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Microwave bands

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Microwave bands
Usual meaningAmateur bands above about 1 GHz; this article covers 2.3 GHz and up
Lowest band23 cm (1.24–1.3 GHz)
HighestAbove 275 GHz
US licenseTechnician and above, full privileges
Operating
Usual equipmentTransverter driven by an HF or VHF radio
AntennasDishes, horns and long Yagis
PropagationLine of sight, tropo, rain scatter, aircraft scatter, moonbounce
Geostationary satelliteQO-100: 2.4 GHz uplink, 10.489 GHz downlink
Sharing
StatusMostly secondary; a few small primary segments

The microwave bands are the amateur allocations above about 1 GHz, starting with the 23-centimeter band at 1.2 GHz and running through bands at 2.3, 3.4, 5.7, 10 and 24 GHz into the millimeter-wave bands and beyond 275 GHz.[1] This article concentrates on the bands from 2.3 GHz up; 23 cm, which has ready-made radios and repeaters, has its own article. The lowest microwave bands are formally part of UHF. In the US, Technician licensees and above have full privileges on these bands.[2] Almost all of this spectrum is shared, usually with amateurs as secondary users.

The bands

Each country decides what its amateurs may use within the ITU's international table, and the differences are largest on the lower bands. The US figures below are from Part 97;[2] see IARU regions for how the world is divided.

Band US frequencies Other regions and notes
13 cm 2300–2310 and 2390–2450 MHz Internationally 2300–2450 MHz, but national rules carve it up; the IARU Region 1 SSB center of activity is 2320.200 MHz[3]
9 cm 3300–3450 MHz, temporary secondary use only Being phased out in the US; IARU Region 1 plans 3400–3475 MHz, but some countries allow far less, such as the UK's 3400–3410 MHz[4][5][1]
5 cm 5650–5925 MHz 5650–5850 MHz in Regions 1 and 3[2]
3 cm 10.0–10.5 GHz Same in all regions; the RSGB calls it the most popular band above 23 cm[2][6]
1.2 cm 24.00–24.25 GHz 24.00–24.05 GHz is primary worldwide[7]
6 mm 47.0–47.2 GHz Primary worldwide[8]
4 mm 76–81 GHz 77.5–78 GHz is primary[8]
2.5 mm 122.25–123.0 GHz Secondary[8]
2 mm 134–141 GHz 134–136 GHz is primary[8]
1 mm 241–250 GHz 248–250 GHz is primary[8]
Above 275 GHz All frequencies above 275 GHz Not allocated in the ITU table; US amateurs may use it but must protect radio astronomy in listed segments, and UK amateurs need a special permit[8][9][1]

How microwave stations work

Main article: Transverter

A few commercial radios now cover the lower microwave bands, such as Icom's IC-905 with 2.4 and 5.6 GHz built in and 10 GHz through an add-on, but most microwave stations use a transverter, which converts a low-power signal from an HF or 2-meter radio up to the microwave band and converts received signals back down.[10] Feed line loss rises steeply with frequency, so the transverter, a power amplifier and a preamplifier are often mounted right at the antenna. At 10 GHz and above, many stations use waveguide, hollow metal pipe that carries microwaves with far less loss than coax.

Antennas are small but powerful. A dish about 2 feet (60 cm) across has a gain of more than 30 dBi at 10 GHz, with a beam only a few degrees wide, so two stations must aim carefully at each other. RF exposure precautions apply in front of a dish.

Frequency accuracy is the other challenge. A tiny oscillator error is multiplied many times at 10 GHz, so serious stations lock their oscillators to a GPS-disciplined 10 MHz reference. That lets narrowband SSB, CW and digital modes such as Q65 from WSJT-X work reliably. Wide segments carry amateur television and high-speed data on adapted commercial hardware. Networks of low-power beacons, transmitting continuously in each band's narrowband segment, help operators test equipment and spot openings.[5]

Propagation

Microwaves mainly travel by line of sight, so operators often head for hilltops. Several other mechanisms stretch the range:

  • Tropospheric ducting can trap microwave signals in layers of air and carry them hundreds of miles, especially over water.
  • Rain scatter. Both stations point at a heavy rain cell and bounce signals off it. It works best on 5.7 and 10 GHz, and signals have a rough, rasping sound.[11]
  • Aircraft scatter. Reflections from passing airliners briefly link stations beyond the horizon, though fast-changing Doppler shift makes it hard at 24 GHz.[1]
  • Moonbounce. Dishes make EME practical, and well-equipped stations use it on several of the microwave bands.[12][13]

Above about 20 GHz the atmosphere itself absorbs signals. Water vapor has an absorption line near 22 GHz,[14] so humid weather shortens range on 24 GHz, and the millimeter bands are affected even more.

Activities

  • Contests. The ARRL 10 GHz and Up Contest in North America and national societies' microwave contests elsewhere send operators to high ground.[15] Many work from several locations as rovers.
  • Distance records. Societies keep lists of record distances on each band, such as ARRL's list of claimed North American records.[16]
  • Mesh networks. In the US, AREDN reprograms commercial Wi-Fi hardware to run high-speed data networks on 2.4 and 5.8 GHz, and on 3.4 GHz while that band remains available.
  • QO-100. The first geostationary amateur satellite transponders, aboard the Es'hail-2 satellite at 25.9 degrees east, were launched in 2018.[17][18] Stations transmit near 2.4 GHz and receive near 10.489 GHz, often with a small dish and a satellite-TV downconverter.[19][6] The satellite covers Europe, Africa, the Middle East, much of Asia and the eastern edge of South America.[17] Published footprint charts leave out North America,[20] but on May 11, 2024, a visiting operator in Newfoundland, just outside the coverage area with the satellite slightly below the horizon, made the first contact from North America through QO-100 and then worked several more stations.[21]
Microwave contacts are usually arranged in advance. Agree on a frequency and antenna heading by phone, an online chat page or a 2-meter liaison frequency, then try the microwave band with both beams aimed.

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 The Microwave Bands, RSGB.
  2. ↑ 2.0 2.1 2.2 2.3 47 CFR 97.301, eCFR.
  3. ↑ IARU Region 1 UHF band plan, IARU Region 1, December 2020.
  4. ↑ 3 GHz Band, ARRL.
  5. ↑ 5.0 5.1 IARU Region 1 SHF band plan, IARU Region 1, December 2020.
  6. ↑ 6.0 6.1 5.7 and 10 GHz band plan, RSGB.
  7. ↑ Table of Frequency Allocations: SHF, ITU.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 Table of Frequency Allocations: EHF, ITU.
  9. ↑ 47 CFR 97.303, eCFR.
  10. ↑ IC-905, Icom America.
  11. ↑ Rain Scatter Propagation, RSGB.
  12. ↑ Band Plan, ARRL.
  13. ↑ 24, 47 and 76 GHz, RSGB.
  14. ↑ On the potential for reconstructing the moisture field using commercial microwave network data, N. David et al., arXiv.
  15. ↑ 10 GHz & Up, ARRL.
  16. ↑ Distance Records, ARRL, April 2026.
  17. ↑ 17.0 17.1 Es'hail 2 / QO-100, AMSAT-UK.
  18. ↑ Es'hail-2 / AMSAT Phase 4-A / Qatar-OSCAR 100, AMSAT-DL.
  19. ↑ QO-100 NB Transponder Frequency Ranges, AMSAT-DL.
  20. ↑ Making QO-100 contacts from North America – A new challenge, AMSAT-UK, November 2022.
  21. ↑ Newfoundland QO-100 Contact Successful – More Planned, AMSAT-UK, May 2024.
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