Landa

[dr.power]

Hi guys,

What is the magic behind the wavelength at landa/2 ?

For instance if my brain helps, 2 Antennas/Speakers or sources will add each other at a distance of landa/2 or something so.

Thanks.

 

[JimB]

The word you are looking for is LAMBDA not landa.

I suggest that you try drawing some sinewaves with varying phase shifts.
Add the two waveforms together.
When the phase shift is 180 degrees (half a wavelength) they will cancel out.

JimB

 

[DerStrom8]

post removed--JimB beat me to it

 

[dr.power]

Sorry Guys, Yes I ment LAMBDA.

 

[dr.power]

The word you are looking for is LAMBDA not landa.

I suggest that you try drawing some sinewaves with varying phase shifts.
Add the two waveforms together.
When the phase shift is 180 degrees (half a wavelength) they will cancel out.

JimB

I know that 2 waves having a 0 degree out of phase will add each other and 2 waves having a 180 degree out of phase will cancel each other, But How to translate this for 2 speakers haing a distance of say LAMBDA or LAMBDA/2 to each other?

 

[Nigel Goodwin]

I know that 2 waves having a 0 degree out of phase will add each other and 2 waves having a 180 degree out of phase will cancel each other, But How to translate this for 2 speakers haing a distance of say LAMBDA or LAMBDA/2 to each other?

It doesn't apply - speakers lamba/2 apart would be in different countries.

Audio and radio waves are COMPLETELY different things.

 

[dr.power]

It doesn't apply - speakers lamba/2 apart would be in different countries.

Audio and radio waves are COMPLETELY different things.

Thanks but I actually want to know the magic behind it.

 

[JimB]

Audio and radio waves are COMPLETELY different things.

True.

It doesn't apply - speakers lamba/2 apart would be in different countries.

Not True.
Don't forget that the velocity of sound is only 330metres/second, compared with radio waves at 300,000,000 metres per second.

A radio wave of frequency 1khz would have a wavelength of 300km

An acoustic wave of frequency 1khz would have a wavelength of 0.33meters.

Thanks but I actually want to know the magic behind it.

No magic, just simple maths!

Look here, just simple googling!
https://en.wikipedia.org/wiki/Interference_(wave_propagation)


JimB

 

[dr.power]

Thanks guys, but yet I have no idea why the LAMBDA/4 is a matter... Is that due too this fact that in lambda/4 the we reach to the Peak of the waves?
What about the relationship betwwen the Lambda and the distance in 2 or more sources?

Thanks

 

[dr.power]

Ok, so please just tell me why the length of an one-pole Antenna should be 1/4 of the signal wavelength so that the maximum power is sent?

 

[JimB]

Ok, so please just tell me why the length of an one-pole Antenna should be 1/4 of the signal wavelength so that the maximum power is sent?

There is a lot of scope for misunderstanding in that statement!

"One-pole antenna"
All antennas must have two poles, the second pole may not be obvious, but it will be there or else it would not work at all.
I assume you mean a single vertical wire or rod.
That single wire should be above a conductive ground plane for it to work correctly.
Many radios have just a single antenna and rely on the rest of the circuit of the radio to provide the ground plane. Not very efficient but it does work.

"1/4 of the signal wavelength so that the maximum power is sent"
Lots of possible variables here.
Depending on the length of the antenna as a number of wavelengths at the operating frequency, so the radiation pattern of the antenna varies, it puts more signal in one direction than another.
Also, as the length and configuration of the antenna varies, so does its feedpoint impedance.
A quarter wave monopole above a ground plane has a feed impedance of about 35 ohms.
A halfwave dipole has a feed impedance of about 72 ohms.
A folded dipole has a feed impedance of about 300 ohms.

The transmitter (a real transmitter, not the kiddie FM noise toys so often discussed here on ETO) will be designed to produce its rated output power into some defined load, usually 50 ohms.
If the transmitter is connected to a load other than what it was designed for, it will not produce its rated output power.
A matching network is used to transform the antenna feed impedance to that which the transmitter is expecting.

So going back to your question:

why the length of an one-pole Antenna should be 1/4 of the signal wavelength so that the maximum power is sent?

There is not a simple answer, and depending on the configuration of the various parts of the system, a quarter wavelength antenna may not be the one which transmits maximum power.

JimB

 

[cowboybob]

Ok, so please just tell me why the length of an one-pole Antenna should be 1/4 of the signal wavelength so that the maximum power is sent?

There is not a simple answer

Wave propagation theory and antenna design is a course unto itself.

I've included a site with a .pdf (Military. Sorry. But it's designed for entry level) that will take you through it all.

https://www.electro-tech-online.com/custompdfs/2012/02/4466.pdf

Read and weep.

 

[simonbramble]

You might want to Google Standing Wave Ratio.. This is a measure of transmitted power against reflected power and hence determines how much signal goes out of your antenna (hence transmits) against how much comes back (and heats up your transmitter stage)