PDC & Videoplus+TM Video Recording

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Many people have difficulty setting their video recorders to make timer-controlled recordings. There are two areas of difficulty. One is the setting of the correct programme channel and time into the machine. The other occurs when the broadcaster alters the transmission time of the programme at short notice. Recent developments have provided solutions to these problems.

What is PDC (Programme Delivery Control)?

PDC is a system, developed in Europe, to enable video cassette recorders (VCRs) to start and stop at the precise time that a programme is broadcast, rather than the times preset from Radio Times or other listings.

Why do I need PDC?

Live programmes sometimes overrun, or there may be late changes to the schedules, but video recorders set up using PDC will still make a complete recording. Recorders set up using only the on-board clock or VideoPlus+^TM system will lose the end of the programmes following the overrun, or record the wrong programme altogether.

How does it work?

Using the Ceefax signal the BBC broadcasts a "label" which the PDC video recorder uses to start and stop the recording. The "label" is normally transmitted automatically at the programme’s scheduled time, but when a programme overruns or is re-scheduled, it is delayed until the programme actually starts.

What is the connection between PDC and Videoplus+^TM?

PDC shares the VideoPlus+^TM published codes to program suitably equipped video recorders. These codes, to be found printed against the programme listing, represent the date, channel, and start & stop times. Simple VideoPlus+^TM video recorders take no account of overruns, and are dependant on the vcr clock or handset being set very accurately.

Are there any problems?

Sometimes the vcr does not make the recording as expected, and it is worthwhile trying to find out why.

Were the codes transmitted correctly?

During the trial phase of PDC, the BBC encountered some situations where the codes were not transmitted automatically. As mistakes were spotted, so they were fixed.

There will always remain a slight possibility that a mistake has occurred. This can be verified by contacting Engineering Information. However first you should try to ensure that it was not a machine or programming problem.

Did the machine malfunction?

Some older vcrs are not fully PDC compliant, and thus fail when you try to make a recording.

Try repeating the recording on the same channel with perhaps the same programme or a series at the same time of day. If this is unsuccessful see if the vcr fails on all channels, or just those of one broadcaster, e.g. the BBC.

Check with your dealer or manufacturer to see if they are aware of any problems, and if they have produced a modification for your machine.

Was the machine programmed correctly?

It is not unknown for newspapers to print the incorrect codes, or for the operator to mis-read or mis-key the entry.

Try to check and confirm the details as you programme the vcr.

Check also that any "timer recording" functions have been enabled; some machines need to be in a "standby" mode before PDC will work. Check the handbook for details.

What is a decibel (dB)? 

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The initials "dB", or "decibels", indicates that the measurement is a ratio measured on a logarithmic scale. Every time you add 6 dB, the signal level doubles. Since a decibel only indicates a ratio, you have to specify what the value is measured relative to.

In the case of radio and television field strengths, we effectively measure the voltage across one metre of space. 1uV is one microvolt, which is one millionth of a volt so 1 uV/m indicates a voltage of one millionth of a volt when measured across one metre of space.

"6 dB relative to 1 uV/m", often written as 6 dBuV/m, would be 2 uV/m and 12 dB would be 4 uV/m, remembering that every time you add 6 dB, the voltage doubles. The reason we use the dB ratio is to make the figures easier to handle when you have larger signals. 1000 uV/m is 60 dB uV/m, and 1,000,000 uV/m is 120 dB. It is also very useful when estimating aerial sizes, as the calculations involving aerial gain and feeder losses illustrate.

We always measure field strengths at 10 metres above ground level (a.g.l.), as that is where most outdoor aerials are located, at roof height.

Loft Mounted Aerials

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Mounting your TV and FM radio aerials in the loft has a number of advantages and disadvantages when compared with mounting them outside on the roof. The purpose of this page is to help you decide where is the best place for your aerial.

The Disadvantages

1. Signal Strength.

   The roof and gables of a house can screen the aerial from the incoming signal. In areas where the signal is already weak this can make a big difference to the quality of your reception. A roof which is insulated with metal foil, or roof tiles which contain metal, can block out signals completely, rendering a loft mounted aerial useless. On television a weak signal gives rise to a snowy or grainy picture. A weak signal on FM radio will cause hissing, and it will be difficult to receive stereo.

2. Signal Corruption.

   Roof spaces often contain a lot of things which can corrupt the television or FM radio signal. Amongst these are water tanks and pipes, electrical cable, and all those pieces of junk being stored there. Signals can be reflected from these objects and the reflections may interfere with the main signal and degrade it. On television this may blur the fine detail of the picture, cause "ghosting" or just lead it to be snowy. On radio the effect will be harsh noise and distortion.

   If you live in a terraced or semi-detached house you may also have problems arising from your neighbours' lofts. If, for example, your neighbours suddenly move the junk in their loft, it could have a serious effect on the quality of your reception.

The Advantages

1. Corrosion.

   A loft mounted aerial is a lot less susceptible to corrosion than one which is mounted outside in all weather conditions. Corrosion is a major factor in the deterioration of aerials and cables, and the subsequent deterioration of TV or FM reception.

2. Maintenance.

   An aerial mounted in the loft is normally a lot easier to access than one on the roof . It is also safer to install and position because there is no need for precarious excursions onto the roof or up ladders.