Electrically length

[thejim]

What do we mean by saying "electrical length" of an antenna?

 

[DecaturTxCowboy]

What do we mean by saying "electrical length" of an antenna?

Physical length based on the frequency.

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

Google is your friend.

 

[Phil Allison]

What do we mean by saying "electrical length" of an antenna?

** Depends on the CONTEXT - idiot !!






........ Phil

 

[Abstract Dissonance]

** Depends on the CONTEXT - idiot !!






....... Phil

I'm tired of your crap. Killfiled.

 

[Phil Allison]

"Abstract Dissonance"

I'm tired of your crap. Killfiled.

** Thank god.

Another ASD fucked, public menace bites the dust.





........ Phil

 

[Rich Webb]

I'm tired of your crap. Killfiled.

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

 

[Ralph Mowery]

What do we mean by saying "electrical length" of an antenna?

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.

 

[John Popelish]

What do we mean by saying "electrical length" of an antenna?

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.

 

[Hans Lohninger]

What do we mean by saying "electrical length" of an antenna?

Here's an explanation of short-wire antennas:

http://www.vias.org/basicradio/basic_radio_37_03.html

Regards,

Hans

 

[Chris]

What do we mean by saying "electrical length" of an antenna?

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:

http://en.wikipedia.org/wiki/Wavelength

Cheers
Chris

 

[Pooh Bear]

In free space a very thin 1/2 wavelength antenna will have a lenght equal to
492 devided by the frequency in MHz.

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

Graham

 

[Ralph Mowery]

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

Graham

Feet.

 

[tombiasi]

** Depends on the CONTEXT - idiot !!






....... Phil

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

 

[Tim Williams]

Why did you have to be rude

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

 

[Phil Allison]

"tombiasi"

Phil,

** Piss off - shithead.

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

** 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

 

[Phil Allison]

"Tim Williams"


** This trolling cretyn is human garbage.






......... Phil

 

[tombiasi]

"tombiasi"


** Piss off - shithead.




** 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

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

 

[Rikard Bosnjakovic]

** This trolling cretyn is human garbage.

It's cretin, you cretin.

 

[Phil Allison]

"Rikard Bosnjakovic"

It's cretin, you cretin.

** LOL.

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






......... Phil

 

[Jamie]

What do we mean by saying "electrical length" of an antenna?

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.