Thursday, November 13, 2008

10 meter repeater range

I've written about 2 meter repeater range before, and actually this is an area I spend not a small amount of time fiddling with, what with my ongoing splat project to generate coverage details for every repeater in Tom's database.  However, there's a big difference between 2 meters and 10 meters when it comes to range, due to the difference between VHF and HF.

Two meters is a VHF band.  As such, it is mostly line-of-sight.  2 meters is somewhat prone to various long-distance effects, mainly in the summer, due to sporadic E skip, ducting, or other phenomena.  There's a site that provide nice real-time estimates of VHF propagation by examining APRS packet hops.  However, for the most part these effects are unpredictable and sporadic, and do not reflect the normal state of affairs.  When we talk about range for a two meter repeater, or any repeater operating in VHF or above, it's going to be based on the radio horizon without much regard to the possibilities of skip.

There are also repeaters in six meters, also considered a VHF band; six is more prone to skip than two, and can pretty reliably be expected to skip in certain directions at certain times of the year, depending on where you are.  However, the number of six meter repeaters is much smaller than that of two meter repeaters, probably because of the larger antennas required for good operating performance.

However, the search that prompted this article was seeking information on "ten meter repeater range".  Ten meters is an HF band, and as an HF band is much more amenable to skip.  In fact, when the sunspot cycle isn't in the doldrums like it is now, ten meters is pretty consistently a worldwide band; it is quite possible to work a contact all the way around the world with just a few watts if you know what you're doing.  So while the "space wave" component of a ten meter repeater is going to be substantially similar to that of a six meter or two meter repeater, the "sky wave" component will be completely different.  You can use splat, or any other line-of-sight (or Longley-Rice, preferably) modeling tool, to get a pretty good prediction of the space wave component of a ten meter station's listening zone.  For the sky wave component, though, you have to look into ionospheric modeling, which is much more complicated and less predictable.  In practice, a ten-meter repeater operator should assume and expect worldwide exposure and plan accordingly.

There are only nine repeaters in Tom's database that operate in 10 meters, and one of them is a crossbander.  I haven't splatted any of them yet; only one of them is in the United States (the crossbander) and I don't have terrain data for non-US locations anyway.  If you happen to have a 10 meter repeater, please consider adding it to Tom's database.