Channel 37 is an unused television channel in countries using the M and N broadcast television system standards. Channel 37 occupies a band of UHF frequencies from 608 to 614 MHz, frequencies that are particularly important to radio astronomy because they allow observations at a frequency between the dedicated frequency allocations near 410 MHz and 1.4 GHz. One radio astronomy application in this band is for Very-long-baseline interferometry. In 1963, when there were very few stations in the UHF band, the US Federal Communications Commission (FCC) adopted a 10-year moratorium on any allocation of stations to Channel 37. A new ban on such stations took effect at the beginning of 1974, and was made permanent by a number of later FCC actions. As a result of this, and similar actions by the Canadian Radio-television and Telecommunications Commission, Channel 37 has never been used by any over-the-air television station in Canada or the United States.
- The Canadian Radio-television and Telecommunications Commission (CRTC) also enacted such a ban on channel 37.
- It appears that Mexico may also observe a similar ban on the use of this TV channel, if only informally.
- Guatemala has a ban on Channel 37.
- Most NTSC System-M countries have an informal ban on channel 37 as well.
Since July 2000, channel 37 may also be used in the U.S. for medical telemetry equipment on a co-primary basis. This equipment must emit no more than one watt of effective radiated power, and is for use in hospitals and other such facilities.
- The power level permitted by the FCC is many times more than the amount allowed for Part 15 unlicensed broadcasting.
Even this seemingly low power level can be troublesome for radio astronomy, which depends on detecting extraordinarily low signal strengths. Any use of the same frequencies raises the noise floor, thereby decreasing the signal-to-noise ratio, and making the work more difficult.
Channel 1 was also removed from the TV bandplan in the late 1940s, channels 70 to 83 by the 1980s mainly for AMPS mobile phones and, in June 2009, channels 52 to 69 for mobile phones, emergency services and mobile TV services such as Qualcomm's MediaFLO (channel 55). Certain channels, 14 through 20, are used for land mobile communications in some large metropolitan areas in the U.S.
The channels displayed by cable converter boxes under these numbers are not on the same frequencies as their over-the-air counterparts; there are also virtual channel numbering schemes in use in digital television which do not map directly to fixed frequency channel assignments. As such, a "cable 37" channel may (and most often does) exist, but on a much lower frequency.
Channel 37 has been used as a hypothetical example in instruction manuals, where it serves a role analogous to the fictitious example.org and example.net Internet domains and the 2001:db8 IP address. The "Channel 37" newsroom also occasionally has made a fictional appearance on sites such as YouTube and MySpace.
Outside North America
In NTSC-M countries
Outside North America, channel 37 is actively used in these countries where NTSC-M is used:
- in the Philippines (UNTV Channel 37)
- in Trinidad and Tobago, WIN-TV is broadcast on Channels 37 and 39, using NTSC
- In Dominican Republic channel 37 is also used for the CDN news channel
In other countries
In these other countries, the frequency allocation for these TV channels is different:
- in the UK (many transmitters used by the Five network actually broadcast on channel 37)
- in Western Europe, Channel 37 is used fairly widely as a relay transmitter frequency.
- In Malaysia, NTV7 broadcasts in PAL on CCIR Channel 37 (599.25 MHz)
Channel 37 is not the same frequency as it is in the countries using the System-M/N standard. At least in the UK, 606–614 MHz is reserved for radio astronomy.
The UK's namesake "Channel 37", while different in frequency, was formerly part of a small group of channels reserved for non-broadcast purposes such as RF modulators in video players. The UK-named 34-37 channel range is no longer reserved in this manner.
Global UHF TV allocation table (605–615 MHz)
This Radio Astronomy Allocation is between the following wavelengths:
- 605 MHz = 0.49552 m = 49.55 cm
- 615 MHz = 0.48747 m = 48.75 cm
- Assume either a 100 kHz or a 250 kHz guardband with respect to this allocation.
DVB-T adoption note : The tables above are not accurate for nations that have adopted DVB-T. The frequencies for audio and video are merged with DVB terrestrial television. The new DVB frequencies are rounded off to an even number in MHz as a general rule.
National Arrangements for Radio Astronomy different from ITU-R
National Arrangements for Radio Astronomy different from ITU-R Radio Regulations
- Armenia: no allocation
- Austria: no allocation - only mention of No. 5.149
- Bulgaria: no allocation
- Belgium: assignment to radio astronomy (shared with active services)
- Finland: no allocation
- Estonia: no allocation
- Iceland: no allocation
- Liechtenstein: no allocation
- Luxembourg: no allocation
- Netherlands: primary status
- Portugal: no allocation
- Russian Federation: no allocation
- Spain: no allocation
- Sweden: no allocation
- Turkey: no allocation
- United Kingdom: no reference to No. 5.149
- No Allocation and Primary Status could be considered equivalent legal status. Very often the lack of allocation implies an internal regulatory coherence with ITU-R regulations freeing up this band for Astronomy.
- Assignment and Primary Status could be considered equivalent legal statuses as well.
- FCC database for Channel 37, had shown possible usage conflict with Mexico but now has the channel entirely clear in Can/USA/Mex.
- US FCC's attack on Channel 37
- W9Wi.com: An article about channel 37 and channels above 69
- craf.eu: Astrophysical importance of the band 608 - 614 MHz
- Spare That Channel, Time, 10 May 1963
- FREQUENCIES ALLOCATED TO RADIO ASTRONOMY USED BY THE DSN
- McAdams On: Channel 37
Rest of World