Electrically length

Physical length based on the frequency.

Roughly speaking, a quarter wave antenna is: VHF - 18" UHF - 6" CB - 108"

Google is your friend.

** Depends on the CONTEXT - idiot !!

....... Phil

I'm tired of your crap. Killfiled.

"Abstract Dissonance"

** Thank god.

Another ASD f***ed, public menace bites the dust.

....... Phil

I suspect that most regular readers have killfiled Phil. See: Noise, signal to, ratio of.

--
Rich Webb   Norfolk, VA

In free space a very thin 1/2 wavelength antenna will have a lenght equal to

492 devided by the frequency in MHz. In practical applications this length will be somewhat shorter depending on several factors such as the diameter of the conductor,if it is insulated, and what it is near. For frequencies up to about 30 MHz the electrical length will be around 468 devided by the frequency in MHz.

The same applies to the feedline. If you see something like velocity factor of .66 or .8. This is the number you multiply the 492 by to get the electrical length of 1/2 wavelength of the feed line.

It usually means the length as measured in units of wavelength at a particular frequency and at the propagation speed of light in that medium.

For instance, a quarter wavelength long whip (one who's electrical length is 1/4 wave) is a vertical antenna that is a quarter of a wavelength long at one operating frequency, and at the slightly less than free space speed of light for RF energy traveling attached to that diameter conductor. This also has lots of uses when you are using specific length of transmission line to perform impedance matching functions, since all the calculations of what length is needed for a particular effect are calculated in electrical length or specific number of waves or fraction of waves that are stored in that length (based on the speed of propagation along the line, and the operating frequency), not the external physical length. But to cut the cable you have to convert electrical length to physical length. This is why every transmission line specification includes propagation speed relative to free space.

Here's an explanation of short-wire antennas:

Regards,

Hans

The other posts happened not to mention the most basic newbie fact: wavelength is inversely proportional to frequency. For electromagnetic radiation,

l(wavelength in meters) = c(speed of light, about 3 * 10^8 meters/sec) / f (frequency)

For air or other non-vacuum mediums, you have to tweak a bit. It's explained here:

Cheers Chris

492 what ? Feet, inches, yards, furlongs, metres, cm, mm ?

Graham

equal to

Feet.

Phil, Why did you have to be rude to the guy for asking a basic question on a basic group? Tom

Because he's Phil, duh.

Best solution would be to stick "killfile P.A." in the FAQ's to all the NG's he frequents... not to mention encourage voluminous abuse reports to his ISP.

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

"tombiasi"

** Piss off - s*****ad.

** So you have no appreciation of the importance of CONTEXT either ?

Read the OP's asinine question more carefully.

HE **removed** a technical phrase from its context so that it no longer had a meaning.

THEN the wanker asked this NG to explain it to him.

Only a congenital, idiot does that.

You must be one as well.

........ Phil

"Tim Williams"

** This trolling cretyn is human garbage.

........ Phil

Thank you Phil, I now have a better understanding of the situation. Tom

It's cretin, you cretin.

-- Sincerely, |

Rikard Bosnjakovic | Code chef - will cook for food

------------------------------------------------------------------------

"Rikard Bosnjakovic"

** LOL.

Says some wanker who's name looks like a demented monkey was loose at the keyboard !

........ Phil

i'll give it a shot. in free space the wave is traveling in space of wavelength = 300/ ?? Mhz which basically means the distance the wave will travel in 1 full cycle.. now here is the real kicker, the energy being emitted from the radiator does no leave its end point in a perfect line. picture in you mind an omnidirectional antenna. " that would be a vertical with ground mass on it" the energy leaves the elements at an angle and if you were to map the actual point of where it completes a full cycle at this angle it would be shorter than the vertical element if you were to use a free space vertical element length. the larger diameter of elements will cause this effect to be increased thus making your electrical length shorter. then you have the velocity factor which is used to help reduce the wave length constant used in the math. normally the smaller mass elements has lower velocity and closer to free space size.. if you were to look at a dipole and see the graph chart you will see how the electrical length is being effected. that is the closes i can explain it with out getting into a pile of mess . just think of Trig, that mite give you some insight.

--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5