Monthly Archives: March 2022

PropLab-PRO 3.2: “Dead Zone” now living!

Around Issoudun’s transmitter (data of reception see below), all propagation software will show a doughnut-like Dead Zone. – as around each and every station transmitting with an antenna having a low vertical angle for DX. PropLab-Pro’s Broaadcast Coverage map duly shows this effect. But …
… the new version nearly fills the gap by backscatter – like Mother Nature does! Here, only backscatter is shown to see how this new feature works. You may merge both results in Proplab’s Backscatter menue.

PropLab is the Gold Standard in available raytracing software for propagation analysis on HF. To its already unique features, like 3D-raytracing revealing x- and o-rays, an updated version added a “Backscatter” option. This even more mimics reality.

From most of their literature, radio amateurs know that there is a “Dead Zone” surroundig a transmitter, where no signal is said to be available from antennas radiating their electro-magnetic field with a low elevation angle for DX. However, a steeper angle for NIVS overcomes this. But from our practice we know that this “Dead Zone” isn’t flat dead but is filled with (weak) signals.

Those can be observed at best with strong broadcasting station some 50 to 1000km near to you, but pointing to region far away. In Central Europe, transmitters in Issoudun (France) and Nauen (west of Berlin/Germany) are great candidates for such effect, called backscatter.

Cary Oler, author of PropLab, now literally fills this gap, ans shown in the tow screenshots at top of this page.

Where’s the beef? OK, among radio amateurs, backscatter is not the preferred method of establishing contacts. The professionals, however, enjoy a relatively stable signal via backscatter. And for us radio amateurs and SWLs, it gives an explanation for some weird propagation, e.g., the near-enhancement of scattered signals by aircaft scatter – see screenshot at the bottom of the page.

Thanks, Cary, for continously improving PropLab!

P.S. (12MAR2022)
Today, Cary released version 31 which many improvements don’t reflect the small change of version numbers from just 28. He wrote:

There were some changes / improvements made to the signal strength calculations. We are using some improved absorption calculations. The latest update ( also includes some additional revisions, including the display of signal power in ray-tracings and broadcast coverage maps in dBm that may be more handy for people who work in dBm. A researcher at MIT also caught a bug in our backscatter engine that we have now corrected in the new version. Bugs were also squashed in the broadcast coverage maps. The broadcast coverage section now also supports large ray-tracing datasets much better than prior versions. The software doesn’t choke like it used to on large datasets of even a million ray-tracings or more. With prior versions, the software looked like it was hanging, it took so long. We also added a simple theoretical noise floor calculator in the antenna tab. And we have revised the manual again to discuss some of the new functionality and improve clarity on the backscatter features. All in all, this is a fairly substantial update given that we only bumped the version number from build 28 to 31.

RFI Issoudun, 500kW with an HR 4/4/.75 curtain array tansmitting towards Africa (190°) on 15’300kHz at 09:30 UTC on March 8, 2022. I am living about 900km east of this transmitter, well in the “Dead Zone”. But the carrier is recevied via backscatter (in the middle), and in this case it is beautifully anhanced by aircraft scatter just 10dB down at a Doppler distance of about 20Hz. The artifacts right near the carrier do stem from meteorite’s Doppler.