Technical Topics, March 1999
Last Updated on October 13, 2005 by Ralph Brandi
The Sun And Short-Wave Reception
(Part 10)
This month we conclude our examination of how the sun influences shortwave propagation. We will look at some of the information available on the Internet at a click of the mouse to help you make your own propagation predictions. I will be presenting some pretty complicated URL’s (Internet web site addresses) so you may want to wait for this article to be posted on the NASWA web site so you can then just copy and paste the URL’s.
Some SWLs lament the fact that the Internet is supplanting shortwave radio as a way to deliver international broadcasts. Better to think of the Internet as a tool for the SWL. You can download software to permit calculation of optimum frequencies and times to hear a specific country or you can use already existing web sites to do the numbers for you.
There is no way I can cover all the Internet sites that are out there. I will provide information on some sites I personally use. My computer is about four years old and runs on Windows 3.1. The hard drive space is limited to only 400 megabytes. So I try to use web sites with bigger, more modern computers behind them to assess and predict propagation conditions. I will describe what each site does for me and tell you why I find these sites interesting.
There are two places I would recommend you begin your quest for information. You should check both resources as good entry points to the entire subject. The first is a page operated by Radio Netherlands. You can get there through the URL: <http://www.rnw.nl/realradio/practical/html/propagation.html>. This site features short descriptions and links to many sources operated by governments, commercial enterprises, or individuals. A similar site is operated by by NASWA member Pete Costello at URL <http://itre.ncsu.edu/radio/srcrs2.html>. Pete’s site also features short descriptions of each linked site and what kind of information you can get from each link. Pete’s site has links to several software providers for those of you who would like to roll your own detailed propagation predicts.
We all know that the sunrise/sunset terminator line (the grayline) provides enhanced propagation especially on the 90 and 60 meter bands. There are two pages that provide realtime maps of the earth showing where this line is at any instant. The first provides a Mercator projection and can be seen at: <http://www.fourmilab.ch/cgi-bin/uncgi/Earth/action?opt=-p>. The other site provides a 3D view of the earth from space. You can position yourself over any point on earth by clicking on that point. You can set your apparent distance above the earth through the interactive options provided starting with this URL: <http://www.fourmilab.ch/cgi-bin/uncgi/Earth?imgsize=320&opt=-l&lat=-1.45833&ns=North&lon=174.583&ew=West&alt=147807488&img=learth.evif>. You can change the “lat”, “lon” and “alt” terms in this URL to move around the earth.
A very complete site for propagation related data and useful predict maps comes from the Australian IPS. The IPS Forecast Centre produces an extensive range of daily, weekly, and monthly reports of space weather conditions as well as warnings and alerts of significant events. These can be viewed at their web site or alternatively are available via a mailing list server. Their home page is <http://www.ips.oz.au/>. Warning, much of the information available on this site requires a browser equipped for Javascript.
The IPS Hourly Area Predictions Charts provide maps of optimum frequencies centered on major cities. The maps have contour lines circling the city of interest showing the best frequency range to use to reach target areas on the same continent. The North American charts can be centered on any of the following cities: Boston, Boulder, Kansas City, Minneapolis, Montreal, New Orleans, Orlando, Phoenix, San Francisco, Vancouver, Washington DC, White Horse, and Winnipeg. Predicts are updated every hour and include effects of current ionospheric conditions.
My favorite propagation site is in Canada. For a real time map showing maximum usable frequencies, sunrise/sunset gray-line corridor location, latitude and longitude of the sun, and the location of the polar auroral absorption zones go to <http://solar.uleth.ca/solar/www/realtime.html>. The image is a high-resolution Mercator projection map of the earth with contour lines showing maximum usable frequencies (MUFs) for 3,000 kilometer radio signal paths. This is one of the constructable maps produced by PROPLAB-PRO Version 2.0, a radio propagation software package for IBM type PCs. The map is updated every 30 minutes. They sell the software and register you for propagation training classes from this same page.
The map can be used to determine the MUF for any 3,000 kilometer path by finding the midpoint of the path and reading the labelled MUF contour value. For 4,000 kilometer paths, you should multiply the given MUF contour value by 1.1 at the midpoint of the desired path. For longer path lengths, which require two hops, you divide the path into equal 3,000 or 4,000 km segments and compute the MUFs corresponding to the two midpoints that are 1,500 or 2,000 km from each end of the path. Then select the lower of these two MUFs. The map also shows the radio auroral zones as green bands near the northern and southern poles. Radio signals passing through these auroral zones will experience increased signal degradation in the form of fading, multipathing and absorption. The picture shows what their page looks like.
That’s it for this month. Hope to see you at the Kulpsville SWL fest. Next month our annual progress report from the NASWA Research Laboratory. Don’t miss it.