Revisiting DAB - and maybe FM

[Dave2002]

I realise that devices such as the Squeezeboxes contain fairly simple and now relatively slow processors by modern standards, but I'm surprised that a change in the audio file format by the BBC can create an audio stream which such units can't hope to handle Where does the extra complexity come from?

I have a vague recollection, from having looked at the details of the new method for the streams, that the data is handled in larger blocks using Apple HLS. Even so, I doubt that either memory or processor limitations would prevent such devices from being able to run appropriate software to handle the new formats.

This article suggests that the BBC has been working with Logitech users to enable development of software on Squeeze devices which sill work with the new HD streams - http://www.bbc.co.uk/blogs/internet/...5-563428fb74f5

However, some domestic equipment is definitely much better now, due to various factors, than similar kit from a few years back. Our Humax Freesat box which mostly works very well, has a feature to display slide shows from a USB stick. As many cameras now generate large files, even in jpeg format, there can be a lot of processing. The Humax box does show the slide shows, but by modern standards it's almost unusable, even allowing for the rather crude and clunky user interface.

To get reasonable performance using that box, it is necessary to pre-process the image files on the USB stick so that they are smaller. Moore's Law really does show up from time to time. It's probably 6 years since the Humax box was introduced, so depending on what exponential factor one uses for Moore's Law scaling (1.5 or 2 per year), it would be reasonable to expect this year's equipment to be between 8 times and 64 times faster on similar tasks. In the context of a slide show, that might be the difference between 30 seconds between each slide versus somewhat less than 4 seconds for some large images. That can make the difference between a new device being easy and pleasant to use, with older devices being completely unmanageable.

However, for audio work, I would still expect it to be possible to provide updates for older kit to make the audio streams work, as I would expect there to be sufficient memory for buffering and for the programs, and for the cpu loading to be sufficiently low that even a moderate increase in processing load would not present an impossible task. Sometimes though, it's just not worth the effort, which seems to be the view being put forward by the BBC, though the Logitech users appear to be trying to make their devices work.

[umslopogaas]

I have a Creek FM tuner connected to my hi fi amp and speakers. I had an external aerial installed on the roof six years ago at a cost of £104 and reception is loud and clear (its dreadful without the aerial). I live in Bampton, East Devon, just south of Exmoor. So long as the BBC continues to broadcast in FM, I'm perfectly happy with it.

[Dave2002]

I have a Creek FM tuner connected to my hi fi amp and speakers. I had an external aerial installed on the roof six years ago at a cost of £104 and reception is loud and clear (its dreadful without the aerial). I live in Bampton, East Devon, just south of Exmoor. So long as the BBC continues to broadcast in FM, I'm perfectly happy with it.

One doesn't see many FM aerials up on roof tops round these parts. I have spotted those circular DAB aerials on occasion, and maybe there are dipoles. I am rather coming back to the view that the FM services should not be discontinued, but that doesn't mean that anyone in government will take any notice. There would be two major issues - (1) the cost of replacing the existing transmitting equipment, which I understand is gradually nearing end of life, and (2) the cost of operating new stations if the old ones are replaced.

Of course HMG would have at least one other factor to consider - (3) loss of opportunity, as they would see continuing to support FM as blocking yet another chance to flog off public assets - so that spectrum which is currently available for public service broadcasing would be sold to private operators for other purposes. I am somewhat opposed to that.

OTOH now that digital TV has replaced analogue TV, and analogue TV has been switched off, does anyone miss that? For the most part digital TV is better than analogue TV was - though I did once see a superb picture from an analogue service quite by chance with one piece of kit which I installed here briefly. I suspect that level of quality was only ever experienced by a few people living within an optimum distance of a transmitter. The rest of us, most of the time, would have experienced wavy lines, snow, interference, drop outs - all sorts of other problems, so digital beats typical analogue hands down. Also digital services support HD TV (now) which analogue in the UK never did.

[Cockney Sparrow]

This may not address the main thrust or all of the points made in this thread - but here goes, my experience. I realised my chimney mast was too large and had broken one of the brackets, so needed to be attended to by someone willing to go on the roof (definitely not me, I'm only willing to go up to gutter level).

I researched the option using this extensive aerial installer's site. On reflection a lot to have to go through.

http://www.aerialsandtv.com/

I replaced my FM 3 element aerial plus "digital switchover compromise" yagi TV aerial with a much smaller pole and one Log 36 aerial which suits my transmitter and the digital TV signal has vastly improved.

As I had a diplex system installed in the loft (with wiring in the plaster to various rooms) I tried taking off the 3 elements of my old FM aerial, and just rigged up the dipole (think that is the name for the loop bit with the wiring connector) vertically in the loft, using the original long pole (on which the elements had been attached) and cord (string) to adjust the direction of the dipole. I had nothing to lose as I could easily connect into the diplexer a few feet away and in the event it worked well and gives a good FM signal (with concrete tiling and a brick eaves wall not far from the direction this was a surprise but the aerial shop website says FM is an easier signal than digital to capture (please do forgive my very non tech speak)). If this hadn't worked I would have tried the FM on the side of the house (not too high up) where I can work on a flat roof extension. When I moved here I had a 15 element Ron Smith Galaxy aerial I'd bought when I lived in a marginal signal aerial (neighbours joked I was running a listening station!). (To explain diplexer - a unit which combines TV and or FM and or Satellite signals near the aerials into one cable for distribution in the house. At the appliance end, there is a socket plate & assembly which unravels the signals and you connect your unit to the relevant output socket on the plate)

As we have about 5 or 6 FM radios around the house (all in one phase for walking between rooms, plus tuners in audio systems, I am mightily offended by the high handed decision to force us to ditch these effective devices - effective not least because they have much longer battery life than DAB radios. I make a point of telling politicians I come across this is a prime example of the anti democratic nature of both government and the BBC in forcing this change upon us whether we want it or not.

Incidentally, the aerial website makes the point it has never been stated that local FM services would be discontinued.

OTOH when we visit the Scottish borders (in a holiday property with no installed internet) we use a DAB radio to get Radio 4, which is not obtainable on FM. I'd seen that page with a DIY DAB aerial (referred to above) and intend to try it when we visit at Easter as signal strength can be marginal at times.

[Dave2002]

OTOH when we visit the Scottish borders (in a holiday property with no installed internet) we use a DAB radio to get Radio 4, which is not obtainable on FM. I'd seen that page with a DIY DAB aerial (referred to above) and intend to try it when we visit at Easter as signal strength can be marginal at times.

It doesn't take long to make up that coax wire based DIY antenna, but I suspect it only really works in areas with a reasonable signal. If the signal strength in one of the holiday properties is low I wouldn't expect very much from it.

There are a whole bunch of TV signal strength meters on ebay - http://www.ebay.co.uk/sch/i.html?_nk...v+signal+meter

I am not absolutely sure whether these would work for DAB or even for FM. Some sets/tuners do have signal strength meters, but most of the ordinary ones don't these days, and in any case you'd probably not want to take a large set to your holiday home. I might try your pragmatic approach in our loft - cannibalise older aerials and see if we can get good results.

Thanks for the reminder about the diplexer - I'd forgotten about them, but we did have a setup like that put in by an aerial installer in our previous house - as you said, to distibute the TV and radio signals down one coax wire. Do these things work with DAB and FM too? If so, that could simplify wiring both up to the loft and within it.

Not that I want to do it, but are there such things as triplexers to take DAB, FM and TV signals?

[Dave2002]

Not that I want to do it, but are there such things as triplexers to take DAB, FM and TV signals?

Seems there are - http://www.ebay.co.uk/itm/Labgear-LM...item35d5b7f918

Don't know if that one is any good - presumably need two - one at the top, one at the bottom. Maybe other outlets like Maplin will have some. I wonder if they degrade/attenuate the signals significantly. I think there are some powered ones too, which amplify the signals at the sending end.

[Gordon]

Seems there are - http://www.ebay.co.uk/itm/Labgear-LM...item35d5b7f918

Don't know if that one is any good - presumably need two - one at the top, one at the bottom. Maybe other outlets like Maplin will have some. I wonder if they degrade/attenuate the signals significantly. I think there are some powered ones too, which amplify the signals at the sending end.

Any Diplexer, and more so a Triplexer, that is, like the aerials themselves, passive [the cheap ones] will lose signal to some extent perhaps a couple of dB at each end. That's partly what you're trying to avoid!! A powered one, just like an aerial amplifier on a rooftop aerial, will not have that problem but will be fiddly and more costly. Aerial amplifiers don't improve reception directly, they balance the downlead losses and its own noise contribution against receiver noise figure when presented with low signal.

The greatest problem of poor local signal strength is that without an aerial [and that includes those rats tails dangling from the back or those telescopic things] any receiver at ground level and indoors has two very significant losses to deal with:

Firstly "Height Loss" due to being at ground level and thus in the lossy clutter area of houses, trees etc so that there is no direct line of sight strong signal available only multiple low level reflections or "multipath" that don't always add up usefully, and

Secondly "Penetration Loss" due to the radio signal having to get through walls, particularly internal thermally efficient plasterboard ones with a metal film layer.

These losses are highly dependent on frequency, vary dynamically and depend on precise local environment including areas of conductive material like the sides of electrically earthed fridge-freezers/cookers etc which affect radio waves in kitchens. Similarly metal window frames. At DAB frequencies [ca 220 MHz] these can add up to as much as 15-20dB and even at FM [ca 100 MHz] as much as 12-15dB. DTV is even worse at ca 470 to 700 MHz. Aerials provided with portable receivers and even some good ones with an aerial socket are usually pretty poor having negative "gain".

So what matters is Height and Outdoors; some radio services like FM Stereo [mono is a lot more tolerant] were planned on the basis of external rooftop aerials and so "audiophile" FM performance [if there is such a thing] needs a lot of aerial input signal to keep hiss levels down to acceptable levels. The fact that portables in kitchens can work is not by design but by improvements in receiver performance over the years.

DAB WAS in principle designed for portable/mobile reception but its poor network build out in the early days gave rise to many reception issues as did rather nastily poor receivers. The minimum spec published by DCMS [link in post above somewhere] requires state of the art sensitivity from cheap portables and is not a trivial target to meet.

ANY kind of external aerial high up at roof level will avoid most if not all these losses and so even a non optimum "aerial" made up of old TV aerials even in lofts [incurring wet roof tile penetration losses] might be better than nothing and provide better consistency eg variance with people moving around.

Most aerials that are not large [say 4 elements] Yagis [a type of aerial named after its Japanese inventor, and the most common one seen on rooftops] have small "gain", perhaps 6dB at best [that means twice as much as a reference aerial], with diminishing returns as more elements are added. IOW adding twice as many elements does not double the gain; more elements help with bandwidth rather than gain as such. Being passive resonant devices they also have to have physical dimensions related to the frequency range of the wanted signals ie the bandwidth of the aerial. What these aerials do is provide directional advantage to the wanted incoming signals and reduces any unwanted ones, including any interference, coming in from behind or the sides. Interference can be the problem in some cases rather than low wanted signal strength per se. The longer a Yagi, and certain other types of aerial, is the more carefully it needs to be pointed in the right direction and also aligned to the radio wave electric field.

Simple Dipoles, one of the simplest forms of aerial and an integral, functional part of a Yagi structure, are poor in directional properties needing to be broadside on to the incoming wave but they are equally receptive to signals from "behind" and not receptive at all to the "sides" at 90 degrees. Aerials can only take power out of the radio wave front that it immediately intercepts - there is a notional volume of space around it that an aerial is able to tap into and the amount of power in a typical aerial's "space" is very small. An aerial therefore needs to occupy a lot of space to get a lot of power - but its size is limited by the wavelength of the wave it is required to intercept and so this gets worse the higher the wanted frequency is. Practical and economic factors also mean that this volume is not large and that individual aerials are therefore not efficient - but interconnected "phased" arrays of them will be better because the total intercepted space volume is increased. For cosmetic reasons mobile phones have no visible aerials which means they are far from good, often operate at ground level and indoors which means that mobile multiband telephony [one aerial can't serve all bands well] is appallingly inefficient in power but also, as a result, in spectrum.
.

[Bryn]

Just a little reminder that for DAB, even a purpose designed Yagi may pull in a lower total signal than a simple dipole. This is due to DAB's use of a single frequency network. When signals from multiple transmitters of even reflections are intercepted by the aerial, as long as the guard frequency is not exceeded there is an additive effect. Trouble is, in some meteorological conditions that guard frequency can indeed be exceeded, leading to further reception problems.

[Gordon]

Just a little reminder that for DAB, even a purpose designed Yagi may pull in a lower total signal than a simple dipole. This is due to DAB's use of a single frequency network. When signals from multiple transmitters of even reflections are intercepted by the aerial, as long as the guard frequency is not exceeded there is an additive effect. Trouble is, in some meteorological conditions that guard frequency can indeed be exceeded, leading to further reception problems.

Good point Bryn. That feature of OFDM in DAB is not repeated for FM. One of the limiting factors of SFNs is their self-interference outside the guard interval. In areas of rugged terrain this tends not to be a problem but in areas with lots of flat terrain like East Anglia/Midlands/SYorks it is a possibility. Suitable choice of transmitter sites - not easily acheved - and also adjusting their relative timing can help minimise the problem.

There is an argument for using a simple omnidirectional aerial to capture all the local transmitters in SFN so that they all add usefully under normal propagation conditions. If those weather conditions cause an even more distant constribution or even more than one to come in at a significant level then it will be counterproductive if the delays are outside the guard interval and so a directional aerial that can reduce their effect might be useful if you can identify the potential sources and their directions. Depends on detail of location - a bit swings and roundabouts - in relation to the various transmitter sites and their power levels.

[Dave2002]

Sounds as though it might be best to go for multiple cables up and down to our loft after all, if I decide to try it. Presumably satellite coax would give the lowest loss - though whether it would be worth the extra expense would perhaps be doubtful. An alternative method would be to put a wideband amplifier in the loft and use that with a triplexer at each end of a single cable run. That would be more complex, and would require a power feed to the amplifier. I think some systems can feed power (DC?) back up the cable to drive a suitable amplifier.

This project may be one which is never going to happen!

[Cockney Sparrow]

The ATV site indicates DAB signals are close to the frequency band of FM

http://www.aerialsandtv.com/fmanddabradio.html

"Historically radio in the UK was always broadcast in three distinct bands, from Long Wave through Medium Wave up to VHF/FM (Very High Frequency), but in 1995 a new digital system was introduced just above the FM band. This was christened Digital Audio Broadcasting, or DAB, and, unlike FM, it is transmitted on a Single Frequency Network. Also, unlike FM, packages of stations are transmitted together (a bit like the Freeview MUXES). These were originally called ensembles
I think on the site it indicates that DAB or FM signal can be input to the diplexer and one or the other taken from the wall socket. "

This page also shows
a "TV + FM/DAB + Satellite" triplexed surface outlet plate.

http://www.aerialsandtv.com/onlinecableandmisc.html#TVFMsurfacePlate

I think I also read on their site that affordable signal strength meters are pretty useless, and I think they suggest trial and error (shouting up to and down from the loft to an assistant - or taking a tuner with a signal strength indicator up to the loft (or onto my flat roof, etc) as that will give a better indication.

I'll still take the DIY aerial to the Borders as I suspect it may well be better (and can be better positioned) than the pull out aerial on the Pure DAB aerial (F connector, so easy to swap). As it happens a friend will also lend me a disused DAB aerial so I may take that and play with it in the loft to see if there is any difference, although it wouldn't be easy running the co-ax wiring permanently in the cottage.

(sorry I've not been on the forum since I posted - I only look in occasionally)
Edit - note - sorry, I thought the discussion ended with Dave's post at end of page 1. So my response above takes no account of the more informed contributions of Gordon and Bryn.

[Dave2002]

I think I also read on their site that affordable signal strength meters are pretty useless, and I think they suggest trial and error (shouting up to and down from the loft to an assistant - or taking a tuner with a signal strength indicator up to the loft (or onto my flat roof, etc) as that will give a better indication.

Good luck in your cottage.

I don't know enough about signal strength meters to really be able to comment on whether cheap ones can be useful. For aligning the satellite dish on our house (it has gone out of alignment a few times, due to maintenance work ...) I certainly found it very useful to have a cheap satellite TV tuner with a signal strength readout wired in, and since the dish is just outside the living room or kitchen, by leaving the window open it was possible for an assistant to shout out the readings. That turned out to be really rather critical, as a very small adjustment could make a big change in the strength and/or quality. Some satellite dish alighment gadgets don't give a readout, but apparently give some form of audible output - I've not tried them. Once the alignment with the cheap tuner had been done, it was simple to substitute the Humax PVR. Without that approach I think it would have been almost impossible.

The situation with DAB will be rather different, but I still feel that the task will be easier with some form of metering device. This will be particularly so if the signal is weak. My old JVC FM tuner has a useful set of meters, but some newer ones do not. Many DAB tuners seem simply to be "suck it and see" devices.

Also, trying to yell commands and feedback up and down the stairs may turn out to be less than easy, and could be frustrating, and you may need a lot of the aforementioned luck.

Do let us know how it went, once you have tried this.

[eighthobstruction]

Did I hear on the radio this morning that Mr Seddon is about to announce that FM will now continue indefinitely allong side DAB

Edit http://www.bbc.co.uk/news/entertainment-arts-43458695

[cloughie]

Did I hear on the radio this morning that Mr Seddon is about to announce that FM will now continue indefinitely allong side DAB

Edit http://www.bbc.co.uk/news/entertainment-arts-43458695

That to me is excellent news as although I do listen on certain sets around the house on Digital to R5L and R Cornwall, my main sources from my ageing Hi-fi systems rely on my trusty FM tuners, on which my R3 listening and any recording to MD is done.

[french frank]

Did I hear on the radio this morning that Mr Seddon is about to announce that FM will now continue indefinitely allong side DAB

Edit http://www.bbc.co.uk/news/entertainment-arts-43458695

Yes, that is the case. All to give listeners more choice. Mr Shennan, Director of Radio and Pop Music.