2. Background

2.1  LPFM Services

The LPFM GURL is available to the public to provide radio broadcast services at low power without registration or payment of radio licence administration or spectrum usage fees.

The purpose of the GURL is to provide opportunities for hobbyists, special interest groups, remote communities and others to provide broadcast services in the guard bands between the high power VHF-FM broadcast band and adjacent landmobile and aeronautical bands, i.e. in bands that would otherwise be unused.

Use of the GURL requires that the services provided comply with operational and technical requirements included in the terms, conditions and restrictions.
The current LPFM GURL was published in 2003 to replace earlier LPFM arrangements introduced after the extension of the VHF-FM broadcast band from 88.8 - 100 MHz to 88.8 -106.63 MHz. A copy of the current LPFM GURL can be found on the RSM website¹.
 

2.2  2006 Consultation and Decisions

MED’s 2006 consultation document “VHF-FM Broadcasting, Frequency Availability and Allocation”, requested views on a broad range of proposals associated with changes to the VHF-FM broadcast band. The consultation document and report on submissions is also available on the RSM website².

Following the VHF-FM broadcast consultation, the Government agreed that;

1. Additional commercial, Maori and non commercial VHF-FM broadcasting licences be created;
2. The VHF-FM broadcast band be extended from 88.8 -106.63 MHz to 88.4 - 106.63 MHz to facilitate new licences;
3. Landmobile licensees would be relocated from the 87.5 - 88 MHz portion of landmobile A band to maintain an appropriate guard band between those services and VHF-FM high power broadcaster band; and
4. Broadcasting services in the lower LPFM band, 88 - 88.8 MHz, would be relocated to the 87.5 - 88.4 MHz band. The upper LPFM band 106.7 - 107.7 MHz would remain unchanged.
    

As a result of those requirements, projects were initiated by MED to:
 

1. Plan the extension of the VHF-FM broadcast band to accommodate additional licences and integrate with plans for the roll-over of existing VHF-FM broadcasting licences into a new management right when the existing management right (MR143) expires on 2 April 2011;
2. Consult with and plan the relocation of incumbent users from the 87.5 MHz to 88 MHz portion of the landmobile A band;
3. Consult with LPFM users and plan for the relocation of the lower LPFM band;
4. Identify the potential for interference into aeronautical radionavigation services in the 108 MHz to 117.95 MHz band from high power VHF-FM broadcast services and LPFM broadcast services with a transmit power level of 1 Watt eirp;
5. Prepare a new LPFM GURL for the period 1 June 2010 until late 2011 (when the new aeronautical standard ICAO 1998 is implemented); and
6. Prepare a temporary LPFM GUSL for the period 1 June 2010 to 2 April 2011.

A temporary LPFM GUSL is proposed to ensure current LPFM operators would have alternative frequencies to those they currently use during the transition period. That is, until the current management right ends on 2 April 2011.

2.3  Coordination of Broadcasting and Aeronautical Services

Aeronautical navigation and voice services are located in the frequency bands above 108 MHz and adjacent to VHF-FM high power broadcast services. MED is in regular contact with the Civil Aviation Authority (CAA), NZ Defence Force and Airways Corporation to discuss issues relating to the potential for interference to their services.

2.3.1  Receiver Intermodulation

One significant concern with LPFM services within 6 km of aircraft is that their signals, when mixed with signals from high power VHF-FM broadcasting services, can result in intermodulation (IM) in aeronautical receivers. This can interfere with aeronautical navigation services in the 108 - 117.95 MHz band and aeronautical voice communication services (COM) in the 117.95 - 137 MHz band.

There have been no reports to MED of such interference issues but calculations indicate that specific combinations of LPFM and VHF-FM broadcast signals could exceed the receiver interference protection margins.

2.3.2  Transmitter Intermodulation

During 2009 and already in 2010, MED has received reports from pilots of low flying helicopters and other aircraft of interference to COM services from broadcast services. Investigations determined that the interference was a result of IM emissions from co-sited LPFM transmitters.

Further investigation identified that similar incidents occurred prior to 2009. The repetition of these incidents and the increasing use of LPFM facilities suggest that there is a likelihood of further interference risks unless appropriate measures are taken.
 

Footnotes

¹ Direct link at http://www.rsm.govt.nz/cms/licensees/types-of-licence/general-user-licences/low-power-fm-broadcasting-short-range-devices.
² Direct link at http://www.rsm.govt.nz/cms/policies-and-planning/current-projects/broadcasting/vhf-fm-broadcasting-frequency-availability-and-allocation.