Tagged: 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 Firstly one criticism is that the online documentation is all over the place, and a lot of it seems to be out of date.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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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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RTLSDR4Everyone: Review of the Nooelec SMArt SDR, Direct Sampling and Generic vs Premium Dongles

RTL-SDR enthusiast and blogger Akos has recently uploaded three new articles. In his first article he discusses what he believes is the differences and advantages of Generic vs Premium branded RTL-SDR dongles.

In his second article he shows how easy it can be to perform the direct sampling mod on newer dongles, as most have the direct sampling break out pads. He shows how it can be as easy as sticking a wire into these holes. Please note that if doing this we would caution you to take decent ESD precautions as these pins are not ESD protected.

In the third article he reviews the recently release Nooelec SMArt dongle. The SMArt is a new RTL-SDR variant which comes in a smaller black case, cooling via thermal pads and with an SMA connector. With these modifications it is very similar to our RTL-SDR.com units, however the one advantage of the SMArt is that it is small enough to fit two side by side on closely spaced USB ports, like on the Raspberry Pi. In the post he shows what is inside the SMArt and discusses various points such as heat generated, included antennas and performance.

Inside the new Nooelec SMArt RTL-SDR dongle.
Inside the new Nooelec SMArt RTL-SDR dongle.

Review of the Airspy Mini

The Airspy Mini is a recently released $99 USD software defined radio with a tuning range of 24 MHz to 1800 MHz, 12-bit ADC and up to 6 MHz of bandwidth. The Mini is the younger brother of the $199 USD Airspy R2, but despite the $100 USD price difference, both units are very similar, which makes the Mini a very attractive option. The idea is that the Mini is the cheaper version for those who do not need the more advanced features of the R2.

In a previous review we compared the Airspy R2 with the SDRplay RSP and the HackRF. In those tests we found that the Airspy had the best overall RX performance out of the three as it experienced the least amount of overload and had the most dynamic range. The SDRplay RSP was the main competitor in performance to the Airspy R2, and was found to be more sensitive due to its built in LNA. But the RSP experienced overloading and imaging problems much easier. With an external LNA powered by its bias tee, the Airspy gained a similar sensitivity and still had very good dynamic range. The main downside to the Airspy R2 was its higher cost compared to the $149 USD SDRplay RSP, and needing to fork even more for the $50 USD SpyVerter if you want to listen to HF signals.

In this review we’ll compare the difference between the R2 and Mini, and also see if the cheaper Airspy Mini ($99 USD), or Airspy Mini + SpyVerter combo ($149 USD) can compete in this lower price range. 

Difference Between the Mini and R2

  Airspy Mini Airspy R2
Price $99 USD $199 USD
Tuning Range 24 – 1800 MHz 24 – 1800 MHz
ADC Bits 12 12
Maximum Bandwidth (Alias Free Usable) 6 MHz (5 MHz) 10 MHz (9 MHz)
Extras Bias Tee Bias Tee, External clock input, Multiple expansion headers
Dimensions (Including USB and SMA ports) 7.7 x 2.6 x 1 cm 6.4 x 2.5 x 3.9 cm
Weight 21 g 65 g

Right now the “early bird” price of the Mini is $99 USD. We are unsure if this price will go up in the future.

The external design between the two units is different. The Mini comes in a USB dongle form factor which is very similar to a standard RTL-SDR, whilst the R2 comes in a larger box with a female Micro USB input. In our tests this metal enclosure appears to provide good shielding from strong signals. One thing that was missing on the unit was a nut and washer on the SMA connector. Adding a nut helps the PCB ground make good contact with the aluminum enclosure. The Airspy team have said that future units will come with this nut provided.

Airspy R2 (top), Airspy Mini (Middle), RTL-SDR (bottom) for size comparison.
Airspy R2 (top), Airspy Mini (Middle), RTL-SDR (bottom) for size comparison.

Apart from the price and enclosure, the most noticeable feature difference between the two is the smaller bandwidth of the Airspy Mini. Unlike the Airspy R2, the Airspy Mini does not use a Si5351 clock generator chip. The lack of this chip limits the Mini’s maximum bandwidth to 6 MHz and eliminates any ability to use an external clock. The main applications that you miss out on from the lack of an external clock input include: coherent clock, passive radar and direction finding experiments.

From the circuit photos below we can see that the Mini consists of mostly the same parts used in the Airspy R2. Missing is the Si5351 clock controller, expansion headers and the external clock input. 

The Airspy Mini Circuit Board.
The Airspy Mini Circuit Board
Airspy R2 PCB.
The Airspy R2 Circuit Board

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Review: FlightAware ADS-B RTL-SDR + LNA Positioning

Recently FlightAware released a new RTL-SDR dongle sold at zero profit at $16.95 USD. It’s main feature is that it comes with an ADS-B optimized low noise amplifier (LNA) built directly into the dongle. FlightAware.com is a flight tracking service that aims to track aircraft via many volunteer ADS-B contributors around the world who use low cost receivers such as the RTL-SDR. In this post we will review their new dongle and hopefully at the same time provide some basic insights to LNA positioning theory to show in what situations this dongle will work well.

FlightAware Dongle Outside
FlightAware Dongle Outside

A good LNA has a low noise figure and a high IIP3 value. Here is what these things mean.

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Review: Airspy vs. SDRplay RSP vs. HackRF

asvsrspvshackrf

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

  Airspy SDR Play RSP HackRF
Price (USD)

$199 / $ 249 USD (with Spyverter) + shipping ($5-$20).

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 SDRplay is currently selling about 1000 units a month according to electronicsweekly.com.

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.

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HAMSPIRIT.DE’s Review on Airspy vs SDRPlay

Over on the hamspirit.de blog author January has just uploaded his latest review comparing the Airspy with the SDRPlay (article in German, so use Google Translate if necessary). These are two mid price range RX only software defined radio receivers that many people see as a first upgrade from an RTL-SDR dongle. Currently, the Airspy sells for $199 USD and the SDRPlay sells for $149 USD.

In his review January uses the SDR# to compare both devices on a wide range of signals include a beacon in the 10M band, broadcast FM stations, another beacon in the 2M band, TETRA signals and trunked radio in the 70cm band. He ran the SDRPlay at a bandwidth of 1.536 MHz and the Airspy at a bandwidth of 2.5 MHz, with decimation set to 2 in order to get comparable bandwidths.

From the results it appears that overall the two SDR’s are quite comparable to one another. But the SDRPlay has the advantage that it’s frequency range covers shortwave frequencies and his results show that the SDRPlay had better SNR in the FM broadcast band (although these results may be incorrect as it appears that his gain settings were not set properly, as the Airspy guide recommends that Airspy gains be adjusted to keep the noise floor near -80 dBFS). On the other hand the Airspy was much better when strong FM overload was present as shown in his TETRA results. In his conclusion he writes (translated from German to English):

If one value to a SDR, which covers with the short wave, it is running out on the SDRplay.

If one is interested in the field below the 70cm amateur radio bands, is in my view the Airspy front.

The Airspy software defined radio    The SDRPlay software defined radio