How to (Accurately) Determine the Coordinates of Your Repeater Antenna (and help the coordinators retain their sanity and remaining hair) July, 2012 WB1GOT ARCC V.P. Coordination ARCC uses a repeater s coordinates to: 1) Accurately determine the elevation at the base of the antenna support structure, to 2) Accurately determine the HAAT (Height Above Average Terrain), to 3) Create a (reasonably) accurate coverage plot which we then use to identify possible interference. Accurate Coordinates Are Essential to Our Main Task! ARCC Policy requires repeater transmitter coordinates to be accurate within ± 1 arcsecond of true. Generally stated, coordinates must be accurate to within 75 of true. Anything greater may make it difficult or impossible for us to accurately determine the location of your repeater s antenna support structure and be forced to reject your application. Why All the Fuss and Bother? First, it s not that much fuss or bother: We NEED accurate coordinates to accurately do our job. And, in this business a miss can be a mile : Imagine if the coordinates for this tower were reported a leeeetle to the right. Oops it s a 300 drop behind that particular tower which would make a slight difference in HAAT to say the least. That s why we actually need to see your antenna support structure when we confirm coordinates. In MOST instances a 1 arcsecond tolerance will be OK; we can usually find it. However, as in the example above, and several other instances, we might need to determine coordinates to within 1/10 arcsecond. If we NEED better coordinates AND we can spot your antenna support structure we can usually get coordinates that are usually accurate to within feet! NOTE: Don t use the coordinates written on the shelter wall or filed in the ASR: they are probably wrong! We have seen instances of towers being 12.5 MILES from where they are claimed to be in the ASR registration. ARCC uses Google Earth as the primary source for establishing accurate coordinates. Multiple tests (comparisons) with other modern mapping programs have shown agreement throughout our coordination area to within a few feet. Therefore we ask you to use Google Earth to verify your coordinates prior to filling out your coordination application. When in doubt, trust Google Earth we do. Version 1 July 16, 2012 Copyright 2102 Area Repeater Coordination Council of EPA/SNJ Inc www.arcc-inc.org Page 1
Here s how to do it: 1) Get Google Earth : http://www.google.com/earth 2) Use Google Earth to fly to your antenna support structure: Here, we typed in Laurel Rd. 18963 that is street name and Zip code. Please note that although Google Earth is usually very accurate for coordinates it cannot be relied on for correct street addresses or elevation. 3) Zoom in and move till you find the antenna support structure: We NEED to find the BASE of the antenna support structure. Can you find it? Notice the distinctive shadow? Version 1 July 16, 2012 Copyright 2102 Area Repeater Coordination Council of EPA/SNJ Inc www.arcc-inc.org Page 2
Here s another one. Is the tower base on the left or the right? The base of this tower is on the right behind the garage. The towers shadow is under the tower; hidden from this view. 4) Now you need to place a marker on the ground at the base of your antenna support structure. Use the Add Placemark tool to place a placemark on the middle of the page Version 1 July 16, 2012 Copyright 2102 Area Repeater Coordination Council of EPA/SNJ Inc www.arcc-inc.org Page 3
5) Here we see the placemark and the placemark properties box. Note that the placemark properties box shows the coordinates that lie under the center of the placemark NOT at the tip of the tack! We need to change to a less ambiguous ICON. 6) Click on the placemark icon box and change the placemark icon to a small dot: Note: You can also change the color and size (Scale) of the icon. Click OK to close the Placemark Icon box Version 1 July 16, 2012 Copyright 2102 Area Repeater Coordination Council of EPA/SNJ Inc www.arcc-inc.org Page 4
7) Alternately zoom in and drag the placemark icon to the base of the antenna support structure: where the antenna support structure connects with the ground. Your coordinates are displayed in the placemark Latitude and Longitude boxes in this case: 40 23' 6.52" N Latitude, 75 0' 33.39" W Longitude or as 40 23 06.52, -75 00 33.39 8) Double check your coordinates by closing the placemark window and manually entering the coordinates into the Fly To search box and clicking on the magnifying glass. Google Earth should bring you right back to the base of the antenna support structure. Q and A Q. My antenna support structure isn t up yet. What do I do? A. Run out to the site with a can of fluorescent orange paint and oh wait. That won t work... If there are identifiable landmarks you can drive a stake where your antenna support structure will be located and measure distances to the landmarks. Then use Google Earth and its Ruler tool to lay out a map and determine the coordinates for your future antenna support structure. Q. I can t see my antenna support structure with Google Earth. What do I do? A. Get Google Earth as close as you can to your antenna support structure and record the indicated coordinates. Then use those coordinates to direct Bing Maps to the location. Switch to Birds Eye view, zoom in, rotate and have a look. NOTE: Bing maps aren t accurate enough to determine coordinates; do NOT report coordinates derived from Bing Maps! ONLY use it to help locate your antenna support structure and nearby landmarks. Then return to Google Earth and have another look. You may be surprised to be able to see the antenna support structure on the second or third try. Hint: If you can t see your antenna support structure, look for its shadow! O. My antenna is on the roof of a large building (office, hospital, etc). How do I obtain accurate coordinates? A. Get coordinates as close as you can and let us know your antenna structure is a building and we ll work with you to nail down the coordinates. Unless the building is HUGE, you can look at the apparent angle of the aerial photo and guesstimate. Unless the photo is straight down on the roof unusual - the coordinates of your antenna are NOT where the mounting point appears on the map. As for antenna height you ll either have to measure (drop a tape or line) or get the building height from the plans filed with the city / county. DO NOT GUESS! Note: Google Earth and Bing Maps and other trademarks are property of their respective owners. Version 1 July 16, 2012 Copyright 2102 Area Repeater Coordination Council of EPA/SNJ Inc www.arcc-inc.org Page 5