2009 NZART Comments on Options for Control Channels in TV Wireless Cameras
23 July 2009 Mr Brian Miller Manager, Radio Spectrum Policy and Planning Radio Spectrum Management Ministry of Economic Development P O Box 1473 WELLINGTON 6015
Discussion Paper on Spectrum Options for Control Channels in Wireless Cameras- NZART Comments
Thank you for the opportunity to comment on your discussion paper on control channels in wireless television outside broadcast cameras.
This submission contains our comments on Question 5 in your discussion paper:
How feasible is it to allocate the high power control channel service on a shared basis with the existing amateur service in the 434.1375 - 434.4625 MHz frequency range?
After carefully considering your proposal, we have formed the view that there is a high probability of interference between these devices and other users of this spectrum and that it is therefore not feasible to allow TVOB remote controls to share this frequency range.
The detailed reasons for this conclusion are given in the attached NZART Commentary.
Once again, we would like to thank you for the opportunity to comment on your Discussion Paper and we look forward to further constructive dialogue on the issues it raises.
NZART Administration Liaison Officer.
NZART Commentary on the Feasibility of Allowing High Power TVOB Remote Controls to Share Spectrum with the Amateur Service and Other Users in the 434.1375 - 434.4625 MHz Frequency Range
The Ministry of Economic Development is currently consulting regarding suitable spectrum for remote control of TV outside broadcast cameras. The paper1 asks questions about two prime options:
* Sharing with Amateur radio and short range devices (SRDs) in the frequency range 434.1375-434.4625 MHz (i.e. within the SRD allocation in the 70 cm Amateur band); and
* Sharing with SRDs in the 821-822 MHz band
NZART View on the Options
The NZART views on the two options in the paper are:
* We believe it is not feasible for reasons stated below, for TVOB remote controls to share the frequency range 434.1375-434.4625 MHz; and
* We have no opinion on TVOB remote controls sharing spectrum with SRDs in the 821-822 MHz band.
The following material explains why NZART believes it is not feasible to allocate TVOB remote controls spectrum in the range 434.1375-434.4625 MHz
Current Usage of the Frequency Band 430 - 440 MHz
International and New Zealand Allocations
The 2008 Radio Regulations state that the 430 - 440 MHz band has the following allocations in Region 32:
* Primary: Radio Navigation3
* Amateur Radio
* Earth Exploration Satellites (432-438 MHz only) and
Within New Zealand4, the Crown has allocated the frequency range 433.05 to 434.79 to Industrial Scientific and Medical applications5 and SRDs.
With respect the 430-440 MHz Amateur band, the Amateur GURL notes that:
* These frequencies are, or may be, allocated for use by other services. Amateur operators must accept interference from, and must not cause interference to, such other services. (Note 2) and
* These frequencies may also be allocated to Short Range Device (SRD) services. Amateur operators must accept interference from ISM and SRD services within these frequency ranges. (Note 3)
The New Zealand Amateur Radio Bandplan6 allocates a number of services to the 70 cm Amateur band as shown in the diagram below:
As will be seen from the diagram, the proposed sub-band 434.1375-434.4625 MHz overlaps with current voice and amateur television allocations within the 70 cm Amateur band. In particular, it overlaps with:
* the output of one existing licensed Amateur television repeater;
* the inputs to 2 existing licensed Amateur voice repeaters;
* the inputs to 30 existing licensed Amateur television repeaters; and
* ad-hoc point-to-point amateur television transmissions;
* As noted above, the Crown has also allocated the sub-band 433.05 to 434.79 MHz to Industrial Scientific and Medical applications and SRDs. It is not known what quantities or volumes of devices are currently using this allocation but it is understood that these frequencies are particularly popular for car remote access keys7.
Potential Interference Issues
This section considers three different interference issues that are likely to occur if TVOB remote controls are allocated frequencies in the sub-band 433.05 to 434.79 MHz:
* Interference to Amateur transmissions from TVOB remote controls; and
* Interference from Amateur transmissions into TVOB remote controls; and
* Interference between TVOB remote controls and other SRDs.
Interference to Amateur Voice Transmissions
As noted above, the input frequencies for two currently licensed 70 cm voice repeaters are located in the 434.1375-434.4625 MHz frequency band:
* 915 Mt. Cargill, Dunedin; and
* 9175, Clifton Trig, Hawkes Bay
At the least, these repeaters are likely to suffer from false triggering from any TVOB remote controls and, if the devices are used close to the repeaters, they could also suffer from de-sensing and/or interference with traffic on the repeaters.
The first of these issues, false triggering, could potentially be mitigated by using CTCSS or similar to control access to the repeater.
The second and third issues are much harder to combat. The only way to avoid interference is likely to be to change the operating frequency of the repeater which would require retuning of repeaters and duplexers and may, in some cases, require additional filters and/or new aerials to be fitted.
Interference to Amateur Television Transmissions
As noted above, the proposed allocation also overlaps the band used for Amateur television. The vestigial sideband of the amateur TV repeater vision spans the segment proposed for TVOB remote controls.
The band 430 - 438 MHz is used both for simplex communications and also as the input frequency to most8 of NZART's Channel 39 (614 to 622 MHz) Amateur television (ATV) repeaters. There are currently 30 ATV repeaters licensed and an unknown number of individual amateurs whose transmissions are likely to be interfered with by the proposed devices.
Unlike voice repeaters, there is little ATV repeater trustees (or individual Amateurs) can do to avoid interference from TVOB remote controls; the 70 cm band is only 10 MHz wide which makes it impracticable to move the (8MHz wide) ATV signals away from the potential interference sources.
Interference from Amateur Transmissions
TVOB remote controls are likely to receive interference from:
* The output of 1 Amateur television repeater;
* Amateurs accessing 2 voice repeaters
* Amateurs accessing 30 television repeaters
* Amateurs point-to-point television transmissions and
* Other ad-hoc Amateur transmissions
Amateur transmissions are likely to have two main effects on TVOB remote controls:
* improper activation of remote controls - causing cameras to move, change focus, etc; and
* blocking of remote control signals - preventing them from obeying legitimate commands.
The first of these should be easily overcome by the use of appropriate coding of the signal between the transmitter and the receiver. It is expected that properly designed TVOB remote controls would prevent this from happening except in very extreme signal overload conditions.
The second is however, a quite likely occurrence and difficult to prevent. An Amateur transmitting well within legal powers connected to a reasonable aerial on a frequency close to that being used by a TVOB remote control could easily cause blocking of a TVOB remote control receiver located quite some distance away.
The Paper's solution to this seems to be to require the Amateur concerned to stop transmitting in accordance with Note 2 to the GURL:
These frequencies are, or may be, allocated for use by other services. Amateur operators must accept interference from, and must not cause interference to, such other services.
In normal operation, this means that if an Amateur finds the band is busy with other traffic, or if a non-Amateur station suddenly appears, all Amateur traffic must cease. Such a mechanism is only practicable, however, if the Amateur concerned has some way of detecting that the other signal is present. In this case:
* the remote control signals are likely to be used only when a race meeting is in progress;
* the signal itself is likely to be intermittent in nature (only transmitting when a command needs to be sent); and
* even if a signal is heard, the Amateur, (depending on the modulation scheme used) may not be able to tell if it is a "real" signal or just noise.
It is therefore extremely unlikely that an operator would be aware of causing interference and hence the operator would not know to cease transmission.
Interference between TVOB remote controls and other SRDs.
As noted above, the SRD section of the 70 cm Amateur band is widely used for car remote access keys. The allocation of this frequency range to high power TVOB remote controls is likely to cause interference problems between these two types of devices.
Again there are two likely interference effects; noise in the TVOB remote control receivers and blocking of car door opener receivers9. The latter is likely to be the more serious - especially at racecourses where the majority of the attendees arrive by car.
The previous sections have outlined the interference problems that are likely to occur if TVOB remote controls are allocated frequencies in the sub-band 434.1375 - 434.4625 MHz and the (lack of) mechanisms to combat such interference.
For these reasons, we believe it is not feasible to allocate the high power control channel service on a shared basis with the existing amateur service (and SRDs) in the 434.1375434.4625 MHz frequency range and we recommend that the Ministry abandon this option.
See Discussion Document On Re-Planning The Band 406.1 -449 MHz, page 16.
The exception is one "inverse" ATV repeater in Wellington which uses Channel 39 for its input and has its output frequency in the 70 cm band - see discussion under Interference from Amateur Television Transmissions.
It is understood that one Amateur repeater in the UK was shifted to another location at the request of their landlord as it was blocking car door openers in a nearby car park.
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