why antenna work?

Climbing a ladder does not make your eyes stronger but does give you a better view.

Maybe because the antenna doesn't come with an amplifier? If it does, try plugging it in.

All physically realizable antennas have gain, ask specific more question as to why work.

I always figured if God didn't like antenna gain, He wouldn't have created earlobes.

snipped-for-privacy@hotmail.com hath wroth:

Antennas do not generate or amplify anything. What they do is redirect signal that would normally go in unwanted directions, to the direction that you want the signal to go. A tolerable analogy is a garden hose nozzle. You can set the nozzle to a fine wide spray, or to a pointed narrow stream. The volume of water delivered in both cases is the same and is the transmit power.

As the stream gets narrower and narrower, it will go farther and farther, which is the whole idea. How much farther is a function of this directionality or gain. In RF terms: +6dB = 2 times as far +8dB = 2.5 times as far +12dB = 4 times as far +24dB = 16 times as far

You might find the FAQ for alt.internet.wireless worth skimming:

Another reason to install an external antenna is that your RV probably has aluminum sides and foil backed insulation in the walls. No RF is going to penetrate that much metal. So, you're only alternative for getting a decent connection at the RV park, truck stop, or coffee shop, from the RV, is with an external antenna. Highly directional antennas are also very useful for eliminating interference from nearby users and systems.

Antenna has gain. Think of it as concentrating the energy. Some antennas have unity gain, and by adding elements to the antenna you can increase its gain.

The garden hose analogy is a good one, Jeff! I'll have to remember that one.

Pete

snipped-for-privacy@yahoo.com hath wroth:

Thanks, but like all analogies, it somewhat fails in the end. The common garden hose cylindrical nozzle changes orifice area with different spray patterns. Therefore, the flow rate (tx power output) will be larger with a stream than with a spray. I got into a debate over the issue many years ago. Rather than do the calculations, I convinced the local grade skool brats to do a quick measurement. Well, it wasn't so quick and bribes were required for motivation, but the experiment was successful. I had them build a really crude paddle and counter flow meter with all the technology that could be borrowed from the neighborhood landscape contractor. I have photos somewhere. There was something like 50% more flow with the nozzle in stream than in spray. However, when we tried different style nozzles, there were some substantial differences. The more expensive nozzles, that resemble a fire hoze nozzle with a handle, have almost a constant flow rate with any pattern. Despite being not exactly perfect, it's good enough for explaining how antennas operate.

Hi, Ever heard about antenna gain, radiation angle, pattern(horiz. vs vert.) as an example? Antenna theory is very complex subject which needs lot of real world experiments.

Is this what you're looking for? LZ

OK, you guys said the antenna concentrating the energy to a narrow direction. But how does the omni wifi antenna work? why it has a gain?

I connect my linksys 802.11g router to a TV antenna (like this one

by using a normal wire. The wire is just a very normal copper wire. The result is : i don't see the signal become stronger. I think i need a dish antenna. Any idea?

thanks from Peter

Your TV antenna isn't resonant at the right frequency, the impendence is mismatched, if you have an amplifier in the TV antenna line it may be filtering out the WiFi frequency and a whole lot of other possibilities. Bottom line is that your TV antenna isn't designed to work for WiFi.

Omni directional antennas can also have gain. A "5/8 wave length" vertical antenna has gain, but is not directional in the sense "concentrating energy in a narrow direction".

There are lots of books out there on antenna theory and antenna construction, but you probably don't want to go into the subject far enough to understand what does what and why. Many variables have to be considered such as wavelength, impedance, reactance, height above ground, and many others.

A simple WiFi antenna mounted on top of your RV may well do what you want to do.

Ron

snipped-for-privacy@hotmail.com hath wroth:

The garden hose nozzle analogy won't work for an omni. For that, I offer the rubber inner tube analogy. The antenna pattern for an omnidirectional antenna looks much like a donut (torus). A relatively low gain antenna, such as the 2dBi rubber ducky commonly found on wireless routers, looks like a "fat" donut. However, if you apply vertical pressure to the donut, the donut will become widers as it becomes flatter. What we've done is trade signal in the up and down direction, for gain in the horizontal. Push hard enough, and the donut becomes almost a flat pancake, with lots of horizontal gain, and almost no signal above or below horizontal.

Note that the volume of the donut (torus) remains the same no matter how flat you adjust the pattern. This volume is the transmit power which remains unchanged.

Give up while you're still sane. You need to deal with the basics. Most antennas are resonant or optimized for a specific frequency or frequency band. TV antennas are quite broadband but generally give up at the high end of the UHF band (about 900MHz). Above this frequency, they have no gain. Since the TV antenna is also off resonance, it will reflect most of the power back to your unspecified model Linksys router.

If you have some interest in building your own Wi-Fi antenna, there are a substantial number of construction articles available. For RV use, I suggest a biquad, or coffee can directional antenna. A dish is usually too big. Omni antennas tend to be a problem because by the time you get sufficient gain to be useful, the differences in vertical elevation between the RV and the access point will cause access point to be outside of the antenna pattern. RV parks also tend to be infested with trees, which block the signal. You'll need all the gain you can get to penetrate the foliage.

Because of the way the antenna is constructed. You would have elements contstructed in the antenna in such a way they add constructively to the signal, hence giving gain. This is a very high level over view. Do a google on Antenna design to get more detail.

While using a dish antenna does have higher gain than an omni, it also becomes more directional, hence you have to point the antenna towards the transmitting device.

"Dana" hath wroth:

Well, there's another problem. He's connecting it to a wireless router instead of a wireless client, or wireless ethernet bridge. Only a few wireless routers and access points have a "client mode" available, which can be used to connect to a remote hot spot. It would be interesting to know what he's trying to accomplish.

Perhaps it might be best to start over and supply the basics necessary to answer any technical question: 1. What are you trying to accomplish? 2. What do you have to work with? (hardware and software names and versions). 3. What have you done so far and what happened? (error messages, problems, complications).

Drivel: I modeled Radio Shack yagi and log periodic TV antennas to see how well it worked. On some channels, the yagi had more gain pointed backwards than forwards. On some channels, one could do better with a pair of rabbit ears. The log periodic is quite good for bandwidth, but has little gain (about 4dBi). Bigger also isn't better. However, building a functional antenna that works from 54 to

800MHz (4 octaves) bandwidth is not easy. I don't think I could do much better.

I see where "Ron Recer" contributed:

Excuse me for interrupting, but antenna gain figures are totally meaningless UNLESS they are given with respect to some known reference. For example, expressed as "dBd" (with respect to a dipole).

Will Sill The Curmudgeon of Sill Hill

Well this is what keeps people who know with work. I also do a lot of free consulting, and assistance, like replying to questions to newsgroups and boards.

I missed that the first time. I did not notice that he was trying to connect a tv antenna to his router. Then you are correct, it will not be of the proper impedance, frequency, etc.

dBi is the typical reference used for antenna and most on the newsgroup is aware of that.

"Dana" wrote

That may well be true, but the OP is a nitwit who cross posted the question to a "non-antenna" group, so many of the people reading your responses may not have your awareness of antenna related issues.

Bruce