Category: Reviews

ADALM-PLUTO SDR: Unboxing and Initial Testing

The PlutoSDR (aka ADALM-PLUTO) is a new RX and TX capable SDR from Analog Devices who are a large semiconductor manufacturer. The PlutoSDR covers 325 – 3800 MHz, has a 12-bit ADC with a 61.44 MSPS sampling rate and 20 MHz bandwidth. It is also priced at the bargain price of only $99 USD over on Digikey, although it seems they only produced a small batch as at the moment they seem to be already sold out. This may also be a promotional price, with the normal price $149 USD as that is the price we see on the analog.com store. But even at $149 the value for what you get is very high.

A few months ago we preordered a PlutoSDR from the analog.com store, and it was received it a few days ago.

Unboxing

The unit comes in a nice professionally designed cardboard box. Inside is the unit itself, two small 4cm long whip antennas a short 15 cm SMA cable and USB cable. The PlutoSDR unit itself comes in a blue plastic box which measures 11.7 x 7.9 x 2.4 cm and weighs 114 g in total. Two SMA ports are available, one for RX and one for TX. At the other end are two LEDs, a USB port and a power only USB port.

The PCB itself looks to be designed nicely. On the PCB you can see the main AD9363 front end chip, which is actually a 2 x 2 transceiver chip. It supports a tunable channel bandwidth of up to 20 MHz. The other chip is the ZYNQ XC7Z010 which is an ‘All Programmable SoC’. This is an FPGA, processor and ADC for the unit.

Hardware

The PlutoSDR can tune from 325 to 3800 MHz. It has an ADC which can sample at up to 61.44 MSPS with a resolution of 12-bits. There is no TCXO used, so the frequency accuracy is only 25 PPM. Although the maximum sample rate is 61.44 MSPS, the front end AD9363 only has a maximum signal bandwidth of 20 MHz, so that limits the available bandwidth.

For TXing, a claimed TX power of up to 7 dBm is available which is comparable to the TX power of the HackRF.

The unit has no shielding on it via PCB cans or a metal box, so may pick up spurious signals. However, for the intended purpose of learning and testing, no shielding is fine.

Software

Unfortunately software for the PlutoSDR is quite lacking. At the moment there is only really support for MATLAB and GNURadio.

That’s quite understandable however as the PlutoSDR is designed and promoted as a ‘learning module’ or in other words a device for students to learn with. However, if software support for SDR#, HDSDR, SDR-Console, GQRX etc was available it would also make a great unit that could not only compete with the HackRF and LimeSDR SDRs, but also perhaps the Airspy and SDRplay RSP RX only units, at least for UHF applications above 325 MHz.

In a previous post in February we’ve seen on Twitter that Alex Csete (programmer of GQRX) has had his PlutoSDR running on GQRX, but it seems the current public release does not yet support the PlutoSDR (please correct me if i’m wrong!).

The documentation is mostly all available on the PlutSDR wiki. However documentation for setting the unit up with MATLAB and GNURadio, and examples for actually using it is also still quite poor. There is a quickstart guide, but this barely helped. Presumably once more units ship out the documentation will be enhanced. 

To install the PlutoSDR drivers on Linux we used the instructions kindly provided by xavier_505 in this Reddit thread. Once GNU Radio was installed, installation of the gr-iio driver was as simple as running the two lines provided in the thread.

Testing

We’ve given the PlutoSDR a few tests in Linux with GNURadio, and very quickly with the ADI IIO Oscillioscope software for Windows.

In GNU Radio the PlutoSDR source can be found under the “Industrial IO” heading in the block menu on the right, or simply by doing CTRL+F “Pluto”.

One important note is that when using the source you need to set the “Device URI” to ip:pluto.local. This feature presumably allows you to control multiple devices via the network, but for now we’re just using it locally. Also, this may have been a problem related to running Linux in VMWare, but PlutoSDR creates new “Wired Connection” in Linux and we had to always remember to set the network connection to the PlutoSDR using the the network selector in the Linux taskbar for the network to be able to see it.

First we tested a simple FFT and Waterfall sink using the PlutoSDR source. We set the sample rate to the maximum of 61.44 MSPS, and the RF bandwidth to 60M (although the max is 20 MHz). The demo ran well and we were able to see the 900 MHz GSM band. It seems the max sample rate is not used as the output is only 30 MHz, or perhaps it’s only one ADC.

Next we adapted a simple FM receiver from csetes GNU Radio examples by replacing the USRP source file with the PlutoSDR. After adjusting the decimation we were able to receive NBFM clearly.

Next we tried adapting a simple transmit test by creating a flowgraph that would transmit a .wav file in NBFM mode using the PlutoSDR Sink. Again this ran easily and we were able to verify the output in SDR# with an RTL-SDR. No harmonics were found (the one seen in the screenshot is a harmonic from the RTL-SDR).

Finally we tested using the PlutoSDR ADI IIO Oscilloscope software and were able to generate a FFT spectrum of the GSM band.

Conclusion

This is a very nice SDR with good specs and a very very attractive price. However, it is mostly aimed at experimenters and students and you’ll need to be comfortable with exploring GNU Radio and/or MATLAB to actually use it. If you’re okay with that, then adapting various GNU Radio programs to use the PlutoSDR is quite easy.

In the future hopefully some programmers of general purpose receiving programs like SDR#/GQRX etc will release modules to support this unit too.

This is a good alternative to more expensive experimenter TX/RX SDR units like the HackRF and LimeSDR, although you do lose out on frequencies below 325 MHz.

ADALM-PLUTO SDR: Unboxing and Initial Testing

The PlutoSDR (aka ADALM-PLUTO) is a new RX and TX capable SDR from Analog Devices who are a large semiconductor manufacturer. The PlutoSDR covers 325 – 3800 MHz, has a 12-bit ADC with a 61.44 MSPS sampling rate and 20 MHz bandwidth. It is also priced at the bargain price of only $99 USD over on Digikey, although it seems they only produced a small batch as at the moment they seem to be already sold out. This may also be a promotional price, with the normal price $149 USD as that is the price we see on the analog.com store. But even at $149 the value for what you get is very high.

A few months ago we preordered a PlutoSDR from the analog.com store, and it was received it a few days ago.

Unboxing

The unit comes in a nice professionally designed cardboard box. Inside is the unit itself, two small 4cm long whip antennas a short 15 cm SMA cable and USB cable. The PlutoSDR unit itself comes in a blue plastic box which measures 11.7 x 7.9 x 2.4 cm and weighs 114 g in total. Two SMA ports are available, one for RX and one for TX. At the other end are two LEDs, a USB port and a power only USB port.

The PCB itself looks to be designed nicely. On the PCB you can see the main AD9363 front end chip, which is actually a 2 x 2 transceiver chip. It supports a tunable channel bandwidth of up to 20 MHz. The other chip is the ZYNQ XC7Z010 which is an ‘All Programmable SoC’. This is an FPGA, processor and ADC for the unit.

Hardware

The PlutoSDR can tune from 325 to 3800 MHz. It has an ADC which can sample at up to 61.44 MSPS with a resolution of 12-bits. There is no TCXO used, so the frequency accuracy is only 25 PPM. Although the maximum sample rate is 61.44 MSPS, the front end AD9363 only has a maximum signal bandwidth of 20 MHz, so that limits the available bandwidth.

For TXing, a claimed TX power of up to 7 dBm is available which is comparable to the TX power of the HackRF.

The unit has no shielding on it via PCB cans or a metal box, so may pick up spurious signals. However, for the intended purpose of learning and testing, no shielding is fine.

Software

Unfortunately software for the PlutoSDR is quite lacking. At the moment there is only really support for MATLAB and GNURadio.

That’s quite understandable however as the PlutoSDR is designed and promoted as a ‘learning module’ or in other words a device for students to learn with. However, if software support for SDR#, HDSDR, SDR-Console, GQRX etc was available it would also make a great unit that could not only compete with the HackRF and LimeSDR SDRs, but also perhaps the Airspy and SDRplay RSP RX only units, at least for UHF applications above 325 MHz.

In a previous post in February we’ve seen on Twitter that Alex Csete (programmer of GQRX) has had his PlutoSDR running on GQRX, but it seems the current public release does not yet support the PlutoSDR (please correct me if i’m wrong!).

The documentation is mostly all available on the PlutSDR wiki. However documentation for setting the unit up with MATLAB and GNURadio, and examples for actually using it is also still quite poor. There is a quickstart guide, but this barely helped. Presumably once more units ship out the documentation will be enhanced. 

To install the PlutoSDR drivers on Linux we used the instructions kindly provided by xavier_505 in this Reddit thread. Once GNU Radio was installed, installation of the gr-iio driver was as simple as running the two lines provided in the thread.

Testing

We’ve given the PlutoSDR a few tests in Linux with GNURadio, and very quickly with the ADI IIO Oscillioscope software for Windows.

In GNU Radio the PlutoSDR source can be found under the “Industrial IO” heading in the block menu on the right, or simply by doing CTRL+F “Pluto”.

One important note is that when using the source you need to set the “Device URI” to ip:pluto.local. This feature presumably allows you to control multiple devices via the network, but for now we’re just using it locally. Also, this may have been a problem related to running Linux in VMWare, but PlutoSDR creates new “Wired Connection” in Linux and we had to always remember to set the network connection to the PlutoSDR using the the network selector in the Linux taskbar for the network to be able to see it.

First we tested a simple FFT and Waterfall sink using the PlutoSDR source. We set the sample rate to the maximum of 61.44 MSPS, and the RF bandwidth to 60M (although the max is 20 MHz). The demo ran well and we were able to see the 900 MHz GSM band. It seems the max sample rate is not used as the output is only 30 MHz, or perhaps it’s only one ADC.

Next we adapted a simple FM receiver from csetes GNU Radio examples by replacing the USRP source file with the PlutoSDR. After adjusting the decimation we were able to receive NBFM clearly.

Next we tried adapting a simple transmit test by creating a flowgraph that would transmit a .wav file in NBFM mode using the PlutoSDR Sink. Again this ran easily and we were able to verify the output in SDR# with an RTL-SDR. No harmonics were found (the one seen in the screenshot is a harmonic from the RTL-SDR).

Finally we tested using the PlutoSDR ADI IIO Oscilloscope software and were able to generate a FFT spectrum of the GSM band.

Conclusion

This is a very nice SDR with good specs and a very very attractive price. However, it is mostly aimed at experimenters and students and you’ll need to be comfortable with exploring GNU Radio and/or MATLAB to actually use it. If you’re okay with that, then adapting various GNU Radio programs to use the PlutoSDR is quite easy.

In the future hopefully some programmers of general purpose receiving programs like SDR#/GQRX etc will release modules to support this unit too.

This is a good alternative to more expensive experimenter TX/RX SDR units like the HackRF and LimeSDR, although you do lose out on frequencies below 325 MHz.

Our Review of the Airspy HF+: Compared against ColibriNANO, Airspy Mini, RSP2

Over the last few months we’ve been posting and getting excited about the Airspy HF+, an upcoming high dynamic range HF/VHF receiver designed for DXing. The Airspy team were kind enough to supply us with an early pre-production unit for review.

Long story short, the Airspy HF+ is probably one of the best low cost SDRs we’ve seen for DXing or weak signal reception out there. So far few details on the availability of the HF+ have been released, but we’re aware that preorders are due to start soon, and the target price is expected to be $149 USD from iTead Studio in China. 

What follows is the full review and comparisons against other similarly priced SDRs. The Airspy team want us and readers to understand that our review unit is a pre-production model, and apparently already the matching and thus SNR has already been improved by about 2-4 dBs, so the sound samples we provide in the review below should sound even better with the newer revision.

Disclaimer: We received the HF+ for free in exchange for an honest review, but are not affiliated with Airspy. We’ve been in contact with the Airspy team who have helped clarify some points about the architecture and technology used in the design.

Introduction

The Airspy HF+ is designed to be a HF/VHF specialist receiver with a frequency range of DC to 31 MHz, and then 60 to 260 MHz. It has a maximum bandwidth of 768 kHz. So the question is then, why would you consider buying this over something like the regular Airspy R2/Mini or an SDRplay RSP2 which both have larger frequency ranges and bandwidths? You would buy the Airspy HF+ because has been designed with DXing and weak signal reception in mind. Basically the main idea behind the HF+ is to design it so that it will never overload when in the presence of really strong signals. Combined with it’s high sensitivity, weak or DX signals should come in much clearer than on the other radios especially if you have strong blocking signals like broadcast AM/FM around.

Aside: What is overloading, intermodulation and dynamic range?

Basically strong signals can cause weak signals to be drowned out, making them not receivable, even though they’re there at your antenna. This is called overloading or saturation. Intermodulation occurs when the SDR overloads and results in images of unwanted signals showing up all over the spectrum.

A simple analogy is to think about what happens when you are trying to drive, but there is sunstrike. The road is very hard to see because the sun is so bright and right in your eyes. The human eye does not have enough “dynamic range” to handle the situation of sunstrike. Dynamic range is a measure of how well a radio (eye) can handle strong (bright) and weak (dark) signals at the same time. The same analogy applies to radios which can struggle to ‘see’ weak signals if there is a very strong signal nearby on the frequency spectrum. There are a few ways to solve this:

  • Filtering: Block the strong signals that you don’t want using LC filters.
    • Eye analogy: using your sun visor to block the sun.
  • Attenuation: Reduce the strength of all signals.
    • Eye analogy: using sunglasses or squint.
  • Increase dynamic range: Get a better SDR with better design/technology and more bits in the ADC.
    • Eye analogy: upgrade your eyes.

Technology and Architecture

The HF+ uses a typical Filter->Tuner ->ADC architecture. So it is not a direct sampling receiver like most of the more expensive SDRs. Direct sampling receivers directly sample the analogue spectrum, without the need for a tuner so they avoid losses and the intermodulation problems that usually come from the mixing stages. But there are some major cutting edge technology differences in the HF+ architecture that should make its performance even better than direct sampling receivers.

Tuner: The tuner on the HF+ is one of the first to use a “Polyphase Harmonic Rejection” architecture. Essentially this means that harmonics produced in the mixing stages are naturally rejected, making the front end filtering requirements much more relaxed. So unlike the tuners used in other SDRs, this one is extremely unlikely overload in the mixing stage.

An additional benefit to this architecture is that the mixer is very low loss, so the LNA in the tuner only needs to use low gain, giving it a very high IIP3 value. So the first LNA which is typically another point of saturation and imermodulation, is very unlikely to saturate in the HF+ design. Most of the amplification only occurs after the mixing stage with the filtered narrowband output of the tuner.

Analogue to Digital Converter (ADC): The ADC is 16-bits and uses a “Sigma Delta” (ΣΔ) design. Basically a Sigma Delta ADC has a natural filtering ability due to its narrowband nature. Instead of seeing say a 30 MHz signal, it only sees 1 – 2 MHz, thus increasing dynamic range and reducing the likelihood of out of band overload.

Digital Down-Converter (DDC): Then after the ADC is a DDC which decimates the output from the ADC, increasing the effective number of bits. The more bits the larger the resolution of the digitized RF signal, so weak signals are less likely to be lost when converted from analogue to digital.

The HF+ Block Diagram
The HF+ Block Diagram

So the block diagram flow goes like this:

A weakly filtered signal enters the tuner, is weakly amplified by the tuner LNA, mixed down to baseband and filtered to 1-2 MHz. It is then amplified and sampled with the sigma delta ADC into 16-bits. The DDC decimates the output into 18-bits which is then sent to the microcontroller and PC via USB.

The Airspy team also compiled this comparison chart for us to understand the differences in architecture between the current SDRs on the market (click to enlarge). This shows that the HF+ is a different type of design compared to other SDRs. Generally the best SDRs out the market right now are direct sampling receivers with many filter banks. The HF+ approaches the problem in a different way, and according to the specs seems to match or better the performance of heavily filtered direct sampling receivers.

Performance from the Airspy HF+ product page is stated as:

  • -141.0 dBm (0.02 µV / 50 ohms) MDS Typ. at 500Hz bandwidth in HF
  • -141.5 dBm MDS Typ. at 500Hz bandwidth in FM Broadcast Band (60 – 108 MHz)
  • -139.5 dBm MDS Typ. at 500Hz bandwidth in VHF Aviation Band (118 – 136 MHz)
  • -139 dBm MDS Typ. at 500Hz bandwidth in VHF Commercial Band (136 – 174 MHz)
  • -138 dBm MDS Typ. at 500Hz bandwidth in the upper VHF Band (> 174 MHz)
  • +26 dBm IIP3 on HF at maximum gain
  • +13 dBm IIP3 on VHF at maximum gain
  • 110 dB blocking dynamic range in HF
  • 95 dB blocking dynamic range in VHF

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A Review of the KiwiSDR: 10 kHz – 30 MHz Wideband Network SDR

The KiwiSDR is a 14-bit wideband RX only HF software defined radio created by John Seamons (ZL/KF6VO) which has up to 32 MHz of bandwidth, so it can receive the entire 10 kHz – 30 MHz VLF/LF/MW/HF spectrum all at once. However, it is not a typical SDR as you do not connect the KiwiSDR directly to your PC. Instead the KiwiSDR is a cape (add on board) for the Beaglebone single board computing platform. If you’re unfamiliar with the Beaglebone, it is a small computing board that is similar to a Raspberry Pi. The KiwiSDR is designed to be a low cost standalone unit that runs 24/7, connects to your HF antenna and internet network, and shares your 10 kHz – 30 MHz reception over the internet with up to 4 simultaneous users.

The KiwiSDR
The KiwiSDR

The KiwiSDR kit retails for $299 USD (Amazon) (Direct from Seeed Studio), and with that price you get the KiwiSDR cape, a Beaglebone Green board, an enclosure, microSD card and a GPS antenna. If you already have a Beaglebone lying around, then you can purchase the KiwiSDR board only for $199 USD. 

Because the KiwiSDR is a network SDR, instead of connecting it to your PC it connects to your home internet network, allowing you to access it from any computing device via a web browser. Direct access to the SDR is not possible (actually it seems that it is, but it’s not easy to do), and all the computing is performed on the KiwiSDR’s on board FPGA and Beaglebone’s CPU before being sent to the network. Thus raw ADC or IQ data is never touched by your PC, your PC only sees the compressed audio and waterfall stream. So a powerful computer is not required to run the SDR. In fact, a mobile phone or tablet will do just fine.

In comparison, a $299 USD wideband non-networked SDR such as the LimeSDR uses a 12-bit ADC and can do up to 80 MHz of bandwidth over USB 3.0. But even on our relatively powerful PC (i7-6700 CPU, Geforce GTX 970 and 32 GB RAM) the LimeSDR can only get up to about 65 MHz on SDR-Console V3 before performance becomes too choppy.

But the real reason to purchase a KiwiSDR is that it is designed to be shared and accessed over the internet from anywhere in the world. You can connect to over 137 shared KiwiSDRs right now over at sdr.hu which is a site that indexes public KiwiSDRs. To achieve internet sharing, the KiwiSDR runs a modified version of András Retzler’s OpenWebRX software. OpenWebRX is similar to WebSDR, but is open source and freely available to download online. The standard OpenWebRX is also designed to support the RTL-SDR. Of course if you don’t want to share your receiver over the internet you don’t have to, and you could use it on your own local network only.

Some applications of the KiwiSDR might include things like: setting up a remote receiver in a good noise free location, helping hams give themselves propagation reports by accessing a remote KiwiSDR while they are TXing, listening to shortwave stations, monitoring WSPR or WEFAX channels, education, crowd sourced science experiments and more.

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Testing the Outernet Dreamcatcher: Linux Based ARM PC with Built in RTL-SDR

Last week we posted about Outernet’s new Dreamcatcher unit which is an RTL-SDR + L-band LNA + computing board all on the same PCB. The Dreamcatcher comes with a new active ceramic L-band patch antenna, costs $99 USD (plus shipping) and can be bought directly from their store. Outernet were kind enough to send us a review unit, and we’ve been testing it for the past few weeks. This post is a review of the unit.

Background

Outernet is a free data service that uses L-band satellites to beam down information like news, weather updates, Wikipedia articles, books and more.

In the past Outernet have used the $9 USD C.H.I.P computing board, an RTL-SDR dongle and an external LNA as the receiving hardware for their data service. However, popularity of the Outernet service has been severely hindered by the huge supply shortages of the C.H.I.P. Over the past year or so it has been almost impossible to get a hold of a C.H.I.P unit if you did not back the Kickstarter or buy one from Outernet’s first initial stock. By manufacturing their own PCB including the computing hardware, Outernet must be hoping to be able to control their stock situation, and not rely on third parties who may not be able to deliver.

At the moment the Dreamcatcher can only be run on their new Armbian image. The older Skylark image has been removed from their servers presumably because the Outernet signal is going to change in the near future and the old demodulator on Skylark may no longer work. The Armbian image is basically just standard Armbian and at the moment does not actually run any Outernet software, and cannot decode their signal, but this is being worked on. Eventually they hope to replace Skylark with a standard decoding app that runs on Armbian.

In this post we’ll review the Dreamcatcher with Armbian and consider it as a general purpose receiver (not just for Outernet), and we’ll also review the new active ceramic patch antenna as well.

Dreamcatcher Overview

The Dreamcatcher is a single PCB that combines an RTL-SDR, Linux (Armbian) based computing hardware, and an L-band LNA and filter. 

On first impressions we noticed that the PCB is relatively large square at about 12 cm by 12 cm. The most prominent chip is the Allwinner A13 SoC. The RTL-SDR circuitry is positioned in the upper right with the RF sections (R820T and LNA) both covered with RF shielding cans. There is no onboard WiFi circuitry, but a small ‘EDUP’ branded WiFi dongle is included and plugs into one of the USB ports on the PCB.

We measured the Dreamcatcher to be using about 400 mA – 600 mA while idle and 800 mA while utilizing the RTL-SDR and 100% CPU. Heat is not an issue as the Dreamcatcher stays relatively cool during its operation even at 100% CPU with the CPU only getting up to about 45 degrees C.

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A Review of the SpyVerter R2

The SpyVerter is a high performance upconverter that enables HF reception on SDR’s that aren’t able to tune directly to HF frequencies. Like any upconverter it works by converting those lower HF frequencies ‘up’ into a higher frequency range that is actually receivable by the SDR.

Back in December 2015 when the SpyVerter first came out we reviewed the unit and found that it was probably the best and highest value upconverter on the market. It was priced at a similar or cheaper price to competitors, came in a metal enclosure and had excellent performance. The main reason for its high performance is due to the architecture. While most upconverters on the market like the ham-it-up use an ADE-1 double balanced mixer component, the SpyVerter instead uses an H-mode mixer design. This design is harder to engineer, but it provides better dynamic range meaning that strong signals are less likely to overload the upconverter.

The SpyVerter was recently given a refresh, and the SpyVerter R2 is now available. The changes are small and are mostly centered around the clock. The oscillator is now a 24 MHz 0.5 PPM TCXO, run through a SI5351 clock generator to produce the 120 MHz upconversion frequency. A new onboard microcontroller programs the SI5351 on power up.

This change in clock design also now allows you to connect a 10 MHz reference frequency if ultra stable, or phase coherent frequency operation is required. A u.FL connector is provided next to the output SMA connector on the PCB for connecting a 10 MHz reference. Unfortunately there is no breakout hole in the metal enclosure, meaning that you’ll need to drill your own hole in the enclosure to get the u.FL clock cable out. Few people will need this feature however, as thanks to the 0.5 PPM TCXO stock frequency stability is now excellent.

The new design also uses less power, only drawing 10 mA of current compared to 47 mA in the SpyVerter R1. It also has 12 dB lower local oscillator leakage meaning that the gains might be able to be pushed slightly higher without overload. Once again, just like with the SpyVerter R1 the R2 is also powered via the bias tee on the Airspy, and so is compatible with the bias tee on our RTL-SDR V3 dongles.

There’s also an interesting mod that can be performed with the SpyVerter R2. The LO frequency can be modded to run at 58 MHz instead of 120 MHz. 58 MHz is just low enough to avoid the broadcast FM band, and the lower frequency allows the switches used in the H-mode design to run at a lower frequency. This results in an insertion loss better by about 3 dB’s and less LO leakage meaning that the RF gains can be pushed higher. The main disadvantage to this mod is that the lowest input frequency will only be 28 MHz.  The mod details don’t seem to be published yet, but we’ll update this post once they are.

The cost of the SpyVerter R2 remains the same as before at $49 USD. Compared to the Ham-It-Up v1.3 which costs $41.95 USD and does not come with an enclosure or TCXO, the SpyVerter still seems to be the best value. Currently you can buy one internationally from iTead who ship from China, at Airspy.us for US customers, and there are several European distributors linked on the Airspy website.

Disclaimer: The SpyVerter R2 was sent by the Airspy team to us for free in exchange for an honest review.

LimeSDR Unboxing and Initial Review

A few days ago we received our early bird LimeSDR unit from CrowdSupply. The LimeSDR is advertised as an RX/TX capable SDR with a 100 kHz – 3.8 GHz frequency range, 12-bit ADC and up to 80 MHz of bandwidth. Back in June 2016 they surpassed their $500k goal, raising over $800k on the crowdfunding site Crowdsupply. Just recently some of the first crowdfunding backers began to receive their units in the mail. We paid $199 USD for an early bird unit, and currently a preorder unit costs $289 USD on Crowd Supply.

Unboxing

Inside the shipping box is a smaller black and green box with the LimeSDR itself inside, and a short USB pigtail with extra power header. Note that no pigtails for the u.FL antenna connectors are provided, so you will need to source these yourself, but they can be found quite cheaply on Aliexpress.

The PCB itself is intricate and heavily populated with many components. You certainly to feel like you are getting your moneys worth of engineering effort with this SDR. An enclosure is probably highly recommended if you intend to take your LimeSDR out and about, as some of the SMD components look like they could be easily knocked off with a drop.

The parcel was declared at the full value, so this may be a problem for those in countries with low customs tax thresholds.

Driver and Software Installation

For this first initial review we decided to set the LimeSDR up in Windows, with SDR-Console V3, and try to get wideband reception and some simple transmit working.

Installation was a bit rocky. Firstly one criticism is that the online documentation is all over the place, and a lot of it seems to be out of date. It was very difficult to find the current USB drivers as many links redirected to the older drivers. Finally we found drivers that work on the Lime Suite page.

Secondly there have been some apparent changes with hardware revision 1.4 which is shipping to Crowd Supply backers.  This resulted in the current version of SDR-Console V3 being incompatible with the newly shipped boards, and throwing the error “Encountered an improper argument”. We had to search through the LimeSDR forums, and there we found a beta LimeSDR fix version of Console V3 released by Simon. This version worked with our board. 

Once we had the LimeSDR drivers and SDR-Console V3 installed we decided to update the firmware as we’d seen on the forums that the latest firmware supposedly improved a few things. Again, performing this task was quite confusing as there was several links to outdated documentation and software all over the place. Finally we found what we think is the latest instructions, which had us download Lime Suite which comes together with the PothosSDR software. In this version of Lime Suite there is an automatic firmware update option which downloaded and flashed the new firmware easily.

It’s clear that the LimeSDR is very much a development board made mainly for experimenters, but some decent up to date documentation and a quick start guide would help new users tremendously.

Problems with HF and reception below 700 MHz

By browsing the LimeSDR forums we came across a topic where several users had claimed that the LimeSDR v1.4 (the one shipped to CrowdSupply backers) has abysmal HF sensitivity, and poor sensitivity below 700 MHz. 

It seems that this lack of performance is due to the matching circuit which they have implemented. For better impedance matching at frequencies over 700 MHz they added a parallel 8.2 nH inductor. This unfortunately attenuates HF frequencies severely to the point of no reception, and also other frequencies below 700 MHz to some extent. This is a bit troubling as from the very beginning the LimeSDR has been advertised as working down to 100 kHz.

A hardware fix was found by forum user @sdr_research but this only works if you are comfortable taking a soldering iron to the board to remove that inductor. On this official blog post they also mention more fixes (EasyFix1 is the one recommended on the forums) to improve HF performance that include removing more components, and replacing some others. 

The HF fix for the LimeSDR. Remove this inductor.
The HF fix for the LimeSDR. Remove this inductor.

We performed the EasyFix1 mod, which involved removing one inductor on the PCB. Removal was very simple with a soldering iron. Even without a soldering iron it could probably be forcefully removed with some tweezers. After removing that inductor we saw HF spring back into life, with reception working all the way down to the MW broadcast AM band.

LF reception still seems to be a bit weak. We were able to receive an NDB down to about 300 kHz, but very weakly in comparison to other SDRs.

The image below shows the difference in HF reception before and after the mod.

Before and after the mod. Bottom waterfall shows signal levels before the mod, top waterfall shows signal levels after removing the inductor.
Before and after the mod. Bottom waterfall shows signal levels before the inductor mod, top waterfall shows signal levels after removing the inductor.

Fortunately it seems that LimeSDR is trying to make this right, and just today they issued an update that confirms the issue and offers a fix. They are offering an option for unshipped boards to be modified to improve HF performance before they ship out, and a replacement option for those who have already received boards. The deadline for applying for a modification is February 21, 2017.

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Review of the ThumbNet N3

Back when it was released in November we posted an initial unboxing and initial first impressions review of the ThumbNet N3 RTL-SDR dongle. In this post we continue that review and post a few more in depth results.

The ThumbNet N3 is the latest iteration of ThumbNet redesigned RTL-SDR dongles. It’s main features include a shielded PCB, metal enclosure, F-type connector, Mini-USB connector, all linear power supplies and an external power mode. It is designed specifically to be used in the ThumbNet system, but because they need to order the units in bulk they sell the excess off to other users too on their new site Nongles.com. The N3’s list of features is shown below.

  • Full backward compatibility with existing RTL-SDR dongles and software
  • High stability TCXO (+/-0.5ppm) (ensuring rock-solid stability from start-up and over a wide range of temperatures)
  • Standard R820T2 + RTL2832U (plus 24C02 EEPROM) chipset
  • Improved/enhanced decoupling. (Common-mode choke on USB port)
  • Low-noise, linear only power regulation (separate 1.2v and 3.3v regulators)
  • External DC (+5v, 450mA) supply connector
  • Mini-USB connection (allows easy separation of the RF unit from the noisy PC)
  • F type RF connector (very common and compatible with existing ThumbNet tracking stations)
  • Large (6x4cm) contiguous ground-plane (for better thermal dissipation)
  • Static drain-away resistor on the RF input (1K to ground)
  • All unnecessary parts (IR receiver, high-current LED etc.) eliminated to reduce parts count and noise
  • Circuit board can be mounted into a common 1455 case

ThumbNet/ThumbSat is a company that hopes to help experimenters get mini satellites into orbit starting from $20k USD. The ThumbNet project aims to provide hundreds of schools and educational institutions with RTL-SDR based satellite receivers in the hope that they will use them as an educational resource, and at the same time help set up a worldwide monitoring network, so that the live data from the launched satellites is always available to the satellite experimenters.

The ThumbNet N3
The ThumbNet N3

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Leif (SM5BSZ) Compares Several HF Receivers

Over on YouTube well known SDR tester Leif (SM5BSZ) has uploaded a video that compares the performance of several HF receivers with two tone tests and real antennas. He compares a Perseus, Airspy + SpyVerter, BladeRF + B200, BladeRF with direct ADC input, Soft66RTL and finally a ham-it-up + RTLSDR. The Perseus is a $900 USD high end HF receiver, whilst the other receivers are more affordable multi purpose SDRs.

If you are interested in only the discussion and results then you can skip to the following points:

24:06 – Two tone test @ 20 kHz. These test for dynamic range. The ranking from best to worst is Perseus, Airspy + SpyVerter, Ham-it-up + RTLSDR, Soft66RTL, BladeRF ADC, BladeRF + B200. The Perseus is shown to be significantly better than all the other radios in terms of dynamic range. However Leif notes that dynamic range on HF is no longer as important as it once was in the past, as 1) the average noise floor is now about 10dB higher due to many modern electronic interferers, and 2) there has been a reduction in the number of very strong transmitters due to reduced interest in HF. Thus even though the Perseus is significantly better, the other receivers are still not useless as dynamic range requirements have reduced by about 20dB overall.

33:30 – Two tone test @ 200 kHz. Now the ranking is Perseus, Airspy + SpyVerter, Soft66RTL, BladeRF+B200, Ham-it-up + RTLSDR, BladeRF ADC.

38:30 – Two tone test @ 1 MHz. The ranking is Perseus, Airspy + SpyVerter, BladeRF + B200, ham-it-up + RTLSDR, Soft66RTL, bladeRF ADC. 

50:40 – Real antenna night time SNR test @ 14 MHz. Since the Perseus is know to be the best, here Leif uses it as the reference and compares it against the other receivers. The ranking from best to worst is Airspy + SpyVerter, ham-it-up + RTLSDR, BladeRF B200, Soft66RTL, BladeRF ADC. The top three units have similar performance. Leif notes that the upconverter in the Soft66RTL seems to saturate easily in the presence of strong signals.

1:13:30 – Real antenna SNR ranking for Day and Night tests @ 14 MHz. Again with the Perseus as the reference. Ranking is the same as in 3).

In a previous video Leif also uploaded a quick video showing why he has excluded the DX patrol receiver from his comparisons. He writes that the DX patrol suffers from high levels of USB noise.