Air

Air has a slightly higher dielectric constant than free space, and has some conductivity. However, these electrical properties do not make air different enough from free space to make much difference. This is why the antenna books mostly ignore air.

Thank you Ermi Roos for addressing my air question. Wondering about the effect of air on transmission of radio waves is bundled with a whole string of curiosities that I'll compare to the fabled "super conductor," a wire that does not impede the speed or bandwidth of an electrical signal. It would seem that by comparison a field in space is also a conductor, and although it may travel at light speed, the power level is impeded. That's what the whole antenna game is all about. What about temperature? We know that in a wire or circuit absolute zero makes thermal noise disappear. What does temperature do to a radio signal in space? Heat is generated by the sun and arrives on upper radio spectrum as radiation, but there is no apparent cold generator, except the absence of a heat source. Therefore temperature isn't radiation per se, radiation is only a carrier. What effect does gravity have on radio? In the forum my "AM Verticals vs. Hills" suggests a relationship. My thoughts may not be as scattered as they appear. What I am simply doing is considering everything that shares a field in space with a radio signal.

To continue my exploratory logic, an antenna system creates a circuit using "air" and ground as conductors. Not only are those two elements extremely unbalanced- the "air" presents a high impedance; the ground, ideally, a low impedance, but under Part 15 a further imbalance is forced by the 3-meter above-ground limit, while full-wave buried radials are not prohibited. Many comments have been filed about improving ground conductivity, I am wondering about improving "air" conductivity.

Carl,

I'm reading with great interest your theories on the propagation of radio waves through the "air". You've made some very interesting observations that have caused me to look at the environment that our radio signals travel through. Unfortunately, I can't help you with any of your questions but there are a number of individuals that post here on a regular basis that are more than capable of offering assistance. In the mean time, thanks for giving me a new perspective on how this really cool thing we call radio works!!

gronsk

In 1919, it was observed by Sir Arthur Eddington that light is slighly deflected by gravity. I think, however, that gravity is not responsible for the observation (if true) that ground waves have more trouble going uphill than downhill, because the Eddington effect is just too small.

One of the explanations for the ability of LF ground waves to go a long distance beyond the horizon is that the the wavefront is slightly tilted forward because of the finite conductivity of the earth. I think that this also does not explain the observation about hills, because the earth slopes downward very gradually at the horizon, and hills have much bigger slopes. The upward slope must be an obstruction to ground waves, while the downward slope is not.

This is really a significant observation. A rigorous analysis needs to be done to explain it.

I can state from experience that air does make a difference. When I first started my low power (in Canada) FM station, I would routinely drive to various parts of the little island I'm on and listen to the signal. That signal would definitely be stronger on cool clear days, and correspondingly much weaker on hotter, hazier days. Rain, interestingly enough, would make the signal stronger (I think it increased the ground effect - my transmitter is in a weatherproof box on top of a roof).

I too looked for something to explain what I was seeing, but couldn't find anything.

The atmosphere certainly affects radio propagation. An effect more local to the antenna is that air increases dielectric strength compared to a vacuum. It isn't that air has no effect at all, but that it makes littke difference to the idealized generalities in antenna books.

Anecdotally, I haven't seen much impact on my AM BCB range, other than general dampness tending to improve range a bit. When I was running a part 15 FM I definitely saw a difference in range during rain and I've also observed apparently negative impact on wifi during light rain and fog. There seems to be a potentially logical connection there base on the sizes of the wave forms...

The Ionosphere is a part of the atmosphere, and it certainly affects MW AM. When explaining the fundamentals of antennas, however, authors rarely deal with reflection from the Ionosphere, or other atmospheric effects.