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#140599 - 04/10/04 04:45 AM Ashburton Aerials
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Ever wondered what a TV aerial looks like down here?.
Well here's the answer:
here's my set-up.



And here is my next door neighbours set up that I installed about 11 years ago:

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#140600 - 04/10/04 09:41 AM Re: Ashburton Aerials
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Mike, although all the ‘rules’ have changed in North America with regard to commercial/terrestrial TV broadcasting, there used to be two distinct bands—VHF at ~55-215MHz {12 channels} and UHF at ~471-805MHz {±56 channels.}

It looks by the pictured antenna elements that there may be a roughly similar situation in NZ. Is that the case?

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#140601 - 04/10/04 10:05 AM Re: Ashburton Aerials
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
According to my references, New Zealand has 11 VHF TV channels, 1 thru 3 in the low band (~44 to 68MHz) and 4 thru 11 in the high-band (~174 to 230MHz), plus UHF in the usual range.

The VHF allocations were pretty similar in much of the western world. The old British VHF channels ran 1 thru 5 in the low range (called Band I here) and 6 thru 14 in the high range (Band III).

VHF TV was phased out here in 1985, so it's rare to still see a house with an old VHF TV antenna on the roof. The top Yagi array on Mike's house is also fairly typical of the UHF TV antennas used in Britain these days, although in areas closer to the transmitters fewer directors and a plain "grid" reflector are perhaps more common.

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#140602 - 04/10/04 10:14 AM Re: Ashburton Aerials
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
The little grey plastic "bird baths" seem to be everywhere now, too.

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#140603 - 04/11/04 06:43 AM Re: Ashburton Aerials
C-H Offline

Member

Registered: 09/17/02
Posts: 1508
Loc: Stockholm, Sweden
Mike,

the first picture is identical to what you see in Sweden. I thought you people down under had your aerials up side down

By the way, is NZ going digital or will it stick to analogue for the time being?

[This message has been edited by C-H (edited 04-11-2004).]

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#140604 - 04/11/04 11:38 AM Re: Ashburton Aerials
classicsat Offline
Member

Registered: 11/23/02
Posts: 449
Actually, in North America, there are 2 separate VHF sub bands for OTA TV, Chs 2-6 in 54 to 88 Mhz (except 72-74 Mhz, which is used for RC controls), and 174-215 Mhz for 7-13.

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#140605 - 04/12/04 12:19 AM Re: Ashburton Aerials
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
On top, we have a 91 Element UHF Aerial, made by Hills Aerials
Below that we have a 6 Element VHF Low and High Band Aerial, made by Lincrad Aerials, below that on the mast is a 34dB Mast-head Amplifier + Diplexer, amplifies UHF only, VHF is only Diplexed, 0.5 dB loss and at 85dB(i) signal level at the TV, this is not a problem
On the roof we have a 600mm dia Sky Digital Dish, pointed towards Optus B2 at a Field Strength of 75 dB(m) we have a good picture.
UHF is a different story though, it hates mountains, as we have here and it is Line of Sight at the best of times, hence the Mast-head amp, the best I have seen is 35dB(i), at the Aerial.
Trees here block the signal out.
Anyone else have ideas on UHF signals?.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#140606 - 04/12/04 12:37 AM Re: Ashburton Aerials
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
C-H,
Everything is Upside down here, didn't you know that?.
Most TV services here are Terrestrial Analouge: TV1, 2, 3 and 4 are like this but, if you have Sky Digital you can get these Channels, in Digital.
These are the VHF channels here, but get a decent snow storm and the dish craps out,that's why the VHF aerial is still up there!.
UHF still carries the Regional TV station, CTV, Canterbury Television and also Prime Television another National TV station that has a lot of Australian content.
For some odd reason my 2 metre Transciever knocks out some of the UHF Channels, call it Harmonic Interference, I'm not sure, anyone care to explain?.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#140607 - 04/12/04 03:50 AM Re: Ashburton Aerials
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Mike,
Are all VHF TV broadcasts in NZ horizontally polarized, or just the ones from your local transmitter?

When VHF was used for TV in the U.K. we had a mix of vertically and horizontally polarized transmitters (I have some links to websites with the old assignments somewhere -- I'll try to find them later).

Combined band I (low VHF) and band III (high VHF) antennas were available, but separate aerials and a diplexer were more common in many areas, as the BBC and ITA transmitter sites were often in different directions.

When the UHF network was planned in the 1960s, they came to co-siting agreements, which meant that only a single UHF antenna would be needed for all stations. (That planning has been totally screwed up in recent years, but that's another story. )

The UHF network here uses horizontal polarization for the main transmitters, with vertical for most of the relays (low-power transposers).

People in parts of Wales and Scotland (the mountainous regions of Britain) were not happym when VHF services were closed down in 1985, as it left some areas with very poor signals from the UHF broadcasts.

 Quote:
For some odd reason my 2 metre Transciever knocks out some of the UHF Channels


Could be harmonics, although you'd be looking at the 4th harmonic and above, which should be pretty well suppressed. Many of the UHF masthead preamps for TV use tend to be easily de-sensitized by strong fields nearby, or you may be getting cross-modulation products.

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#140608 - 04/12/04 04:48 AM Re: Ashburton Aerials
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Paul,
I used to come up to Ashburton as a young kid, we have family here and I could never get over the Horizontally-Polarised VHF Aerials, considering that all of our Aerials in Temuka were Vertically-Polarised.
Being an Aerial Technician, that has worked with both Polarisations, you have a 20dB "out of Polarisation" loss, regardless of where you point the Aerial.
In Temuka these days, the UHF Signal is Vertically Polarised.
Ashburton is a real nuisance as far as TV Signals go, we are half way between the "Sugar-loaf" Transmitter in Christchurch and the Cave Transmitter west of Timaru.
160 km's each way
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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