Radio spectrum use

tvman2

Was wondering about this recently. What determines what part of the broadcast frequency spectrum is used for what? Like could DAB, Digital TV, FM etc be broadcast on any part of the radio spectrum if we were starting all over again. Are specific parts of the spectrum more suited to certain types of transmission. Is the present order all down to when the various types of broadcasting were invented.

Thanks

Ronnie Raygun

Lower frequency bands don't have the bandwidth for tv signals (top MW frequency is around 1.6 MHz, 1/5 of an 8 MHz tv channel). Also the RF carrier must be at least twice the highest baseband frequency.

After that, the next problem will be running out of space for new channels, so you up the frequencies again to find more bandwidth, with propagation tending to be more "line of sight" as frequency increases.

tvman2

Thanks,

One last question, could DAB be transmitted on current fm frequencies rather than the former vhf tv frequencies.

Ronnie Raygun

Yes, DAB was conceived with frequencies from 30-3000 MHz in mind, terrestrial & satellite delivery.

tvman2

Would it not have been a better idea to convert radio services to DAB using current fm frequencies - like was done with DTTV switchover, was it ever considered?

coylemj

tvman2 wrote: »

Would it not have been a better idea to convert radio services to DAB using current fm frequencies - like was done with DTTV switchover, was it ever considered?

You'd still need a new receiver to receive DAB (to decode the digital data) so what difference does it make where the frequencies are?

DTTV also needed new h/w but by staying within the UHF band most people didn't need a new aerial which would have been a big deal (cause most of them are on the roof) but not for radio.

tvman2

Thought FM would be more robust reception wise than the higher frequencies now being used.

Ronnie Raygun

tvman2 wrote: »

Would it not have been a better idea to convert radio services to DAB using current fm frequencies - like was done with DTTV switchover, was it ever considered?

There's isn't the same pressure to shift analogue transmissions off VHF band II. Not sure if it's apathy on the part of the broadcasters or the listening/buying public (or both), also the fact nobody else wants the spectrum.

The Cush

And what technology uses which slice of spectrum and where in the world it is used is set down in the ITU's Radio Regualtions. The Radio Regulations are reviewed every couple of years via World Radio Conferences (WRC) to take account of new technologies and remove obselete requirements. The last one was WRC-12 and next will be WRC-15. All national and regional administrations take part in the conferences, the Dept of Comms and Comreg in Ireland case and CEPT as the European regional organisation.

One of the issues to be decided at WRC-15 will be to allow mobile services to use the upper TV band (UHF Chs. 49-60) in ITU Region 1 (Europe/Africa) later this decade.

The European Radiocommunications Office (ERO) publish the European Common Allocation Table (ERC Report 25) and Comreg publish the Radio Frequency Plan for Ireland to include any changes to the ITU Radio Regulations applying to the European region/Ireland.

zg3409

tvman2 wrote: »

Would it not have been a better idea to convert radio services to DAB using current fm frequencies - like was done with DTTV switchover, was it ever considered?

I think they just copied the UK. The UK had VHF band III empty and it made sense to put a new audio service there. We just followed their lead.

The new TV system was specifically designed to allow switchover and dual running of old and new.

However in the USA they have a DAB like system, however this system is designed to be compatable with existing receivers, and use the same frequency. It's a bit like stereo or RDS (station name display), whereby older radios do not use the information, but newer sets can pick up the newer features.

There are many benefits to a combined system, such as one transmitter for old and new, one aerial, no need to use new frequencies, same coverage as old system etc.

However there are valid reasons why each system has chosen their own way of doing it. One massive consideration is the cost of receivers for Joe Soap, making old receivers obsolete, and world standardisation to keep costs down. For example Jap import cars have radios that don't really work in Europe, so need to be changed.

tvman2

Thanks for all the replies, there's a lot more to it than my initial simple thought on the subject - as it is with most things!

winston_1

zg3409 wrote: »

I think they just copied the UK. The UK had VHF band III empty and it made sense to put a new audio service there. We just followed their lead.

Band III was not empty in the UK, it just was not being used for broadcast services. Room had to be found for DAB as band III European channels were split into 4 sub channels suffixed A, B, C, & D specifically for DAB use. Ireland complied with the rest of Europe rather than copy the UK.

Sam Russell

One of the problems with the DAB radio is they are much more power hungry than FM receivers, and considerably more expensive. An FM receiver can cast as little as a few Euro in the pound shop not great but great price. DAB radios cost hundreds of Euro, and cannot run on batteries like an FM radio can.

FM transmitters are also cheaper, and the possibility of better quality through digital transmission is normally lost through the cramming of the bandwidth with extra channels to increase revenue.

Digital systems allow defined performance without degradation until the signal disappears, while analogue has a continued degradation as the channel degrades. If the design parameters are set for poor performance, then that is what you get.

DAB is a poor design as it is - there are better ways to get the same result. All our RTE DAB channels are currently broadcast on the Saorview signal. Why do we need DAB?

zg3409

DAB was designed for in car use, so automatic retuning without any break in shows, and elimination of flutter and resistance to normal interference.

Try listen to Saorview radio while driving down the road!

Fuzzy Clam

Sam Russell wrote: »

One of the problems with the DAB radio is they are much more power hungry than FM receivers, and considerably more expensive. An FM receiver can cast as little as a few Euro in the pound shop not great but great price. DAB radios cost hundreds of Euro, and cannot run on batteries like an FM radio can.

FM transmitters are also cheaper, and the possibility of better quality through digital transmission is normally lost through the cramming of the bandwidth with extra channels to increase revenue.

Digital systems allow defined performance without degradation until the signal disappears, while analogue has a continued degradation as the channel degrades. If the design parameters are set for poor performance, then that is what you get.

DAB is a poor design as it is - there are better ways to get the same result. All our RTE DAB channels are currently broadcast on the Saorview signal. Why do we need DAB?

BIBs
I think Tesco sell DAB radios for less than a tenner. Also battery life is getting better afaik.

Re your second point, It can't be that difficult to manufacture a radio to receive Saorview and/or Freeview transmissions and decode only the radio channels, can it?
In this day and age of increasing concern about energy effiency (not to mention the costs of the equipment to the broadcaster) , every DAB transmitter in these isles could be switched off and still maintain the same, or even better, level of digital radio.

zg3409

Fuzzy Clam wrote: »

It can't be that difficult to manufacture a radio to receive Saorview and/or Freeview transmissions and decode only the radio channels, can it?
.

Firstly Saorview is not intended for mobile reception. The signal is also weak, designed for rooftop aerials in many places. However if they designed the system for indoor, and mobile TV reception, then possibly yes, but it would mean as many TV masts as mobile phone masts, to ensure a strong signal indoors.

The main issue with DAB is that is offers practically nothing over FM radio with RDS. The way it is currently set up it has less stations, less coverage, and lower sound quality. DAB radios are not even installed as standard to cars, let alone popular.

As to the future? If I was paying for it I would kill it immediately, unless someone is willing to rollout nationwide coverage, lots of stations and a PR campaign to promote it, it will never gain sufficient listenership to compete.

Wifi radios (using internet streaming) offer far better choice, audio quality and even offer playback of old shows on demand.

Fuzzy Clam

zg3409 wrote: »

Firstly Saorview is not intended for mobile reception. The signal is also weak, designed for rooftop aerials in many places. However if they designed the system for indoor, and mobile TV reception, then possibly yes, but it would mean as many TV masts as mobile phone masts, to ensure a strong signal indoors.

.

Well the transmitter powers used on the main sites (10s of killowatts) are many time that of DAB radio or mobile phone so that weakness of signal should not be an issue.
I was thinking that the high frequency might be an issue but since mobile phones are higher again, thst also shouldn't be an issue.
There may be an issue with mobile reception ut I don't believe it's down to power levels.

Sam Russell

Fuzzy Clam wrote: »

BIBs
I think Tesco sell DAB radios for less than a tenner. Also battery life is getting better afaik.

Re your second point, It can't be that difficult to manufacture a radio to receive Saorview and/or Freeview transmissions and decode only the radio channels, can it?
In this day and age of increasing concern about energy effiency (not to mention the costs of the equipment to the broadcaster) , every DAB transmitter in these isles could be switched off and still maintain the same, or even better, level of digital radio.

If you design a radio receiver for Saorview without the video, you will of course get the radio stations and the audio off the TV. It is a very limited market. STB for Saorview retail north of €50 and do not have audio amps or speakers.

If there was no DAB, there would be more FM. give the band to FM. DAB is not much more efficient than FM with not much better quality. It does have a much higher component cost, a royalty cost, and higher energy consumption.

So why DAB?

zg3409

They could not give the band to "FM" as no radios currently sold cover those frequencies. They only cover 88 to 108.

Someone suggested a much better use would be for TV use, however we have lots of unused TV frequencies at the moment, with no sign they will all be used shortly.

The issue is these (DAB) frequencies are normally for TV or DAB. They could be used for some other services but in reality they will be left empty for the moment.

Sam Russell

zg3409 wrote: »

They could not give the band to "FM" as no radios currently sold cover those frequencies. They only cover 88 to 108.

Someone suggested a much better use would be for TV use, however we have lots of unused TV frequencies at the moment, with no sign they will all be used shortly.

The issue is these (DAB) frequencies are normally for TV or DAB. They could be used for some other services but in reality they will be left empty for the moment.

Obviously such a change would need to be done over the whole of the EU or even the EBU. To convert an existing FM radio would just require a down-converter of simillar complexity to the devices that allow mp3 players to be received on FM car radios. All do-able.

One major draw back to this scheme. No-one makes any money out of it.

I think DAB stands for Daft And Bonkers.

TAFKAlawhec

VHF Band III is still being used in some parts of Europe for DTT delivery, so converting it for analogue FM radio use isn't a great suggestion. What's more likely is that the band could be extended downwards from 87.5MHz - the Americans are considering releasing TV channel frequencies A5 & A6 (76-88MHz) for an extended FM radio band, especially as very few TV transmissions remain on these frequencies. One advantage is that many "world band" radio receivers can already cover 76-108MHz (to cover Japan as well as elsewhere other than the OIRT band), new receivers could catch up quickly with only small modifications based on existing receivers. Edit: Just to add, many smart phones that are capable of receiving FM radio can also cover 76-108MHz, and could access lower frequencies with a software update presumably.

Fuzzy Clam

Sam Russell wrote: »

Obviously such a change would need to be done over the whole of the EU or even the EBU. To convert an existing FM radio would just require a down-converter of simillar complexity to the devices that allow mp3 players to be received on FM car radios. All do-able.

Not sure what you're saying here. The devices for MP3 players are simply low powered FM transmitters transmitting on the 88-108 band. No down converting.
If the broadcast FM band was to be extended, then extended range on the receiver would be required.