let me chime in here with a personal note, hoping it's not offending 

Although I like having accurate and detailed computation of our 
real-world simulation, I'm not really a friend of the radio propagation 
code with the level of detail given. Please let me explain why that is 
the case:
The radio stations used for aviation purpose certainly follow the same 
physical laws as any other radio station does. However, their 
performance have to adhere to some specific rules, mostly set up by the 
ICAO. Service volumes is on of these rules, a straight ILS final track 
is another etc. If real life's environment disturbes the performance of 
the radio stations, the operator has to work hard to override these 
environmental impacts. As we usually do not have any detailed 
information about how the radio station is set up (and I doubt, we will 
ever get those), it's close to impossible to correctly model radio 
probagation of a specific station. Adding envirionmental factors besides 
terrain and terrain cover and the factors of aircraft installations will 
result in a wide range of uncertainty, spoiling all the detailed 
computation of the radio signal propagation.

As a pilot, I am usually just interested in the factor, if I am within 
the service volume of a radio station. If so, I'd expect a clear and 
correct indication, probably with the well-known system errors applied. 
If I am outside the service volume, the systems may show "something", 
but I do not really care about what exactly an ILS indicator (as an 
example) is showing.

 From real life experience, I can say that barely two stations behave 
the same if you are outside their published range. Sidelobes of a 
localizer may appear at on site and may not at another site. False 
glideslopes appear here but do not show up somewhere else. It depends 
heavily on the local setup of the base equipment (and to some degree on 
aircraft installations). However, I have seen the shoreline effect of 
ADF stations deflection my ADF needle heavily and I have seen effects of 
nearby thunderstorms and lightning on the instruments. I'd love to see 
these effects modeled.

That said, I think doing realtime radio signal propagations is much more 
that we need and much more than we want. At least unless we are 
multi-threading and have a spare CPU for those computations.

This is certainly just my personal point of view.


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