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.
Note this though, while the ARRL database doesn't provide lat/lon, it's pretty good about the location names and even big cities are usually broken into much smaller locales, with their own names. This makes the issue a less critical one.
One other point as well: ARF is not about leading you directly to the repeater. It's to let you know what's nearby and what the parameters are for using that repeater. If it happens that the repeater is really 15 miles away, instead of 10, there's a good chance you can still use that repeater!
A few things are available to help with making things more accurate:
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. Uploading and downloading the database is as simple as using a terminal application (such as Hyperterminal or Procomm) that supports XMODEM. The database is a distinct downloadable file, separate from the unit's firmware.
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.
The distance calculations are of course straight-line from your location to the repeater. Last I heard, radio waves don't follow local roads!
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. At my last check, there are only something near 20,000 repeaters in the ARRL database, and so I'll be including them all. Also, 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...!