Revised-Maximum Range of VOR's and NDB's

I have done some additional experimenting with the radio navaids, and have come up with some interesting new results. Apparently, the maximum range at which you can receive the navigation signals from a VOR or NDB depends not only on their type ("HIGH" for VOR/DME's and "HH" for NDB's gives maximum range), but also on the altitude of both the aircraft and the transmitter. In my earlier experiments, the beacons were only 10 meters (30 feet) above sea level. and the aircraft were flying at about 6,500 feet. I got a max range of about 140 nautical miles. In this new experiment, I created a VOR and an NDB at the summit of Mt. Everest - the highest point of land you can get too in both the real world and FS2020. In the sim, this comes out to 8,741 meters, about 28,677 feet MSL, which is actually lower than the summit in the real world, which is 29,035 feet; the DTM that FS2020 is using apparently isn't 100% accurate. The "range" value for both transmitters was set to 199 nm. 

I then started a flight in the Turbo Bonanza from Lukla, and flew south, on a radial directly away from the transmitters, and climbed to 30,000 feet - just about as high as the plane could get without stalling - and watched the DME and the gauge needles. At 168nm, the needle for the NDB snapped back to the neutral position, although I was still hearing the Morse code audio signal. At 199nm, I lost the VOR/DME signals, and oddly, I was still hearing the Morse code from the NDB, although I was now more than 30 miles past where the navigation signal had dropped off.

I flew several loops back and forth to test the range for consistency. The VOR always cut in or out at 199 nm. The NDB cuts out at 168 nm when you are flying away from it, and cuts back in at 164 nm when flying toward it. The conclusion I draw from these two experiments, is that the sim may actually be accounting for line-of-sight and height above the apparent horizon. With the transmitter at sea level, and the aircraft at relatively low altitude, you don't have to get very far away before the transmitter drops below your horizon. With the transmitter and the aircraft both at 30,000 feet, you still have clear line-of-sight between them for about 400 miles before the curvature of the earth would cut off the direct line of sight between them. In reality, it's more complex than this, because radio waves get refracted by the atmosphere and the "maximum range" at which you can hear a radio signal changes from hour to hour. Also, in the real world, I've read that VOR's and NDB's aren't reliable beyond about 100 miles even for the high-power ones.

If anyone would like to try this on their own, here's the XML code for placing these two beacons on the summit of Mount Everest. You get two visual scenery objects, a VOR/DME and an NDB transmitter tower from the scenery library, and the radio parameters for the two transmitters.  It's created on a fictional airport I call "Everest_Base_Camp", but there's no runway, just the two nav aid scenery objects. Create the new airport in the SDK, using your own name, then open the XML file in a text editor, paste in my code and save the file, then Build it in the Project Editor. If the Console doesn't report any errors, you can then copy the Package to your Community folder, start the sim, and try it yourself. I suggest using a turbine aircraft like the Beech King Air, or maybe the Cessna 208. It needs to have an avionics package that supports NDB/ADF navigation (not all of the planes do). The Garmin G1000 has this, but if you are going to start the flight from Lukla, remember that the runway there is less than 2,000 feet long, and the elevation is something like 9,500 feet. They fly Twin Otters from Lukla, and I was able to fly the Bonanza G36 Turbo from there, although it took a long time to climb to 30,000 feet. Here's the XML code:

<?xml version="1.0"?>
<FSData version="9.0">
    <!--SceneryObject name: OCE_APT_NZGS_VORDME-->
    <SceneryObject lat="27.98881833921670" lon="86.92376212320278" alt="0.00000000000000" pitch="0.000000" bank="0.000000" heading="-179.999995" imageComplexity="VERY_SPARSE" altitudeIsAgl="TRUE" snapToGround="TRUE" snapToNormal="FALSE">
        <LibraryObject name="{3CC5CC14-8178-463E-BC9F-DFE5CDD34AC3}" scale="1.000000"/>
    </SceneryObject>
    <!--SceneryObject name: ndb-tower-25m-cbj-->
    <SceneryObject groupIndex="1" lat="27.98899383407348" lon="86.92390485546913" alt="0.00000000000000" pitch="0.000000" bank="0.000000" heading="-179.999995" imageComplexity="VERY_SPARSE" altitudeIsAgl="TRUE" snapToGround="TRUE" snapToNormal="FALSE">
        <LibraryObject name="{78531B6D-0968-4AD8-DBFC-1633590B8E9D}" scale="1.000000"/>
    </SceneryObject>
    <Airport displayName="EVEREST_BASE_CAMP" groupIndex="2" groupID="1" groupGenerated="FALSE" region="NP" country="NEPAL" city="EVEREST_BASE_CAMP" name="EVERST_BASE_CAMP" ident="ICAO" lat="27.98881833921670" lon="86.92376212320278" alt="0.00000000000000" magvar="-0.300000" trafficScalar="1.000000" airportTestRadius="22000.00000000000000" applyFlatten="FALSE" isOnTIN="FALSE" tinColorCorrection="TRUE">
        <Aprons/>
        <PaintedElements/>
        <ApronEdgeLights/>
    </Airport>
        <Ndb lat="27.98899383407348" lon="86.92390485546913" alt="8741.0M" type="HH" frequency="0425.00" range="199.0N" magvar="-0.3" region="NP" ident="NDEV" name="EVEREST_NDB"/>
        <Vor lat="27.98881833921670" lon="86.92376212320278" alt="8741.0M" type="HIGH" frequency="114.950" range="199.0N" magvar="-0.3" region="NP" ident="VREV" name="EVEREST_VOR" dme="TRUE" dmeOnly="FALSE">
            <Dme lat="27.98881833921670" lon="86.92376212320278" alt="8741.0M" range="199.0N"/>
    </Vor>
</FSData>