Taking a look at the 900 MHz band and it's other users


The largest concern with coordinating amateur systems on 900 MHz may be and potential of interference to primary and secondary users.   Part 97.303. Frequency sharing requirements spells this out:

(g) In the 33 cm band:

(1) In the States of Colorado and Wyoming, bounded by the area of latitude 39� N. to 42� N. and longitude 103� W. to 108� W., an amateur station may transmit in the 902 MHz to 928 MHz band only on the frequency segments 902.0-902.4, 902.6-904.3, 904.7- 925.3, 925.7-927.3, and 927.7-928.0 MHz. This band is allocated on a secondary basis to the amateur service subject to not causing harmful interference to, and not receiving any interference protection from, the operation of industrial, scientific and medical devices, automatic vehicle monitoring systems, or Government stations authorized in this band.

(2) No amateur station shall transmit from those portions of the States of Texas and New Mexico bounded on the south by latitude 31� 41' N, on the north by latitude 34� 30' N, on the east by longitude 104� 11' W, and on the west by longitude 107� 30' W.

So lets take a look at the use of the band as Amateur Radio is secondary in this band to federal radiolocation systems, industrial, scientific and medical devices, federal fixed and mobile systems and the M-LMS. (Multilateration Location Monitoring Service)

902 - 928 MHz
What is an ISM (industrial, scientific and medical) device (Part 18)?

Part 18 ISM devices utilize RF energy for non-communicative purposes. They radiate only and do not receive therefore it is highly unlikely that you would ever interfere with an ISM device. See the definition of ISM equipment in 47 CFR 18.107(c).

Shrink wrappers are a fine example of an ISM device. The plastic is heated and semiliquified by a very strong RF field only a few inches away. The sheet of plastic is then lowered onto the rest of the packaging, clings to the product and the cardboard, and resolidifies. Since telecommunications are precluded, and ISM signal will contain not data. The third character of the emission designator for a Part 18 device will always be N (N0N or P0N are most likely). Other ISM devices include; RF lighting systems, paint dryers, jewelry cleaners, industrial microwave ovens, and MRI equipment.  Most ISM energy is centered at 915 MHz.

The FCC opened the industrial, scientific and medical (ISM) bands to Part 15 radio users in 1985.  Prior to about 1980, the ISM bands were considered unacceptable for radio communication because of harmful interference created by such equipment. But several companies and industry groups petitioned the FCC and showed that by using spread spectrum modulation, low-power radios could coexist with ISM radiators.

Part 15

Part 15 devices (example: cordless phones) must not interfere with primary or secondary users.  Section 15.5(b) is printed on all Part 15 devices and states; "This device complies with FCC Rules Part 15. Operation is subject to the following two conditions: This device may not cause harmful interference. This device must accept any interference received, including interference that may cause undesired operation."

Location and Monitoring Service/ Automatic Vehicle Monitoring Service

LMS systems utilize non-voice radio techniques to determine the location and status of mobile radio units.  The 900 MHz M-LMS service is recognized by many as a failed service.  Progeny appears to be the only LMS deployment on this band.

It was intended to be developed into an automated highway system that would provide for safer and better informed travelers, improved traffic control systems, systems aimed at increasing the efficiency of commercial vehicle and transit operations, and increase national productivity.  In 1995 the FCC adopted rules for Automatic Vehicle Monitoring (AVM) under a new Subpart M starting at Part 90.350.  The title of Subpart M is "Transportation Infrastructure Radio Service" AIRS) and is intended to allow new radio-based technologies for Intelligent Transportation System (ITS) applications. Later the AVM name is changed to Location and Monitoring Service (LMS).  It's defined in two general categories of LMS technologies; multilateration, or wideband including direct sequence spread spectrum, and non-multilateration, or narrowband.   In this system, a vehicle location unit installed in a vehicle communicates with a computer at a network control center through a network of transmission and receiving towers. Within a defined geographic area, a host of practical applications can be provided: monitoring the location of fleet vehicles, accurate tracking of stolen vehicles, and helping motorists in distress.

What is Radiolocation?

Military radiolocation systems include low-power devices, such as those for tactical and nontactical intrusion detection at military facilities, and high-power radars used for long-range search, many of which are employed on U.S. Navy ships and aircraft or at shore stations. These radars serve a critical role in defense of the fleet.

Federal mobile communications applications include video surveillance for law enforcement missions, transmission of infrared scanner imagery during overflights of disaster areas, and use of high power packet radio systems.

Fixed use includes point-to-point TV links for monitoring unmanned ports of  entry along borders. Though most low capacity links will be moving to the 932-935�MHZ and 941-944�MHZ bands, this band will continue to be used for a variety of resource management, power administration and law enforcement purposes, as necessary.

Bandplans for hams

The "old" (ARRL endorsed) 900 MHz amateur band plan was designed with no consideration to the fact that ham radio is secondary in the band, and no consideration to the available equipment. That plan specified -12mhz offsets and is used in very very few areas. The 900mhz band is shared with many other services, and they all tend to leave the bottom and top megahertz alone as guard bands. The 12mhz plan has the ham repeaters right in the middle of the commercial users (and they are primary in that allocation) and they do not take kindly to hams. Due to this hostility the ham repeaters have migrated to the outer two megahertz - 902 to 903 as repeater inputs, and 927 to 928 as repeater outputs.

ARRL band plan for 33 Centimeters (902-928 MHz):
902.0-903.0 Narrow-bandwidth, weak-signal communications
902.0-902.8 SSTV, FAX, ACSSB, experimental
902.1 Weak-signal calling frequency
902.8-903.0 Reserved for EME, CW expansion
903.1 Alternate calling frequency
903.0-906.0 Digital communications
906-909 FM repeater inputs
909-915 ATV
915-918 Digital communications
918-921 FM repeater outputs
921-927 ATV
927-928 FM simplex and links

While the national band plan as well as many state band plans call for a -12 MHz split for FM repeaters, an increasing number of states are changing their band plans to reflect the growing number of FM repeaters using -25 MHz splits. Many amateurs feel that eventually the -25 MHz split will become commonplace and all state and national band plans will adopt it.  SERA (SouthEastern Repeater Association), the largest coordinating body in the US has gone to 25 MHz split. The SCCRBA (Southern California Repeater and Remote Base Association) bandplan has been 25 MHz for some time. 


902.0000 - 902.2875    SSTV, FAX, ACSSB, Experimental
902.2125 - 902.4625    Auxiliary FM Duplex Link Input Frequency Pairs
902.4875 - 902.7250    FM Repeater Inputs & designated simplex (25 MHz split - 12.5 KHz spacing)
902.5000 -                    FM Simplex Calling Channel (1 of 2)
902.7375 - 903.0500    EME Exclusive
903.0700 - 903.0800    CW Beacons
903.1000 -                    CW, SSB Calling Frequency
903.4000 - 903.6000    Cross Band Linear Translator Inputs
903.6000 - 903.8000    Cross Band Linear Translator Outputs
903.8000 - 904.0000    Experimental Beacons Exclusive
904.0000 - 906.0000    Digital Communications
906.0000 - 907.0000    Narrow Band FM Simplex (grandfathered system - 25 KHz channels)
906.5000 -                    Old National Calling Frequency (granfathered)
907.0000 - 910.0000    FM Repeater Inputs (12 MHz split - 100 KHz spacing)
910.0000 - 916.0000    ATV
916.0000 - 918.0000    Digital Communications
918.0000 - 919.0000    Narrow Band FM Control Links/Remote Bases
919.0000 - 922.0000    FM Repeater Outputs (12 MHz split - 100 KHz spacing)
927.0125 - 927.9875    Auxiliary Simplex & Link Frequencies
927.2125 - 927.4625    Auxiliary FM Duplex Link Input Frequency Pairs
927.4875 - 927.7250    FM Repeater Outputs & designated simplex (25 MHz split - 12.5 KHz spacing)
927.5000 -                    FM Simplex Calling Channel (2 of 2)
927.7375 - 927.7875    Old SERA FM Voice Simplex Channels (grandfathered)   
922.0000 - 928.0000    Wideband Experimental, ATV, Simplex, Spread Spectrum

One of the purposes of a frequency coordinator is to recommend standard operating procedures.  The frequency coordinator's main job is to make sure your repeater will not interfere with nearby repeaters already established.

They have the duty to not only produce bandplans that satisfy the needs of repeater owners within its area but also to protect the interests of coordinated systems in adjacent areas, weak signal modes, digital communications, AM and FM simplex, and satellite uplinks and downlinks.   They define the bandplan for both coordinated and non-coordinated activities within its territory.

In the event your coordination body's band plan is behind the times; Aside from the FCC's frequency limits spelled out in Part 97, everything else is technically a voluntary band plan.  If you decide not to comply with the voluntary plan, you should have good reason to do so, and should try your best not interfere with others.

As of the time of writing, the AR902 900 MHz repeater list, shows 25 MHz split systems in about 20 different states.  It should be clarified that the coordination bodies may not have officially adopted the combination 12 MHz & 25 MHz split accommodating plan in the states where these systems are located.  For a more accurate look, the following coordination bodies have adopted the 25 MHz split and 12 MHz split band plans:

Colorado Council of Amateur Radio Clubs, Illinois Repeater Association, Metropolitan Coordination Association serving New York and New Jersey, Western Washington Amateur Relay Association, Southern California Repeater and Remote Base Association, Arizona Repeater Owners Frequency Coordination Committee, Florida Repeater Council, Kansas Amateur Repeater Council, the South Eastern Repeater Association serving Kentucky, Tennessee, North Carolina, South Carolina, and Mississippi, the New England Spectrum Management Council serving Massachusetts, New Hampshire, Rhode Island & Maine, Michigan Area Repeater Council,� Oklahoma Repeater Society, Western Washington Amateur Relay Association�


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