AREG’s HF Spectrograph shows the effects of Solar Flares

An X-class Solar Flare imaged by the Solar Dynamics Observatory in 2012.

An X-class Solar Flare imaged by the Solar Dynamics Observatory in 2012.

Solar flares from the sun can result in many different effects on High Frequency (HF) propagation. The most immediate and noticeable is when the increased solar X-Ray flux resulting from a flare interacts with the ionosphere. These X-Rays charge the ionosphere’s D-layer (responsible of the absorption of the lower HF band during the daytime), and results in higher levels of absorption extending right up to the top of the band. This has the effect of reducing signal strengths right across the band, resulting in what is known as a ‘HF fadeout’.

X-Ray Flux data from the GOES satellites, provided by NOAA

Solar flares are categorised based on the peak X-ray flux they emit, with the different levels given letters A, B and C for relatively weak flares, and M and X for stronger flares, with X-class flares being the strongest. HF fadeouts are generally caused by M and X-class flares. A live plot of X-Ray flux data as observed by the Geostationary Operational Environment Satellites (GOES) is available here:

Short Wave Frequency Coverage Prediction

HF Fadeout Coverage area for a M1.2 class flare, from the Space Weather Service website.

The Australian Space Weather Service provides a HF fadeout warning service via email, and you can also see reports of the most recent HF fadeout on their website.

AREG’s HF Spectrograph Service

AREG hosts many services at its remote HF receive site located near Tarlee, including multiple KiwiSDRs, skimmers for WSPR, FT8 and SSTV, and other higher performing receivers reserved for club members. We thank Swoop Internet for providing us with the internet service at this site, for free!

The HF receiver antenna (a broadband monopole) at AREG’s remote HF receive site.

Using software written by Mark VK5QI, AREG also generates a Spectrograph showing the state of the HF band over the last 3 days. A spectrograph is similar to the waterfall display you might have seen on other SDR receiver software, though in this case covering the entire HF band (0 – 30 MHz), and looking over a much longer timescale. Warmer colours (reds and yellows) represent stronger signals, and cooler colours (blues and greens) represent weaker ones. The spectrograph updates approximately every 30 minutes, and is available at the bottom of the Remote HF Receiver site page, or directly here.

A typical HF Spectrograph, with some features annotated.

The spectrograph gives us a ‘quick look’ at the state of the HF band. The strongest signals (red) are the bands of shortwave stations around 6, 7, 9 and 11 MHz, mostly propagating in from south-east Asia. The most obvious time-varying effect is the change in propagation conditions from day (propagation mainly at the higher end of the band), to night (propagation mainly at the lower end of the band), but we can also see other effects such as solar radio bursts, local noise issues, and of course HF fadeouts.

In the above figure, a number of HF fadeout events over the 18th through 20th May 2023 period have been marked, showing the X-Ray flux event they correspond to. The HF fadeouts can be seen as a sudden reduction in signal strength right across the HF band, followed by a slow return to normal. Note that we don’t see the effects of X-ray flux events occurring during our local night, due to the Earth sheltering us from those X-rays.

So, next time you think the HF band seems a bit dead, maybe go take a look at the AREG HF Spectrograph to see if there’s a HF fadeout in progress!

73 Mark VK5QI

VK5ARG HF SDR Site: New FT8 Skimmer Installed

FT8 Multi-Band Skimmer

AREG has today added a new experiment to the club’s remote SDR site that can help monitor HF propagation and provide insights into where in the world the bands are currently open to. Using a 125-14 Red Pitaya multiband SDR and software from Pavel Demin (see here) AREG is now able to give you a near real time view of what FT8 signals are audible here in central southern Australia.

The Red Pitaya is on loan from Josh VK4JNA. Thank you for contributing this very interesting experiment to the project. It certainly provides an interesting insight into what bands are open when! You can access the output from the skimmer via the website

Project Horus Balloon Project: Digital ATV DVB-T Terrestrial Testing – Success!

Today Mark VK5QI took the Balloon ATV transmitter out for a terrestrial test. He carried out line-of-sight testing of the DVB-S payload from BlackTop Hill to the AREG remote site near Tarlee – a distance of 54km!

First test – could he see the signal on the SDR up at the site (RTLSDR, Diamond X-50, no preamp)… yes!

Next, Mark dumped some samples with rtl_sdr, then transferred them back to his laptop. He processed them through leandvb – and got video!!! A bit of fading, but for an omni receiver with no preamp, this is a pretty damn good result!

… and here’s some of the raw video

The MER as reported by leandvb was around 8-11 dB, right on the edge of what is decodable. Still, with such a basic system, a good result!

Based on the path, it is estimated to give us a working range of about 150km from the balloon given a receiving station with 15dBi gain and a good low noise preamplifier.

Stay tuned for more information on how to receive and decode the Digital ATV signal and save the date – we hope to launch the transmitter into the stratosphere on Sunday March 7th. (We also plan on streaming the event on Youtube).

For those who missed it late last year here is a bit more information about the Balloon ATV payload and some minimum signal testing that was carried out.

AREG Remote HF Receive Site – Now Open to the Public

AREG is pleased to announce that we can finally open ports on our HF Remote receive site to the general public.

The AREG HF receive site, located ~100km north of Adelaide, in South Australia, is now operating a publicly accessible KiwiSDR 4 channel receiver. This is the first active public service that the club is offering from the site. The system is currently using a broadband mono-pole vertical antenna.

AREG members also have access to much, much more, including dedicated members only KiwiSDR receiver channels, band by band high performance SDRs (Airspy HF+ Discovery, via SpyServer) on 160-20m, APRS-IS HF RX gateways and Weather Stations. If you are interested in joining the club to experiment with these other services, please (click here).

The site, which has been in development now for approximately a year, has other member services planned into 2021. Stay tuned as we continue to experiment and expand our capabilities at the site, including potential Reverse Beacon nodes, FT8 skimmers, WSPR skimmers and VHF monitoring services.

How to Access the Public KiwiSDR?
You can access the public service from the following web address:

Thanks Beam Internet!

AREG wouldn’t have been able to make this possible without the support of Sam from Beam Internet, who have sponsored our internet feed at the site.

Beam provide wireless internet connectivity to communities right across the Barossa Valley and northern Adelaide Plains.

Thanks team for your support of experimental Amateur Radio!

Using the KiwiSDR
For first time KiwiSDR users the following notes should be considered

  • Windows: Firefox, Chrome & Edge work; IE does not work.
  • Mac & Linux: Safari, Firefox, Chrome & Opera should work fine.
  • Open and close the panels by using the circled arrows at the top right corner.
  • You can click and/or drag almost anywhere on the page to change settings.
  • Enter a numeric frequency in the box marked “kHz” at right.
  • Or use the “select band” menu to jump to a pre-defined band.
  • Use the zoom icons to control the waterfall span.
  • Tune by clicking on the waterfall, spectrum or the cyan/red-colored station labels.
  • Ctrl-shift or alt-shift click in the waterfall to lookup frequency in online databases.
  • Control or option/alt click to page spectrum down and up in frequency.
  • Adjust the “WF min” slider for best waterfall colors.

AREG Projects: Remote HF receive site development gathers pace!

Several years ago, AREG first attempted to establish a remote HF receive site. The aim was to help members who were finding it tough to retain access to HF from home due to growing urban interference levels. The early attempt failed due to problems obtaining affordable internet access at the original site. However, the project didnt die, and the core team kept exploring options.

Then, over the last 12 months, the group finally found a willing land owner coupled with a helpful and supportive Internet provider (thanks to Beam Internet in the Barossa Valley). This has allowed the project to change gears.

Work has been gathering pace and a number of test receivers are now available for members to experiment with. As the site capability grows, AREG hopes to open up at least some channels to the general public as well.

Currently the group has a 4 channel KiwiSDR operational as well as several Airspy HF+ SDR receivers on 80/40/20m. For now, these are only accessible by AREG members. In time, as capability expands, there are plans to open some of the systems to the general community as well.

This phase of the project has been a team effort from multiple members across AREG. Special thanks to Steve VK5SFA, Mark VK5QI, Peter VK5KX, Kim VK5FJ and Jeff VK5AC who have lead much of the installation and construction to date, along with contributions of hardware and time from several others.

AREG is also considering other future developments for the site. These include:

  • a lightning detector receiver as part of the network
  • a multi-band HF APRS Receive gateway
  • A Reverse Beacon Network CW and RTTY node for 160-10m
  • A PSKReporter FT8 spotting node (160-10m)
  • A WSPRNet WSPR spotting node (160-10m)

If you would like to access the SDR services today, consider becoming become a member of AREG! The service is accessible now for group members.