled. But this is different from the term instantaneous dynamic range, which generally refers to the difference between the minimum discernible signal in the presence of the largest signal that can be handled at the same time. What this ‘number’ is in each case will depend upon the type of signal. So for example, a receiver with a given noise figure and linearity performance will have a different instantaneous dynamic range when receiving a 8 MHz wide 256-QAM CATV signal than when receiving a FM signal that is a few kHz wide. This is simply because the SINR (Signal to Interference + Noise Ratio) requirement for a given BER for a 256-QAM signal is very different than that required for a FM signal and also the peak to average ratio of the two signals is very different.
Compared to the RSP1 the RSP1A PCB is significantly more populated due to the additional filter banks.
RSP1A PCB Top
RSP1A PCB Bottom
RSP1 vs RSP2 PCBs
Testing the RSP1A
Below we show some screenshots of tests that we made to compare the three RSP units. We focused on bands where the RSP1 or RSP2 had issues, and try to show how much improvement you can get from the RSP1A.
Medium Wave Broadcast AM Band
In the screenshots below we compare the three SDRs on the broadcast AM band which has some very strong signals. The RSP1 definitely shows signals of overloading and turning the gain down did not reduce the interference shown between 0 - 500 kHz.
The RSP1A on the other hand does not overload that easily. In the third screenshot we turn the MW notch on half way through the waterfall. The notch does not cover the entire AM band and signals at around 500 - 700 kHz are attenuated less. But turning it on does seem to do enough to solve most imaging problems as will be seen in the next tests.
SDRplay Limited has today announced the launch of a new Software Defined Radio product – the RSP1A.
The SDR-play RSP1A is a major upgrade to the popular RSP1 and is a powerful wideband full featured 14-bit SDR which covers the RF spectrum from 1 kHz to 2 GHz.
Due to its exceptional combination of performance and price, the RSP1 has proved to be a very popular choice as an “entry level” SDR receiver. Since launching the RSP1, we have learned a great deal about what people are looking for in SDR receivers, and where possible, we have incorporated these improvements and new features into the RSP1A.
The RSP1A therefore delivers a significant number of additional features which result in benefits to amateur radio enthusiasts as well as significant benefits for the scientific, educational and industrial SDR community.
Here are the main additional features of the RSP1A compared to the original RSP1:
ADC resolution increased to 14-bit native for sample rates below 6 MHz, increasing to 16 bits with decimation.
Enhanced RF pre-selection (greater filter selectivity plus 4 additional sub-bands compared to the original RSP1) for reduced levels of spurious responses
Improved LNA architecture with variable gain. The RSP1 had just a single gain step.
Improved intermodulation performance
Performance extended to cover 1kHz to 2GHz with a single antenna port.
Improved frequency stability incorporating a 0.5ppm TCXO (software trimmable to 0.01ppm)
Selectable broadcast AM/FM/DAB notch filters
RF shielding within the robust plastic casing
When used together SDRplay’s own SDRuno software, the RSP1A becomes a high performance SDR platform. The benefits of using the RSP1A with SDRuno include:
Highly integrated native support for the RSP1A
Calibrated RF Power Meter with more than 100 dB of usable range
Calibrated S-Meter including support for IARU S-Meter Standard
The ability to save power (dBm) and SNR (dB) measurements over time, to a CSV file for future analysis
The IQ output wav files can be accessed for 3rd party applications
SDRplay has also worked with developers of the popular HDSDR, SDR-Console and Cubic SDR software packages to ensure compatibility. As with the RSP1, SDRplay provides multiplatform driver and API support which includes Windows, Linux, Mac, Android and Raspberry Pi 3. There is even a downloadable SD card image available for Raspberry Pi3 which includes Cubic SDR.
The RSP1A is expected to retail at approximately £76 (excluding taxes) or $100 (excluding taxes) For more information visit our website on www.sdrplay.com
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
We've had a RSP1A beta preproduction unit for a few weeks now and will be releasing a full review comparing it against the RSP1 in a day or so. For a quick review conclusion we note that we've noticed that the filters are significantly more effective on the RSP1A compared to the RSP1, and the inclusion of the MW/FM and DAB notch filters help a lot in certain situations. The increased ADC resolution is due to decimation on board the MSi2500 chip and is noticeable in some situations, but does not seem to cause a huge improvement. Overall compared to the RSP1 some overloading problems are still present with strong signals, but intermodulation and imaging is reduced significantly and in some cases the RSP1A even outperforms the RSP2.
Also, Mike Ladd KD2KOG a member of the SDRplay technical support team has uploaded a video announcing and demoing the RSP1A.
SDR#'s SpyServer streaming server now supports the direct sampling mode on RTL-SDR dongles and it's probably the cheapest way to set up a HF streaming server. SpyServer is a streaming server for SDR# and Airspy products. Although it's designed for Airspy products it also works well with RTL-SDR dongles.
On RTL-SDR dongles the direct sampling mode allows you to receive HF frequencies by bypassing the tuner. The dynamic range is not quite as good as using an upconverter and there are Nyquist images from sampling at 28.8 MHz centered around 14.4 MHz, but in most cases it is good enough to give people decent HF results especially if filtering is used. Normally a hardware hack is required to enable direct sampling, but our RTL-SDR Blog V3 units have direct sampling built in and ready to go just by connecting an HF antenna to the SMA port, and enabling the Q-branch direct sampling mode.
There is a sample server set up at sdr://126.96.36.199:5555.
Direct Sampling for #RTLSDR was added to Spy Server. This must be the most affordable networked HF radio ever.
The FaradayRF is not a software defined radio, but it is a computer controlled digital TX/RX radio device. Basically it is a radio designed to communicate digital data over the 33 cm ham/ISM band. The 33 cm band is between 902 to 928 MHz in the ITU Region 2 area (Americas, Canada, Greenland and some pacific islands). It was designed for amateur radio operators out of the need for a device that allows for easy experimentation with digital radio. An amateur radio licence is required, but only at the technician level which is the easiest licence to obtain.
The product itself is a simple PCB which has on board a low power microcontroller (no OS), a GPS module, and an RF front end that can TX up to 400 mW. They write that with 400 mW a signal at 900 MHz can be transmitted up to 40 miles away. Also, by using low power micro-controllers and hardware radio (instead of SDR), they write that they were able to power the device from a single 9V battery for over 12 hours. The hardware and software is also all open source.
In some ways the FaradayRF is kind of similar to the Yardstick One/PandwaRF radios which were designed for reverse engineering or security research on digital signals. But the FaradayRF comes with SAW filtering to provide a clean output, an amplifier to boost the signal, and software aimed at providing digital comms making it more for amateur radio use.
Some applications might include point to point telemetry/comms, high altitude balloons, ocean buoys, digital voice, APRS, text messaging etc.
The FaradayRF starter set currently costs $300 USD and includes two units (one with GPS included and another without) or $330 USD with two GPS capable units.
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.
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.
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)
The Radio Society of Great Britain (RSGB) and AMSAT-UK recently presented a number of talks at their latest convention held in October of this year. Some of the talks are SDR related and are interesting for those interested in satellite reception. A couple of interesting SDR related talks are presented below, and the rest of the talks can be accessed on their YouTube page.
Software defined radio for the satellite geek - Alex Csete OZ9AEC
In this talk Alex Csete (Oz9AEC) who is the programmer behind the popular GQRX software that is often used with RTL-SDRs discusses his latest work and some of his experiences with writing software for SDRs.
Going to space the libre way - Pierros Papadeas, Libre Space Foundation
In this talk Pierros Papadeas who is the founder of the Libre Space Foundation discusses their SatNOGS project. SatNOGS is a project that uses RTL-SDRs in custom 3D printed home made satellite tracking ground stations. It aims to enable easy access to live satellite data online by significantly increasing ground station coverage.
Over on the crowd funding site crowdsupply.com there have recently been several updates on the Fairwaves XTRX SDR. The XTRX is an upcoming TX/RX capable SDR in a tiny Mini PCIe form factor. Mini PCIe is the expansion slot system used on some laptops. The SDR itself will be 2 x 2 MIMO, with a tuning range of 10 MHz - 3.7 GHz (down to 100 kHz with some degradation), and have a sample rate of up to 120 MSPS. It uses the LimeSDR RF chipset which provides most of the hardware required.
The XTRX is not yet for sale, and is planned for a crowdfunding run on Crowdsupply 'soon'. You can subscribe to future updates on their page. No word yet on pricing, but according to one of the developers comments on Reddit the price will be somewhere between the LimeSDR ($299 USD) and LimeSDR Mini ($139 USD). Eventually in the future if they can tap into a mass market they hope to get the price down to $50 USD.
Features & Specifications
RF Chipset: Lime Microsystems LMS7002M FPRF
FPGA Chipset: Xilinx Artix 7 35T
Channels: 2 × 2 MIMO
Tuning Range: 30 MHz - 3.8 GHz
10 MHz - 3.7 GHz
100 kHz - 3.8 GHz with signal level degradation
PCIe x2 Gen 2.0: 8 Gbit/s
PCIe x1 Gen 2.0: 4 Gbit/s
PCIe x1 Gen 1.0: 2 Gbit/s
Sample Rate: ~0.2 MSPS to 120 MSPS
Frequency: 26 MHz
Stability: <10 ppb stability after GPS/GNSS lock, 500 ppb at start up
Form Factor: full-size miniPCIe (30 × 51 mm)
Bus Latency: <10 µs, stable over time
Synchronization: synchronize multiple XTRX boards for massive MIMO