My understanding is that an antenna is just a metal conductor where the length is proportional to its intended frequency used in communication. So why is that some antennas used for wireless transmission is very costly and looks complicated as well. Can I get the same functionality with just a piece of wire of the same length?

 

Simple antennas (dipole) send energy more or less equally in all directions. More complicated antennas "focus" the energy so more of it goes in a "useful" direction, and less goes where you dont need it...

Analogy : a reflector close to a lamp...

 

To express my doubt more clearly, lets consider a monopole DVB-T TV antenna. One antenna is claimed to have 20dbi and the other 5dbi. The price differs by about 5 times. My doubts is, if both antennas are monopole, how come the quality and cost vary significantly?

 

tv antennas look that way to impress customers into buying them. they always have, from the expensive "color " tv antennas and now the dtv antennas, even a piece of wire will replace most of them.

 

It gets worse. If you read antenna reviews (talking about TV antennas), the more thorough the review is, the more likely it will come to the conclusion that "it depends". Some antennas will be clearly superior in one setting, but lose out to another in a different setting. I have never seen an objective test using testable parameters. Very frustrating in this day and age. It reminds me of the nonsense that goes on with speaker wires.

 

Another reason that a TV antenna looks complicated is that it has to function over a very wide frequency range. Channel 4 is about 54 MHz and channel 13 is about 210 MHz. This is quite a wide frequency range.

 

Ummm. The VHF channels 2-13 are now defunct in the continental US since the switch from analog to digital in 2009(?)
Such an antenna would serve no useful purpose.

 

then a uhf antenna has to work over a much wider range of frequencies than a vhf one. and being shorfter wavelengths, would need even more elements.

 

...would need even more elements.

Could you please elaborate this further?

 

One more thing, How does the antenna gain (dbi value) vary from 20dbi to 5 dbi for a monopole TV antenna?

Since a monopole antenna will have the same strength in all directions, a monopole antenna meant for a given frequency should have similar antenna gain, shouldn't it? This antenna gain variation is seen for even a 2.4Ghz wireless transceiver module antenna.

 

Shorter wavelength do not necessarily require more elements, but a wider bandwidth certainly does.

The "i" in dBi refers to an isotropic radiator. The radiation patter is identical for all values of azimuth. There is also an elevation angle at which the radiation is a maximum, and a null along the axis of the conductor, and another null perpendicular to the axis of the conductor. This assumes the feedpoint is at one end of the conductor and that the orientation is vertical. Also the concept of a monople is erroneous. To work properly there must be a conductor perpendicular to the conductor. This is usually accomplished with ground radial or a conductive metal plate such as the roof of a vehicle.

One way of constructing an isotropic radiator is to cut a conductor that is one-quarter wavelength. Another way is to make it 5/8 of a wave length and so forth. So comparisons depend on the selection of the "isotropic" radiator. Of course marketing people love to play these kinds of games where they quote a measurement without telling what the comparison is related to.

 

Ummm. The VHF channels 2-13 are now defunct in the continental US since the switch from analog to digital in 2009(?)
Such an antenna would serve no useful purpose.

If that were true it would make OTA TV life in the boonies much easier.
http://www.oregon150.org/tv-radio/index-tv.php

 

" lets consider a monopole DVB-T TV antenna"

To me, that is a short vertical wire.

What does your antenna look like?

 

Hello,

There are many types and shapes of antennas.
Have a look at this radio amateur site with a lot of links for antennas:
http://ac6v.com/antprojects.htm

Bertus

 

Why do antennas look so complicated?

1. Frequency coverage
2. Directionality

 

If you read carefully you will find that numbers in the range 2-13 don't actually refer to the former VHF channels in the ranges 54-88 MHz and 174-216 MHz. The new digital channels were carved out of the former UHF space. The former VHF space is now white space and has or will be auctioned off at some point for other services.

 

the reason uhf antennas need more elements is that path loss is greater at uhf than vhf and the in the rating of antennas for microvolt/meter, uhf antennas are shorter, less micorvolts per meter. remember the digital tv mantra, "you wont loose any range, but you might need a longer antenna."

 

If you read carefully you will find that numbers in the range 2-13 don't actually refer to the former VHF channels in the ranges 54-88 MHz and 174-216 MHz. The new digital channels were carved out of the former UHF space. The former VHF space is now white space and has or will be auctioned off at some point for other services.

VHF DTV is a reality for those away from large citys. If you see my link chart they have the VC (digital virtual channel) and the RF allocation channel. I don't know where the idea that VHF is gone came from but it's wrong. Some of the upper UHF TV space was reallocated but the RF allocation for VHF DTV remains the same as always.

http://en.wikipedia.org/wiki/Televi....2C_South_Korea.2C_Taiwan_and_the_Philippines

http://www.fcc.gov/guides/antennas-and-digital-television

 

Where I live (northern Illinois), I can see about 10 transmitters, and just one of them is VHF on channel 13. It's much lower power than the UHF channels but it comes in well with just my UHF antenna.

Handy tool for finding transmitters here.