33 centimeters
Encyclopedia
The 33-centimeter or 900 MHz band is a portion of the UHF radio spectrum internationally allocated to amateur radio
on a secondary basis. It ranges from 902 to 928 MHz and is unique to ITU Region 2
. It is primarily used for very local communications as opposed to bands lower in frequency
. However, very high antennas with high gain have shown 33 centimeters can provide good long range communications almost equal to systems on lower frequencies such as the 70 centimeter
band. 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 but may receive protection from unlicensed devices.
In ITU Region 3, New Zealand
domestically allocates 921 MHz to 928 MHz to amateurs.
allocated the frequency band between 902 and 928 MHz to ISM
(Industrial, Scientific, and Medical) devices. In that proceeding, the band was also allocated to the Amateur Radio Service on a secondary basis meaning amateurs could use the band as long as they accepted interference
from and did not cause interference to primary users.
service with which they share frequencies.
or with Nextel, DirectTalk, uses the 900 ISM band. It uses FHSS
and employs 10 "channels" and 15 "privacy codes". This is available as a feature on several of the walkie-talkie phones, for "off network" simplex communications.
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 it has not been confirmed that they can interoperate with DirectTalk units.
Trisquare makes a line of walkie-talkies (the eXtreme Radio Service
family) that are also license free FHSS units, operating in the 900 MHz band. They are similar to DirectTalk but not compatible.
is arguably the most popular activity on the 33 centimeter band with some manufacturers actually producing ATV equipment for the band. The first repeater to use the new band, the NU6X/R (Amateur TV Network) on 923.25 MHz, was activated and used at the minute the FCC allowed amateur use of the band and featured in QST Magazine. The repeater moved to 919.25 MHz and call changed to W6ATN because AVM part 90 service at 927 MHz began operation as a primary user of the band.
s to operate CW
and SSB on the lower end of the band, either just above 903 MHz or just above 902 MHz. SSB/CW operations usually use horizontal polarization for most contacts. VHF/UHF contests are conducted by the ARRL several times each year to encourage operations across all ham bands. Contacts must be made in the simplex mode - that is, without using a repeater. Any mode (FM, SSB, CW) and be used. Contact scoring is higher for 33 cm than the lower bands (6m through 70 cm).
repeater for the 33 centimeter band. Amateurs who wish to build a repeater
and those who wish to use that repeater must do so using modified commercial equipment designed for use in the mid-800 MHz and mid-900 MHz range. The bulk of modified commercial equipment is manufactured by two companies, Motorola and Kenwood.
With the explosion in popularity of Nextel phones with a push to talk
feature, the marketplace has seen a flood of newer 800 and 900 MHz commercial mobile radios that are designed to the following specifications:
The receivers on many of these modern 800 MHz radios can be easily modified to receive higher than 870 MHz, to about 904 MHz with good sensitivity
. In addition, the transmitters on many of the aforementioned 900 MHz radios can be easily modified to transmit lower than 935 MHz, to about 926 MHz with acceptable power output. With this in mind, many amateurs have opted to set up repeaters with -25 MHz splits using modified 800 MHz radios as receivers and modified 900 MHz radios as transmitters.
A number of resources are available for amateurs to build repeaters that can be used on the 33 cm band. Some of those resources are:
http://www.repeater-builder.com/motorola/msf/msf-index.html - for use with conversion of the Motorola MSF5000 and PURC stations;
http://www.repeater-builder.com/motorola/nucleus/nuc-article.html - for use with adding analog modulation to the Motorola Nucleus paging station;
http://www.repeater-builder.com/motorola/gtx/gtx-index.html - for use with conversion of the Motorola GTX-series radio;
http://www.repeater-builder.com/maxtrac/maxtrac-900mhz-vco.html and
http://www.repeater-builder.com/maxtrac/maxtrac-900-t2c.html - for use with conversion of the Motorola MaxTrac radio.
Resources are also available via several e-mail discussion groups (such as the Yahoo Groups: "AR902MHz" and "900mhz") where information regarding conversion of other brands commonly used (such as Kenwood, EF Johnson, and GE/Ericsson) can be found/discussed.
The advent of issues involving interference to the PAVE PAWS
RADAR systems located on the East and West coasts of the United States has pushed many amateur repeater operators to vacate the 70 cm band in favor of 33 cm, and proliferation of 33 cm repeaters has understandably increased exponentially in the past few years.
. Because of this, many wide-area coverage systems like repeaters are located on top of large hills and mountains which overlook a vast area. This ensures that the transmitting antenna is higher than terrestrial obstructions such as trees and buildings. Assuming that the transmitting antenna's
wavelength
, height above average terrain
, and effective radiated power
is equal, a transmitted signal on 33 centimeters will, generally speaking, usually travel about 3/4 of the distance that the same signal would if transmitted on the 70 centimeter
band. 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 easier than signals lower in frequency.
In many areas, the 33 centimeter band also has a very low noise floor
as compared to bands lower in frequency.
Amateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
on a secondary basis. It ranges from 902 to 928 MHz and is unique to ITU Region 2
ITU region
The International Telecommunication Union , in its International Radio Regulations, divides the world into three ITU regions for the purposes of managing the global radio spectrum...
. It is primarily used for very local communications as opposed to bands lower in frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
. However, very high antennas with high gain have shown 33 centimeters can provide good long range communications almost equal to systems on lower frequencies such as the 70 centimeter
70 centimeters
The 70-centimeter amateur radio band is a portion of the UHF radio spectrum. This band is used by amateurs engaged in emergency communications where portable and mobile radios are frequently used. Many such radios have dual-band capabilities, operating on both the 70-centimeter and 2-meter bands.-...
band. The band is also used by industrial, scientific, and medical
ISM band
The industrial, scientific and medical radio bands are radio bands reserved internationally for the use of radio frequency energy for industrial, scientific and medical purposes other than communications....
(ISM) equipment, as well as low powered unlicensed devices. Amateur stations must accept harmful interference caused by ISM users but may receive protection from unlicensed devices.
In ITU Region 3, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
domestically allocates 921 MHz to 928 MHz to amateurs.
History
The 33 centimeter band has a somewhat short history, being one of the newest amateur radio bands.The beginning
In 1985, the Federal Communications CommissionFederal Communications Commission
The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...
allocated the frequency band between 902 and 928 MHz to ISM
ISM band
The industrial, scientific and medical radio bands are radio bands reserved internationally for the use of radio frequency energy for industrial, scientific and medical purposes other than communications....
(Industrial, Scientific, and Medical) devices. In that proceeding, the band was also allocated to the Amateur Radio Service on a secondary basis meaning amateurs could use the band as long as they accepted interference
Co-channel interference
Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency. There can be several causes of co-channel radio interference; four examples are listed here....
from and did not cause interference to primary users.
900 MHz cordless phones
In the mid 1990s, many cordless phone manufacturers started producing phones that used the lower and upper ends of the 33 centimeter band for communication between the handset and base. These phones, which are regulated by Part 15 of the FCC's regulations, have made amateur use of the upper and lower end of the 33 centimeter band somewhat tricky due to the amount of these phones being used by the general population. Part 15 devices, by law, must accept interference from any licensed radioRadio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
service with which they share frequencies.
900 MHz wireless networking
In the early 1990s, wireless computer networking was just becoming affordable. Several competing technologies emerged that made use of the 902-928 MHz ISM band, such as:- NCR/AT&T/DEC/Lucent WaveLANWaveLANWaveLAN is a brand that describes two completely different families of wireless network solutions:* Pre-IEEE 802.11 WaveLAN, also called Classic WaveLAN* IEEE 802.11-compliant WaveLAN, also known as WaveLAN IEEE or ORiNOCO-History:...
. 915 MHz, 250 mW transmit power. Obsolete, but still in use in certain areas. - AironetAironet Wireless CommunicationsAironet is a maker of wireless networking equipment currently operated as a division of Cisco Systems. It was started by ex-Marconi Wireless employees in 1986 as Telesystems SLW in Canada, right after the United States Federal Communications Commission opened up the ISM bands for spread spectrum...
(now Cisco) ARLAN. 902-928 MHz with 12 channels, 450 mW transmit power. Obsolete, but still in use in certain areas. - AlvarionAlvarionAlvarion Ltd. , is a 4G communications company. The company manufactures and exports a range of network solutions, including WiMAX, IEEE, PtMP, TD-LTE and WiFi to service providers and enterprises covering a variety of industries such as mobile broadband, residential and business broadband,...
BreezeACCESS 900. 902-928 MHz, 200 mW transmit power. Still being sold and in use in certain areas as of 2008. - A now defunct commercial user of 900 MHz wireless networking was RicochetRicochet (internet service)Ricochet was one of the pioneering wireless Internet services in the United States, before Wi-Fi, 3G, and other broadband technologies were available to the general public. It was developed and first offered by Metricom Incorporated, which shut down in 2001.-History:Metricom was founded in 1985,...
. They used 900 MHz for the "last mile" connection to the user in an early wide area mobile wireless network. - Motorola Canopy is also used by WISPs depending on the Line-of-sight propagationLine-of-sight propagationLine-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
- XG Technology, Inc. xMaxXMaxxMax developed by xG Technology, Inc. is a cognitive radio based mobile VoIP and data system operating in the license-free ISM 900MHz band . xMax is built upon an end-to-end Internet Protocol system infrastructure that includes a line of base stations, mobile switching centers , handsets, and...
. 902-928 Mhz. Less than 1 W. A cognitive radioCognitive radioA cognitive radio is a kind of two-way radio that automatically changes its transmission or reception parameters, in a way where the entire wireless communication network -- of which it is a node -- communicates efficiently, while avoiding interference with licensed or licensed exempt users...
system still being sold and in use as of 2011.
Walkie talkies
MotoTalkMOTO Talk
MOTO Talk is a feature on some Motorola iDEN cellular phone handsets which allows users to make short-range 'push-to-talk' calls to other such handsets without being on the iDEN network. This feature goes by different names on iDEN service providers. In the US, Nextel calls it 'DirectTalk' and...
or with Nextel, DirectTalk, uses the 900 ISM band. It uses FHSS
Frequency-hopping spread spectrum
Frequency-hopping spread spectrum is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver...
and employs 10 "channels" and 15 "privacy codes". This is available as a feature on several of the walkie-talkie phones, for "off network" simplex communications.
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 it has not been confirmed that they can interoperate with DirectTalk units.
Trisquare makes a line of walkie-talkies (the eXtreme Radio Service
EXtreme Radio Service
eXtreme Radio Service is a proprietary personal communication technology marketed by in the United States. The radios, which are similar to other walkie-talkies, use the 900 MHz band, and employ frequency-hopping spread spectrum technology to attempt to address some of the perceived shortcomings...
family) that are also license free FHSS units, operating in the 900 MHz band. They are similar to DirectTalk but not compatible.
Amateur radio use of the 33 centimeter band today
Today, the 33 centimeter band is rapidly becoming popular with many UHF enthusiasts. Currently, it is used by amateurs for a variety of purposes.- The Radio Regulations of the International Telecommunication Union allow amateur radio operations in the frequency range from 902.0 to 928.0 MHz.
Amateur television
Amateur televisionAmateur television
Amateur television is the transmission of Broadcast quality video and audio over the wide range of frequencies of allocated for Radio amateur use. ATV is used for non-commercial experimentation, pleasure and public service events...
is arguably the most popular activity on the 33 centimeter band with some manufacturers actually producing ATV equipment for the band. The first repeater to use the new band, the NU6X/R (Amateur TV Network) on 923.25 MHz, was activated and used at the minute the FCC allowed amateur use of the band and featured in QST Magazine. The repeater moved to 919.25 MHz and call changed to W6ATN because AVM part 90 service at 927 MHz began operation as a primary user of the band.
CW and single sideband
Amateurs who are involved in contesting use home-made or commercially available transverterTransverter
A transverter is a radio frequency device that consists of an upconverter and a downconverter in one unit. Transverters are used in conjunction with transceivers to change the range of frequencies over which the transceiver can communicate....
s to operate CW
Continuous wave
A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...
and SSB on the lower end of the band, either just above 903 MHz or just above 902 MHz. SSB/CW operations usually use horizontal polarization for most contacts. VHF/UHF contests are conducted by the ARRL several times each year to encourage operations across all ham bands. Contacts must be made in the simplex mode - that is, without using a repeater. Any mode (FM, SSB, CW) and be used. Contact scoring is higher for 33 cm than the lower bands (6m through 70 cm).
FM repeaters
No amateur radio equipment manufacturer has ever made an FMFrequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
repeater for the 33 centimeter band. Amateurs who wish to build a repeater
Repeater
A repeater is an electronic device that receives asignal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.-Description:...
and those who wish to use that repeater must do so using modified commercial equipment designed for use in the mid-800 MHz and mid-900 MHz range. The bulk of modified commercial equipment is manufactured by two companies, Motorola and Kenwood.
Building repeaters
For many years, repeaters on the 33 centimeter band used a split of -12 MHz with inputs between 906 and 909 MHz and outputs between 918 and 921 MHz. Today, many new repeaters are using a split of -25 MHz with inputs between 902 and 903 MHz and outputs between 927 and 928 MHz. The reason behind this is that the selection of equipment that can be modified for a -12 MHz split is mainly limited to commercial repeaters and data radios which tend to be older, more expensive, harder to maintain, harder to find parts for, and very time consuming to modify.With the explosion in popularity of Nextel phones with a push to talk
Push to talk
Push-to-talk , also known as Press-to-Transmit, is a method of conversing on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode....
feature, the marketplace has seen a flood of newer 800 and 900 MHz commercial mobile radios that are designed to the following specifications:
- 800 MHz Radios:
- Transmit: 806 - 821 MHz and 851 - 870 MHz
- Receive: 851 - 870 MHz
- 900 MHz Radios:
- Transmit: 896 - 902 MHz and 935 - 941 MHz
- Receive: 935 - 941 MHz
The receivers on many of these modern 800 MHz radios can be easily modified to receive higher than 870 MHz, to about 904 MHz with good sensitivity
Sensitivity (electronics)
The sensitivity of an electronic device, such as a communications system receiver, or detection device, such as a PIN diode, is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.Sensitivity is...
. In addition, the transmitters on many of the aforementioned 900 MHz radios can be easily modified to transmit lower than 935 MHz, to about 926 MHz with acceptable power output. With this in mind, many amateurs have opted to set up repeaters with -25 MHz splits using modified 800 MHz radios as receivers and modified 900 MHz radios as transmitters.
A number of resources are available for amateurs to build repeaters that can be used on the 33 cm band. Some of those resources are:
http://www.repeater-builder.com/motorola/msf/msf-index.html - for use with conversion of the Motorola MSF5000 and PURC stations;
http://www.repeater-builder.com/motorola/nucleus/nuc-article.html - for use with adding analog modulation to the Motorola Nucleus paging station;
http://www.repeater-builder.com/motorola/gtx/gtx-index.html - for use with conversion of the Motorola GTX-series radio;
http://www.repeater-builder.com/maxtrac/maxtrac-900mhz-vco.html and
http://www.repeater-builder.com/maxtrac/maxtrac-900-t2c.html - for use with conversion of the Motorola MaxTrac radio.
Resources are also available via several e-mail discussion groups (such as the Yahoo Groups: "AR902MHz" and "900mhz") where information regarding conversion of other brands commonly used (such as Kenwood, EF Johnson, and GE/Ericsson) can be found/discussed.
The advent of issues involving interference to the PAVE PAWS
PAVE PAWS
PAVE PAWS is a United States Air Force Space Command radar system operated by three 21st Space Wing squadrons for missile warning and space surveillance. Operational PAVE PAWS radars are located at:...
RADAR systems located on the East and West coasts of the United States has pushed many amateur repeater operators to vacate the 70 cm band in favor of 33 cm, and proliferation of 33 cm repeaters has understandably increased exponentially in the past few years.
Using repeaters
Amateurs who use local repeaters on the 33 centimeter band usually use commercial handheld or mobile 900 MHz radios. As shown above, these radios can transmit between 896 and 902 MHz and receive between 935 and 941 MHz. Getting many of these radios to transmit on the repeater's input frequency (between 902 and 903 MHz) and receive on the repeater's output frequency (between 927 and 928 MHz) usually requires very little or no circuit modification, depending on the choice of radio. For instance, the Motorola model GTX (mobile and handheld versions) do not require any hardware modifications at all. Using these commercial radios however, has one handicap: flexibility. Unlike most other ham radio bands, in which one can tune to any frequency within an amateur band, modification of "Channelized" commercial radios maintains them in a channelized state. Therefore, once programmed, the frequencies they operate on cannot be changed at will without re-programming. However, since almost all FM radio equipment used on the 33 cm band amateur band was previously designed for and internally programmed for frequencies outside the 33 cm band edges, reprogramming is always necessary to get them working properly between 902-928 MHz after any physical modifications have been made. This includes the GTX.Linking
Many amateurs have found the 33 centimeter band to be ideal for linking repeaters together. Some of the biggest linked repeater systems in the United States use the 33 centimeter band as their link backbone.Propagation characteristics
Signal propagation on the 33 centimeter band is very dependent on the transmitting and receiving antenna's line of sightLine-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
. Because of this, many wide-area coverage systems like repeaters are located on top of large hills and mountains which overlook a vast area. This ensures that the transmitting antenna is higher than terrestrial obstructions such as trees and buildings. Assuming that the transmitting antenna's
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
, height above average terrain
Height above average terrain
Height above average terrain is used extensively in FM radio and television, as it is actually much more important than effective radiated power in determining the range of broadcasts...
, and effective radiated power
Effective radiated power
In radio telecommunications, effective radiated power or equivalent radiated power is a standardized theoretical measurement of radio frequency energy using the SI unit watts, and is determined by subtracting system losses and adding system gains...
is equal, a transmitted signal on 33 centimeters will, generally speaking, usually travel about 3/4 of the distance that the same signal would if transmitted on the 70 centimeter
70 centimeters
The 70-centimeter amateur radio band is a portion of the UHF radio spectrum. This band is used by amateurs engaged in emergency communications where portable and mobile radios are frequently used. Many such radios have dual-band capabilities, operating on both the 70-centimeter and 2-meter bands.-...
band. 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 easier than signals lower in frequency.
In many areas, the 33 centimeter band also has a very low noise floor
Noise floor
In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system, where the noise is defined as any signal other than the one being monitored....
as compared to bands lower in frequency.
Popular equipment used on the 33 centimeter band
- EF Johnson models 8615, 8640, 8644 and 8655
- GE DTMX 9315B (TMX)
- Ericsson MDX
- GE Mastr II
- GE Mastr III
- MA/Com Orion
- Kenwood TK-480 / Kenwood TK-481
- Kenwood TK-980 / Kenwood TK-981
- Kenwood TK-931
- Motorola MaxTrac
- Motorola Spectra
- Motorola MSF 5000
- Motorola GTX
- Motorola MTX
- Motorola MCS 2000
- TAIT T800 Series
- "eXRS" 900 MHz FHSS Part 15 radios
- Downeast Microwave 902-144HP3 transverterhttp://www.downeastmicrowave.com
- Georgia 900 MHz Group