Wikipedia
jarhead said:
I'd have to say that installation quality and aircraft altitude are the two biggest factors that determine how far away you'll be able to hear/be heard. In my mind, they're interchangeable - a crappy com system installation won't talk very far even at high altitudes, but at the same time a pro-quality installation won't talk very far if you're down in the weeds or in among the mountains. As already said, line-of-sight is the rule.
I was going to say 150 miles if high enough, and that is about right. VHF is slightly affected by atmospheric conditions, but not as much as lower Freqs. The formula for distance is square root of altitude in feet times 1.5:
distance miles = ( 1.5 x altitude )^sqrt ; altitude in feet.
I looked it up in Wikiped. THAT SITE IS INCREDABLE. Here is a link to VHF and everything you want to know about it.
http://en.wikipedia.org/wiki/Very_high_frequency
I like many pilots take it for granted, push button, talk. When taking off from BOS I can get a JFK ground frequency, but not till well above 10,000 feet, say FL180, which is a little over 150 miles away at that point. From the formula it works out to 164 miles. So it is line of site and getting away from the gound where it can be absorbed and reflected?
However in my example above I am sporting a higher powered radio (16 watts?), so 100 miles for a low powered 5 watt radio might be better. The ICOM A200 is 7 watts, Garmin is 8 watts. Range and power no doubt related but not sure it's one-to-one directly proportional, ie double the power does not double range, but I could be wrong. Clearly the more power the better, but altitude, line of sight and weather conditions are also big factors.
According to the article FM radios of 50 watts can get almost 500 miles with the right conditions. (I assume two ground stations with tall towers over flat land.) So with high altitude 5-8 watts can no doubt get 100-150 miles. What is the longest VOR/VOR Airway in the US? I found a high alt airway that was 300 stat miles? So 1/2 way between, 150 miles is the top range for VHF VOR's. That matches the "service volume" for a HVORTAC, which is 100 nm above 14,500 ft, 130 nm above 16,000 feet. So there's the 150 mile number again. That is about all you can hope for.
That's why oceanic planes use HF radios (low freq). Of course the wattage is much higher, but the range is big time affected (helped or hurt) by time of day and weather, since it does bounce between the ionosphere (the layer of atmosphere that reflects radio waves). That bounce or skip is where the range comes from. The range can be way over 1000 nm, sometimes it is less just based on atmosphere, which is a pain. Solar flairs can affect it also.
George
What about a BWA (with helium of course)?
