Amateur television
Amateur television transmits broadcast-quality video over ham radio frequencies.
Amateur television (ATV) is the practice of sending broadcast-quality video and audio on amateur radio frequencies. It is used for non-commercial experimentation, recreation, and public service events. In many cities, ham TV stations were operating before commercial television stations existed. ATV can use various broadcast standards, such as NTSC in North America and Japan, or PAL and SECAM elsewhere, all at their standard refresh rates. The field also involves designing and building transmitters and receivers, as well as studying how radio signals propagate between stations. ATV is a branch of amateur radio, also known as ham TV or fast-scan TV (FSTV), to distinguish it from slow-scan television (SSTV).
In North America, the amateur radio bands wide enough for a television signal are higher in frequency than VHF broadcast TV. The lowest such band is 70 centimeters, which sits between broadcast channels 13 and 14. This frequency range falls into CATV channels 57 to 61 (IRC), from 420 to 450 MHz. As a result, ATV signals can be received by tuning a cable-ready television or analog cable box to cable input and using an outdoor antenna. For better sensitivity, some users employ a dedicated ATV down-converter, a type of set-top box. Other bands used for ATV are mostly in the UHF range, above broadcast UHF TV. The 33-centimeter and 23-centimeter bands are also common, but receiving them requires a down-converter.
Most ATV signals use either amplitude modulation (AM) or vestigial sideband (VSB) with NTSC, the North American analog TV standard. Double-sideband AM and VSB AM are inherently compatible, and most televisions can receive both. DSB-AM includes the carrier and both sidebands. VSB-AM filters out most of the lower sideband beyond 1.25 MHz from the carrier. A VSB filter can be added to a DSB-AM transmitter, costing between $100 and $1,000 depending on power. For practical reasons, most individual ATV users transmit in DSB-AM, while repeaters typically use VSB. On the 33-centimeter band and higher, frequency modulation (FM) ATV may be used, and on SHF and EHF ham bands, FM is more common than VSB or AM. FM ATV is not compatible with AM or VSB ATV, so it requires a separate demodulator, such as an analog satellite receiver.
- Distance record
- 2,518 miles (Hawaii to California) on 434 MHz
- Lowest frequency ham band for atv in nor
- 70 centimeters (420–450 MHz)
- Common 2 meter atv liaison frequency
- 144.34 MHz
- Most commonly used ham band for atv
- 70-centimeter band (420-450 MHz)
- Popular 23 cm fm channels
- 1.255 GHz, 1.265 GHz
- First datv repeater in the us
- WR8ATV (using DVB-S)
Lore & Background
Amateur television (ATV) has a history predating commercial television, with ham TV stations on the air in many cities before commercial stations began. In North America, the lowest frequency ham band suitable for television transmission is 70 centimeters, which lies between broadcast channels 13 and 14 and falls into CATV frequencies on channels 57 to 61 (IRC). Most ATV signals are transmitted in either amplitude modulation (AM) or vestigial sideband (VSB) NTSC. DSB-AM and VSB-AM signals are inherently compatible, and most televisions can receive either. For practical reasons, most individual ATV users transmit in DSB-AM, while VSB is transmitted by repeater stations. On the 33 cm and higher bands, frequency modulation (FM) ATV may be used, and on the SHF and EHF ham bands, FM is more common than VSB or AM. FM ATV is incompatible with AM/VSB ATV and requires a separate demodulator. The 2-meter band is often used by ATV operators for coordination via FM voice transmissions, with a commonly recognized liaison frequency of 144.34 MHz. The 70-centimeter band is the most commonly used ham band for ATV, as signals propagate longer distances than on higher frequency bands for a given power and antenna gain. The 33-centimeter band is unique to ITU Region 2 and is shared with ISM devices and unlicensed Part 15 users. The 23-centimeter band is the most popular band for FM amateur TV due to the low cost and ease of repurposing old analog satellite receivers.
Reader's Guide
Amateur television holds significance as a non-commercial medium for experimentation, pleasure, and public service events. Its legacy includes being on the air before commercial television stations in many cities. The article describes various bands used for ATV in North America, each with specific usage notes and restrictions. For example, in Canada and areas of the US north of a designated 'Line A' boundary, amateurs are not allowed to transmit on certain channels. The 70 cm band may not be used within 160 kilometers of Joint Base Cape Cod to protect PAVE PAWS. The 33 cm band is unavailable in portions of Colorado and Wyoming for ATV. The 23 cm band is not available in certain New England states due to interference with FAA surveillance radar. The distance record for ATV is between Hawaii and California (2,518 miles) on 434 MHz. Experiments with digital modes have lagged behind those in Europe, but have taken on new urgency given the transition of broadcast television. WR8ATV currently has an output using DVB-S, believed to be the first DATV repeater in the US. There is now a DATV downlink on the ISS operating in the amateur 2.4 GHz band, and the QO-100 geostationary satellite wideband transponder has DATV uplinks in the 2.4 GHz and downlinks in 10 GHz amateur bands.
Did You Know?
- Ham TV stations were on the air in many cities before commercial television stations came on the air.
- The distance record for ATV is 2,518 miles between Hawaii and California on 434 MHz.
- The 33-centimeter band is unique to ITU Region 2 and rarely available for amateur use in Regions 1 or 3.
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