why antenna work?

On 5=A4=EB6=A4=E9, =A4U=A4=C811=AE=C905=A4=C0, "Ron Recer" w= rote:

ys said the antenna concentrating the energy to a narrow

No , my TV antenna is just a piece of metal. No electronic component inside. This experience told me if i plug my router antenna wire to a metal, it will enlarge the signal thanks from Peter

For me, light works as a better analogy for radio signals than water.

You can have a candle, that will light the whole room dimly.

If you put a nice shiny reflector on it, you can concentrate that candle in one direction and get more light where you want it, though the candle itself is no brighter.

If you take a magnifying glass to it, you can also concentrate and focus the light to make it quite a bit brighter, but in a very narrow direction only.

OK. Jeff, get out your analogy bashing hammer! (is that an analogy or a simile?).

Steve

No , my TV antenna is just a piece of metal. No electronic component inside. This experience told me if i plug my router antenna wire to a metal, it will enlarge the signal thanks from Peter

Sorry Peter, but that is not how it works. You have to use an antenna for the frequency you are using.

seaweedsteve hath wroth:

Yeah, but water is more fun for live demonstrations.

Sure, as long as you don't set off the smoke detector.

Good analogy.

Also good analogy.

The parts that you mentioned are quite good analogies. After all, light and RF are both electromagnetic phenomenon.

Where the light versus 2.4GHz analogy falls apart is in fringing, dispersion, and edge effects. The Fresnel Zone for light is almost zilch and can usually be ignored. You can't do that for 2.4GHz. Obstructions just outside of the line of sight act differently. Dielectric lenses function at microwave frequencies, but are not commonly understood by RV enthusiasts.

There's also a scaling problem. A reflector the size of a flashlight reflector has quite a bit of gain at optical frequencies, but is next to useless at 2.4GHz. Plenty more differences but I don't want to get into quantum mechanics.

I use water instead of light because I've found that it prevents interruptions and topic drift (like this posting). That applies to both the dull and the bright people in the audience. The clueless usually have some misconceptions and weird illusions about how light and RF propagate. The "more metal makes a better antenna" rubbish in this thread is typical. However, even the dimmest wit can see how a water nozzle works, without all the preconceived notions. When using water, I don't have to explain why a bigger antenna isn't necessarily a better antenna.

The bright people in the audience are a bigger problem. They know that there are plenty of situations where light works differently from microwaves. That's not the point, but there's always someone with a clue in the audience that brings up the differences. That creates an instant diversion that rapidly progresses into irrelevant drivel. The same person would not think of suggesting similar differences for a water versus microwave analogy, because it's obvious to everyone involved. So, my song and dance continues uninterrupted.

Therefore, water is a better analogy than light because it creates a smaller catalyst for endless debate (and is far more fun for live demonstrations).

Those that really want to know should buy and read a copy of this...

Only $273.50 in hardcover from Powells. Ouch(tm). Somewhat less on Amazon:

or used for as low as $35.

I have the original version, which is an excellent reference if you happen to have an advanced degree in electronics or physics. The current version is suppose to have dumbed down the math to something students can understand and is apparently intended to be text book instead of a reference guide. I haven't seen the new version.

If you really want to know how antennas work, the ARRL Antenna book is informative, practical, understandable, fathomable, and relatively cheap.

If you're into modeling antennas, there are quite a few good free or cheap programs that can help beginners visualize how changes in construction, design, and environment affect the various parameters. My favorite is 4NEC2:

It also includes a substantial number of examples.

Other programs are listed at:

Yes, but threads like this, where the question has been answered 5x over, are, at least, relatively better places to digress!

For me, from my Television/Film lighting past, I recognized the term "Fresnel" for the Fresnel lenses used on certain types of TV and film spotlights.

Oh, I see here, that it's more that it's named after the same guy, but it's different.

In digression, Steve

seaweedsteve hath wroth:

Well, I'm guilty of one indiscretion. I prefer complete, detailed, and comprehensive answers, to one-line pontifications. I could have simply stated "water is better, trust me" and left it at that. I didn't. In theory, people asking such theoretical questions would search with Google or Google Groups before asking, and find all 5x rehashes of the same topic. However, they don't. So, it amuses me to answer the same question over and over, but each time in a different manner. Perhaps next time, instead of a water nozzle, I'll use a different analogy. If quality doesn't work, perhaps quantity will suffice.

Yes, very different. Think "edge diffraction". You don't get much of that with light and optics unless you're into exotics and esoteria. That's the problem with the Fresnel Zone calculations. People tend to understand it in terms of optics (something anyone can see) and it fails. The usual result with wi-fi is "I can see it, but I can't talk to it" type of problems. The longer the path, the worse the problem.

Incidentally, 60% clearance is not the rule of thumb. More like 80%.