Therefore, in order to solve the antenna problem, we modulate the information that we wish to send on a
carrier signal. The carrier signal is heavily regulated by the FCC (Federal Communications Commission)
and some are reserved for cell phones, some for police bands, hospital bands, radio amateur bands, etc.
For example, some police bands are at 70 and 144 MHz carrier frequency, while many cell phone bands
are at 850 MHz, 1900 MHz, 2100 MHz, etc. At 2000 MHz (2 GHz), the antenna dimension in air is about 3.5-7 cm, which is quite small. Also, a 1 MHz bandwidth signal which is placed on the 2 GHz carrier
occupies only 0.05% bandwidth and most antennas have 3-10% bandwidth (in general, a 2 GHz cell phone band is allowed a 60 MHz bandwidth so as to handle hundreds of different channels, each about
200 kHz to 1 MHz wide, and therefore, the antenna bandwidth needs to be 3.5%