New Zealand analogue switch off looms.

[Synchrodyne]

In the early days ignition and other impulsive interference was certainly a problem in Band I. I can recall that when the Waiatarua (Auckland) Channel NZ2 transmitter was only 10 kW erp, line-of-site reception in west Auckland was affected by passing vehicles, visible noise spikes and loss of line synchronization. Domestic appliances such as sewing machines caused visible interference patterns. Reception with “rabbit ears” was quite variable, and even a three-element rooftop Yagi did not fully clear the interference problems. When the new 100 kW erp transmitter opened in 1964, the signal was strong enough to overcome the interference. With the benefit of hindsight, I wonder if positive vision modulation system would have been a better choice for Band I.

Cheers,

[arjoll]

Originally Posted by Billy T

...and thus avoid co-channel interference, which was very rare here, even on low band VHF and mostly came from Australia during the summer months.

Except for Invercargill of course, where TV One on channel 1 from Hedgehope can be unwatchable for days at a time because of interference from Kaukau!

[Synchrodyne]

I wonder if that was a one-way effect, north to south, ducting maybe just east of the Southern Alps. When I was doing time in Wellington, I do not recall that Kaukau suffered co-channel interference from Hedgehope. The biggest problem, with all of the hills, was getting a clean signal. Even close-in and high-up at Newlands, an outdoor antenna was very necessary, and then much attenuation (around 24 dB as I recall) was needed to prevent overload and very visible cross-modulation with the not-very-good Philips VHF tuners of the period. (I forget the exact model involved, but it was circa 1983, probably one or two iterations after the K9, and that was bad, too, choking on signals that were easily handled by valve tuners.)

Re the long-distance interference, NZ1 was one of the lowest frequency channels anywhere, with vision carrier at 45.25 MHz, not much different to B1, 45.00 MHz, so it was inherently prone to occasional long-distance transmission. But it was used at three of the seven main VHF transmitter sites, Te Aroha (1V), Kaukau (1H) and Hedgehope (1H).

Cheers,

[arjoll]

Hedgehope is roughly north-north east to north-east from Invercargill - if you trace a line you'll find that's not too far off a straight line from Invercargill-Hedgehope-Kaukau, at least straight enough for a fair amount of signal into a 3 element yagi! I suspect that Wellington being so hilly would also help - there's probably a huge chunk of rock in the way of any signals coming from Hedgehope (not that I know Wellington's geography that well; I just know how to walk from the Novotel to the pubs on Cuba Mall and then down to the Westpac Stadium for the Sevens ).

[Billy T]

Originally Posted by SteveCG

Billy, What I was getting at was the clicks and pops that you get when light switches are operated, 'fridge doors are opened and closed, domestic applicances switched on and off, etc.

I don't recall switch problems, and our appliances were mostly suppressed, but now that you mention it, for a while we were bugged by a motorbike that created an awful lot of ignition noise as it roared past. Most other vehicles had suppressor leads by the time TV arrived here, but I remember mine didn't, so maybe I was the problem not the complainant.

Cheers

Billy

[colly0410]

Yes Billy I know the feeling of causing TV interference, my Mums neighbours cheered when I replaced my moped with a Triumph Herald...

[SteveCG]

As a slight aside, how well did NZ Channel 1 aerials survive the weather? Were Hpol designs/usage better than Vpol?
I had a Antiference booklet describing the Band I and III aerials they sold for use in Australia. Did Antiference sell them in NZ I wonder?

[Synchrodyne]

In and around Wellington, channel 1H aerials with missing, broken, bent or drooping elements were commonplace. But then Wellington is allegedly the world’s windiest city (apparently proved during the mid-1970s when a 230 ft tower was specially built for extended wind measurements.)

In the Bay of Plenty one saw some damaged channel 1V arrays, but my recollection is that they were not as common as in the Wellington area. Also, with the arrival of TV2 on channel 3 in the mid-1970s, there was a move to wideband Band I arrays, typically 3-element, and identifiable because the director was much shorter than the reflector. So probably a lot of the 1960s channel 1 aerials were replaced. In Wellington the TV2 arrival saw some replacement with combined Band I/Band III arrays, but also some addition of Band III arrays to existing channel 1 installations.

I do not know if Antiference sold aerials in New Zealand, but through the 1970s at least it was very likely a protected market for the domestic producers, with imports either not allowed, restricted in number or subject to heavy import duties.

Australian channel 1, at 56 to 63 MHz, was somewhat higher in frequency than New Zealand channel 1, at 44 to 51 MHz. In fact it was between NZ2 (54 to 61 MHz) and NZ3 (61 to 68 MHz). The Australian channel 0, a later addition (1970s?) was much closer to NZ1, at 45 to 52 MHz.

Mention of the Bay of Plenty reminds me of the interference issue. When my parents moved to Tauranga, their house had a 3-element wideband vertical Band I array pointed at Te Aroha. I recall that interference from passing vehicles was noticeable on both channel 1 (TV1) and channel 3 (TV2), but worse on channel 1. Both channels had 100 kW erp senders. During one visit in the 1990s I arranged installation of an FM aerial (4-element, I think, slant polarization, also pointed at Te Aroha) for good RNZ Concert FM reception; with an NAD tuner (I forget the model) there was still occasional passing vehicle interference. I’d need to look at the map to estimate distance from the transmitter site, but being at the top of Mt. Te Aroha, it was quite high, say 200 ft or so then with a 400 ft tower.

Cheers,

[Ebrew567]

I use a Chinese made Chan 29-Chan 69 mid gain antenna for NZ Freeview at my location in Wellington, NZ and as expected it cannot handle the local wind.

Can anyone suggest a website where I can design a 600Mhz Yagi (say 5-8 elements) but strong enough to handle 140Km/Hr winds?
(Yes we have quite special antennas here for the current Wellington TV 1 (approx 54Mhz) service.)

[SteveCG]

So from what has been said it would be reasonable to think that the NZ experience of interference was such that Band I digital would have had problems...

BTW when System I UHF TV started in the UK in 1964 great play was made of negative modulation meaning that ignition interference would not be such a visible problem. My experiences with DX TV a couple of decades later taught me that this BBC claim was not true, as I was getting noticable white interference streaks on my negative modulated DX signals. Thinking on it I decided that low levels of interference might appear as less noticable black streaks, but if the interference was strong then it appeared 'white'. The interference was not much of an issue with the 'new' UHF TV broadcasts, not because of negative modulation, rather because of the use of UHF where the spectrum of the interference signals petered out.

I bet there are places in NZ that will no longer be able to receive terrestrial TV when the far better propagating Band I signals are shut down.

[paulsherwin]

Originally Posted by SteveCG

I bet there are places in NZ that will no longer be able to receive terrestrial TV when the far better propagating Band I signals are shut down.

Ah, but it's a different culture Steve. The population density is massively lower and they don't share our expectation that everybody should be able to receive a terrestrial TV service, no matter where they live. There will be a lot less resistance to using satellite there.

[arjoll]

Originally Posted by Ebrew567

I use a Chinese made Chan 29-Chan 69 mid gain antenna for NZ Freeview at my location in Wellington, NZ and as expected it cannot handle the local wind.

The Hills Signalmaster ones seem to cope ok here, and we're the second windiest part of the country! Installers seem to be using a lot more of those phased arrays here at the moment.

Originally Posted by SteveCG

I bet there are places in NZ that will no longer be able to receive terrestrial TV when the far better propagating Band I signals are shut down.

Absolutely - massive chunks of the country will only have satellite coverage, but terrestrial is something like 86% of the population now.

Even here in Southland MCH have decided to use Forest Hill instead of Hedgehope, meaning that areas like Gore and anywhere north of Winton have to use satellite. It's not so much a UHF vs VHF issue, but an inferior site used to save costs. I've grumbled about it in my blog (which I really should update....!).

There's more detailed coverage information here.

[SteveCG]

Arjoll,

I presume satellite equipment is inexpensive in NZ, so switching to it from terrestrial is not a big issue - unless you are forced to pay subscriptions!

For nostalga reasons I use the digital terrestrial TV - like quite a few on this forum I've grown up with Yagi aerials. However, I have a friend who has a cheap satellite receiver and he watches stuff originated all over Europe and beyond. He has never fully understood why I liked terrestrial DX TV and not satellite DXing - I tell him 'it's the dipoles!'.

Did the NZ authorities say why they went only to UHF digital and not even Band III ?

[Synchrodyne]

Originally Posted by SteveCG

BTW when System I UHF TV started in the UK in 1964 great play was made of negative modulation meaning that ignition interference would not be such a visible problem. My experiences with DX TV a couple of decades later taught me that this BBC claim was not true, as I was getting noticable white interference streaks on my negative modulated DX signals. Thinking on it I decided that low levels of interference might appear as less noticable black streaks, but if the interference was strong then it appeared 'white'. The interference was not much of an issue with the 'new' UHF TV broadcasts, not because of negative modulation, rather because of the use of UHF where the spectrum of the interference signals petered out.

I think it is worth referring to the original (1941) NTSC deliberations on the question of negative vs. positive vision modulation:

“The effect of interfering signals is about equally objectionable with either polarity of transmission. The synchronizing difficulties of negative transmission are offset by the more noticeable effect of the interference in the picture with positive transmission. With either polarity of transmission, it is possible to reduce the effects of interference on both the picture and synchronizing by the proper use of limiter circuits in the receiver. From the tests that were made, it was decided that the decision as to which type of transmission should be used should be based on other considerations of one polarity over the other.

“The remaining major consideration is the use of an automatic volume control. With negative transmission, a very simple and effective a-v-c circuit can be built into the receiver. It is possible,
however, to design an automatic volume control for positive transmission. It will be inherently more complicated. Its performance will also be inferior and its cost greater than that of an automatic volume control designed for negative transmission.

“Since all tests have shown that technically there is no choice between positive and negative transmission in regard to receiver performance, the transmitter power gain, the a-v-c complexity and cost should determine the choice of polarity. It is therefore recommended that negative be adopted as standard.”

Since then I suspect that more advantage has been imputed to negative modulation than would be supported by the NTSC work, which also essentially informed the early development of the 625-line systems.

In practice, negative modulation receivers operating at VHF, particularly Band I, required noise-gated sync separators, which was an added complexity not needed with positive modulation. Hence the development of dual-control gating valves such as the 6BY6 and 6CS6 (EH90) in North America, and the ECH84 in Europe (before which Philips used the ECH83 for the same purpose). And the agc advantage was perhaps not as great as first imagined. True, simple peak level agc based upon sync tips could be used as this preserved the dc component, but in practice line-gated agc was used both to allow a shorter time constant and to confer some noise immunity. In fact both noise-gating and line-gating of agc were provided for in the late 1950s 6BU8 double dual-control pentode valve, which suggests that in practice line gating alone did not always provide enough protection. Thus negative modulation agc systems ended up with complexity comparable to those required for line-gated (back porch) positive modulation systems, although the latter still required higher gain. For example the Mullard development of the sync-cancelled agc system shows but minor differences between the positive and negative modulation variants. And anyway, whilst one might not want to condone the practice, quite a few positive modulation receivers had simple mean level agc, that idea being extended into the IC age, for example with the TDA2542. Perhaps too the noise-inverters included in that generation of ICs would have gone a long way to eliminating positive vs. negative differences.

So maybe positive modulation got something of an unjustified bad rap. But Carnt & Townsend did come down quite heavily in favour of it for NTSC-type colour systems. And one wonders whether there was a technical element in the Belgian (System C) and French (System L) choices for 625 lines. The conventional wisdom is that the Belgian choice was made largely for “political” reasons. The French chose positive modulation for its domestic 625-line TV service, ostensibly to simplify dual-standard receiver design, but on the other hand chose negative modulation (System K’) for the Outré-Mer territories. The latter was intended for use only Band III as far as I know, where impulsive interference level would be lower than in band I, whereas System L, although originally intended for UHF, was later also used in Band I. So if that move was anticipated, just maybe it was another reason to choose positive.

Cheers,

[Billy T]

Originally Posted by SteveCG

I presume satellite equipment is inexpensive in NZ, so switching to it from terrestrial is not a big issue - unless you are forced to pay subscriptions!

Satellite is indeed by subscription only, and at a significant cost as well!

Conversely, Digital receivers for UHF terrestrial transmissions range in price from a current low (on special a few days ago) of $38, up to $200-300+. The range of programming for Freeview is limited, but quite adequate if you are not a TV addict or a sports enthusiast.

My decoders cost $99 each and can also act as a PVR using either a USB stick or USB disk (neither supplied) which makes them pretty good value. These days most TVs come with a built-in Freeview decoder anyway.

There are also a wide range of other satellite transmissions receivable in NZ, including US sources I believe, but they require very large ground-mounted dishes aimed at a low-horizon azimuth and are very popular with immigrants, particularly from Asia.

Did the NZ authorities say why they went only to UHF digital and not even Band III ?

IIRC they wanted to clear Band III for other services, but I don't recall what those services will be. Time will tell, or Google might know, but it is of little consequence to the man in the street.

Cheers

Billy

[arjoll]

Originally Posted by Billy T

Satellite is indeed by subscription only, and at a significant cost as well!

Um... no. Freeview is free on Optus D1, no subscription, just a receiver (< $100) and dish (about $100-150 depending on size, or use an old Sky one).

Originally Posted by Billy T

There are also a wide range of other satellite transmissions receivable in NZ, including US sources I believe, but they require very large ground-mounted dishes aimed at a low-horizon azimuth and are very popular with immigrants, particularly from Asia.

There's a lot of European and Christian stuff on Optus D3, which is only a few degrees over from D1 (Sky & Freeview) and plenty of signal on my 88cm dish (would probably be acceptible on a 65cm Sky dish).

I suspect you're thinking of the Indian/Asian stuff on Asiasat 3s C-band - that's where a lot of those mesh 2.4m dishes you see around the place will be pointing.

Until recently you could also get BBC World News, Australia Network and feeds from Intelsat Napa on Intelsat 5 C-band on a smallish dish - I have a 1.2m but reports are that 90cm was possible. This stuff has moved and I haven't gotten around to repointing that dish yet, so not sure if it's still easy to pick up.

[Billy T]

Originally Posted by arjoll

I suspect you're thinking of the Indian/Asian stuff on Asiasat 3s C-band - that's where a lot of those mesh 2.4m dishes you see around the place will be pointing.

You are right there arjoll, I just didn't want to attribute it to any particular group in our society. Mea Maxima Culpa on Freeview Satellite I didn't mention it because there is a significant cost involved in setting up with a dish etc whereas Freeview terrestrial seems to be pretty much plug and play on any existing aerial if the signal is half reasonable.

Mine is operating via a combined VHF log-periodic and modest UHF antenna system that originally pulled in Prime ok but that signal faded out several years ago and the rest of the UHF channels dropped in strength. The drop off coincided with a major construction job on the immediate horizon (shopping centre) which was right on-beam and we are well below that height.

I have a distriibution system that feeds a number of outlets on two levels of my home, plus an underground feed to the garage, and once I installed my Freeview arrangements (two Freeview-enabled TVs and three $99 Loranz decoders) I turned the distribution amp down to its lowest setting on UHF and I still had reliable performance on all Freeview channels so I left it there. None of the analog UHF channels were watchable at that setting.

On that basis it does seem that UHF Freeview is either running a much higher Tx power than the old analog transmitters, or the digital transmission can cope with significantly weaker signals. If pressed, I'd pick the latter, but I don't really know.

Cheers

Billy

[SteveCG]

On that basis it does seem that UHF Freeview is either running a much higher Tx power than the old analog transmitters, or the digital transmission can cope with significantly weaker signals. If pressed, I'd pick the latter, but I don't really know.

I've found that there is quite a sharp threshold between all or nothing on terrestial digital TV, so I'd go with your latter thought.

[arjoll]

Originally Posted by Billy T

You are right there arjoll, I just didn't want to attribute it to any particular group in our society.

There was (and my still be, I need to check Lyngsat) some good stuff on that bird - Al Jazeera International, NOW!TV and a couple of others that used to be rebroadcast on NSS5 by an Auckland outfit that was "testing" for a year or so then disappeared. They also rebroadcast NASA TV, which was handy seeing the service needed a huge dish with circular polarisation from Intelsat 701. It's been 6 years since I first installed our satellite system though so all this has probably changed .

Originally Posted by Billy T

Mea Maxima Culpa on Freeview Satellite I didn't mention it because there is a significant cost involved in setting up with a dish etc whereas Freeview terrestrial seems to be pretty much plug and play on any existing aerial if the signal is half reasonable.

Setup cost will depend largely on whether the house has ever had Sky, and if you're ok to do it yourself. You can usually reuse the Sky install, although if it's got an older LNB that may need replaced. I did my parents' and brother's places for about $120 plus the decoder, and that was with 88cm dishes (less rain fade), but I do get a good deal on parts!

In terms of the Freeview system here, I'm still using the same UHF aerial that did pull in Prime ok, but have upped the splitter from 4 way to 6 way. It's feeding the media centre (1x Hauppauge dual DVBT tuner, 2x Hauppauge single DVBT/DVBS tuners I bought to experiment with and never got aroudn to, and the old Hauppauge analogue for Cue and FM), lounge TV (Panasonic 42" LED LCD) and the bedroom TV (Sony 26" LCD analogue, via a Freeview satellite box). The TV in the second lounge is our old Sony 29" CRT fed from the satellite box.

I've yet to work out what's happening long term with the bedroom TV - possibly just a cheap $69 DVBT box via HDMI.