November 14, 2016

Portable Shortwave Spectrum Capture with an Airspy + Spyverter and Tablet

Over on his blog London Shortwave writes how difficult it can be trying to listen to shortwave radio stations when you’re indoors and in a big city filled with RF noise. His solution is a portable lightweight shortwave travel kit that he can take to the park. The kit that he recommends using includes an Airspy SDR with SpyVerter upconverter, a Toshiba Encore 8″ Tablet and an OTG USB adapter. His antenna is a portable dipole made from two pieces of 6m copper wire connected to a balun, then connected to the SDR with 3m of coax. The whole kit easily fits into a small metal brief case.

For the software London Shortwave uses SDR# and he enjoys capturing large chunks of the HF spectrum for replay later using the base band recorder and file player plugins for SDR#. In his post he also shows how he runs the Airspy in debug mode to restrict it to 6 MHz which is the maximum bandwidth that his tablet’s CPU can handle.

His post shows various example videos of his setup receiving some nice shortwave signals.

London Shortwave's SDR Kit. — London Shortwave’s SDR Kit.

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November 14, 2016

RTLSDR4Everyone Four New Posts: FlightAware Pro Stick Plus Review, Avoid FlightAware Ripoffs, Review of two BCFM Filters, Getting Started with Outernet

Akos from the RTLSDR4Everyone blog has recently uploaded four new articles. The first article reviews the new FlightAware Prostick Plus. The Prostick Plus is an RTL-SDR dongle optimized for ADS-B reception. It contains a LNA and 1090 MHz filter on board the dongle. In his review Akos tests the FlightAware Prostick Plus and compares it against the regular Prostick with external filtering. His results show that the Prostick Plus gets 18.45% more position reports and 5.4% extra max range in his location. His second post continues with the Prostick topic and warns customers to look out for sellers reselling, or relisting the Prostick for much higher ripoff prices.

In his third post Akos reviews our RTL-SDR.com broadcast FM filter and compares it against another similar filter from another seller. His test results show that both filters can improve performace.

Two BCFM band stop filters tested by Akos.

Finally in his fourth post Akos writes a tutorial on getting started with Outernet reception. He bought the full Outernet bundle which comes with a battery bank, CHIP single board computer, E4000 with bias tee RTL-SDR, LNA with filter and patch antenna. His post describes what each component is, then shows how to use them to receive Outernet. His results also seemed to show that our V3 dongle significantly outperformed the E4000 dongle at Outernet reception. The V3 received the Outernet signal with a SNR of 6.39 dB vs only 2.58 dB with the E4000.

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November 14, 2016

Combining the Bandwidth of two HackRF’s

RTL-SDR.com reader Syed Ghazanfar Ali Shah Bukhari from the Frequency Allocation Board in Pakistan recently emailed us to let us know a trick he's found which lets you combine the bandwidths of two HackRF software defined radios in GNU Radio. Syed's program is based on Oliver's flowgraph that we posted previously, which was used to combine the bandwidth of two RTL-SDR dongles.

Syed also sent us the GRC file to share which we've uploaded here.

He writes:

I have used grc flow graph of Oliver as mentioned in the link :-
https://www.rtl-sdr.com/combining-the-bandwidth-of-two-rtl-sdr-dongles-in-gnu-radio and modified it to be used with 2 HackRF Ones. I also shifted the two bandwidths inward by 1 MHz instead of 0.2 MHz to make a smooth continuation for a 38 MHz spectrum. Unfortunately one of my HackRF Ones has its RF Amp burnt up so I adjusted its IF and BB gain to have same noise floor as that of other HackRF One. It's really awesome. I am sending you the diagram and grc file. The attached image is showing complete GSM900 downlink spectrum (38 MHz) in my area with active 2G and 3G signals.

September 2018 Update:

An rtl-sdr user with nick JAAP had some query pertaining to calculation of center frequency of each HackRF. The values I used were a bit erroneous. If you the previous flow graph I sent you, the center frequencies for both HackRFs are same in the SDR source box. That should be different for both with a 20 MHz difference between the two. Some spectrums started repeating themselves on those values. I have improved the flowgraph using variables and equations to remove the logical bug. I have added a slider for bandwidth cropping that can be used for test pupose only to understand the concept behind the frequency shifting and cropping of spectrum of both HackRFs. I have attached the new grc file and the image. Gain values can be adjusted as per user requirement and sensitivity of your own SDRs. I am working on grc which will show a spectrum using 5 rtl-sdrs and two hackRFs thus combining BWs to give a span of 50 plus MHz.

Update GRC File available here.

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November 12, 2016

SDRuno Updated to V1.1: Now supports up to 2.4 MSPS for the RTL-SDR

SDRuno is the official software for the SDRplay RSP software defined radio. Recently they’ve released version 1.1 which contains various new features and bug fixes for the RSP. The SDRuno Cookbook by NN4F & KD2KOG has also accordingly be updated with information about the new features.

In addition they’ve also now increased the previous 0.96 MSPS sample rate limit which was enforced for all third party radios running via EXTIO drivers. The new limit is 2.5 MSPS (with 2.4 MSPS being the limit for the RTL-SDR). This is great news for RTL-SDR users as SDRuno for the RTL-SDR is now almost as functional as in other SDR software like SDR#, HDSDR and SDR-Console. The change log is pasted below:

Version 1.1 (11th November 2016)
Bug Fixes

1.04.1 – fixed issue where highlighted filter wasn’t always the one loaded.

Waterfall in combo mode now flows the same direction as other modes

Updates (RSP only V1.1)

Tighter integration of RSP controls

Calibrated power measurement

Automatic S-Meter calibration

SNR meter

dBm scale for both SP1 and SP2 windows

Automatic frequency calibration

Support for IARU S-Meter standard

Zoom to VFO button in SP1 window

More improvements to AGC scheme

More improvements to DC offset compensation scheme

Reversed default mouse wheel scroll direction

Waterfall in combo mode direction can be reversed in the same way as other modes

Added extra frequency step sizes

LSB / USB filter presets back to being the same

USER filter preset renamed to DIGITAL

Support for both gain and gain reduction displays

Updated hardware driver – now reports as SDRplay device

Updates (EXTIO only V1.05)

maximum bandwidth changed to 2.5MHz

SDRuno Version 1.1 Running a RTL-SDR at 2.4 MSPS

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November 11, 2016

The ThumbNet N3 is now Shipping

The latest RTL-SDR receiver from Thumbnet, the Thumbnet N3 is now shipping out. Back in October we received a sample of one of their prototypes and found it to have a very low noise floor since they have replaced the 1.2v switching regulator with a linear regulator.

ThumbNet is a company that is hoping to provide low cost satellite deployments, and make use of volunteers around the world with RTL-SDR’s to help track them. The RTL-SDR’s and antenna kits are provided to schools and educational institutions for free by ThumbNet, in exchange for students setting up and monitoring a satellite tracking station.

In their release email they wrote:

ThumbNet would like to send a very large “Thank You!!” to all of you who have supported us by purchasing one of our surplus N3 SDR receivers, and we wanted to take a second and let you know that we’re excited to announce that the N3’s have left the factory and will begin shipping.

The support has been tremendous and we have a backlog of many hundreds of receivers to get out. We will be working extremely hard, over the coming days to get them all delivered as quickly as possible (Orders will be shipped in the order they were received.).

Don’t forget that there are accessories in the ThumbSat Store (http://www.thumbsat.com/thumbnet-sdr-hardware/thumbsat-store-4 ) that may be of value to you, such as adapters, cables or power supplies to let you get the maximum performance from your ThumbNet N3.

A handful of independent tests have been done on the Qualification Models of the N3, and the results have been quite positive. If interested, you can read some of the reviews at the following links.

RTL-SDR.com – https://www.rtl-sdr.com/rtl-sdr-com-quick-review-of-the-thumbnet-n3-prototype/

RTLSDR4EVERYONE – http://rtlsdr4everyone.blogspot.com/p/thumbnet-n3.html

Thank you again for supporting ThumbNet and we hope the N3 exceeds all of your expectations!!

The Thumbnet N3 with its metal case add on.

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November 8, 2016

Demuxing Frames and Generating Images from the GOES Weather Satellite

In his latest two posts Lucas Teske continues with his series about receiving and downloading weather satellite images from the GOES satellites. In past posts he’s show us how to receive the signal with a satellite dish and Airspy or RTL-SDR (part 1), how to demodulate the signal (part 2), and how to extract frames from the demodulated signal (part 3). Lucas has recently completed his series with parts 4 and 5 having just been uploaded.

In part 4 Lucas shows how to parse the frames and get the packets which will ultimately be used to generate the weather image files. His post explains how to de-randomize the frame data which is initially randomized to improve performance, how to add Reed Solomon error correction, how to demux the virtual channels and the packets and finally how to save the raw packet.

In part 5 Lucas shows us how to finally generate weather satellite images from the GOES satellites. He notes that there is a problem with the LritRice compression method used by NOAA, because the library is currently broken on Linux. So he made a workaround which involved making a Windows application that runs through Wine for decompressing the data. Once the files are decompressed he uses the xrit2pic program which can open the generated .lrit files and convert them into images.

In the future Lucas mentions that he will write a user guide to his LRIT decoder, and make the whole decoding process more user friendly for people who do not care so much about the actual decoding process. Below are some images that Lucas was able to receive with his system.

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November 7, 2016

Mile Kokotov’s SDR Overview and Dynamic Range Explanation

Mile Kokotov (Z33T) has been working on creating an overview page of some of the most popular software defined radios and software applications. In the past we’ve featured Mile’s videos several times on our blog and his page ties all the videos together nicely with text. On his page he briefly reviews the different types of RTL-SDR dongles as well as the Airpsy and SDRplay.

One very useful page he’s put together is his explanation of the “dynamic range” concept, which is probably the most important characteristic when it comes to a radio. According to Miles description dynamic range measures the ability of a radio to “receive very weak and very strong signals at the same time, without overloading”. His page also explains how decimation in software can help improve the dynamic range without needing to improve the hardware.

Mile’s page is not yet 100% finished, so we advise you to keep an eye on it for new information.

Explaining dBFS (decibels relative to full scale)

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November 7, 2016

Solving APRS Interference Issues with a Bandpass Filter and Coax Notches

John, DK9JC N1JJC wanted to set up an RTL-SDR APRS packet iGate. APRS stands for “Amateur Packet Reporting System”, and is a type of packet radio communications system used by Amateur Radio operators. They often use them to transmit short messages, weather sensor updates, and for vehicle tracking. An iGate allows APRS messages to be transmitted over the all world via the internet like so RF->iGate RX->Internet->iGate TX->RF.

When trying to receive the APRS packets John discovered a problem. He discovered that there was a very strong 100kW broadcast FM and 50kW DAB transmitter on a transmission tower in line of sight of his antenna. The strong signals were overloading the dongle and completely wiping out the APRS packets that he was trying to receive at 144.8 MHz.

First John tried a simple bandpass filter with 0.8 dB insertion loss and 20dB attenuation. The filter still wasn’t enough, so he went and made a several coax notch filters to take out each of the interfering signals. A coax notch filter is simply a length of coax connected via a “T” junction to the main coax cable. This creates a notch of attenuation at a frequency depending on the length of the notching coax. With these notches combined with the bandpass filter he was finally able to receive APRS packets.

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