The band is also used by industrial, scientific, and medical (ISM) equipment, as well as low-powered unlicensed devices.
Amateur stations must accept harmful interference caused by ISM users[1] but may receive protection from unlicensed devices.
In 1985, the Federal Communications Commission allocated the frequency band between 902 and 928 MHz to Part 18 ISM (industrial, scientific, and medical) devices.
Part 15 devices, by law, must accept interference from any licensed radio service with which they share frequencies.
Motorola makes a line of walkie-talkies (the DTR family) which are FHSS digital units.
They are very similar to the DirectTalk-capable iDEN cellphones, even sharing some accessory items, but they can not interoperate with DirectTalk units.
Trisquare made a line of walkie-talkies (the eXtreme Radio Service family) that were also license free FHSS units, operating in the 900 MHz band.
Until recently, no amateur radio equipment manufacturer has ever made an FM repeater for the 33 centimeter band.
In 2012, the first two-way 900 MHz radio made specifically for the Amateur Service was introduced by Alinco.
The primary reason being that most amateur repeaters in this band are built from commercial equipment that has been modified to transmit and receive in the amateur 33 centimeter band and modification complexity increases rapidly as target frequencies are moved further from the original design frequencies.
Amateurs who use local repeaters on the 33 centimeter band use commercial handheld or mobile 900 MHz radios.
For instance, the Motorola model GTX (mobile and handheld versions) do not require any hardware modifications at all.
Signal propagation on the 33-centimeter band is very dependent on the transmitting and receiving antenna's line of sight.
Because of this, many wide-area coverage systems like repeaters are located on top of large hills and mountains which overlook a vast area.
[citation needed] The reader is advised to note that receiver front-end noise figure and antenna gain are the defining factors in line-of-sight signal propagation in the local area.
The 33 centimeter band offers excellent building penetration characteristics since the wavelength is relatively small and can fit through windows more easily than signals lower in frequency.