Distance to the DC area repeaters

Use this page to figure out how far you are from various repeaters in the Washington, DC area and what direction to point towards to reach these repeaters.

Enter your position

You must have the lattitude and longitude coordinates of your position to use this calculator. A site for looking up coordinates for a given address is available here. When entering the values, note that one arc second is equal to about 101 feet, so it doesn't really help to go past whole second values.

If you know your coordines in decimal (such as -77.1674 longitude) then enter that value for degrees and leave minutes and seconds empty or set to '0'.

You can also try one of these predefined locations:

• Washington Monument
• The Pentagon
• Goddard Space Flight Center

Your grid location: (undefined)

Distance and direction to area repeaters

Note: When one frequency is listed it is the output (your receive) frequency. The '+' or '-' following the frequency is the offset direction. Offsets are the standard amount of 600KHz for 2-meter band, 1.6Mhz for 1.25-meter band, and 5MHz for 70-cm band. If the frequency is followed by a 's', then it is a simplex frequency. If two frequencies are given, then the repeater uses non-standard offset and the second frequency is the input (your transmit) frequency.

* = Estimated position based on city

Abbreviations:
   ARA = Amateur Radio Association
   ARC = Amateur Radio Club
   ARG = Amateur Radio Group
   PSC = Public Service Club

How this was done

This page was done using JavaScript for the calculations. Originally, I scrounged the far corners of the Internet to find formulas for calculating the distance and heading between two coordinate pairs. The formula for finding the distance between two points was found here. The formula for finding the heading from one point to another was found here. Later, while reading in the ARRL Operating Manual (7th edition, paperback page 15-4) I found the two formulas sitting right together. Even better is that the heading formula in the Operating Manual is much better than the one I originally used.

A variety of techniques were used for finding the locations of repeaters and sample points. Where an address was known, that address was put into the GeoCode locator service, which yielded the lattitude and longitude. Coordinates for other sites were found using the Tiger Map Server. For some repeaters, all I had was a city name to go by, so these locations are only good to within a few miles.

If anyone has good location information for repeaters and notable ground points, or would care to double check points using a GPS unit, I like to be updated.

Any suggestions for improvements may be sent to me by E-Mail.

Formulas

Distance

lng_dif = lng_a - lng_b
arc_dist = arccos(sin(lat_a) x sin(lat_b) + cos(lat_a) x cos(lat_b) x cos(lng_dif))

Direction (new formula)

lng_dif = lng_a - lng_b
arc_dist (from above)
bearing = arccos((sin(lat_b) - sin(lat_a) x cos(arc_dist)) / (cos(lat_a) x sin(arc_dist))

Direction (old formula)

a = sin((lat_b - lat_a) / 2)² + cos(lat_a) x cos(lat_b) x sin((lng_b - lng_a) / 2)²
d = 2 x arctan2(a^1/2, (1 - a)^1/2)
Direction = arccos(sin(lat_b) - sin(lat_a) x cos(d)) / (sin(d) * cos(lat_b))

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