Hi Guys,
Saw some unusual download activity on these maps and it looks like this is the source of interest. Glad these maps are useful to you.
They are created from the current FCC database, US stations only, as much of the Canada and Mexico (and others) data is out of date or inaccurate. I could easily include it, but many Canadian and Mexican stations have multiple and redundant entries. Weeding out the actual correct ones, if there are even correct ones, is nearly impossible.
The patterns are indeed based on station's power, array directivity, ground conductivity and earth dielectric constant for a groundwave situation. But be sure to note that they are groundwave or daytime representations and NOT skywave (nighttime) representations. The actual distant skywave pattern calculation and expected received signal levels at distant points for nighttime service are way beyond my mathematical abilities. The patterns presented, however, do show approximate groundwave signal levels for each station's service (daytime, nighttime, critical hours), the stated soil conductivity, and provide a comparable and portable reference which I can easily update.
At the moment, they are all based on a flat conductivity of 6 millisiemens/meter all across the country. I am in the process of interpreting the FCC's M3 ground conductivity database and writing code to show a more accurate representation according to actual local ground conditions. The code is very complicated and will ultimately generate virtually millions of calculations to arrive at the final patterns.
The Google Map also has the ability to trace a ray from your location to each station to aid in showing you where you fall in the station's pattern.
As stated in the original article, be careful about posting direct links to the downloadable pattern reference .zip. The link will change each time I post a new set of maps as it is delivered by my storage host box.com. Visit the main page of the blog instead. At the top right corner of the blog is a section called Latest US Mediumwave Files. That link is the only link and will be current.
robotique asked about the 660kHz WLOY/WLFJ situation in North Carolina. The pattern interference is mostly due to the overstated ground conductivity of 6 mS/m. Ground conductivity in that area generally ranges 1-4 which would reduce signal range considerably.
Best DX,
Bill
RADIO-TIMETRAVELLER
