33-centimeter band
| 33-centimeter band | |
|---|---|
| Frequency range | 902–928 MHz (ITU Region 2 only) |
| Wavelength | About 33 cm |
| Group | UHF |
| US license | Technician and above, full privileges |
| Operating | |
| Common modes | FM, SSB, CW, digital voice, data, amateur television |
| Common repeater split | 25 MHz (outputs near 927 MHz, inputs near 902 MHz); varies by region |
| Weak-signal calling frequency | 902.100 or 903.100 MHz, depending on region |
| Quarter-wave whip length | About 3.2 inches (8 cm) |
| Sharing | |
| Status | Secondary; shared with government radar, ISM equipment, location services and unlicensed devices |
The 33-centimeter band is the amateur allocation from 902 to 928 MHz, often called "902" or simply "900 MHz". It is a UHF band found only in ITU Region 2, the Americas, and in the US it is open in full to Technician licensees. At 26 MHz it is wide, but amateurs are far from alone on it. The same frequencies carry government radar, vehicle-location and toll-tag systems, industrial, scientific and medical (ISM) equipment, and a flood of unlicensed devices, from smart utility meters and wireless sensors to LoRa radios, so the band is at once roomy for hams and noisy. Its amateur users are a small community of repeater builders, weak-signal operators and experimenters, many of them using converted commercial radios.
Sharing the band
Amateurs are secondary users of 33 centimeters. The primary users are government radiolocation (radar) systems and the Location and Monitoring Service, which covers systems such as vehicle tracking and electronic toll collection. Amateur stations must not interfere with them and must accept interference from them. The band is also designated internationally for ISM equipment, devices that use radio energy for purposes other than communication, such as industrial heating, and amateurs have to accept whatever interference that equipment produces.
Unlicensed devices operating under Part 15 of the FCC rules, such as cordless phones, baby monitors, utility meter networks and wireless sensors, rank below the amateur service: they may not cause harmful interference to licensed users and must accept any they receive. In practice there are so many of them that much of the band carries a steady background of short bursts and hopping signals, which varies a great deal from place to place.
In addition, Part 97 bars amateurs from transmitting on all or part of 33 centimeters from certain areas, including parts of Colorado and Wyoming and an area of Texas and New Mexico. Operators in those states should check the rules before setting up.
What you'll find on the band
The ARRL band plan for 33 centimeters is adapted heavily by regional coordinators, but a few patterns are common.
- Weak-signal SSB and CW gather near the bottom of the band, around a calling frequency of 902.100 or 903.100 MHz, depending on the region. Horizontally polarized Yagis and loop Yagis are the usual antennas, and tropospheric ducting occasionally carries signals hundreds of miles.
- FM repeaters are found in many metropolitan areas. In much of the country they transmit near 927 MHz and listen 25 MHz lower, near 902 MHz, though some regions use other pairings, so check with the local frequency coordinator. Some repeaters carry digital voice such as DMR.
- Data and experiments. The band's width makes room for high-speed data links, amateur television and experimentation. Some hams run LoRa-based mesh messaging under their amateur license instead of under Part 15; amateur rules allow more power but forbid encryption and require station identification.
Because few people use the band, a repeater or simplex frequency here often has room for long, uninterrupted conversations.
Equipment
Ready-made amateur radios for 33 centimeters are scarce; only a handful of handhelds and mobiles have ever been built for it. Most FM operators instead use surplus commercial land mobile radios designed for nearby 900 MHz business channels, which can often be reprogrammed to cover the amateur band. Weak-signal stations typically use a transverter, which converts a signal from another band, such as 2 meters or 10 meters, to 902 MHz and back.
Antennas are small: a quarter-wave whip is about 3.2 inches long. Losses in coaxial cable are high at this frequency, so low-loss cable or hardline and type N connectors are worth the cost, and the shortest practical cable run pays off.