Wave length and transmission line

[likephysics]

I think pretty much everybody knows the length of the transmission line should be less than the wave length of the RF signal.
How do you explain it to some one who is not from engineering background.

I myself can't get it some times.
Say for example the wavelength of a wave is

2" =
------------------

The conductor length is 1/10=0.1" (approximately the '-' below)

-

If you draw a sine wave of wavelength 2", the the voltage amplitude is different over the
0.1" line. It does vary by some amount and its definitely not flat. Maybe flat for 0.001".

So why is it ok if the conductor length is 1/10th of the wavelength even though the amplitude of the wave varies over the length of the conductor?

 

[berkeman]

I think pretty much everybody knows the length of the transmission line should be less than the wave length of the RF signal.
How do you explain it to some one who is not from engineering background.

I myself can't get it some times.
Say for example the wavelength of a wave is

2" =
------------------

The conductor length is 1/10=0.1" (approximately the '-' below)

-

If you draw a sine wave of wavelength 2", the the voltage amplitude is different over the
0.1" line. It does vary by some amount and its definitely not flat. Maybe flat for 0.001".

So why is it ok if the conductor length is 1/10th of the wavelength even though the amplitude of the wave varies over the length of the conductor?

No. Please google transmission line and termination...

 

[Pumblechook]

A transmission line can be and in many cases is many times longer than a wavelength.

The coaxial cable from you TV aerial might be 10 metres long and the wavelength is 50 cm. ... 20 wavelengths.

The cable from your satellite dish might be 10 metres with signals at 15 cm ... 67 wavelengths.

The voltage and current will be constant (apart from the fact that it is AC) along the line if the line is perfectly matched to the load.

 

[likephysics]

ah! Thanks.
In case of 60Hz AC, if the transmission line is longer than wavelength how do you terminate it. I mean what impedance.
So the goal is to stop or minimize reflection from the load?

 

[Corneo]

60 Hz is way too low in frequency for transmission line theory to come into effect. When RF people talk about transmission lines, they aren't talking about the big lines that deliver your AC power.

 

[dlgoff]

ah! Thanks.
In case of 60Hz AC, if the transmission line is longer than wavelength how do you terminate it. I mean what impedance.
So the goal is to stop or minimize reflection from the load?

High voltage power transmission lines (3 phase) have the conductors spaced to minimize lose. And at the substations, you'll find inductors and capacitors that do the impedance matching. If not, you would be transmitting power to the moon.