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The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
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PostPosted: Thu Jul 02, 2020 8:09 pm 
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Joined: Tue Oct 15, 2019 9:00 pm
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Another thing, for an electronics philistine, whats the gig with DAB? In fact what IS DAB? It seems to be a load of expense and bother, for what exactly? Explanation at a 5 year old level please! I have to admit, I rarely listen to the radio, the Carledo doesn't even HAVE one, let alone a posh one. On shorter journeys I prefer the "straight through orchestra" anyway and on longer journeys the local nature of FM means regular retuning, a CD stacker or memory stick is easier (no adverts either)

Steve
D.A.B. = Dodgy At Best :lol:

It actually stands for Digital Audio Broadcast. Basically a new(ish) method of radio broadcasting. Its Digital so it has to be good right? Actually development started in the early 80's and the BBC started broadcasting it in the mid 1990's !

Now for the laymans history lesson!

In days gone by we had Long Wave and Medium Wave Radios where the information (speech and music) was "encoded" by changing the amplitude of the transmitted wave - AM - amplitude modulation. Simple and easy to do and also simple and easy to make a crude receiver -think "cats whisker" - basically an aerial (long bit of wire) and a diode and a speaker and you could in theory hear a broad cast -- in reality you will need to tune it by adding a variable capacitor and a coil - but simple enough for the electronics philistine :wink: Next came Frequency Modulation (FM) or sometimes referred to a VHF radio. Where, you guessed it, the music/speech is "encoded" by changing the frequency. More complicated but still doable in an understandable way for the "non-philistine"! Why bother - well Long Wave/ Medium Wave (AM) is very susceptible to interference, crackles, pops etc. where as frequency modulation is not affected by changes in amplitude (size!) of the received signal. The down side is it needs a higher frequency for the transmitters and receivers to work well so range is reduced. Longwave can and does travel 100's if not 1000's of miles. VHF/FM range is much shorter.

Now the big disadvantage with both of the above there are still interference issues, even with FM and each radio station needs a finite amount of bandwith - range of transmitting frequencies. The stations cannot be too close together or they interfere with each other . The radio spectrum is a valuable commodity and is used for lots of things. At the low end it is mainly radio communication transmission, then terrestrial TV (remember that? 4 or 5 channels and that's yer lot? Higher up you enter into mobile phone terratory, then satellite communications, with other little bits in between for things like wireless remote keyfobs - This is a gross over simplification but you get the idea. As Digital stuff was developed and the boffins (non philistines!) got better at electronikery they could do stuff at higher and higher frequencies. They also found ways to cram a digital data stream (lots of bits of information) all together and stuff it into a single transmission frequency band . (multiplexing!). They could basically mix dozens of individual radio stations (or in a different band - TV channels - think Freeview and Satellite (sky etc)) and send them down a single part of the radio spectrum ( i.e. a single frequency band) . This basically meant we could have access to lots more radio stations. In theory they should be able to transmit higher quality (CD quality) audio. But penny pinching by broadcaster trying to reduce costs mean they reduce bit rates (sample rate think poor quality MP3 - or crackly 78 rpm shellac!) so the audio can sound bad - not all are guilty of this! It also operates at a higher frequency - around 200MHz, about twice that of FM - cutting range and making it more line of site. The receivers were/are also more complex and hence expensive than LW/MW and FM ones. They basically need a small computer to process and decode the signals in addition the the receiver and amplifier that a FM radio needs. In theory they should be more immune to interference but it is often total loss of signal that is the issue - especially on earlier car receivers. It is getting better slowly, but FM still works for me locally.

DAB has made slow head way, especially in cars, as there are so many "embedded" FM radios in cars and DAB receivers until recently have been expensive, coverage has also been patchy. Also many more people do as you say, they plug in their iPod, USB key or what ever with their favourite playlist stored, so they actually listen to the radio less. You can also live stream on 4G or 5G on you smart phone - so many ways to listen to stuff. My preference is to turn it all off, wind the window down and head for the nearest tunnel where I can change down, put my foot down and listen to some real "music" !

The above is not all strictly correct but gives the gist of what is going on. The government originally wanted to switch off analogue radio as they did with TV so they could free up that part of the radio spectrum, but uptake has been so slow they have effectively given up.

One irony of DAB is that the BBC 6 o'clock pips actually occur about 10 seconds late due to the delays caused by the computer processing required to encode and decode the signal. If you listen on FM, DAB and internet radio simultaneously you will find the FM pips are pretty much spot on, DAB is delayed by around 10 seconds and internet radio can be 30 seconds out! So much for digital!

Roger

_________________
1975 Sprint Man O/D in Honeysuckle Yellow
1971 Stag Auto White

Too many cars, too little time!


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