1-Why the antenna of the radio of cars is located outside the car and not inside?
2-If the answer to 1 is because that cars are like Faraday cages then how come my cell phone can receive signal inside the car?
3-To receive a strong tv/radio signal the antenna must be oriented in a specific way. Why the strength of the cellphone signal seems independent of the orientation of the cellphone?
4-It seems to me that the length of the antennas of cell phones or that of a tv or radio is of the same order as the corresponding wavelength used, why is that?
Best Answer
(I'm not exactly sure of this, comments greatly appreciated)
Radio waves have a longer wavelength (3-4 m) than cell phone waves(fractions of a meter). Thus these are easy to block. They can travel around buildings &c, but can't enter cars because the windows are tiny. Cell phone waves are small enough to enter the windows of a car.
Radio waves have large antennae due to their wavelength. So reorienting them makes a difference as the effective size of the antenna facing the wave changes drastically. A cellphone jas a tiny antenna. Reorienting it makes little difference. Imagine making the antenna shorter and shorter till it becomes a ball. Reorienting that makes no difference at all. And a cellphone does change quality on rotation, but its less evident. There may be some smoothing circuitry involved.
Edit: Antennae need to be with the same order of magnitude as the radiation as they need to resonate. See http://enwp.org/Antenna_(radio)#Resonant_antennas . A short antenna cannot effectively acheive resonant frequency of a long wave.