# Why do cell phones use 1800/1900 mhz?

S

#### sf1

Jan 1, 1970
0
when frequency is that large doesnt it mean shorter wavelength
power line can travel 10000km because of extremely low frequenc
doesnt it mean that cell phone signals travel very short distanc
then
i dont understand this at all please hel

J

#### John Popelish

Jan 1, 1970
0
sf1 said:
when frequency is that large doesnt it mean shorter wavelength?
power line can travel 10000km because of extremely low frequency
doesnt it mean that cell phone signals travel very short distance
then?

Long wavelength implies a long distance with little phase shift. When
you try to connect the same signal together at many points, like a
power grid, it gets really messy if the waves coming around through
the grid via different paths have different phases where they meet
again. This causes big circulating energy loops in the grid.

Cell phones do not use a grid of conductors, but make use of waves
traveling through space. So the phase is unimportant when the waves
reach a receiving antenna. All the various paths add together, and
some effective phase results. But any phase will do, since the
information being carried by those waves uses many cycles to carry
each bit of information.

L

#### Lord Garth

Jan 1, 1970
0
sf1 said:
when frequency is that large doesnt it mean shorter wavelength?
power line can travel 10000km because of extremely low frequency
doesnt it mean that cell phone signals travel very short distance
then?

Yes, high (not large) frequency means a short wavelength. Very high
frequencies are used to transmit data between the Earth and space probes
which are also many thousands of km distant.

Cell phones need to be compact and short range because they operate in
CELLS which are limited geographical areas. They are also low power
which helps extend battery life.

R

#### Rheilly Phoull

Jan 1, 1970
0
sf1 said:
when frequency is that large doesnt it mean shorter wavelength?
power line can travel 10000km because of extremely low frequency
doesnt it mean that cell phone signals travel very short distance
then?
Of course the cables used to transmit POWER have some bearing
Whereas the whole idea of the cordless phones is just that, no cables
trailing around behind you. The signal (very low POWER) is transmitted from
a RF transmitter, there is extremely little actual POWER transmitted to the
phones.

A

#### andy

Jan 1, 1970
0
when frequency is that large doesnt it mean shorter wavelength?
power line can travel 10000km because of extremely low frequency
doesnt it mean that cell phone signals travel very short distance
then?

One reason for using a high frequency is that high frequencies can carry
more data per second than low frequencies. (Over to you to think about why
this is). So a mobile phone mast can fit many 'virtual circuits' into
one frequency band, and talk to lots of phones at once.

D

#### DBLEXPOSURE

Jan 1, 1970
0
Rheilly Phoull said:
Of course the cables used to transmit POWER have some bearing
Whereas the whole idea of the cordless phones is just that, no cables
trailing around behind you. The signal (very low POWER) is transmitted
from a RF transmitter, there is extremely little actual POWER transmitted
to the phones.

Because that is the spectrum God gave them.

You are correct that higher frequencies require more power to propagate an
equal distance as say low band VHF. However, there is no room in those
bands for cellular phones. Also there is no need with cell phones to reach
out that far, (unless you live in South Dakota as I do) Also, Wavelength
has a bunch to do with the antenna size. You do not want a 6 foot whip
antenna on your cell phone or a large coil.

http://e-parts.netfirms.com

N

#### Nog

Jan 1, 1970
0
sf1 said:
when frequency is that large doesnt it mean shorter wavelength?
power line can travel 10000km because of extremely low frequency
doesnt it mean that cell phone signals travel very short distance
then?
http://www.jneuhaus.com/fccindex/spectrum.html
It's because the FCC said so. See ?

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