Over on his blog András Retzler has created a post that discusses his research work on creating a fast networked wideband HF receiver. András is the creator of the web based OpenwebRX software, which allows RTL-SDR and some other SDR’s to efficiently broadcast their SDR data over a network and onto the internet. Some live SDR’s can be found at the OpenWebRX directory at sdr.hu.

The problem with the current implementation, András writes, is that while OpenWebRX works well with the RTL-SDR’s 2.4 MSPS sampling rate, it can not work so well with very high sampling rates, such as 60MSPS due to excessive computational requirements when several channels need to be monitored. András’ solution is to use his Fast Digital Down Conversion (FastDDC) algorithm which is significantly more CPU efficient. András writes that the FastDDC algorithm improves computation by up to 300% in some cases, can speed up calculations on low powered computers like the Raspberry Pi 2 and can be implemented on a GPGPU for even higher performance. He is still working to implement the algorithm in OpenWebRX.

In addition to his work, András has also posted about what he feels is a bit of an injustice between his work on OpenWebRX and the KiwiSDR designers. The KiwiSDR is a new wideband HF SDR that has recently been successfully funded on Kickstarter. Andras writes that he is discontented with the fact that the KiwiSDR developers have forked his open source software (OpenWebRX) and are now profiting from it, without contributing back to the original project.  András writes:

John Seamons has forked OpenWebRX, and sells his own hardware with it. The web interface is clearly the selling point of the device. After getting a lot of help from me, most of which was inevitable for his success, now John and ValentF(x) are leaving me with nothing, except a ‘Thank you!’. John has told me that OpenWebRX is a large part of his project, and he also claimed that my work has reduced the time-to-market of his product by maybe a year or so.

Why I’m standing up here is that forking open source software (which means changing the code in a way that is incompatible with the original version, and taking development in another direction), and funding it through Kickstarter is a very unusual way of getting things done. I acknowledge that John has very much work in his board and the accompanying software, however, he treated me and my project in an unethical manner.

In the Kickstarter comments section, the KiwiSDR creators reply back with their side. It is hard to say who is in the right in a situation like this. While what KiwiSDR have done is legal according to the licence, the ethics of doing so are questionable. We hope that both parties can successfully come to an agreement in the end.

If you want to directly support András and his work on OpenWebRX and other projects like FastDDC, then please consider donating to him at http://blog.sdr.hu/support. If you are a KiwiSDR backer, donating to Andras may be one way to right the situation if a deal cannot be reached.

The post Working Towards a Fast OpenWebRX HF Web Receiver + The Ethics of KiwiSDR appeared first on rtl-sdr.com.

Differential GPS (DGPS) are signals that exist between 285 – 325 kHz and are used to enhance the accuracy of GPS receivers. The system can improve GPS accuracy from 15m down to 10cm in some cases. It works using a network of ground stations at a very accurate known location that continuously measure the GPS error they receive. They then broadcast this error to DGPS capable receivers. The receiver can then use this error knowledge to correct their own readings.

With an VLF capable radio these DGPS beacons can be received and decoded on your PC. Over on swling.com guest poster Mario has submitted a post showing that these DGPS beacons can be received with a HackRF SDR and the MultiPSK software. The HackRF is a $299 SDR that can tune down to VLF (at reduced sensitivity). We note that the same or better results could also be achieved with a HackRF or RTL-SDR with upconverter.

The post Receiving Differential GPS Beacons with a HackRF appeared first on rtl-sdr.com.

Over on YouTube user London Shortwave has uploaded a video showing a comparison of the FunCube Dongle Pro+, Airspy with SpyVerter upconverter and SDRplay on shortwave reception. The Funcube, Airspy and SDRplay are all $150 – $250 USD software defined radios that have much higher performance compared to the RTL-SDR.

In the video he tests the reception of Radio New Zealand International (RNZI) at 9400 kHz using a 6m copper wire dipole and 9:1 matching balun raised 2m off the ground. He did not use any external antenna preselectors. The RNZI station is weak and appears to be almost blocked by a stronger station so reception of the station is difficult.

In his results it appears that the FunCube and Airspy/SpyVerter are able to clearly receive the RNZI station, but the SDRplay has trouble with images of other stations mixing into the signal.

If you are interested in a comparison of the Airspy, SDRplay and HackRF we previously did our own review here.

The post Comparing the FunCube Dongle Pro+, Airspy/SpyVerter and SDRplay on Shortwave appeared first on rtl-sdr.com.

Over on the SWLing Post blog contributor Mike Ladd has posted up a review of the Soft66RTL3 software defined radio. The Soft66RTL3 is a fully enclosed SDR unit that consists of a standard mini RTL-SDR dongle, a selectable upconverter circuit, several switchable bandpass filters for HF and a UPC1688 RF amp which is enabled in HF mode and is controllable through a trimmer pot. The selectable bandpass filters are from 0.4 MHz to 1.2 MHz, 1.2 MHz to 5 MHz, 5 MHz to 15 MHz and 15 MHz to 30 MHz. The unit also comes enclosed in an aluminum box with an SMA input connector and Micro-B USB port.

The Soft66RTL3 is custom produced by Kazunori Miura (JA7TDO) who is based in Japan. The Soft66RTL3 sells for $40 USD shipped, or $46 USD shipped with registered air mail. 

In the review Mike shows us the insides of the Soft66RTL3 and discusses its features. Later he also shows an installation and user guide.

The post A review of the Soft66RTL3 RTL-SDR + Upconverter + RF Amp Combination Circuit appeared first on rtl-sdr.com.

In the HF region between about 0 – 30 MHz it is common to see and hear “chripers” – signals which quickly sweep through the HF frequency band and produce an audible chirp. These chirps are actually signals from Ionosondes which is a type of radar system used to monitor the Ionosphere. The Ionosphere exists about 50km above the surface of the earth and is the atmospheric layer responsible for a large part of long range HF communications. In a previous post by Mario Filippi we also discussed Ionosondes.

Usually it is scientists who transmit and monitor these Ionosondes, however if you have wide band radio that can cover a majority of the HF spectrum then you can also monitor these chirpers yourself. Over on his blog Fabrizio Francione has created a post showing how to use a USRP, together with a GNU Radio Program called GNU Chirp Sounder to create his own amateur Ionogram monitoring station. The USRP is a fairly expensive SDR with a bandwidth of 25 MHz, but we add that we think that next generation of low cost wide band SDRs like the up and coming LimeSDR should also be able to do the same job.

The Ionograms show at what frequencies HF propagation is currently optimal for a specific distance (or number of signal bounces from the Ionosphere). Below is an example Ionogram animation showing the reception of Ionosondes taken over time. Video from the GNU Chirp Sounder page.

The post Monitoring Ionosondes and Creating Ionograms with a USRP and GNU Chirp Sounder appeared first on rtl-sdr.com.

Over on YouTube LimeSDR beta tester Marty Wittrock has uploaded several videos showing the LimeSDR receiving HF frequencies. In the first video Marty shows it receiving the USB voice on the 20m band during the 2016 ARRL field day. The second video shows reception of PSK31 signals. More videos are available on his channel if you are interested.

In the videos he uses GQRX and his own KN0CK HF upconverter. The LimeSDR should be able to receive HF on its own without an upconverter, but at the moment the HF capabilities have not been programmed into the drivers yet, so during this beta testing period an upconverter is required.

Marty also wrote in to us to make some comments on his experiences with the LimeSDR. He believes that the LimeSDR is amazing and writes:

The quality of the receive and audio [of the LimeSDR] is incredible against other SDRs I have in the house (Flex 5000A, RTL-SDR, HackRF, Red Pitaya – and soon SDRPlay).

Marty also writes that he will soon have more videos of the LimeSDR operating in Windows with SDRConsole in the near future, and we will post those videos too when they are ready.

The post Videos showing the LimeSDR in Action on HF with GQRX appeared first on rtl-sdr.com.

Over on YouTube user Full spectrum technician has uploaded an interested video where he shows how he used a beam deflection tube to create an upconverter for his RTL-SDR. A beam deflection tube is a type of vacuum tube that can be used as a mixer. If you aren’t aware, a vacuum tube (a.k.a tube or valve) is an electrical component that was used in electrical equipment heavily back in the first half of the 1900’s. They could be used to implement circuits like amplifiers, mixers, switches, oscillators and more. Even today they are still used in some high end audio equipment because many people believe they produce superior audio quality. Full spectrum technician writes on his video:

A simple test using a 6ME8 beam deflection tube as a balanced mixer up converter for an RTL-SDR to enable HF reception.

The only problem I had was too much conversion gain. Even with a relatively short antenna, and literally starving the tube for voltage, the signal output levels were high enough that I had to crank back the gain of the RTL SDR and/or use padding on the input of the RTL-SDR.

The LO was feed to grid 1 for common mode input.
The antenna was feed to the two deflection plates via a transformer as a differential input.
The output was taken from the two anode plates via a transformer as a differential output.

That resulted in the LO balancing it’s self out on the output so that the LO would not overload the front end of the receiver.

Operating voltages at the time were..
20V anode.
5V deflection plates.
20V accelerator grid.
Cathode tied to ground.

The post Using a Beam Deflection Tube as a Mixer for an RTL-SDR Upconverter appeared first on rtl-sdr.com.

Over on YouTube user icholakov shows a video where he compares our new RTL-SDR V3 dongles with direct sampling against an SDRplay and Icom 7100. The video shows reception at various HF frequencies on AM shortwave, time signals and SSB signals during day time reception. The performance seems to be fairly decent, but of course not as good as the more expensive SDRplay or Icom receivers.

This was originally posted on swling.com.

The post A Preliminary Review of the HF Mode on Our V3 Dongles appeared first on rtl-sdr.com.

In this video icholakov from our last post continues his testing, and does some more tests on daytime HF reception.

In his third video he tests night time reception against the SDRplay.

In this video YouTube user Michael Jackson tests his RTL-SDR V3 at 8 MHz, with a dipole antenna.

Finally, in this video YouTube user jonny290 tests the V3 dongle on HF reception using CubicSDR.

The post More videos showing HF reception on the RTL-SDR V3 Dongle appeared first on rtl-sdr.com.

Recently this week three new reviews of our RTL-SDR V3 came out, all reviewing its operation on HF frequencies.

In the first review Mike (KD2KOG) reviews the dongle and provides a video of it in action in SDR# receiving AM and SSB signals.

In the second review Gary (W4EEY) posts a review to swling.com and provides various screenshots of the dongle in action in HDSDR.

Finally over on YouTube user Johnny shows the dongle running in CubicSDR and listening to various SSB signals.

The post Three New Reviews of our V3 RTL-SDR using the HF Direct Sampling Mode appeared first on rtl-sdr.com.

The post Two Videos Showing the LimeSDR on HF in SDR-Console V3 appeared first on rtl-sdr.com.

Over on YouTube two new videos comparing the reception on the SDRplay and Airspy have been uploaded. The first is by Mile Kokotov and he compares the reception on a very weak broadcast FM station, with several strong signals surrounding it. He writes:

In this video I am presenting Airspy+SDR# vs SDRplay+SDRuno in the real world, receiving very weak FM broadcast station in the terrible conditions, with very strong signals around.
The Weak signal was in the lower edge of the FM broadcast spectrum, with very strong local signals close to the weak one, in the upper frequencies of the FM broadcast spectrum.
The antenna for the both SDR receivers was the same – Vertical Dipole for FM BC band.

Both SDR receivers were tuned to maximum possible signal to noise ratio (SNR) of the weak FM broadcast signal.

In SDRuno RSP control panel (for SDRplay receiver) ZERO IF and 0.3/0.6 bandwidth were chosen, and the weak signal of interest was placed on the right edge of IF filter, so that the strong signals from other FM broadcast radio stations were placed right from the weak one in order to minimized the negative influence to the our weak signal.
LNA was switched off. When the LNA was on, there where high distortion level because LNA was overloaded from the strong signals, and SNR was deteriorated regardless of gain reduction.
The best results were achieved with gain reduction set to “0”, without LNA.

In SDR# software (for Airspy SDR receiver) 10 MSPS and Decimation was used.
From the version 1480, in SDR#, when decimation is choosed, there is tracking filter which allow better selectivity, so you can use more gain, increasing the SNR to maximum possible level depending of concrete situation.

The overall receiving conditions was extremely bad. The signals from local FM radio stations were too strong so the weak signal from this video can not be received at all, with many expensive FM tuners which I tried: Pioneer VSX 527, Denon AVR-1802, Marantz SR6300. I was tried RTL-SDR just for fun, but it can not receive weak signal too :-), not because SDR-RTL is not sensitive enough, but because its dynamic range is not so high and it is overloaded by too strong local signals.

The very sensitive receiver is not problem to design and produce. Much more difficult is to design a high dynamic range receiver. which will be able to receive very weak and very strong signals at the same time without overloading.

Overloaded receiver front end means that it is not linear any more, and produces many signals by itself, increasing its noise level.
Very strong signals at the receiver front end makes Desensitization of the receiver, so it could not receive weak signals any more.
We should not forget that the receiver front end “looks” all signals from the wide frequency range even if we want to receive only one signal at the time. The more wideband the receiver is, the higher dynamic range it has to be, for not been overloaded…

In the second video Leif sm5bsz compares the Airspy+SpyVerter with the SDRplay RSP on HF reception. He concludes that the difference between the two radios on HF is small. However, Youssef from Airspy has contested the result, noticing that Leif ran the Airspy at 2.5 MSPS, resulting is significantly less decimation being used. In response Leif updated his video adding an A/B comparison on HF with the Airspy correctly running at 10 MSPS in the last 8 minutes of the video. The results seem to show that the SDRPlay and Airspy+Spyverter have similar HF performance, but when comparing maximum decimation on the Airspy and the smallest bandwidth the SDRplay to obtain similar bandwidth’s, the results seem to show that the Airspy+SpyVerter is about 5 dB more sensitive at receiving weak signals.

The post Airspy vs SDRPlay: Two New Comparison Videos appeared first on rtl-sdr.com.

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.

The post Leif (SM5BSZ) Compares Several HF Receivers appeared first on rtl-sdr.com.

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.

The post Portable Shortwave Spectrum Capture with an Airspy + Spyverter and Tablet appeared first on rtl-sdr.com.

Over the Horizon radar is typically used at HF frequencies and is used to detect targets from hundreds to thousands of kilometers away from the radar station. On HF they are very common and can be easily heard as continuous or bursty buzzing sounds.

Over on his blog Daniel Estevez writes how he was inspired by Balint Seebers GRCon16 talk to perform his own investigations into HF OTH radar. Daniel first analyzed a recorded IQ signal of a presumed Russian radar in Audacity, and noticed that it consisted of 15 kHz wide pulses repeated at 50 Hz intervals. He then used GNU Radio and the Quadrature Demod block to FM demodulate the pulse and see how the frequency changes over time. From this he was able to determine the original transmitted radar pulse characteristics

Next he performs pulse compression, which is essentially a cross correlation of the received pulse and transmitted pulse which was determined from the characteristics found earlier. The signal being received at Daniels location is distorted, because it will arrive from multiple paths, since the signal will bounce of multiple layers of the ionosphere. With this pulse compression technique Daniel is able to determine the time of flight for the different multi-path components of the received pulse. By graphing all the results over time he was able to obtain this image illustrating relative propagation distance over time.

Check out Daniels post for the full details and his code.

The post Analyzing HF Over the Horizon Radar in GNU Radio appeared first on rtl-sdr.com.

Bonito is a company that sells various products such as their own small active antennas. Some examples are the Bono-Whip (20kHz – 300 MHz), GigaActiv (9kHz – 3 GHz) and the MegaLoop (9kHz – 200 MHz). 

Over on their blog they’ve uploaded a post titled “why even good antennas need good coax cable”. The post explains why high quality heavy shielded coax cable may be required to receive HF signals in noisy environments. The author writes how even placing an antenna in a quiet area outdoors may not work if the coax is still run through an high interference environment, such as through a house.

Typically RG58 cable is most commonly used with HF antennas. However, the author noticed that when using RG58 he was still receiving FM stations, even though the antenna that he was using was a MegaLoop with a built in broadcast FM filter. After switching his RG58 cable to H155 coax, the FM station disappeared. H155 coax is low loss and designed for GHz level frequencies, so it has much better shielding from its tighter braid.

The images below also show the difference in noise floor the author saw after replacing all his RG58 with H155 coax. 

Reception with RG58 Coax

Reception with H155 Coax

The post Lowering the Noise Floor on HF with High Quality Coax appeared first on rtl-sdr.com.

Over on our YouTube channel we’ve uploaded a new video that shows how bad the interference from Ethernet over Power devices can be. Ethernet over Power, Powerline Networking, Powerline Communications or ‘HomePlug’ is a technology that allows you to use any of your household power outlets as an internet Ethernet port, completely eliminating the need for runs of Ethernet cabling. They are capable of high speeds and can be used anywhere in the house assuming the two plugs are on the same power circuit.

Unfortunately these devices tend to wipe out almost the entire HF spectrum for anyone listening nearby. As household powerline cables are not shielded for RF emissions they radiate in the HF spectrum quite heavily. In the video we demonstrate what the HF spectrum looks like with one of these devices used in the house. The particular device used was a TP-Link brand adapter, and a WellBrook Magnetic Loop antenna was used outdoors, with the null facing the house. An Airspy R2 with SpyVerter was used to view the spectrum.

The video shows that even when the network is idling there are several brief bursts of noise all over the spectrum. Then when a file is downloaded almost the entire spectrum is completely wiped out.

Interestingly from the video it appears that the amateur radio frequencies are actually carefully notched out and those frequencies remain relatively clean. Most manufacturers of these devices appear to have worked with the ARRL to please ham radio enthusiasts, but SWLers will likely be in trouble if any of these devices are used in your house or neighbors house.

The post Showing the HF Interference Problem from Ethernet over Powerline Devices appeared first on rtl-sdr.com.

Over on the SDRplay blog and forums OH2BUA has been sharing how he has set up ‘propagation triggered recording’ by continuously monitoring JT65/JT9 signals with his SDRplay. The idea is that you leave the radio on receiving all night, and set it to automatically start recording IQ files if good propagation conditions occur as determined by the locations received from the JT65/JT9 signal. This may yield some interesting far off stations that can be listened to in the morning, whilst weeding out hours where nothing but commonplace local stations are heard. The software is a simple Windows batch file that works together to coordinate HDSDR and JTDX. It should work with any HF capable SDR.

JT65/JT9 are weak signal propagation HF modes (also known as WSJT modes) that can be decoded all around the world, even with very weak reception thanks to strong digital error correction. They can often be used to determine propagation conditions by determining where successfully decoded messages are being sent from.

OH2BUA writes:

I have made a set of scripts and other files which can be used to build a system which monitors JT65/JT9 (digital modes) amateur radio traffic on 160m/1.8MHz band, and if nice propagation to area you are interested in exists, a MW-BC-band recording is started. When the conditions fall off, the recording is stopped.

There is an attached zip-file containing all the necessary stuff. Sorry this is a windows thing – but easily portable also for linux. Create C:\bat\ and drop all there. Have a look, starting from README.

The default example is to start a MW-band I/Q-recording, if North American ham signals are heard – but it is fully modifiable according to your target when in comes to areas, bands, schedules etc.

The files are available as an attachment to the forum post.

The post Setting up Propagation Triggered Spectrum Recording appeared first on rtl-sdr.com.

Over on YouTube user Veryokay has uploaded a video that shows how he uses the HF direct sampling mode on one of our V3 RTL-SDR’s to receive WSPR signals. WSPR (pronounced “Whisper”) is short for Weak Signal Propagation Reporting, and is a HF ham mode typically run on very low power levels such as 1W. The data from WSPR reception can be used to determine how good or bad HF propagation is currently around the world as each WSPR message contains the callsign, 6-digit locator and the transmit power level used.

For the antenna Veryokay uses a simple random wire antenna directly connected to the SMA port of the V3 up on top of the roof of his apartment building. This gets him reception good enough to receive many WSPR signals. Then together with SDR#, VB Cable and the WSPR-X decoder software, signals can be received and decoded.

He has also uploaded a document detailing the instructions in text and image form at bit.ly/wspr-rtlsdr.

The post A Tutorial on Receiving WSPR with an RTL-SDR V3 appeared first on rtl-sdr.com.

The WebSDR from the University of Twente, Netherlands is a wideband HF SDR that is accessible from all over the world via the internet. It was first activated in 2008 making it the very first WebSDR ever. The creator of the service Pieter-Tjerk de Boer PA3FWM has recently made available spectrum image archives which show the HF band conditions over the last two years.

Intrigued by this data, London Shortwave decided to make a timelapse animation of this image data. The results are shown in the videos below, and London Shortwave adds:

The X axis represents the frequency and the Y axis is the time of day, starting at the top. Conventional wisdom about band behaviour can be easily confirmed by watching this video: the 60m, 49m and 41m bands are mostly active after dark, with the 60m and the 49m bands being generally busier during the winter months. The 31m band is most active around sunset, but carries on all night until a few hours after sunrise. The 25m band is active during sunrise and for a few hours afterwards, and around sunset during the winter months, but carries on all night during the summer. Peak activity on the 22m and 19m bands is also clustered bi-modally around the morning and the evening hours, though somewhat closer to the middle of the day than on the 31m and the 25m bands. The 16m band is mostly active during the daylight hours and the 13m band is quiet throughout the year except for the occasional ham contest.

The post A Visualization of Yearly Shortwave Activity with WebSDR appeared first on rtl-sdr.com.