US Medium Wave Pattern References


Jump to: Day | Night | Critical Hours

US Mediumwave Pattern References are produced by the Radio Data MW program.

NOTE: These maps are not my work. They are the work of Radio-Timetraveller curated by Bill Scott. Bill’s blog is full of great information on broadcast listening and DXing, with equipment articles and stories about his DXing travels. Please visit his site if you’re interested in some great material on these subjects.

Also please note Google has changed the way that it allows developers to access its map products. From time to time a map application will show an error message and “lock” the map if a developer’s usage exceeded its allowance. Since Google is now charging on a different basis for the use of its maps, this may happen more frequently.

Included is a complete set (daytime and nighttime) of GoogleMap-based, HTML-driven maps which show the most current pattern plots of all licensed US and Canadian mediumwave broadcast stations from 530 – 1700 KHz. The set includes all frequencies for the indicated services: Unlimited, Daytime, Nighttime, and Critical Hours. Individual maps are grouped by channel frequency: 540, 550, 560 KHz, etc. Data for the plots in this offering is based on the current FCC and Industry Canada databases available at the time of its creation (January 22, 2015).

This year the Critical Hours plots have been split off to their own map set. Unlimited, Daytime, Nighttime, and Critical Hours plots are now compressed into one download.

Plot data has been derived from the FCC’s January 20, 2016 database. Be sure to see the readme file for detailed information.


1. Individual station plots can be turned on or off by a checkbox. Click the station flag and you will see the option in a pop-up balloon. Check or uncheck the box, then click the ReDraw button. Be sure to click the ReDraw button!

2. The entire plot set can be turned on or off by the All Plots/No Plots buttons.

3. Additional information has been added to each station’s flag tooltip. Now included are FCC facility ID, engineering (application) ID, and distance of the station from the home location. The home location is user changeable, as before.

4. Skywave calculations have been updated and made more accurate. The latest ITU formulas are used.

5. Unlimited, Daytime, and Critical Hours plots are at the 1.0 and 0.1 mV/m levels. Skywave is at the 0.2 mV/m level. In all cases except for the nighttime graveyard stations, levels have been chosen to minimize pattern overlap and to more closely follow those which might be helpful to the mediumwave DXer.


The daytime map series shows expected groundwave coverage patterns for Unlimited, Daytime, and Critical Hours operations. Daytime signal patterns represent groundwave coverage out to the 0.15 millivolts per meter contour (43.5 dBuV/m, a.k.a. dBu). Note that daytime reception of signals out beyond the depicted pattern is very possible, and in fact likely for the DXer. The contour line represents a signal strength at the station’s fringe distance, a level usually received on a sensitive portable radio with a low ambient local-noise level. I have chosen this signal level to give a good representation of what should be fairly easily received by most DXers during sunlight hours. Also included in the daytime map series is a web-based HTML table listing all daytime stations in the US and Canada. It has clickable links which will take you directly to the FCC pages for that station (US stations only).

The nighttime map series shows expected skywave coverage patterns for Unlimited and Nighttime operations. Nighttime signal patterns represent the standard SS+6 (sunset plus 6 hours, or approximately midnight), 50% signal probability at 0.25 millivolts per meter (48 dBu). Note also that nighttime reception of signals out beyond the depicted pattern is very possible, and in fact likely for the DXer. The maps represent a signal strength between distant and fringe, a level generally easily received at night on most portable radios. I have chosen this signal level to give a good representation of what should be fairly easily received by most DXers on an average evening. The nighttime signal probability of 50% means that the signal will be received at this level approximately 50% of the time at that location for the sunset+6 hour time. Also included in the nighttime map series is a web-based HTML table listing all nighttime stations in the US and Canada. It has clickable links which will take you directly to the FCC pages for that station (US stations only).

Unfortunately, no Mexican patterns are available due to lack of official Mexican engineering information.


Using the actual FCC database files Radio Data MW will auto-generate an interactive HTML pattern map, showing the pattern plots for all stations included at the discretion of the user. A complete set of mediumwave pattern maps can be generated within minutes. Radio Data MW generates a real pattern plot based on ground conductivity, ground dielectric constant, and can display actual (but approximate of course) signal level boundaries for Local, Distant, Fringe, Extreme mV/m levels, or any custom mV/m level chosen by the user.

The online Google Maps API is used to generate and plot each station on a map of the US. An accurate flag pin is placed at each transmitter location, and in satellite view may be zoomed in to see the actual transmitter site. Map flags are color-coded to indicate Unlimited (light red), Daytime (yellow), Nighttime (black), and Critical Hours (grey) services. Each flag has a tooltip-type note, and when hovered over with the mouse will display a note on the station.

A pattern plot for each station is generated and displayed. Each pattern is calculated using standard formulas used by the FCC to compute the base values at one kilometer, and field strength formulas at distance based on the works of many people over the years. See Field Strength Calculations: A History and Field Strength Calculator One, previously posted on RADIO-TIMETRAVELLER.

Finally, an accurate ray path can be drawn from all transmitters to a user-specified receiving location by inputting latitude-longitude coordinates on the heading bar at the top of the map. Super-imposed on the pattern plots, the ray paths show the listener where he or she falls on each station’s pattern, a handy guide to knowing where you stand.


Note again that these maps are web-based. As stated, they use Google Maps and thus require access to Google. In order to view them you need a connection to the internet. They have been tested in the Internet Explorer, Firefox, Chrome, Opera, and Safari desktop browsers. If using Internet Explorer, best results are had with the latest version, IE 10 or greater.

You will also find that the maps will generally work on most tablet or phone browsers, but no guarantee is given. Android and IOS browsers are in a constant flux of change, and in testing the most recent varieties I have had good success. The Google Chrome browser will work the best. Note also that the maps, being script-driven and with many lines of code are very CPU-intensive, and may cause many tablets or phones to choke.

These are the latest US pattern references available, and coverage is based on actual ground conductivities.

  • Lat-Lon boxes (Latitude and Longitude) – Your home location. Modify as you wish. Be sure to use negative values for the western and southern hemispheres. Click ReDraw to redraw the map.
  • Show Paths – Check the box and click ReDraw and great-circle paths will be drawn from each station to your home location, as indicated in the latitude (lat) and longitude (lon) boxes. These paths will help you determine where you fall in each stations broadcast pattern.
  • ReDraw – Redraws the map according to settings.
  • Map/Satellite – Click one or the other to display the map in either map form or satellite form. Subsequently, “Map” form may be displayed as a road map or terrain map. “Satellite” form may be displayed with or without labels (hybrid = labels).
  • mV/m and Conductivity Levels – These maps are produced by Radio Data MW for a specific mV/m (millivolt per meter) level and ground conductivity. The map itself in HTML form, once produced, cannot be altered to change these levels.
  • Station Flags – Station flags are colored according to service:
    • Unlimited: red
    • Daytime: yellow
    • Nighttime: black
    • Critical Hours: grey


The flag pin for each station is accurate, geographically. Zoom in at maximum level in satellite view and you should see the station’s transmitter site. If you are lucky enough that Google has taken a street view photo, you can also see that too.

Other cool stuff

  • FCC has published a series of color high-resolution ground-conductivity (M3) maps for North America including Alaska and Hawaii. The maps are in segments which can be printed and stitched together.
  • Look up US and Canadian broadcast stations at Cavell Mertz’s FCCInfo Search site.