Rumour has it that the VHF and UHF 625 line 50 field PAL transmissions will end in Australia in a few years. That is, if you believe rumours. It remains to be seen if they really do get turned off. Put simply, the demand for digital TV isn't there. Australia is fortunate in using the best TV system in the world. 625 lines and chroma phase error immunity with the PAL system gives us a considerable advantage over certain other countries. In fact, with a good aerial, the digital picture is no better than its analog equivalent. So why is big business pushing the government to implement it?
The main reason from media organisations is that six channels of digital can be put in the same bandwidth of one analog channel. So, six times as much advertising! What really happens is there's six times as much crap; there's only a finite amount of television programming that can be made.
The other main reason comes from electronics manufacturers. What a good way to force everyone to buy new TV sets or digital boxes! All that income for the greedy manufacturers. In reality, people have to buy things they don't and didn't need, and China uses up the world's resources making all this new stuff, furthering environmental damage.
Having said that, there is one useful feature of digital TV. In areas where even the best aerial won't get rid of the ghosts, digital TV will. (At this point I need to mention that anti ghost systems were developed for analog TV during the 1970's & 80's but consumers weren't interested).
Also in areas where the signal is not strong enough to provide a snow free picture, the digital system will...but up to a point. Below a certain signal level, the digital signal is lost, leaving the viewer with nothing, or a blocky jumpy picture at best, with defective sound. An analog picture would still exist at this level.
Conventional signal strength meters do not work with digital signals as they resemble a 7MHz block of noise. A spectrum analyser is the best way to see what's going on with the aerial system.

It surprises me that some people are worried their monochrome VHF TV set won't be useable if the shutdown occurs. There is no need for alarm. A television made in 1956 works on the same 625 line 50 field negative modulation, 5.5MHz FM sound transmissions we use today. The only difference is that in 1974 the chroma subcarrier was switched on at the TV stations (colour had been transmitted experimentally since the late 1960's but as the government didn't want people importing colour sets to view these transmissions, the colour subcarrier was removed prior to transmission).
So, just like with a modern colour set, the method of using your antique for digital is the same. Digital boxes are getting to under $40 now. One model I like is the DVX555 sold by Strathfield Car Radio. This box allows you to install a hard disc which you can record TV on. It costs $69 but you have to supply your own hard disc. Any capacity can be used; the box automatically formats. Obviously the larger the hard disc, the more it can record. There's plenty of info on the internet on this box if you want to search.
An interesting feature of the DVX555 is that you can select NTSC output in the setup menu. This means that you can effectively use an American TV set to watch the Australian digital TV channels, in colour, without any modifications. Programs can also be recorded on an NTSC VCR or fed into an NTSC only video capture card etc. If you like collecting foreign TV sets this is a very useful feature. I discuss it further here.

The DVX555 doing the channel scan at setup. Set is a 1957 Kriesler 79-1 chassis, Model 121-1.

There's a slight problem now; most of these boxes have only baseband audio and video out, and a few have UHF output. Not very useful on a VHF TV with no AV inputs. What to do? Where the box has only AV outputs:
1) Feed the baseband inputs into a VCR that outputs on a VHF channel.
2)Get a VHF modulator and feed the box into that.

Where the box also has UHF output, you can:
1)Feed the UHF into a VCR that outputs on a VHF channel.
2)Use a UHF to VHF converter.

A word on VHF channels:
It is important to know that the VHF channels of 1956 are not the same as the VHF channels of now. In 1961, the number of channels was increased from 10 to 13. The government hadn't anticipated the demand for TV in australia.
Briefly, the old channels 1,4, and 5 were changed in frequency, and new channels 0, 5A, and 11 were added. For commercial interests, the existing channels operating at the time 2,7,9 in the mainland capitals, and 2 and 6 in Hobart, Tasmania did not have their channel number changed. This is why we have channel O and 5A.
The channels that did not change are: 2,3,6,7,8,9,10 (10 did but only by 1Mc/s which is insignificant and well within the range of the fine tuning control). As Australian VCR's with VHF output transmit on either 0/1 or 3/4, you need a 3/4 model for a pre 1961 TV set. The UHF converters once sold by Tandy also output on 3 or 4.
You can use a 0/1 model if you wish...
The old channel 1 is about 4Mc/s higher than channel 0, so providing there's enough adjustment in the local oscillator you can tune down to channel 0. You should really retune the RF circuit but in practice just the local oscillator is enough.
I was doing this since the days of SBS being on channel 0 in Sydney and had good results.
You can also tune up to the present channel 1, but this usually requires a greater range of adjustment.
With my Ekco TX287 I had to add a few pF across the oscillator coil in the tuner to get its channel 1 down to channel 0. Why didn't I use channel 3? Because this biscuit was not fitted in the tuner.

One handy feature is the program guide (this can be done with the analog system as per Teletext)

To keep with the period theme, you can get valve UHF converters off the US eBay. Their channel 6 is close enough to our channel 3.

The other option of course is to simply provide AV inputs on your TV. I'm not recommending this as it means doing mods (i.e.. butchery). The audio level from a digital box is compatible with the typical triode pentode audio stage and can be fed into the set's volume control via a capacitor (something like .1uF). The unterminated video output of the box is 2Vp-p which will drive a video output pentode. Terminating it in the correct 75 ohms will reduce the level and perhaps provide insufficient contrast. In practice with short leads the correct termination isn't important. A potential problem is with sets that have their contrast control as part of the AGC system; this will not work properly with direct video input. I won't go into this any further, but merely mention it as being possible.

Aerials
Outdoor TV aerials and even reception of TV signals off air is almost a thing of the past in many parts of the world due to the penetration of cable systems, and in arrogant stuck up housing estates where they don't allow outdoor aerials. Fortunately, in Australia off air reception rules, and most houses have outdoor TV aerials. Cable TV has been in Australia since around 1996 and due to population density (low..thankfully), and also some obstructive local councils, cabling was installed only in parts of the larger capital cities and towns.
Everywhere else gets pay TV from Satellite. In the past, MMDS was also used but was closed down around 2001. The satellite pay channels do not carry the free channels due to the three time zones, local news, and advertising requirements, so terrestrial VHF and UHF reception is still required.
Don't automatically be conned into needing a "digital" aerial or "digital" whatever. The digital transmissions are in the same VHF and UHF bands used for years.
I live about 80km from Gore Hill and about 90km from Knight's Hill. There are three TV aerials feeding my system. There's a circa 1965 Channel Master 636 Valiant for the Gore Hill VHF channels 2,7,9,and 10. Above this is a 91 element UHF aerial, a clone of the Fuba XC391. This receives Gore Hill UHF channels 28 and 31. A third 91 element UHF aerial receives the Knight's Hill channels, Prime, WIN, Capital, ABC, and SBS.
 All three aerials are connected to my distribution system under the house by 300 ohm ribbon. This has much lower loss than coaxial cable, especially on UHF. The Gore Hill and Knight's Hill UHF signals are combined by a Johanssen band 4/5 diplexer and then  amplified by 28dB. The amplified UHF signals then feed into a VHF/UHF diplexer which also accepts the VHF signal which has 15dB of amplification. The combined signal then passes into a six way splitter for distribution around the house and garage via RG59 coaxial cable.

Aerials for Gore Hill (Sydney) reception. On top is the 91 element UHF aerial connected by slotted 300 ohm ribbon. Under is the Channel Master 636 from the mid 1960's. This aerial was rescued from a building site where it had been trampled on. There's even a toothbrush handle used to splint the low band dipole!

While this system works well on the analog system, there is a slight problem with ABC on digital. I noticed dropouts on ABC1 and ABC2 while other channels were good. These channels are transmitted on Ch 12. Connecting the VHF aerial to a spectrum analyser showed what the problem was. There's a severe roll off at the top end of the VHF band with the old Channel Master aerial. The Ch 12 signal is not only much attenuated but you can actually see the frequency response sloping off! I shouldn't be too surprised given the distance I am from the transmitter and the fact that Yagi aerials do not have an even frequency response like log periodics do. The other factor is the aerial simply wasn't designed for reception of Ch 12. In fact it may be so old as not to have even been designed for Ch 10 reception. Remember that until 1965 there was only Ch's 2, 7, and 9 operating in the larger capital cities.
In my situation the way out of the problem is simple. When I want the ABC channels on digital, I simply use the Knight's Hill signal. That way I can keep using my antique VHF aerial.

For Knight's Hill (Wollongong) reception, this 91 element UHF aerial is used. It's the same model as the one for Gore Hill, which can be seen to the left.

For everyone else, if you have problems with the ABC, and possibly Ch 10, digital channels and you're using a VHF Yagi, you might need to replace it. The only new VHF aerials I recommend are those made by Matchmaster. These are the only ones I will install for other people. Why? Most other aerials are very flimsy and are full of plastic insulators which deteriorate in the weather and their numerous rivetted connections are unreliable. Additionally, their anti ghosting properties are absolutely useless. The AntSig aerials sold by Dick Smith, Bunnings and other discount type stores are amongst the worst. So are those log periodics made by Hills.(Telray and Pathfinder series). (Slight exception given to the EFC2/3/4 which are reasonable for anti ghosting).  I'm not too fond of the Hills UHF aerials either (like the TC18 etc.) these are a copy of the Antiference designs from the UK. The problem is they don't have a balun and have coaxial cable connected straight to the folded dipole. Unbalancing the dipole like this changes the directional characteristics of the aerial.
In my opinion, the best VHF aerial ever made was the Channel Master 3112. What this does in ghost prone areas is like magic. Unfortunately this has not been made for many years but luckily I do have a couple of surviving examples in good condition.
 
 

Digital Channel 44. This has what are termed "narrowcasting" channels. Digital TV wasn't even dreamed of when this set was made but as you can see it performs perfectly with the new signals.

Interference from digital signals
It should also be mentioned that the present transmissions are causing interference to some sets. This is because the digital signals are adjacent to VHF channels in use. Does your set suffer from hiss in the sound on Channel 7 or 9? If so, that's because Ch 7 digital is on VHF channel 6, and Ch 9 is broadcasting its digital signal on channel 8.
This is particularly bad on my  5 inch 5BP1 TV set as I did not incorporate any adjacent channel rejection traps when I built its IF strip.
UHF is just as problematic. Here in the Blue Mountains where I receive snow free the Gore Hill and Knight's Hill transmitters, and numerous weaker low power repeaters, it is impossible to find a clear UHF channel to tune in the output of a VCR, satellite receiver, or digital box. So bad is the situation, I have an RF switch box to disconnect the TV aerial system when viewing from these devices. It seems there's either a repeater, digital channel, or an intermodulation product of same right across the UHF band. It would be nice if these devices had VHF outputs...and while we're at it, how about RF outputs (preferably VHF) on DVD players as well?
The obvious way to solve the interference is to make filters or traps. I did experiment some years ago with quarter and half wavelengths of 300 ohm ribbon for making a diplexer, and I'd say there's possibilities here.
 
 
 

email me: cablehack at yahoo dot com

Home