US Medium Wave Pattern References


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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.

Updated for 2019 with Google maps working properly, apparently. If you are having difficulty, clear your cache or refresh the index pages as the links to map pages have changed. Let me know if you notice any link errors or missing pages.

Notes on the maps

Here are Bill’s notes about the maps:

Included is a complete set 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, .. 1700 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 16, 2019).


The daytime map series, in two parts, shows expected groundwave coverage patterns for Unlimited and Daytime (part 1), and Critical Hours (part 2) operations. Daytime signal patterns represent groundwave coverage at two levels, out to the 1.0 and 0.1 millivolts per meter contours. The choice of these levels is made in order to more closely match those which might be helpful to the mediumwave DXer. Note that daytime reception of signals out beyond the depicted 0.1 mV/m pattern is very possible, and in fact likely for the DXer. The contour line represents a signal strength at the station’s extreme 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 can be received by most DXers during sunlight hours.


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 Central Standard Time), 50% signal probability at 0.15 millivolts per meter. Note also that nighttime reception of signals out beyond the depicted pattern is very possible, and in fact quite likely for a skywave signal. 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 Central Standard Time.


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 in about five hours of processing time. Processing time has increased by nearly two hours in 2019 due to enhanced skywave calculations and other upgrades.

For daytime signal maps, Radio Data MW generates a real pattern plot based on transmitter power, antenna array efficiency and directivity, ground conductivity and ground dielectric constant of the path to the receiver. Increased conductivity of water paths over the Great Lakes are also accounted for. It 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.

For skywave signal maps, predicted signal levels are calculated in accordance with current ITU methods of recent years (1999 onward). A number of parametrics are now analyzed and accounted for in the calculation, namely diurnal and seasonal changes, and daily sunrise and sunset enhancements to the signal. The process is rather complicated.

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 can be calculated using standard formulas used by the FCC or ITU 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. See the RADIO-TIMETRAVELLER blog at:

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.

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. The entire plot set can also be turned on or off by buttons at the top of the map.

Included in each station’s flag tooltip are FCC facility ID, engineering (application) ID, and distance of the station from the home latitude-longitude. Of interest to the DXer, by setting the home location latitude-longitude to your location and redrawing the map, each flag tooltip will have the distance from your location to the station.


The shaded grey colors for all plots have been selected for best contrast over the mostly white Google Road map. The contrast of the same plots over the generally green Satellite Map is less than adequate. Unfortunately, you can’t have both work out. Tip: use the Google Road map for viewing the plots and the Satellite Map to inspect transmitter locations.


A certain amount of pattern overlap exists on these maps, as it does in real life. For the Daytime and Critical Hours plots, the outer 0.1 mV/m signal level ring represents an extreme groundwave fringe distance where a station can be heard. At that level, there may be some overlap with co-channel stations.

Pattern overlap is of course much more severe for skywave on the nighttime plots. A level of 0.15 mV/m was chosen to represent the fringe distance a station is heard at night about 50% of the time.

An unusual case exists on the graveyard channels (1230, 1240, 1340, 1400, 1450, 1490 KHz). The plots are a massive overlay of signals (as it is in real life!). There is no real good way to display a graveyard channel for station-to-station comparison but to throw them all in there and then allow you to choose which ones to compare. Virtually 99% of all graveyarders run 1 KW power to a single tower. The technical reality is that a one kilowatt station does not produce a skywave signal in any direction above a level of about 3 mV/m. Raising the plot mV/m level to reduce the chaos unfortunately results in no plot at all for most stations.

The solution to the graveyard confusion is simple, and one of the enhancements added in 2016. You can turn plots on or off individually, or all at once. Turn all plots off and simply check the plots you wish to see.


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. Maps may not display properly or at all in older browsers. Best results are had with the latest versions. The Google Chrome browser will generally perform the best on desktop or laptop systems.

You will also find that the maps will generally work on most tablet or phone browsers, but no guarantee is given. Android and IOS (Apple) browsers are in a constant flux of change, and in testing the most recent varieties I have had fairly good success. The Google Chrome Android 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, particularly those maps with many stations.

Lat-Lon boxes (Latitude and Longitude)

Your home location. Modify as you wish, but remember, stations displayed here are mainly near or within the continental U.S. 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.


Redraws the map according to settings changes (return ray path, changes in plot checkboxes, etc.).

No Plots

Redraws the map showing no station plots, only flags. Return ray paths can also be drawn.

All Plots

Redraws the map showing all station plots. Return ray paths can also be drawn.


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). Street view can be enabled from the satellite mode.

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 and 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 skywave calculation has been totally overhauled and enhanced to more reflect actual signal expectations across the U.S. at night. The fact of life is that pattern overlay occurs on many frequencies. Simply select the plots you want to analyze. Check the No Plots checkbox then ReDraw to turn off all plots. Click any station flag and check the box to plot that station then ReDraw.

You will occasionally see a skywave plot which looks much smaller than surrounding plots. This is a case where the station’s skywave signal did not meet the mV/m threshold (0.15 mV/m). The groundwave plot level is substituted in this case. The station does in fact have a skywave component, however small, it will be measurably less than the 0.15 mV/m level (very weak). It may be receivable!

The darker line defining the outer edge of the skywave plot shows the location of the 0.15 mV/m signal point at all compass points. Note that skywave signal strength does not decrease linearly with distance from the station. From the station outward, the signal strength will generally increase to a point usually 200-400 kilometers distant where it will peak, then decrease somewhat linearly from there.

Also note that the atmospheric background noise level on the mediumwave band is generally condsidered to be approximately 36 dBu (dBu in this case = dBV/m), equivalent to 0.063 mV/m. Signals below that level will not be heard unless they fade up above the noise. A gain or directional antenna can be used to increase signal strength while limiting or even reducing the overall atmospheric background noise level.


January 16, 2019:

1. The previous 2016 map version became crippled due to Google’s new precondition for all Google Map usage now requiring a user key. I have applied for and received the requested key. It allows a fixed amount of map-usage bandwidth. All maps should now display fully.

Note: Google may throttle map-usage bandwidth based on excessive use. Whether this will happen is unknown at this time.

2. Skywave signal maps have been totally recoded for 2019. Many months of coding and testing were involved. Predicted signal levels are calculated in accordance with current ITU methods of recent years (1999 onward). The following new parametrics are now additionally considered in the skywave calculation:

  • Hourly transitional loss variance from sunset to sunrise.
  • Seasonal gain or loss, January – December.
  • Diurnal enhancement at the sunrise and sunset period.
  • Winter daytime skywave enhancement (only on maps created for times during the day).
  • Daily seasonal nighttime skywave enhancement.
  • Take off angle variances for stations at relatively close distances (experimental).

3. Colored plot (yellow) introduced for groundwave 0.1 mV/m level.

4. Small changes made to the map’s title bar heading.

5. Unlimited, Daytime, and Critical Hours plots are at the 1.0 and 0.1 mV/m levels. Skywave this year is set at the 0.15 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.

January 22, 2016:

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.

January 22, 2015:

1. Groundwave pattern maps have been streamlined and made more accurate.

2. This current set of maps uses an enhanced version of the FCC’s M3 Ground Conductivity data base. Many errors in the original database were found, things like segments not joining properly, missing data, odd values for the Canadian land mass, problems with Alaska and Hawaii. I have corrected all these, plus added the conductivity data for the five Great Lakes bodies of water which were missing from the original database. Even little Lake St. Clair near Detroit has been incorporated.

3. I have written from scratch nighttime skywave mapping code using the standard FCC formulas, and now nighttime skywave pattern maps are newly available in this download.

4. The Industry Canada Canadian database has now also been included in the daytime and nighttime pattern maps, showing each Canadian mediumwave station. A lot of time was also spent incorporating the Canadian engineering data and coding up software to process it. Unfortunately, no Mexican patterns are available. I have elected to exclude them from the maps as the Mexican government does not provide technical engineering data via the internet. FCC Mexican data is redundant and inaccurate at best, though I may at some point offer some pattern maps of what is available.

September 26, 2013:

1. The latest maps show actual calculated received signal strength based on FCC ground conductivity data from the M3 map database.

2. The pinch-to-zoom bug and map scroll bug has been found which caused maps to lose these features when viewed on some mobile browsers.


Possible yet untested: Google may throttle map-usage bandwidth based on excessive use. Whether this will happen is unknown at this time.

Due to FCC database anomalies, duplicate records, or records which the FCC has failed to archive, there may be the rare station on these maps that has two flags at exactly the same location – which has escaped my notice. Unfortunately, this makes the bottom flag unviewable and its plot checkbox unreachable, so you may not be able to turn its individual plot off except by turning off all plots and starting from there. I apologize ahead of time if this situation has occurred. I do the best I can to weed out the duplicate and bad records.

Map plot colors are usually not compatible between the Google Road map and the Satellite map. There is no way to change plot colors. Colors have been selected for best contrast on the Google Road map.

Severe skywave pattern overlap on the graveyard frequencies covers the map. This is unavoidable as it takes a certain mV/m threshold to produce any plot at all with the low power level of graveyarders. The solution is to turn all plots off, then enable plots for only those stations you desire.


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 made street view available for that location, you can 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.
  • FCC has an online database query service for AM, FM and TV stations. These records include each station’s history cards. The history cards were kept on each station until the FCC’s files were computerized in 1980 and provide brief notes on each station’s FCC actions.