Hello, I am trying to learn more about electronics and I am aware that with higher frequencies you have shorter wavelengths and can't travel as far as a lower frequency with a long wavelength ( like a radio tower).
and that the size of the radio tower and the frequency that it transmits is somehow equivalent to the physical length of the tower and its structure acting as an antenna, whether it be (full wavelength, half wavelength, or quarter).
What don't I understand is, how do cell phones transmit and receive power over long distances with such a small antenna?
Thanks
The antenna isnt the only factor that determines range.
Depending on the frequency being used, the terrain between the transmitter and the receiver has a far greater effect than the antenna.
how do cell phones transmit and receive power over long distances with such a small antenna?
Very high frequencies (= very small antennas) are used. For the 1.9 GHz band, a 1/4 wave antenna is about 4 cm long.
jremington:
Very high frequencies (= very small antennas) are used. For the 1.9 GHz band, a 1/4 wave antenna is about 4 cm long.
thanks for replies but i still don't understand how a high frequency can travel so far? Does anyone know how this is?
Radio waves are a form of light, and travel until absorbed by something.
Part of the trick, TJ, is lies in all of those "cell phone towers" that you see dotted all over the place. As long as you can actually "see" one of those towers, your cell phone is probably working fine. "Line of sight" prevents your high frequency cell phone signal from getting attenuated on its way too and from the tower.
As an extreme example of line of sight, one of the reasons we can talk to the Mars Rover with such low power is because we have line of sight with it from here on earth -- at least some of the time.
Even if you can't physically "see" a tower, you may still be able to exchange enough energy with it to get your message across in spite of the attenuation it will experience. All you need to do is exchange enough energy with a nearby tower so that the your "signal" can be separated from the ever present "noise" that pollutes the electromangnetic spectrum. Modern radio frequency technology has made huge strides in making communications possible despite very low "signal to noise" ratios. (Note too that there is less noise at higher frequencies too, and that helps!)
That's all over-simplified and you're bound to learn more about it as you go along. But I hope that helps a little.
Cell phones normally talk to base Stations , and base Stations have BIG hi gain antennas which allows for small antennas in the cell phones.
How well the system works then depends on the link budget which takes into account lots of variables, mainly the path loss which is terrain dependant.
Theres no need for large antennas in cell phones.
CurtCarpenter:
Part of the trick, TJ, is lies in all of those "cell phone towers" that you see dotted all over the place. As long as you can actually "see" one of those towers, your cell phone is probably working fine. "Line of sight" prevents your high frequency cell phone signal from getting attenuated on its way too and from the tower.As an extreme example of line of sight, one of the reasons we can talk to the Mars Rover with such low power is because we have line of sight with it from here on earth -- at least some of the time.
Even if you can't physically "see" a tower, you may still be able to exchange enough energy with it to get your message across in spite of the attenuation it will experience. All you need to do is exchange enough energy with a nearby tower so that the your "signal" can be separated from the ever present "noise" that pollutes the electromangnetic spectrum. Modern radio frequency technology has made huge strides in making communications possible despite very low "signal to noise" ratios. (Note too that there is less noise at higher frequencies too, and that helps!)
That's all over-simplified and you're bound to learn more about it as you go along. But I hope that helps a little.
Helped out alot. thanks for going out of your way to help me!
Google 'path loss' for an introduction to radio propagation - a complex subject.
Allan
The frequency of a signal does not in itself determin how far a signal will go, they can all go the same distance. However when you have a Radio transmitter on a spherical planet surrounded by an ionosphere things get a bit complex. At some frequencies radio signals will bounce of the ionosphere and go a lot further than they otherwise would. Sometimes there are multiple bounces between the ionosphere and the Earth.
The most efficient designs require the antenna length to be some fraction of the wavelength like a half or quarter, so long wavelength need big antennas, very high frequencies like used in cell phones need short ones.
If an object is smaller than the wavelength of a signal it will not block it. That is why longer wavelengths appear to go further.
The size of a tower has nothing to do with the antenna connected to a transmitter.
Note line of sight in this context doesn’t mean you can see it. It means to the horizon which is why antenna are normally put on towers. The term for when there is a direct line of site for a radio path is known as “optical”.
mauried:
Cell phones normally talk to base Stations , and base Stations have BIG hi gain antennas which allows for small antennas in the cell phones.
How well the system works then depends on the link budget which takes into account lots of variables, mainly the path loss which is terrain dependant.
Theres no need for large antennas in cell phones.
Things are getting more complicated. The 5G system specifies dynamically steerable antennas such that each mobile is individually addressed not only in frequency and code but by direction!
good fun.
Allan