On 02/13/2007 09:31 AM, Holger Wirtz wrote: > What I need is a simple number which should describe the > maximum range og a COM1. For example 5 km? oder 20 km???
As others have pointed out, the simple answer is "line of sight". See algorithms below. > COM1 in a Cessna is not as one of an Airbus. Both are limited by the line-of-sight rule, and by interference. Getting a "better" radio for your Cessna will not help at all. Contrary to what others have said, attenuation due to air / cloud / rain / snow is negligible at VHF frequencies. http://www.tapr.org/ve3jf.dcc97.html Except as noted below, a range of 500 km should be no problem for a modest aircraft radio (e.g. KX-165) ... in a line-of-sight situation. http://www.seaerospace.com/king/kx165.htm http://www.isghq.com/calc/path_lossmain.php 1) The most relevant /fundamental/ limitation to usability is frequency congestion. It does not matter if the receiver sensitivity is 2 microvolts or half that or a hundredth of that, if there is 10 microvolts of hash on the frequency. The re-usability of UNICOM frequencies /depends/ on the line-of-sight requirement, to avoid congestive interference from innumerable other users who are out of sight. High-altitude ATC sector frequencies are reusable, but the multiplicity factor is much, much less. A stuck mike can be considered an extreme form of congestion if you like. 2) The most relevant non-fundamental issue is local interference, e.g. from bad brushes in the aircraft alternator. Improving the specifications of the radio (better Tx power and/or better Rx sensitivity) will not help at all; the only thing that will help is to get rid of the interference. In an interference situation, ATC will be able to hear you, even if you are unable to hear them ... which is why pilots are trained to transmit "in the blind" periodic reports of their position and intentions. ======================= Here's a quick and dirty way to tell if two aircraft are in range of each other: For each aircraft, calculate the distance to the horizon, based on the aircraft's height above the terrain. This gives you a "coverage circle". If the two circles overlap, you are in range. That is, if the sum of the radii exceeds the distance between the planes, you're in range. At the next level of fanciness, ask for the Cartesian coordinates of each airplane, interpolate 10 evenly-spaced points on the line between them, and check to see that each point is above the terrain. Ynlike the Q&D algorithm, this can -- roughly -- deal with the case where there is an isolated mountain or something between the two locations. ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier. Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
