hang on. you're telling me that they didnt test the range of their radar, ever? I mean it's not hard, you set one up and have a plane fly away in a straight line. That is the validated information that you easily could have. Fly it only in the area you have air superiority in, some test site somewhere.
I understand that the quality of information drops with distance, but that isn't modeled in HoI3 is it? Anyways, that does not mean that you can't do controlled tests to see how far the thing will go under best circumstances for instance.
Detecting a fighter and hearing radio signals from a transmitting tower are two completely different things. With a large enough reciever, and sensitive enough equipment, you can "hear" radio signals from outer space. However, with that same equipment you probably would not be able to detect an airplane very far away. You would have to be relatively close to pick up something out of a radio headset or see a plane, but could be relatively far away and still pick up something being emitted by a network of towers.
Also, detecting objects that you want to know the location of, takes multiple radar systems. Whereas, all it takes is a reciever and a man listening to it to get information on troop movements (assuming you know their codes).
What you get out of your radar depends on how large of a signal you are emitting (for detections purposes), how large of a signal they are emitting (for listening purposes), the sensitivity of the equipment, and how many stations you have (triangulation). A ham radio is going to be much less effective than a radar tower, which in turn is going to be much less effective than a network of radar towers.
In Game:
Captial provinces and HQs are much easier to see than individual divisions for the simple fact that much more radio signals come from them (assuming that is what is being abstracted here).
With a lvl 10 radar in malta and level 1 decryption, I can "see" individual divisions moving around Italian Africa. With a lvl 10 radar in south eastern England (and lvl 1 decryption), I get intel from Protugal and Yugoslavia (low level intel). I get high level intel a few spaces in every direction from the radar site (essentially I can see out to the sea).
The high level intel range (for lvl 10 radar and lvl 1 decryption) is about 3 provinces over (basically you can actually see everything going on with this intel). Mid level intel is about double that range (seeing divisions move in the fog of war). Low level intel pretty much stretches across Europe (HQs, capitals, and other major cities/areas).
If you want to see the effect of your radar towers, switch to the intel map mode. This will give you a mix of intel from radar and LoS.
While this will not give you an exact max range, it gives you an estimate for various things. The reality of the matter is that the max range of a radar (for listening purposes) depends highly on the power of the the source you are trying to listen too. The amount of useful information you get out of the signal also depends on the encryption methods used by the people that are trasmitting the signal.
While they could give you this info in game (as all the number exist in the background), I kinda like the fact that it is a little fuzzy. Intellignece officers never knew exactly where every unit was (even within the range of their detection).
Personally, I would like some misinformation put into the radar system (instead of the see it or not as it currently stands). I seriously doubt radar towers could pinpoint radio signals halfway across Europe to some HQ in some province without spies that already knew where that HQ was. It would be nice if they put in some randomizer (based on many factors: range, radar level, effeciency, decryption, etc), that could put a HQ or unit a few provinces over from where it actual is. Although, that would probably add more calculations to slow down the game
