33-centimeter band Uses and Applications Explained

The 33-centimeter band is a fascinating topic, and I'm excited to break down its uses and applications for you. This frequency range is commonly used in wireless communication systems, particularly in the field of wireless local area networks (WLANs).

The 33-centimeter band operates at a frequency of 10-10.5 GHz, which is a key characteristic that influences its applications. This specific frequency range allows for high-speed data transmission.

In practice, the 33-centimeter band is used in various devices, including wireless routers and access points. These devices enable wireless connectivity for devices such as laptops, smartphones, and tablets.

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The 33-centimeter band has a dedicated following among amateur television enthusiasts.

Some manufacturers produce ATV equipment specifically for this band.

Amateur television is a popular activity on the 33-centimeter band, with a strong presence of enthusiasts.

The first repeater to use the band, the NU6X/R (Amateur TV Network), was activated at 923.25 MHz.

This repeater later moved to 919.25 MHz and changed its call sign to W6ATN.

If this caught your attention, see: Amateur Radio Frequency Allocations

Amateurs have adapted commercial equipment for use in the 33 centimeter band, with the bulk of modified equipment manufactured by Motorola and Kenwood.

The first two-way 900 MHz radio made specifically for the Amateur Service was introduced by Alinco in 2012, the DJ-G29T is a dual band portable radio operating on the 222 MHz and 900 MHz bands and is fully programmable.

Most amateur 33 centimeter band repeaters use a -25 MHz split with inputs between 902 and 903 MHz and outputs between 927 and 928 MHz due to the complexity of modifications increasing rapidly as target frequencies are moved further from the original design frequencies.

A 25 MHz split results in frequencies fairly close to the original frequencies this commercial equipment was designed for, making modifications relatively simple.

The receivers on many modern 800 MHz radios can be easily modified to receive higher than 870 MHz, to about 904 MHz with good sensitivity, and the transmitters on many 900 MHz radios can be easily modified to transmit lower than 935 MHz, to about 926 MHz with acceptable power output.

Here are some specifications for modified commercial mobile radios:

900 MHz Radios:

FM Repeaters have been a challenge for amateur radio enthusiasts, particularly in the 33 centimeter band.

Until recently, no manufacturer made an FM repeater specifically for this band, so amateurs have had to adapt commercial equipment.

The majority of modified commercial equipment used for 33 centimeter band repeaters is manufactured by Motorola and Kenwood.

Amateurs have found that modifying commercial equipment designed for the mid-800 MHz and mid-900 MHz range is a viable option.

In 2012, Alinco introduced the first two-way 900 MHz radio made specifically for the Amateur Service.

The DJ-G29T is a dual band portable radio operating on the 222 MHz and 900 MHz bands and is fully programmable.

The ARRL has specified that repeaters on the 33 centimeter band use a split of -12 MHz with inputs between 906 and 909 MHz and outputs between 918 and 921 MHz.

However, most amateur 33 centimeter band repeaters use a split of -25 MHz with inputs between 902 and 903 MHz and outputs between 927 and 928 MHz.

Related reading: FM Broadcast Band

This is due to the complexity of modifications increasing rapidly as target frequencies are moved further from the original design frequencies.

A 25 MHz split results in frequencies fairly close to the original frequencies this commercial equipment was designed for, making modifications relatively simple.

Noise floor tests have consistently shown that the noise floor is higher near the center of the band due to other non-amateur services.

As a result, the quieter frequencies near the band limits are more desirable.

Many modern 800 MHz radios have receivers that can be easily modified to receive higher than 870 MHz, up to about 904 MHz with good sensitivity.

Similarly, the transmitters on many 900 MHz radios can be easily modified to transmit lower than 935 MHz, down to about 926 MHz with acceptable power output.

This has led many amateurs to set up repeaters with -25 MHz splits using modified 800 MHz radios as receivers and modified 900 MHz radios as transmitters.

Here are some common specifications for modified commercial mobile radios:

Resources are available for amateurs to build repeaters that can be used on the 33 cm band, including e-mail discussion groups and online forums.

The 33cm band is a popular frequency range for amateur radio enthusiasts, and there are many great pieces of equipment available for use on this band.

One of the most well-known equipment manufacturers for the 33cm band is EF Johnson, which offers several models including the 8615, 8640, 8644, and 8655.

GE DTMX 9315B, also known as TMX, is another popular choice for the 33cm band.

Ericsson's MDX is also a well-regarded option for this frequency range.

GE's Mastr II and Mastr III models are also widely used on the 33cm band.

MA/Com's Orion is another popular choice among amateur radio operators.

The Kenwood TK-480, TK-481, TK-980, and TK-981 are all popular handheld radios that can be used on the 33cm band.

The Alinco DJ-G29T and Motorola MaxTrac are also popular options for this frequency range.

Motorola's Spectra and MSF 5000 are also widely used on the 33cm band.

Motorola's GTX, MTX, and MCS 2000 models are also popular choices among amateur radio operators.

Additional reading: S Band

Motorola's DTR and XTS 2500, XTS 1500 are also widely used on the 33cm band.

Retevis RT10 and TAIT T800 Series are also popular options for this frequency range.

The Downeast Microwave 902-144HP3 transverter and Q5 Signal transverters L33-28HP or L33-144HP are also used on the 33cm band.

M2 directional gain antennas for 33cm are also available for use with this equipment.

Building and planning a 33-centimeter band repeater requires some knowledge of the frequency splits and equipment modifications involved.

The ARRL specifies a -12 MHz split, but most amateurs use a -25 MHz split, which is simpler to implement and provides better noise reduction.

The 25 MHz split is also more desirable due to the higher noise floor near the center of the band caused by non-amateur services.

Most amateur repeaters use a 25 MHz split with inputs between 902 and 903 MHz and outputs between 927 and 928 MHz.

If you're planning to use modified commercial equipment, a 25 MHz split is a good choice because it keeps the frequencies close to the original design frequencies, making modifications relatively simple.

However, if you're using a 12 MHz split, you'll need high-quality duplexer devices to isolate the repeater receiver from the transmitter when sharing a single antenna.

Here are some specifications for modern commercial mobile radios that can be easily modified for amateur use:

Keep in mind that these modifications require careful testing and adjustment to ensure proper performance and compliance with amateur regulations.

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.

A signal on the 33-centimeter band will generally travel about 3/4 of the distance that the same signal would if transmitted on the 70 centimeter band.

In many areas, the 33 centimeter band has a very low noise floor as compared to bands lower in frequency.

The 33 centimeter band has a very dependent signal propagation, relying heavily on the line of sight between the transmitting and receiving antennas.

In fact, the propagation distance on 33 centimeters is about 3/4 of what it would be on the 70 centimeter band, assuming equal transmitting antenna characteristics.

This means that for effective signal transmission, the transmitting antenna should be placed higher than terrestrial obstructions like trees and buildings.

Line-of-sight signal propagation in the local area is also influenced by receiver front-end noise figure and antenna gain.

The 33 centimeter band offers excellent building penetration characteristics, thanks to its relatively small wavelength that can fit through windows more easily than lower frequency signals.

In many areas, the 33 centimeter band has a very low noise floor, making it a favorable choice for signal transmission.

Digital P2P on the 33cm Band is a viable option for higher bandwidth communications. The 33cm band is the lowest frequency band that doesn't have a 100KHz transmission bandwidth limitation, making it attractive for point-to-point communications.

The specific details of the 33cm band are outlined in § 97.301. Permitted signals include MCW, phone, image, RTTY, data, SS, test, and pulse emissions.

RTTY, data, or multiplexed emissions using a specified digital code are authorized. The FCC also allows unspecified digital codes under specific limitations.

Spread Spectrum transmissions are covered separately and have their own set of rules. These transmissions are authorized for communications between points within areas where the amateur service is regulated by the FCC.