About Position Location
While ARF contains virtually the entire ARRL repeater database, there are a few things you need to know about how location is done inside.
First off, the ARRL doesn't publish the latitude/longitude data for the repeaters that it lists. Indeed, it only provides the city and state of the repeater. That's not such a great thing when a particular repeater is located in say, Los Angeles. That's a pretty big city, so locating a repeater based solely on the city it's in is not highly accurate. Without at least a ZIP code, I have to pick the rough centroid of the location as the position of any repeater listed in that city.
To solve for the fact that there is no Lat/Lon data in the ARRL database, I have to correlate the city and state with a ZIP code, then to the latitude and longitude of that ZIP code. This leaves the inaccuracy issue that I mentioned above. Note too that ZIP code isn't the ultimate solution, since the ZIP code that many repeaters are listed under is really the ZIP code of its trustee, who could be just about anywhere. There's no great way to handle this, other than to call on you to help.
A few things are available to help with this:
1. I will be publishing a tool that will allow you to extract the database I provide from the unit. The result is a text file that you can then edit. Once edited, the tool will take the text file and re-create the database that you can send back to the unit. This allows you to edit, add or delete repeaters from your own device.
2. I'd love it if you would send me the changed database you've created. That way, I can integrate those changes into my main database. This will help to evolve the repeater database over time, resulting in an ever-more-accurate result.
3. I will also be providing an on-line, editable database of repeater information. My thinking at this time is that you will be able to edit virtually any aspect of the table, including the all important latitude and longitude, and/or the ZIP code in which the repeater resides. My goal is to have the most accurate repeater database anywhere. That accuracy will be reflected each time I release a new repeater file for ARF. Of course, changes made to the online databases will be vetted before integrating them into the master releases.
Some Details
ARF uses a technique known as the "Haversine formula" for calculating the distance between any two latitudes and longitudes. This technique is known for its accuracy in calculating distances between points that are in the realm of hundreds of miles apart, perfect for ARF's goals. You can set the maximum range that ARF will look in to 100 miles. In practice, you may find it more useful to search in a closer range. ARF defaults to 15 miles. That can be changed at any time.
Something to keep in mind about the location and distance calculations. Remember that these calculations are straight-line radius values. This means that you can be traveling over hill and dale and while you may think you're getting further away from your favorite repeater, in truth you could be getting closer in linear distance. It matters not how far you've traveled over ground.
Also of interest is the fact that at present, ARF returns up to 16 of the closest repeaters, regardless of how far out you allow it to search. If you're looking to find repeaters out at 100 miles, yet there are 16 or more closer to you than that, you're out of luck. That's a feature that will be changed in upcoming firmware releases. In future versions, I will allow you to elect to search for the farthest or the closest. Meanwhile, you'll be getting a list of the closest ones.
On-board Database
Rather than describing the ARF as specifically being able to hold the entire ARRL repeater database, perhaps I should give a few details about its on-board storage capabilities.
ARF has an external 2MB FLASH for database storage. As the database is currently constituted, it can hold up to 32,000 repeater records. If the price for 4MB devices comes into line, that record count will double. In theory, I could put somewhere up to 128MB of FLASH on ARF, giving shall we say, more storage than I can imagine your ever needing...!