[jeffrey4670]

Hi, I have a question regarding DAB Radio. The power of Bilsdale tx on DAB is 5KW, also the output of FM is the same, for BBC Radio 2. Will the coverage be the same? Some high powered stations such as Sutton Coldfield FM are 120KW as opposed to DAB at 10KW. Are we at a position where DAB has the same coverage as FM, in the UK. Such a lot more DAB masts than FM, but much lower output.

[The Installer]

Sutton Coldfield is 250kW on FM not 120kW

[jeffrey4670]

Originally Posted by The Installer

Sutton Coldfield is 250kW on FM not 120kW

250 M or 120 V.

[crusher19860138]

Originally Posted by jeffrey4670

250 M or 120 V.

250KW or 250,000 watts!

[hanssolo]

Originally Posted by jeffrey4670

Hi, I have a question regarding DAB Radio. The power of Bilsdale tx on DAB is 5KW, also the output of FM is the same, for BBC Radio 2. Will the coverage be the same? Some high powered stations such as Sutton Coldfield FM are 120KW as opposed to DAB at 10KW. Are we at a position where DAB has the same coverage as FM, in the UK. Such a lot more DAB masts than FM, but much lower output.

DAB coverage planning is done with smaller "cells" than FM, so there are more lower power transmitters up to 10kw covering smaller areas, but overlapping and sharing frequencies, so reception from transmitters merges and gets stronger.
Much more at
http://stakeholders.ofcom.org.uk/con...rage-planning/
Where current FM coverage is compared to future DAB coverage?
Some will say the total DAB power levels for each station is lower than current FM making DAB much more efficient for transmitting?

[Mark C]

Originally Posted by hanssolo

DAB coverage planning is done with smaller "cells" than FM, so there are more lower power transmitters up to 10kw covering smaller areas, but overlapping and sharing frequencies, so reception from transmitters merges and gets stronger.

It's also because of the guard interval used, any overlapping reception from transmitters more than 78km apart will have a destructive rather than constructive effect on reception.

In fact a recent BBC/Ofcom paper stated that no more DAB transmitters are possible in East Anglia because of that.

[hanssolo]

Originally Posted by Mark C

It's also because of the guard interval used, any overlapping reception from transmitters more than 78km apart will have a destructive rather than constructive effect on reception.

In fact a recent BBC/Ofcom paper stated that no more DAB transmitters are possible in East Anglia because of that.

P4 of the BBC document on the link

The BBC network has already reached the stage where its coverage is, in places, being
limited by self-interference. This is particularly obvious in the patchy coverage visible in
Map A1 in the East Anglia area. As more transmitters are added to the network to improve
coverage, the interference regime increases, paradoxically making coverage improvements
harder.
Over the coming months, the BBC will be investigating various methods by which this effect
could be mitigated, but it has not been possible to resolve this in time for the publication of
this report.

[Vectorsum]

Originally Posted by jeffrey4670

Hi, I have a question regarding DAB Radio. The power of Bilsdale tx on DAB is 5KW, also the output of FM is the same, for BBC Radio 2. Will the coverage be the same? Some high powered stations such as Sutton Coldfield FM are 120KW as opposed to DAB at 10KW. Are we at a position where DAB has the same coverage as FM, in the UK. Such a lot more DAB masts than FM, but much lower output.

There are more differences than similarities between the DAB and VHF-FM networks, but if all other things were equal (which they never are) then DAB is capable of giving away about 15 to 20 dB while still giving the same noise performance as VHF-FM. The recent ERA receiver testing conducted for Ofcom as part of the DAB coverage consultation showed that DAB receivers on average performed well down to ambient field strengths of 36 dBμV/m at the whip antenna, whereas the VHF-FM networks are engineered to 54 dBμV/m at a 3 element Yagi antenna.

A 3 ele Yagi has forward gain of about 6 dBi, give or take. The ERA Ofcom report doesn't quote a figure that I can easily find for the gain of the telescopic / wire / earphone antennas used on the DAB receivers, but anecdotal sources can be found on then net that estimate these gains between -10 and -20 dB. So you might add another 16 to 26 dB advantage to DAB but the DAB network is engineered for indoor reception, so this roughly corresponds to the indoor penetration loss.

If therefore you call the DAB advantage about a net 18 dB, then that means that a 5 kW DAB TX is roughly equivalent to a VHF-FM TX of just over 300 kW. However, this comparison is muddied by the different planning parameters for DAB and VHF-FM (of which indoor/outdoor is only one of many) the different gallery heights available for mounting the DAB antennas and azimuthal positioning options available that cause different coverage patterns between DAB and VHF-FM services even from the same mast, etc etc etc.

Also, this back-of-the-fag-packet calculation is perhaps being unfair to modern, state-of-the-art VHF-FM stereo receivers. It's been many years since I looked at any performance figures for these, but I should imagine that with advances in DSP these can do many dB better than the 1960s planning parameters and fully quiet with field strengths somewhere in the low to mid 40s dBμV/m at the Yagi. No doubt someone will be along to comment on that presently.

[lundavra]

Originally Posted by hanssolo

DAB coverage planning is done with smaller "cells" than FM, so there are more lower power transmitters up to 10kw covering smaller areas, but overlapping and sharing frequencies, so reception from transmitters merges and gets stronger....

Though in a hilly area it can work out the other way around. You could put a high power DAB transmitter on top of a high hill and leave it to bounce around between the hills and valled giving good reception. You obviously have to be careful with causing problems with other sites outside the 70ish Km separation.

Do the same with VHF FM and you will just get horrible multipath so there tend to lower power transmitters in the valleys covering small areas.

[vinnielo]

Originally Posted by crusher19860138

250KW or 250,000 watts!

250KW would actually be 256000 Watts .

[BMR]

Originally Posted by vinnielo

250KW would actually be 256000 Watts .

No , a kilowatt is a thousand watts.

Not 1,024.


(in this world, there are 2 types of people- those who understand decimal and those who don't )

[vinnielo]

Originally Posted by BMR

No , a kilowatt is a thousand watts.
Not 1,024.

Correct, but that's a kW, not a KW!

Back atcha....

[BMR]

Originally Posted by vinnielo

Correct, but that's a kW, not a KW!

Back atcha....

So what is a KW then?

[Mark C]

Originally Posted by BMR

So what is a KW then?

It's nothing valid

Though you can use a capital K on its own in the SI scheme.

For instance 33K instead of 33km, so perhaps you can use 100K to denote 100kW ?

http://www.ebyte.it/library/educards...dPrefixes.html

But that might confuse with the other use of K as for Kelvin ?

[darkisland]

Originally Posted by BMR

So what is a KW then?

KW was a british company who made various bits of broadcaster kit in the early 90's They did a portable mono, cassette recorder for field use which was all but indestructable although a little cumbersome to use.

[N.Dean]

Originally Posted by jeffrey4670

250 M or 120 V.

Do you mean "250kW mixed polarisation, of which 120kW is vertical polarisation"?

[N.Dean]

Originally Posted by BMR

No , a kilowatt is a thousand watts.

Not 1,024.


(in this world, there are 2 types of people- those who understand decimal and those who don't )

In engineering, "k" means "thousand".
In computing, "k" ( or is it "K"? ) means "1,024".

That explains the sallary difference, too.

[lundavra]

Originally Posted by N.Dean

In engineering, "k" means "thousand".
In computing, "k" ( or is it "K"? ) means "1,024".

That explains the sallary difference, too.

That would only be the case if "k" or "K" both meant a million in banking, or perhaps they do.

[_ben]

Originally Posted by Vectorsum

If therefore you call the DAB advantage about a net 18 dB, then that means that a 5 kW DAB TX is roughly equivalent to a VHF-FM TX of just over 300 kW.

Our BBC FM transmitters here are 250kW (per station, obviously) whereas for the BBC DAB mux its 10kW. Reception on FM is very ropey with big dead patches whereas DAB reception is rock solid.

(The BBC has recently added a second DAB transmitter in the area so its no longer a fair comparison, but the comparison still holds for the commercial mux which still comes from a single transmitter.)

[reslfj]

Originally Posted by hanssolo

Some will say the total DAB power levels for each station is lower than current FM making DAB much more efficient for transmitting?

Some will need to understand the physics of RF transmissions and antenna gain and ... etc.... a lot better.

And we haven't even started to talk about the energi (batteries) needed to receive DAB/DAB+.

Lars

[hanssolo]

Originally Posted by reslfj

Some will need to understand the physics of RF transmissions and antenna gain and ... etc.... a lot better.

And we haven't even started to talk about the energi (batteries) needed to receive DAB/DAB+.

Lars

Here is a bit of Gunnar Garfor's blog which brings some interesting points, it's about Norway but many points are valid for the UK.
http://www.garfors.com/2011/01/dab-v...nsumption.html

A common main transmitter for FM is 10kW, while an FM transmitter can use 70% of the amplifier effect and will therefore draw around 14kW from the power grid. A common main transmitter for DAB is 2kW, but a DAB transmitter can only use 25% of the amplifier effect, thus drawing 8kW from the power grid.

But, as mentioned in an earlier blog post (2034 Transmitters Are 1484 Too Many) one FM transmitter can only transmit one radio station while one DAB transmitter can transmit 10-30 stations (depending on quality and usage of DAB or DAB+).

The power consumption per main transmitter is as follows:
FM: 14kW/1 channel = 14kW per channel.
DAB: 8kW/10 channels = 0.8kW per channel.

One radio channel transmitted via FM does in other words need 17.5 times more power per transmitter than a radio channel transmitted DAB station. Or put in a different way, one DAB channel uses only 5,7% of what is the case for one FM channel, per transmitter.

But that's not all
Since many more transmitters are needed for FM than what is the case for DAB (2034 vs. 5-600), the difference in power consumption between FM and DAB is even higher. Not all FM transmitters are however 10kW. The smallest ones are only 20W, whereas others are 50, 100 or 500W. For DAB the smaller ones are 40, 125, 250 or 500W. I have not had the time to go through all 2,034 transmitters, but to cut 1,484 transmitters will certainly save some wattage. We can safely assume that to cover Norway (99.8% of the population) with digital radio is more than 20 times more environmentally friendly per channel than to do the same with FM, when looking at power consumption.

And finally, the chipsets used for DMB, DAB and DAB+ have improved greatly when it comes to power consumption and a modern DAB chip (25-60mW) now consumes the same amount of power as what is the case for an FM chip (30-60mW). And work is being undertaken to further cut power consumption of DAB. A chipset manufacturer I talked to said that their short term goal is 20mW, which will then be substantially below FM.

DAB. Much Greener Radio.

I would not quite agree with the lat bit about receivers as some analogue FM recovers are based on ceramic filters and single transistor if stages which are low consmption, but as this can be done cheaper by chipsets, however few analogue FM only sets are now being made with ceramic filters, but do agree with Gunnar that modern analogue sets based on FM chipsets can potentially now use more power than a modern DAB chipset!

[hanssolo]

OK lets take R2
On FM there is a total of 3,500kw to cover 98% of UK population on band 2, divided by a sixth for average antenna gain is 600kw out from transmitter, transmitter draws 833kw from electric supply

on DAB there will be a total of 2,000kw to cover 97% of UK population on a SFN band 3 mux where signals in fringe areas merge. divided by a sixth to get average antenna gain is 330kw out from transmitters, transmitters draws 1300 kw from electric supply.
But each mux has 10 stations, ie 130kw

So roughly on FM R2 will use a total electricty supply of 883kw, but on DAB 130kw!
Can someone check this?

(No doubt if DVB T2 lite was used it will be more efficient, but DAB exists now, but sometime DAB+ might be used?)

[hanssolo]

On my rough calculation a national DAB station uses 14% of the electricity of a national FM station!
Notice on another thread 2bdecided spotted this in p26 of a DCMS document, which assumes DAB transmitter efficiency to be a bit better than Gunnar's figures? Also D1 has 13 services compared to the BBC's 10 which also gives a better figure!
http://www.culture.gov.uk/images/pub...ort_July12.pdf

There are also implications for energy use from ceasing national analogue radio transmissions under
the switchover scenarios. This results in a reduction in energy use in comparison to the
counterfactual where both analogue and DAB transmissions continue. Furthermore, DAB networks
can be much more energy efficient than analogue, particularly given that ten or more DAB services
can broadcast on one frequency compared to one service per frequency on analogue. For example,
total annual electricity use of transmitting the existing Digital One (D1) multiplex, which broadcasts
national commercial DAB services, is less than 75% of the electricity for the analogue Classic FM
network. As the D1 multiplex broadcasts thirteen services, electricity use per service is approximately
7% of that for the analogue Classic FM Network.

[wilson500]

Originally Posted by hanssolo

Here is a bit of Gunnar Garfor's blog which brings some interesting points,

A common main transmitter for FM is 10kW, while an FM transmitter can use 70% of the amplifier effect and will therefore draw around 14kW from the power grid. A common main transmitter for DAB is 2kW, but a DAB transmitter can only use 25% of the amplifier effect, thus drawing 8kW from the power grid.

Now this is interesting. What makes the difference? Aerial design, the higher frequency or even the wider bandwidth of the signal?

[hanssolo]

Originally Posted by wilson500

Now this is interesting. What makes the difference? Aerial design, the higher frequency or even the wider bandwidth of the signal?

The wider bandwidth which allows single frequency network multiplexing, the higher number of stations per mux makes for better efficiency (DAB+ even more) and has the secondary advantage of reducing multipath effects.

The higher frequencies used in band 3 over band 2, less efficient digital transmitters and the potential for interference over 75km is a disadvantage, but small compared to the advantages in SFN merging signals from transmitters and multiplexing.

I understand aerial design is similar for band 2 and 3.