33cm Band Plan



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Southern California Adopts A New 33cm Band Plan

May 19, 1990 -- At a meeting in Anaheim, CA, on May 19, 1990, sponsored by the Southern California Repeater and Remote Base Association (SCRRBA), representatives of all southern California 33 cmeter band users' groups discussed proposals, debated alternatives, and then unanimously adopted a new 902-928 MHz band utilization plan.

On November 16, 1985, southern California adopted a 33 cmeter band plan. On March 26, 1988, the American Radio Relay League (ARRL) Membership and Services committee met in Torrance, CA and adopted the present ARRL band plan. This plan is only slightly modified from the SCRRBA plan. In November, 1989, International Teletrac Systems (ITS) and Pacific Telesis Group (PACTEL) commenced testing of an AVM system utilizing 904-912 MHz in southern California. This system is to go into commercial operation in 1990. On December 7, 1989, SCRRBA suspended all coordination on the 33 cmeter band. A meeting in January with ITS/PACTEL yielded sufficient information and data for SCRRBA to determine that it was necessary to call a band planning conference.

Unlike other Amateur Radio Service (ARS) bands, 33 cmeters is shared with several services: Military; Industrial, Scientific and Medical
(ISM, Part 18); Government (Non-military); Automatic Vehicle Monitoring (AVM, Part 90); and Radio Frequency Devices (RFD, Part 15). In all cases except RFD, Part 15, the ARS is secondary and/or must tolerate any and all interference.

Research of current licensing and business activities produced numerous, nation wide AVM systems on line or in development for 33 cmeters.  It is very apparent to SCRRBA that the 90's will be the decade for the explosion of the AVM service.

Much discussion centered around the AVM, Part 90, service and the secondary status of the ARS as defined by CFR, Title 47, FCC Rules & Regulations, 97.303 (g) (1). Southern California has successfully shared other ARS bands such as 75 cmeters with the military but has no experience with part 90 or ISM. Operating specifications for ITS/PACTEL system and the secondary status of ARS convinced the conference that co-channel sharing was not obtainable. Sharing with the ISM service is not equal. ARS must tolerate ISM interference, but by design will not cause interference to ISM (nonreceiving service).

The conference noted that the RFD service (Part 15) is secondary to the ARS. But in noting this, it was also recognized that practical enforcement was pure fiction. Much information was shared by attendees concerning the voluminous and exponentially expanding Part 15 activities. The conference unanimously agreed that the 90's would also prove to be the decade of the "spread spectrum" (Part 15) device, operated to the determent of the ARS on the 33 cmeter band. The direct effect from these devices will be interference and the indirect effect will be an ever increasing noise floor.

The adopted plan recognizes the only segments of the band available to the ARS in urban areas are 902-903 and 927-928 MHz. 912-918 is also available but with reduced capabilities. These segments (8 MHz) represent a 60 percent reduction in ARS 33 cmeter spectrum as listed in Part 97 (26 MHz).

901-902 MHz is currently held in reserve and stands a good chance of becoming LMS repeater input spectrum. 928-932 MHz contains LMS high power paging transmitters without spectrum filtering, multiple address systems, one way signaling, point-to-multipoint, and point-to-point.  The low end of the band, 902-903 MHz, is most suitable for ARS receivers at communication sites (comm. sites). Also this is the cleanest spectrum available for weak signal applications and is most compatible with repeater and link inputs. It was found that repeater and link transmitters best shared the 927-928 MHz spectrum at comm. sites adjacent to the LMS paging systems. This is identical to the long standing practice in southern California of placing ARS repeater outputs (445 to 450 MHz) adjacent to commercial repeater outputs (450 to 455 MHz) at comm. sites. Part 90, 900 MHz, LMS standards for repeater and link operations were adopted to maximize the channel pairs available (72) within the two 900 kHz subbands that are 25 MHz apart.

912 to 918 MHz is the only spectrum wide enough to support ATV and only as simplex and/or an out of band repeater input (typically repeater output is on 23 cmeters).  33 cmeter ARS amplitude modulated fast scan television transmitters are considered to be comprised of an amplitude modulated visual carrier along with a frequency modulated aural signal. This aural signal may be transmitted as a totally separate RF carrier, a separate RF carrier amplified along with the visual carrier, or a low frequency (4.5 MHz) sub-carrier inserted into the video signal before it is amplitude modulated onto the visual carrier.

The spectrum adjacent to this 6 MHz segment is primarily governed by part 90. Discussion ensued as to how ATV could best use this segment.  After the Forum, the Technical Committee pursued this discussion and selected the following standards to be RECOMMENDED as MINIMUMS that should be followed to protect the AVM activity that is in the lower side band of the ATV signal. ITS/PACTEL AVM receivers (904 to 912 MHz, high performance, low noise) are installed and operation at all major southern California comm. sites.

33 cmeter fast scan television transmissions should utilize vestigial sideband emissions.

Frequency Tolerance Description

MHz or Limit

> -40 dBc Output Emissions


> -33 dBc Output Emissions


913.250 +/-25 KHz Visual Carrier

917.750 +/-25 KHz Aural Carrier


> -33 dBc Output Emissions

dBc = Decibel below peak visual carrier. Therefore, > -40 dBc = greater than 40 decibel below peak carrier.

NTSC compatible transmissions are encouraged wherever possible. The visual modulation should not be allowed to go below 10% of peak sync. The aural modulation should not exceed 50 kHz peak deviation.

The conference allocated 400 kHz of spectrum for digital communications.  300 kHz of this spectrum is within the edges of the ATV segment which represents an engineering solution that SCRRBA has successfully employed on other bands. This digital spectrum is to be used in 100 kHz bandwidth segments for 25 kHz or greater bandwidth, high baud rate, backbone type activities, coordinated on a case-by-case basis. This spectrum is not intended for direct use by standard narrow bandwidth (less than 25 kHz) users.

Present at the meeting were a total of 30 persons as representatives for the SCRRBA Technical Committee, ARRL, ATV repeaters, ATV simplex, digital/packet, weak signal, links, remote base, and repeaters.

Bill Kelsey, WA6FVC (W6QC)



Last modified: April 29, 2009