ISSUE 2 2013-04-25
Prepared by Doug Ingham, ZL2TAR, ARE038
This Paper discusses the impact of the SRD GURL on the Engineering and Licensing of 70 cm Repeaters. Reference 1.
The SRD GURL permits transmissions on frequencies between 433.050 MHz and 434.790 MHz. This frequency range is used for the input of the majority of 70 cm repeaters.
National System repeaters use input frequencies above 434.790 MHz and will not be affected by equipment operating in compliance with the SRD GURL.
Several solutions have been suggested, including a variety of changes to the 70 centimetre band plan.
However, considering the harmonic relationship between the 2 metre, 70 centimetre and 23 centimetre bands, implementation of most of these suggestions would also require the re-planning of the 2 metre and 23 centimetre bands.
Considering the cost versus long-term benefit of the various suggestions, two solutions appear to be the best:
1. Add Continuous Tone Coded Squelch System (CTCSS) to the user transmitter and repeater receiver. Or:
2. Invert the affected repeater receive-to-transmit ofsfet, from +5 MHz to -5 MHz.
Under the second option, it may also be necessary to add CTCSS to the repeater transmitter and user receiver, since the user's receiver will now be tuned to a frequency within the SRD transmit band, 433.050 MHz to 434.790 MHz.
Branches owning a non-inverted repeater suffering from interference, should apply to FMTAG for an inverted frequency pair. Many Branches have already applied for, and RSM has granted, a licence for an inverted frequency pair.
An engineering investigation, in accordance with RSM PIB38, confirms that there should be sufficient frequencies in the 70 cm band plan to permit all of the non-inverted repeaters to make a gradual migration, on an as-requested-by-Branches basis, to an inverted frequency pair.
Inverted and non-inverted repeaters cannot use the same frequency pair, since mutual lock-up will occur during periods of enhanced propagation between the two repeater sites. Inverted repeaters need to be allocated inverted-repeater-only frequency pairs.
Existing On-Site, or Near-Site, Licences for transmitting and/or receiving on frequencies just below 430 MHz, or just above 440 MHz, may limit the choice of frequencies for the Amateur Repeater.
1. General User Radio Licence (GURL) for Short Range Devices (SRD). New Zealand Gazette 31/5/2012, No.61, p.1751. Radio Licence 234660. 433.050 MHz to 434.790 MHz.
2. Radio Licence Certification Rules (PIB38).
3. The impact on 70cm repeaters of the revised General User Radio Licence (GURL) For Short Range Devices (SRD). Issue 1, 2010-07-31.
PIB38 requires Certifying Engineers to perform a series of site-specific engineering calculations before Crafting and Certifying a Planned Radio Licence. Reference 2
The following PIB38 sections particularly apply to repeater inversion:
The existing site sense must be preserved.
A proposed licence:
Must not desense an existing service.
Must not be desensed by an existing service.
A proposed licence:
Must not cause interference to existing receivers.
Must not receive interference from existing transmitters.