Longley Rice  field strength plots with a Google Earth overlay


These computer runs generated a .kml (keyhole markup language) file and an associated graphics file which I have converted to .png (portable network graphics) format. Together these files will produce a Google Earth overlay which indicates predicted field strength by displaying six colors representing field strength as follows:

Red:        100 dbu (microvolts per meter) or more; Probably receivable with an indoor antenna.
Orange:   90-100 dbu; Possibly receivable with an indoor antenna.
Yellow:   80-90 dbu; Attic or outside antenna may be required.
Green:    70-80 dbu; Probably receivable with an outside antenna.
Blue:       60-70 dbu; Outside antenna required.
Purple:    50-60 dbu; Extra effort may be required for reliable reception.

The computer runs used the Longley Rice terrain dependent model for predicting field strength  taking into account the transmitter location, height above ground, effective radiated power, and transmitting antenna pattern. The receiving antenna height was set to 10 feet above ground. The colors represent a statistical probability of a given field strength at 50 percent of locations 90 percent of the time. The terrain data used was the 1 arc second SRTM-1 (Shuttle Radar Terrain Mapping) database generated by space shuttle overflights.

With the Google Earth program and overlay you can "fly around" and see what the field strength is predicted to be at a given location. You can type an address into Google Earth and the program will zoom in to show the field strength at that location. You can "tilt" the landscape for a surprisingly realistic computer generated view of hills  that may be blocking reception in an area.




Sample Image (looking straight down)





Sample Image (landscape tilted)


Instructions For Viewing the Maps

Download and install Google Earth if you have not already done so.

Download the .kml and .png files for the transmitters of interest.

Start up Google Earth, go to File/Open, and open the .kml file for a transmitter of interest. You will see a large "X" over the coverage area indicating something is missing.

In the "Places" pane to the left of the Google Earth window there should be an entry under "Temporary Places" with the name "SPLAT! HD" and showing the name of the transmitter coverage overlay.

Click on the + sign to the left of that entry then right click on "SPLAT! Signal Strength Overlay".

Click on "Properties" and near the top of the properties window you should see a "Link" box displaying a file name with a .ppm extension.

Click on the "Browse" button to the right and select the .png file associated with the transmitter of interest.

The overlay colors should now display but for best viewing you need to move the "Transparency" slider to somewhat less than halfway between "Clear" and "Opaque". This reduces the color intensity of the overlay allowing the Google Earth satellite image to show through.When satisfied with the "Transparency" setting click "OK" at the bottom of the window.

To download the overlay images


Right click on the file name and select "Save Target As". (Works with MS Internet Explorer, I don't know about other browsers). When I tested this with the .kml files, Internet Explorer suggested a default file name with a .xml extension rather than the .kml extension. Do not allow the extension to be changed. If it gets the .xml extension by accident, just rename the file.

I have reduced the .png images from 7200 X 7200 to 2048 X 2048 pixels to make the files smaller (still up to 7 MB). This reduces the accuracy somewhat when you zoom in close. I can post the high res file for a given site if anyone wants it (up to 24 MB). Also I can make computer runs for other sites if anyone wants them. Email me at dan at ridgelinebroadcast.com

SLTV_Hansen.kml         SLTV_Hansen.png

SLTV Hawley.kml          SLTV Hawley.png

SLTV London.kml         SLTV London.png

KEPB.kml                     KEPB.png

KEZI.kml                      KEZI.png

KLSR.kml                     KLSR.png

KMTR.kml                    KMTR.png

KVAL.kml                    KVAL.png

WLTV Florence.kml     WLTV Florence.png
       
TIA Ukiah.kml             TIA Ukiah.png

Powers.kml                 Powers.png

KHWB-LP.kml         KHWB-LP