Monthly Archives: February 2021

HF Propagation: Professional, free, and Real-time

IRTAM shows the actual state of the ionosphere – see text.

Without proper propagation, world-wide HF communications simply doesn’t exist. We, hams and SWLs, depend on the supporting power of the ionosphere and sometimes struggling with its capricious behavior. Many forecast models had been developed, VOACAP the most prominent among them. Like some far-looking weather models, they deliver broad probabilities – more the climate of the quarter than the weather in the afternoon. Even smart and processor-hungry 3D-raytracing software, taking into account more factors than just the average sunspot number of the month, do face challenges.

Here, IRTAM comes into play. The acronym means “IRI Real-Time Assimilative Mapping”, where IRI stands for the International Reference Ionosphere. This model is the base which is updated by the data of many of so-called digisondes. They are regularily probing the ionosphere at many locations of the world in time increments up to as short as five minutes.

The processed data reveal the actual space weather at this location. Experience, models and clever algorithms are used to spread (assimilate) these results over a world map, and, even more, to produce an animation of the last 24 hours – see the screenshop on the top. Click here to see the last 24 hours.

They show the frequencies, just reflected by the F2 layer under an angle of 90° (vertical sounding). You have to multiply these frequencies with a factor of about 3 to get the highest frequency, being reflected (indeed: refracted) for usual HF communications, or oblique sounding.

Additionally to this, the map will also show e.g. “deviation from climate”. By this map you can compare your VOACAP results (“climate”) to get an impression of the deviations – plus or minus, location, time.

It is a free service of a team around Prof. Bodo Reinisch, supported by world-wide data of their Lowell Digital Ionosondes, the gold standard in this field.

Medium Wave: Signals May tell sunris/Sunset at their transmitter’s site

The two stronger carriers (Romania left, Algeria right) exhibit Doppler-shifted scatter; see text for a more detailed explanation.

During my expeditions into the thicket of mediumwave offsets, I bumped into pictures like that at the top. In the lower part of the screenshot, you see two carriers mit seahorse-like structures looking to the right. In the evening, they look towards the West.

This is one of the several effects which can be seen at local sunrise/sunset. Here, the carrier gets “clouded” and show frequency changes. These effects are associated with Doppler shift (moving of ionospheric patches/layers) as well as scattering caused by irregularities of the ionosphere, most notably Travelling Ionospheric Disturbances, or TID. Whereas the Doppler shift, by vertical moving of reflecting layers like combining of F1- and F2-layer to one and lower F-layer when approaching darkness, is comparatively small, high wind speeds in these regions can cause a much faster horizontal movement of such regions. This, in turn, may cause a Doppler shift of about 1Hz or even higher in the medium wave range.

The Figure at the top demonstrates this effect at two transmitters on 1422kHz, namely SRR Radio România Actualități from Râmnicu Vâlcea/Olănești (sunrise 05:55 UTC/sunset 15:12 UTC; distance 1433km) and Radio Coran/Radio UFC/Radio Culture/Chaîne 3 from Ouled Fayet/Algeria (sunrise 06:58 UTC/sunset 17:00 UTC; distance 1840 km). Seen from midnight, sunrise first occurs at the Romanian transmitter, followed by the Algerian one with the seahorse-like pattern of the scatter towards the higher frequencies. Around each local sunset, first Romania sees darkness, followed by Algeria. Here, the scatter pattern turns towards the lower frequencies. In the insert at the right, contrast has been sharpened to additionally reveal a split-up of these carriers due to propagation into two paths.

This effect often helps to determine the local sunrise/sunset of a carrier. I marked what presumably is the carrier of MBC Radio 1 from Matiya/Malawi, sunrise 03:22 UTC; listed 02:00 to 22:00 UTC, but obviously on a 24 hours’ service this Tuesday.

Both Figures at the bottom try for some detective work without knowing specific offsets (because not available) but relying only on schedule and the above mentioned propagational effect. Crime scene takes place on 1233kHz, where we want to scrutinize two channels, one on 1232,9937 kHz, the other on 1232,9951kHz.

Distinctive scatter, associated with local sunrise at the transmitter, provides a strong hint towards the location.

The s/off- and the s/on pattern match that of Chinese National Radio #17’s Kazakh service. Incidentally, sunrise takes place in Qinghe at 01:42 UTC, and in Boertala at 02:04UTC – next Figure. Boertala is listed with 10kW (stronger signal), Qinghe with 1kW. Unfortunately, the f/out time of other CNR17 transmitters on this channel is mostly covered by phase noise from Rádio Dechovka in the Czech Republic and Absolute Radio in the United Kingdom.

Some CNR17 locations and the terminator during sunrise in Boertala, see text. Visualized with free Simon’s World Map.

Here I am indebted to Jens Mielich, Head of the ionosonde at Juliusruh/Germany, who was so kind to comment on this observation. According to him, the observed Doppler shift of 1Hz on 1422kHz should have been caused by a refracting medium, moving at an (angular) speed of roughly 105m/s. At Juliusruh, he observed e.g., an ionospheric drift of 311m/s±93m/s from East towards West on January 19, 2021 at 04:19 UTC: “You will get a positive Doppler shift during a West/North drift, and a negative one at East/South drift.” He adds that further investigations on a more longer time series are needed.


PSKOVNDB: An exciting new software for Mediumwave DXers

See the bunch of carriers on 590kHz at the left. PskovNDB shows at the right a diagram of noise, the combined signal strength of the 200Hz window and the signal strength of the carrier just picked.
Here the very carrier of VOCM/St. John’s had been clicked instead. You easily see that this signal is dominating the channel – only one of the many exciting features of free PskovNDB software!

Recently, I came across an upgraded version of Ivan Monogarov’s PskovNDB software, already having collected all laurels available as being the Gold Standard for chasing non-directional beacon, or NDBs. Recently, Ivan had expanded his tool with some as unique as exciting features for the avid medium wave DXer.

At a first view, it converts recorded WAV files (also: RF64 format, done with SDRC V3 software) into spectrograms of high resolution in which you can easily see the number of stations, measure their precise offset and see their signal strength.

A second view reveals the smart feature of producing diagrams of each signal – plus noise level and the combined power of the whole window. You can see both in the screenshots on top of this page.

A third view almost exactly helps to distinguish between signals where you can here music, listen at least to some words or phrases, or which do provide full audio.

Nothing more? Yes. Under the hood, there is much more. So, you can do automatically recordings each day and also automatically send them to PskovNDB software for showing the spectrograms, one after the other, like on a film roll. This enables you to pick the recording of the most promising day(s) for further inspection.

I wrote a short introduction to the beta version of this free software, and Ivan was so kind to add some most helping notes to this. You can download it here. It contains also some additional information, i.e. a link for downloading the software.

Spassiba, Ivan, for another software breakthrough!

Medium Wave: Offset Atlas – all 9 kHz channels Plus VLF & Longwave, 24 hours

The “Atlas” shows screenshots of all 9kHz channels on Medium Wave within a 50Hz window, sometimes better. It also shows some odd channels plus Time Signal Stations on VLF and all Broadcasting Longwave Channels. You can download it for free to determine accurate and stable offset readings over 24 hours (zoom in by e.g. 400%)

With the new Elad FDM-S3 and its OCXO/GNSS-stabilized clock, I did a 24h recording of the whole medium wave band on January 19, 2021 in Northern Germany; plus longwave on Januar 21, 2021. Free software SDRC V3 enabled me to make up a spectrogram of each channel within a window of 50Hz width, and at a frequency raster of 9kHz on medium wave. You can easily see:

  • sign-on/sign-off
  • fade-in/fade-out
  • accurate and stable frequency offset over full 24h down to a millihertz
  • frequency control of the transmitter’s oscillator (stable, drift, sinus, sawtooth …)
  • propagational effects (doppler, scatter …)

The format is PDF, DIN-A4, landscape, resolution 300dpi – see screenshot at the bottom. This allows you to zoom to a factor of about 400% to search for details and better read out of the time/frequency scale. It weighs 865MB. You can download it here, and open it with your PDF reader (you can also point your mouse cursor onto the link, click right mouse key, and choose “Save under …”). Leafing from one page to another gives an interesting overview.

A similar Atlas showing a raster of 10kHz is also available for free – just scroll to the previous post of this blog. It is also planned to publish a general article about the background, about what to do with such a tool, and how to do this by yourself.

I am sure that it will open some new horizons on Medium Wave DXing, including accurate offsets over up to 24h.