Mike Rawlins wrote:
Thanks Jon. But how does one access the DME in
Flightgear? I see that Oakland (KOAK) has a VORTAC,
frequency 116.80. I set NAV1 to 116.80 while on the
runway there, and don't think anything like a DME
engaged. KSFO has a VOR/DME on 155.80. Does one get
distance from this frequency?
(Oh, typo above, you mean 115.80, as you show below.)
The DME transmits on one of 126 channels between 1025 and 1150
MHz, and receives on a corresponding channel between 962-1024
MHz. Obviously, at these frequencies, this is totally line of sight,
so the DME generally does not work on the ground, unless the
VORTAC is RIGHT next to the runway. I don't know how smart
the DME code on FlightGear is, but I'm pretty sure they ARE implementing
some line of sight calculations, or the receiver in the plane would be
getting the software equivalent of all the DME transponders blabbering at once.
A grep of KSFO on ${FG_HOME)/Navaids/nav.dat produced: 12 37.605194 -122.383167 24 10890 1.000 ISIA KSFO 19L DME 12 37.626092 -122.394317 22 10955 1.000 ISFO KSFO 28L DME 12 37.630178 -122.394608 17 11170 2.000 IGWQ KSFO 28R DME
I'm curious why 115.80 does not appear on these lines
with DME.
Who knows. Could be whoever coded the data base, or could be the FAA has reasons to not want that particular VOR to be used for navigation at KSFO. VORs are quite strange under conditions of reflections and refraction, as well as interference from other transmitters. There are some areas where particular VORs give VERY incorrect readings. Due to the higher frequencies and pulsed transmission, the DME generally is pretty reliable.
Jon
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