history of public safety radio in usa

perhaps we have written this up before - lets do it again

history of public safety radio in usa

starting around 1910 or 1920 - shortwave radios were used - channels
near 1 Mhz perhaps - maybe all AM radios

1930 - maybe newer channels began to be used at 35 mhz with fm radios
- cities and towns each had 1 channel - mostly for police - counties
might have 1 channel also (for larger sheriff depts) - state police
maybe had short wave radios and 35 mhz radios

1940 perhaps - 150 mhz radios used - first in big cities - police and
fire started to get different channels from each other

1950s - police and fire had their own channels - countywide channels
at 33 mhz and 46 mhz and 154 mhz for fire - countywide police channels
at 37 mhz and 39 mhz and 45 mhz and 154 mhz for police - larger cities
and towns and villages had their own radio channels - and they were
often on different bands than the surrounding suburban or rural
agencies - FDs had home alert radios and tone activated sirens

1960s - the first handheld portable radios started to come into use -
rechargeable nicad batteries were used to replace alkaline batteries -
UHF radio appeared (453 mhz and 460 mhz) - more radios had PL -
microwave started to be used to link transmit sites - smaller pagers
were able to be carried on hip belts - UHF channels were usually
repeaterized

1980s - first 800 mhz radios went into use and first trunked radios
systems went on the air - trunked radios were used in major cities and
some larger counties

1990s - first P25 digital radios appeared - more units were equipped
with mobile date terminals

2000s - synchronized simulcast became more prevalent for base stations
- internet began to be used to link radio sites

2020s - 700 mhz trs becoming more common - FirstNet is trying to get
started using cellular radio bands

who can make corrections to this?