Editing Advanced Mobile Phone System (section)

==Frequency bands==
AMPS cellular service operated in the 850 [[MHz]] [[Cellular frequencies|Cellular]] band. For each market area, the United States [[Federal Communications Commission]] (FCC) allowed two licensees (networks) known as "A" and "B" carriers. Each carrier within a market used a specified "block" of frequencies consisting of 21 control channels and 395 voice channels. Originally, the B (wireline) side license was usually owned by the local phone company, and the A (non-wireline) license was given to wireless telephone providers.

At the inception of cellular in 1983, the FCC had granted each carrier within a market 333 channel pairs (666 channels total). By the late 1980s, the cellular industry's subscriber base had grown into the millions across America and it became necessary to add channels for additional capacity. In 1989, the FCC granted carriers an expansion from the previous 666 channels to the final 832 (416 pairs per carrier). The additional frequencies were from the band held in reserve for future (inevitable) expansion. These frequencies were immediately adjacent to the existing cellular band. These bands had previously been allocated to UHF TV channels 70–83.

Each duplex channel was composed of 2 [[frequency|frequencies]]. 416 of these were in the 824–849&nbsp;MHz range for transmissions from mobile stations to the base stations, paired with 416 frequencies in the 869–894&nbsp;MHz range for transmissions from base stations to the mobile stations. Each cell site used a different subset of these channels than its neighbors to avoid interference. This significantly reduced the number of channels available at each site in real-world systems. Each AMPS channel had a one way bandwidth of 30&nbsp;kHz, for a total of 60&nbsp;kHz for each duplex channel.

Laws were passed in the US which prohibited the FCC [[type acceptance]] and sale of any receiver which could tune the frequency ranges occupied by analog AMPS cellular services.{{why|date=August 2023}} Though the service is no longer offered, these laws remain in force (although they may no longer be enforced).<ref>{{cite web|url=http://www.arrl.org/forum/topics/view/112 |work=Forum-General discussion about technology and policy |title=Why are cellular bands blocked on receivers? |publisher=Arrl.org |access-date=September 28, 2013}}</ref><ref>47cfr15.121 http://edocket.access.gpo.gov/cfr_2010/octqtr/47cfr15.121.htm and http://wireless.fcc.gov/services/index.htm?job=service_home&id=cellular {{Webarchive|url=https://web.archive.org/web/20111026023132/http://wireless.fcc.gov/services/index.htm?job=service_home&id=cellular |date=October 26, 2011 }}</ref>