Category: HF

Lon.TV Demonstrates Decoding Various Digital Signals with RTL-SDR

Tech YouTuber Lon.TV has recently uploaded a video demonstrating how to identify and decode various digital transmissions with an RTL-SDR dongle. In the video he explains how to use VB Cable to pipe audio from SDR# into various decoders, and then goes on to show DMR, APRS, POCSAG, L-Band AERO, FT8, and JS8/JS8CALL all being decoded via an RTL-SDR Blog V3 dongle.

Software Defined Radio Part 2 - Decoding Digital Transmissions with an RTL-SDR USB Radio

An RTL-SDR Panadapter for the TECSUN PL660 Shortwave Radio

Thank you to Joseph IT9YBG for submitting his article describing how he has made an RTL-SDR based panadapter for his TECSUN PL660 portable shortwave radio. The post is a series of pictures that show how Joseph was able to open the PL660 and connect a coax cable to the IF output, and mount the connector on the plastic cover for easy access. He then connects that IF output to the RTL-SDR via a 10pF capacitor.

The result is that Joseph is able to receive the IF output of the PL660 at 451 kHz in SDRUno with his RTL-SDR Blog V3 running in Q-Branch direct sampling mode. He notes that although the IF bandwidth from the PL660 is small, it is possible to decode digital signals by passing the audio demodulated by SDRUno into decoding software. 

RTL-SDR Blog V3 Panadapter for the Tecsun PL660

Frugal Radio: Testing a Loop on Ground Antenna with an Airspy HF+ Discovery

The KK5JY Loop on Ground (LoG) antenna is a 15 feet per side square loop designed for reception of HF and lower. It simply consists of an isolation transformer and wire that as the name implies is placed somewhere on the ground in a square loop like shape. It is cheap and easy to build and compact in that it does not take up any usable space. 

In his latest video Rob from the Frugal Radio YouTube channel tests out this antenna with his Airspy HF+ Discovery SDR. He uses a bit of wire lying around, and a low cost 9:1 Balun from NooElec as the isolation transformer. With this antenna he was able to pick up signals in the USA and all the way over to Australia from his home in Canada. NDB signals were also receivable.

2022 LoG (Loop on Ground antenna) for SDR radio tested on Airspy HF+ Discovery SDR KK5JY HAM radio

TechMinds: Testing the GA-450 Portable HF Active Loop Antenna

Over on the Techminds YouTube channel, Matt has uploaded his latest video which is a review of the GA-450 portable HF active loop antenna. The antenna costs between US$60-$80 + shipping and is available on Chinese market sites like Aliexpress and Banggood. It's advertised as covering 2.3 - 30 MHz, and uses a very portable and sturdy 20cm stainless steel loop. The active base amplifier is powered via a USB-C connector, and it even has a built in lithium battery for portable field use.

In his review Matt shows the antenna in action, noting that it's performance is quite a lot better than expected for it's small size, but it can't compare to his large half-wave end fed antenna. He notes that it appears to work best from 7 - 21 MHz, but not so well below 7 MHz. Overall he recommends it if you're looking for a small sized loop antenna.

GA-450 Portable Active Small Loop HF Antenna

Nils Critiques the MH370 WSPR Aircraft Scatter Theory

For some time now there has been chatter about the possibility of using WSPR logs to help track the mysterious disappearance of flight MH370. WSPR or the "Weak Signal Propagation Reporter" is a protocol typically used on the HF bands by amateur radio operators. The properties of the protocol allow WSPR signals to be received almost globally despite using low transmit power.  Amateur radio operators use it for making contacts, or for checking HF radio propagation conditions. MH370 is a flight that infamously vanished without a trace back in 2014.

The theory proposed by aerospace engineer Richard Godfrey is to use logs of sent and received WSPR transmissions that may have intersected the potential flight path of MH370, and to look for potential reflections or 'scatter' in the signal from the metal aircraft hull. From the reflections an approximate track of the aircraft could be calculated much in the same way that bistatic over the horizon radar systems work.

While it is an exciting theory, it is unfortunately considered by most experts as highly unlikely to yield any suitable results with the main problems being WSPR transmission power too weak to detect reflections from an aircraft, and the effect of the ionosphere too difficult to account for. 

Over on his blog Nils Schiffhauer (DK8OK) has posted a thorough critique of the idea, explaining the theory, technical details and difficulties in depth, ultimately coming to the conclusion that the idea is based more in wishful thinking than in fact. Nils summarizes:

Time and again, there are news stories in the professional and popular press about the fact that log data from the WSPR data network can help locate aircraft. In particular, the effort is to determine the actual crash site of flight MH370. This effort essentially amounts to detecting "unusual" level jumps and frequency changes ("drift") in the archived WSPR log data and attributing them to reflections from specific aircraft ("aircraft scatter").

In a blog entry, Nils Schiffhauer, DK8OK, for the first time critically evaluates this theory. On the one hand, this is based on years of observation of aircraft scatter on shortwave as well as an investigation of about 30 Doppler tracks. The results of this complex analysis of more than 10,000 data in one example alone are sobering: The effects of aircraft scatter on the overall signal are almost always well below 0.3 dB.

To prove a correlation between level changes of the overall signal and aircraft scatter seems hardly possible on the basis of the WSPR data material. The reasons are manifold, but lie mainly in shortwave propagation, where level changes of 30 dB within a few seconds are the rule rather than the exception.

However, since the local and temporal state of the ionosphere is not known in previous investigations on the WSPR data material - it is recorded in parallel in professional OTH radar systems and calculated out of the received signal - level jumps can hardly be clearly assigned from the sum signal alone. This finding is supported by further arguments in the blog:
https://t1p.de/t5kr

Nils demonstrates aircraft scatter on China Radio International, a 500kW transmitter.

SDRAngel Features Overview: ADS-B, APT, DVB-S, DAB+, AIS, VOR, APRS, and many more built-in apps

SDRAngel is a general purpose software defined radio program that is compatible with most SDRs including the RTL-SDR. We've posted about it several times before on the blog, however we did not realize how much progress has occurred with developing various built in plugins and decoders for it.

Thanks to Jon for writing in and sharing with us a demonstration video that the SDRAngel team have released on their YouTube channel. From the video we can see that SDRAngel now comes stock with a whole host of built in decoders and apps for various radio applications making it close to an all-in-one SDR platform. The built in applications include:

  • ADS-B Decoder: Decodes aircraft ADS-B data and plots aircraft positions on a map
  • NOAA APT Decoder: Decodes NOAA weather satellite images (in black and white only)
  • DVB-S: Decodes and plays Digital TV DVB-S and DVB-S2 video
  • AIS: Decodes marine AIS data and plots vessel positions on a map
  • VOR: Decodes VOR aircraft navigational beacons, and plots bearing lines on a map, allowing you to determine your receivers position.
  • DAB+: Decodes and plays DAB digital audio signals
  • Radio Astronomy Hydrogen Line: With an appropriate radio telescope connected to the SDR, integrates and displays the Hydrogen Line FFT with various settings, and a map of the galaxy showing where your dish is pointing. Can also control a dish rotator.
  • Radio Astronomy Solar Observations: Similar to the Hydrogen line app, allows you to make solar measurements.
  • Broadcast FM: Decoding and playback. Includes RDS decoding.
  • Noise Figure Measurements: Together with a noise source you can measure the noise figure of a SDR.
  • Airband Voice: Receive multiple Airband channels simultaneously
  • Graves Radar Tracker: For Europeans, track a satellite and watch for reflections in the spectrum from the French Graves space radar. 
  • Radio Clocks: Receive and decode accurate time from radio clocks such as MSF, DCF77, TDF and WWVB.
  • APRS: Decode APRS data, and plot APRS locations and moving APRS enabled vehicles on a map with speed plot.
  • Pagers: Decode POCSAG pagers
  • APRS/AX.25 Satellite: Decode APRS messages from the ISS and NO-84 satellites, via the built in decoder and satellite tracker.
  • Channel Analyzer: Analyze signals in the frequency and time domains
  • QSO Digital and Analog Voice: Decode digital and analog voice. Digital voice handled by the built in DSD demodulator, and includes DMR, dPMR and D-Star.
  • Beacons: Monitor propagation via amateur radio beacons, and plot them on a map.

We note that the video doesn't show the following additional features such as an analog TV decoder, the SDRAngel "ChirpChat" text mode, a FreeDV decoder and several other features.

Multichannel ALE and GMDSS Decoding with Black Cat Systems Software

Black Cat Systems have recently released two new programs that may be of interest to HF monitoring enthusiasts. The first is a multichannel capable ALE decoder and the second is a multichannel GMDSS-DSC decoder. Both programs are not free, with an (introductory) price tag of $29.99 each for three parallel input channels, and $99 for up to 24 parallel input channels.

With an appropriate HF capable SDR, like a SDRplay, Airspy HF+ Discovery, or even an RTL-SDR V3 in direct sampling mode, these programs allow you to set up a home monitoring station. 

ALE or Automatic Link Establishment is a digital RF protocol that enables users to initiate a reliable call over HF frequencies, by automatically choosing the best frequency based on propagation conditions, allowing for telephone like calling operation, and enabling short text messages.

GMDSS or Global Maritime Distress and Safety System is a set of radio protocols that enables digital text communications between ship to ship and the shore, as well as weather broadcasts, and distress beacons. 

Over on his blog Nils Schiffhauer (DK8OK) has been testing these two programs out. In his first post about the ALE decoder, Nils explains ALE in more depth, and demonstrates how he uses the multi-channel capable SDR-Console with Virtual Audio Cable to feed 16 ALE channels into the decoder. He goes on to show how to filter by callsign and provides some tips for best reception. He notes that with ALE you might receive messages from:

... forces, diplomatic services, emergency agencies, police, militia, UN missions, drug enforcement, border control and even amateur radio. It is used from aircraft like AWACS, as from aircraft carriers, from mobile units to fixed stations. 

In his second post Nils tests out the GMDSS decoder noting that it is an "extraordinary sensitive decoder" and "it also includes smart processing of the data – from looking up vessel’s complete data from ITU’s Ship Station List (internet connection needed) to saving all data to a fully-fledged database". His post goes on to explain the GMDSS format in more detail and demonstrate multichannel decoding.

Black Cat Systems ALE and GMDSS Decoders demonstrated by Nils Schiffhauer (DK8OK)

Improving Reception on the Malachite DSP via USB Grounding

Thank you to Mitsonobu Saitou for writing in and sharing with us a product that he has created which improves reception on of the Malachite DSP software defined radio and other shortwave radios by up to 20dB by improving the grounding. It appears to work by using the negative USB line as a ground via a modified USB cable with grounding clip on the other end. The product is available via Amazon Japan with international shipping.

The Malachite DSP is a portable battery powered software defined radio with built in screen. It is popular amongst shortwave listeners.

Saitou writes the following summary, and full details about the product are available on his blog (link uses Google Translate to translate from Japanese to English): 

Today's item is "Dokodemo Earth KUN". This is an item to pull the ground wire from the charging connector of DCL radios and Mlachite DSPs.

The sensitivity of the receiver will be improved by strengthening the grounding. This is how I applied it.

It is easy to connect by pulling out the ground wire from the charging connector instead of the antenna jack.

It can also be used as a loop antenna by connecting the ground to the antenna.

We have confirmed the effectiveness of this product outdoors. Users who have used this item have experienced a significant increase in sensitivity. 

Malachite DSP and SWL Radio USB Grounding Enhancement Cable
Malahit/Malachite DSP+「どこでもアースくん」