In a post uploaded last month we noted that Outernet was selling off some of their old L-Band satellite antennas cheaply. Nils Schiffhauser (DK8OK) decided to take advantage of the sale and bought one. Now Nils has created a blog post that shows how he's been able able to decode 12 L-Band AERO channels simultaneously with the Outernet L-band antenna, an Airspy R2 and SDR-Console V3. AERO is the satellite based version of aircraft ACARS, and it's L-band signals contain short ground to air messages like weather reports and flight plans. Multiple channels are often in use at any one time.
To achieve this Nils uses the multi-channel tuning capabilities of SDR-Console V3, which allows him to open up 12-channels, each tuned to a different AERO frequency. He then opens up 12 instances of the AERO decoder known as JAERO, and then uses VB-Cable to pipe the audio from each channel into a JAERO instance. Nils writes that the key to making JAERO run with multiple instances is to install JAERO into different folders on your PC, and give each JAERO.exe a unique file name like JAERO_1.exe.
He collects all the data into a program called Display Launcher and Nils notes that the whole set up has been stable digesting 54,000 messages over the last 24 hours.
Back in April we posted about QuestaSDR, which had just released the Android version of its SDR software. Recently QuestaSDR programmer 'hOne' wrote in and noted that a new update has enabled remote streaming in QuestaSDR.
To get set up, just run the Windows version of QuestaSDR on a PC, and open the "SDR Server" app. Once the server is running, you can connect to it via the Android version of QuestaSDR over a network connection. The server supports the RTL-SDR, Airspy and any ExtIO compatible device such as SDRplay units. As far as we're aware, this is the only Android app that currently supports streaming from non rtl_tcp compatible units such as the Airspy and SDRplay.
Thank you to Michael (dg0opk) who wrote in and wanted to share details of his full SDR monitoring system for weak signal HF modes. His setup consists of nine ARM mini PCs (such as Banana Pi's, Raspberry Pi's, and Odroid's), several SDRs including multiple RTL-SDR's, an Airspy Mini, FunCube Dongle and SDR-IQ, as well as some filters and a wideband amp. For software he uses Linrad or GQRX as the receiver, and WSJTx or JTDX as the decoding software, all running on Linux.
Michael also notes that his Bananapi FT8, JT65 and JT9 SDR monitor has been up and stably running continuously for half a year now. Bananapi's are lower cost alternatives to the well known Raspberry Pi single board computers, so it's good to note that a permanent weak signal monitoring system can be set up on a very low budget. Presumably even cheaper Orange Pi's would also work well.
With his setup he is able to continuously monitor FT8, JT65 and JT9 on multiple bands simultaneously without needing to tie up more expensive ham radios. His results can be seen on PSKReporter. A video of his RTL-SDR Raspberry Pi 3 decoding FT8, JT65 and JT9 can be found here.
Over on YouTube icholakov has uploaded two new comparison videos. The first compares the Airspy HF+ against an RSP-1A on HF signals with a W6LVP receive loop antenna in a noisy suburban backyard in Florida.
Results appear to be quite similar for most signals, although we noted better performance from the HF+ on some particular weak signals surrounded by strong AM stations in the test such as the 810 kHz signal at 3:37, but lower noise on some signals received by the RSP-1A such as at 9:32. The tests were performed with a stock HF+ without any firmware updates applied so it's possible that the updates could improve results further.
In the second video icholakov performs the R3 mod on his Airspy HF+ and compares the results before and after. It appears that shorting R3 improves reception on MW slightly, and has little effect at higher frequencies. We also note that the R3 mod is mostly designed to mostly improve VLF/LF reception which is not tested in the video.
W6LVP receiving loop: Airspy HF+ vs. SDRPlay RSP-1A
Over on his blog, Thierry Leconte has been writing about some IF bandwidth experiments that he's performed on the R820T2 chip. This is the tuner chip that is used in most RTL-SDR dongles, and well as on the Airspy R2 and Mini SDRs. It has a programmable IF bandwidth and high pass filter which can be used to filter neighboring interfering signals out to reduce imaging and overload problems. In the RTL-SDR and Airspy drivers the bandwidth is adjusted to a fixed setting depending on the bandwidth selected.
To perform the tests he uses a noise source connected to his Airspy, varies the IF filter bandwidth and then plots the results. He finds that there are two adjustments for the IF filter, one coarse and one fine, as well as an additional high pass filter. By manually reducing these settings it's possible to get better filtering at the expense of reduced bandwidth.
He notes that reducing the bandwidth is useful for his two apps, acarsdec and vdlm2dec which receive ACARS and VDL aircraft signals. These signals are not high in bandwidth so they can easily benefit from tighter filtering.
I bought the RPi to use it as a Spyserver for my Airspy HF+ SDR.
My main radio listening location is a small house located on a hill outside the city and there is no power grid there (it’s a radio heaven!), so everything has to run on batteries and consume as little power as possible.
My first tests showed that the Raspberry Pi works very well as a Spyserver: the CPU usage stays below 40% and the power consumption is low enough to allow it to run for several hours on a regular USB power bank. If I add a 4G internet connection there I could leave the Spyserver running and connect to it remotely from home.
Then I wondered if the Raspberry Pi would be powerful enough to run a SDR client app. All I needed was a portable screen so I bought the official 7” touchscreen for the RPi.
I installed Gqrx, which offers support for the Airspy HF+. I’m happy to say it works better than I expected, even though Gqrx wasn’t designed to work on such a small screen. The CPU usage is higher than in Spyserver mode (70-80%) but the performance is good. Using a 13000 mAh power bank I get about 3.5 hours of radio listening.
On the swling blog post comments Tudor explains some of his challenges including finding a battery that could supply enough current, finding a low voltage drop micro-USB cable, and reducing the noise emanating from the Raspberry USB bus. Check out the post comments for his full notes.
The Noise Figure (NF) is an important metric for low noise amplifiers and SDRs. It's a measure of how much components in the signal chain degrade the SNR of a signal, so a low noise figure metric indicates a more sensitive receiver. The Noise Figure of a radio system is almost entirely determined by the very first amplifier in the signal chain (the one closest to the antenna), which is why it can be very beneficial to have a low NF LNA placed right at the antenna
It’s a GNU Octave script called nf_from_stdio.m that accepts a sample stream from stdio. It assumes the signal contains a sine wave test tone from a calibrated signal generator, and noise from the receiver under test. By sampling the test tone it can establish the gain of the receiver, and by sampling the noise spectrum an estimate of the noise power.
As expected, Rowetel found that the overall noise figure was significantly reduced with the LNA in place, with the Airspy's measuring a noise figure of 1.7/2.2 dB, and the HackRF measuring at 3.4 dB. Without the LNA in place, the Airspy's had a noise figure of 7/7.9 dB, whilst the HackRF measured at 11.1 dB.
Some very interesting sources of noise figure degradation were discovered during Rowetel's tests. For example the Airspy measured a NF 1 dB worse when used on a different USB port, and using a USB extension cable with ferrites helped too. He also found that lose connectors could make the NF a few dB's worse, and even the position of the SDR and other equipment on his desk had an effect.
The R820T2 is the main tuner chip used in most RTL-SDR dongles. Several months ago Rafael Micro ceased regular production of their R820T2 chip, and the older R820T has also been discontinued for some time too.
However, Rafael are still producing new quality R820T2 chips for factories if they make very large bulk orders. Since it is one Chinese manufacturer producing all of RTL-SDR.com V3, NooElec, FlightAware and most generically branded dongles, the volume restriction is not a problem for them as long as the RTL-SDR is still in demand. So most dongles using R820T2 RTL-SDRs should be able to continue business as usual for the forseeable future. But we have also recently seen that a lot of generically branded RTL-SDR dongles presumably produced at other factories have started to ship with the less desirable FC0012/13 tuner chips instead.
The R820T chip is already 8 years old, and the R820T2 has been around for the last two years. The R820T2 was a slight improvement on the R820T, due to a higher quality manufacturing process used to produce it. The change in manufacturing process resulted in mostly higher yields, less chip-to-chip variance, better sensitivity, reduced L-band heat VCO lock issues, and wider filters.
Recently the Youssef from the Airspy team announced the likely early retirement of their Airspy Mini and R2 line of products(see update below, Airspy Mini/R2 production will continue) These are SDRs that used the R820T2 tuner chip combined with a 12-bit ADC, allowing for significantly better performance compared to an RTL-SDR. It seems that they were able to acquire R820T2 chips from a distributor, but the stock proved to be very low yield. Possibly once discontinued a lot of low quality chips were dumped onto the distributors for final sale. They write:
I have some bad news. Rafael Micro officially discontinued the R820T2 since a few months. This is the tuner we use in the Airspy R2 and Airspy Mini.
We tried to secure an extra batch from Rafael (even at a higher price) but the quality of the silicon of the samples we received wasn't very good and most units didn't pass our automated QA tests. Sacrificing the performance is out of question. The alternatives proposed by Rafael are not pin compatible and require both a significant hardware redesign and new tuner control code - and this is a large investment with very little guarantees on the final result.
I can say this has been one of the longest running designs that resisted the new silicon tuner SDR's popping in and out while setting a standard for performance and price.
For now, our distributors are running out of R2/Mini's very quickly and, until a final solution is found or a new replacement is designed, there won't be any new batches out.
I was checking my notes for alternatives to the current Airspy R2/Mini design and wondered if consulting the community would give some constructive input. As the market is already crowded with low cost receivers and transceivers, but yet Icom manages to sell a 4 figures SDR, I was thinking of making something that is as open as possible for extensions and work good enough for the most demanding operators and pro's, all while being affordable.
The idea is to replace the R820T2 tuner with one of its latest high performance siblings, then replace the old LPC4370 with the brand new i.MX RT1020. This MCU can be interfaced with a good ADC and has enough processing power for oversampling and decimation through the Cortex M7 core, which will bring the final resolution higher. The general goals:
Better RX performance than the general purpose low cost silicon transceivers
12 bit RX at 10MHz bw and up to 16bit at narrow band
Coverage from 30 MHz to 1.8 GHz or more
Same form factor as the Airspy HF+ (same box actually)
Leverage the RF manufacturing and testing capability developed at Itead Studio
UPDATE (May/2018): The Airspy team have managed to acquire a new batch of good R820T2 chips, so production of the R820T2 based Airspies can continue as per usual.
So in conclusion there is no need to panic buy R820T2 RTL-SDRs as production will continue as per normal for the forseeable future as the RTL-SDR demand is high enough for factories to make large bulk orders of new R820T2 chips. Even if the R820T2 is fully discontinued, there are alternative tuners with the same performance that we can switch to after a minor redesign.
Note that we're currently out of stock of RTL-SDR V3's on Amazon and low in stock on our store but this is not related to R820T2, but rather simply shipping delays. We should be fully back in stock within a few weeks.