The Microwave Bands
There are currently eleven microwave bands available to the UK radio amateur in the microwave (and mm-wave) part of the radio spectrum plus access to segments of the terahertz region of the electromagnetic spectrum. To see the latest microwave band plans and any operating restrictions that may currently be in place including whether a Notice of Variation (NoV) is required, please look at the band plan section of the RSGB website.
Each band has a set of characteristics that can be exploited to support various operating modes and propagation modes. These are summarised below:
1.3GHz (23cm): 1240-1325MHz. Narrowband and beacons 1296-1298MHz
The 23cm band is the lowest frequency microwave band available to radio amateurs. Operating modes commonly used include CW, SSB, FM, digital modes and Amateur Television (ATV). There are also a number of repeaters dotted around the UK carrying either voice or ATV.
The main terrestrial DX propagation modes include tropospheric scatter and ducting as well as aircraft scatter. Earth-Moon-Earth (EME), communication by reflecting signals off the surface of the moon, is also popular on this band particularly using CW and digital modes. EME can allow microwave communication with most parts of the world.
2.3GHz (13cm): 2300-2302MHz under NoV, 2310-2350MHz and 2390-2450MHz. Narrowband and beacons 2320-2322MHz.
The main operating modes include CW, SSB and FM together with some digital and ATV. The 13cm band is used for up-linking voice and digital ATV signals to the geostationary satellite OSCAR-100. The band is also used for EME communication. Nowadays only a few repeaters licensed within the 13cm band.
Terrestrial propagation properties are similar to those of the 23cm band.
3.4GHz (9cm): 3400-3410MHz. Narrowband and beacons 3400-3402MHz
CW, SSB and ATV are the main modes in use in the 9cm band with a number of TV repeaters having outputs. There is also some EME operation on this band
Terrestrial propagation properties are similar to those of the 23cm band.
5.7GHz (6cm): 5650-5680, 5755-5765, 5820-5850MHz. Narrowband and beacons 5760-5762MHz.
CW, SSB and ATV are in use on the 6cm band.
Propagation modes include those on the lower frequency microwave bands with the addition of rain scatter. EME operation has shown a gradual increase in activity around the world on this band particularly during EME contests and activity periods.
10GHz (3cm): 10000-10125, 10225-10475MHz. Narrowband and beacons 10368-10370MHz
Modes in use include CW, SSB, FM, digital and ATV.
All the propagation modes in use at lower frequencies are found on the 3cm band. Rain scatter is particularly effective at this frequency. The down link of the OSCAR-100 geostationary is in the 3cm band carrying voice and digital ATV. In some respects EME operation becomes easier at higher frequencies. Successful contacts using small portable setups (dishes) can be relatively easy using digital modes.
24GHz (12mm): 24000-24050MHz. Narrowband and beacons 24048-24049MHz
24GHz is the first amateur band designated as being in the mm wave region of the electromagnetic spectrum. Under normal propagation conditions contacts can be made over paths with limited obstructions, perhaps between 50 and 100km. With enhanced tropospheric conditions paths of several hundred km are workable.
Most activity uses FM, SSB, CW and some digital modes. EME is possible but requires a high degree of skill and experience to put an effective system together and make contacts. Rain scatter is possible although there can be wide spreading of signals making it more difficult to read CW or SSB. Aircraft scatter is generally quite difficult due to high Doppler offsets which can vary quickly requiring continuous tuning to keep signals in the receiver’s pass band. There is some DATV activity particularly during TV contests.
47GHz (6mm): 47000-47200MHz. Narrowband and beacons 47088-47089MHz
With increasing frequency it becomes more difficult to generate power, only mW power levels are usually feasible for most amateur equipment designed for 47GHz and higher frequencies. This has an impact of the type of operation possible. On the 47GHz band operation is almost exclusively by portable stations situated on high spots with good takeoffs. Although contacts can sometimes be made over slightly obstructed paths, most are over line of sight paths. This tends to limit the range obtainable to a 100km or so in the UK. There is limited experience of enhanced propagation, one such mode is thought to be cloud scatter, although signals tend to be very weak and scattered. Tropospheric enhancements cannot be ruled but due to the sporadic nature of operating on this band evidence is required.
CW and FM are the main modes in use, due to the ease of generation of these modes using multiplier diodes to generate the required frequency. Transverter based systems do however do allow SSB and DATV to be used on the band.
76GHz (4mm): 75500-81000 Narrowband operation is around 75976.2MHz
Propagation on the 4mm band is thought to be exclusively over line of sight paths which can be more the 100km in the UK. It is the lowest frequency band where atmospheric absorption becomes a significant factor in whether a contact will be successful or not. Absolute humidity is the key factor; when it is high longer paths are not workable. The ideal operating time would be a cold, low humidity winters’ day.
CW and FM are the main modes in use with some SSB and even contacts using DATV.
122GHz (2mm): 122250-12300 Main UK frequency in use is 122400MHz.
Until 2020 there were only a handful of amateurs with equipment for 122GHz with contacts over short distances being achieved (10-20km). However this has changed dramatically following an article published by Australian amateurs in the Dubus magazine and the availability of ready built systems that have adapted a 122GHz low power radar integrated circuit device. Of the several hundred systems manufactured for amateur use worldwide, a significant number have been purchased by UK amateurs. This should see a large increase in 122GHz operation going forward. CW and FM are possible using these systems.
Like 76GHz, 122GHz is affected by atmospheric attenuation, both by water vapour and by oxygen. Path lengths of several tens of km should be workable in the UK using the 122GHz radar device based systems. Again low absolute humidity conditions are key to making longer range contacts.
134GHz, 241GHz and >275GHz
The top two bands and access to the terahertz region pose a real but achievable challenge to the radio amateur. Nevertheless equipment has been built and contacts have been made in the UK over distance of tens of km at 134GHz and somewhat shorter distances on higher frequencies. Access to even higher frequencies above 275 GHz are available by an Ofcom NoV that can be easily applied for online.
