Wireless Waffle - A whole spectrum of radio related rubbish
90 years of the 'time pips'signal strength
Friday 7 February, 2014, 13:43 - Broadcasting, Licensed, Much Ado About Nothing
Posted by Administrator
What a disappointment it was to find a recording called 90 years of the time pips, to discover that it is a special version of the pips¹ designed to celebrate their 90th birthday.

Wouldn't it have been more fun to have calculated how many pips there have been in 90 years and then created audio that just pipped (or beeped continuously) through all 90 years? How many pips would that be?

90 years × 365.25 days × 24 hours = 788,940 hours²

The first 5 pips have a duration of a tenth of a second, and the final pip has a duration of half a second, so the total duration of the pips each hour is exactly 1 second (5 × 0.1 + 0.5). A constant tone of duration 788,940 seconds (which is 9 days, 3 hours and 9 minutes precisely) would therefore represent '90 years of the time pips' much more accurately.

So here for your listening pleasure, is the Wireless Waffle tribute to the pips... 90 years of pips compressed into 9 days, 3 hours and 9 minutes.

play 90 years of the pips
Just click the play button, sit back and enjoy!

gladys knight and the pips¹ Not to be confused with Gladys Knight's backing group who, whilst also played on the BBC from time-to-time, are not the pips in question here.

² Of course the pips have not been broadcast every hour over that period. Other time signals (such as the chimes of Big Ben) are used on some hours. Equally the BBC has not always been a 24 hour service, so this figure is probably a significant over-estimate.
add comment ( 321 views )   |  0 trackbacks   |  permalink   |   ( 3 / 975 )

Local TV test transmissions on-airsignal strength
Wednesday 29 January, 2014, 11:01 - Licensed
Posted by Administrator
It's a surprise that there haven't been more reports of this, but it seems that the Local TV services licensed by Ofcom last year are beginning to come online. The video clip below shows test of one of the two national channels that will be operated by Comux (to try and generate enough profit to run the transmitters) as received in Clacton, Essex. The signal comes from the Crystal Palace transmitter in London.

There doesn't yet seem to be placeholder for London Live which will launch in the capital in March on channel 8 on Freeview, but the two national channels awaiting launch and currently sat on channels 791 and 792 so you can check whether you will be able to receive it (a re-tune may be necessary).

The first of the new raft of local TV stations on the air was Estuary TV in Grimsby, whose transmitter also does a pretty good job of covering nearby Kingston-upon-Hull.

Wireless Waffle previously reported on the lessons to be learnt from the failed attempts at local TV in the UK in the past, and on the uncanny similarity between Comux (the local TV network operator) and Arqiva (who are providing the transmitters to Comux.

There are still a large number of local TV transmitters to be put on-air, so keep checking your set-top-boxes for new channels. Oh, and whilst you're at it, see if you can get the additional Freeview HD multiplexes that have quietly launched around the UK providing such excitement as BBC4 HD and Al Jazeera HD. Why couldn't they have put something useful in HD such as Dave or Film4?

You can check the channel line up on Freeview at your location by using the handy form below.

Your Postcode
House Number or Name
(Providing a house name or number is not essential but makes your results more accurate)

5 comments ( 1918 views )   |  0 trackbacks   |  permalink   |   ( 3 / 609 )

Wave To Go!signal strength
Monday 27 January, 2014, 15:30 - Broadcasting, Licensed, Spectrum Management
Posted by Administrator
The BBC recently reported that Radio Russia have quietly switched off the majority of their long-wave broadcast transmitters. Whilst the silent passing of Russia's long wave service will not rattle the front pages either in Russia or anywhere else for that matter, it does raise the question of the long-term viability of long-wave broadcasting.

atlantic252During the early 1990s there was a resurgence of interest in long-wave radio in the UK caused by the success of the pop station Atlantic 252. But by later in the decade, the poorer quality of long-wave broadcasting compared to FM, together with the increased proliferation of local FM services in the UK eventually led to the demise of the station. Similar logic appears to have been used by the Russian authorities who now have a much more extensive network of FM transmitters and clearly feel that the expense of operating long-wave is no longer justified.

One of the great advantages of long-wave broadcasting is the large area that can be covered from a single transmitter. For countries whose population is spread over very wide areas, long-wave offers a means to broadcast to them with very few transmitters. Conversely, the large antennas and high transmitter powers required to deliver the service make it an expensive way to reach audiences. Presumably there is a relatively simple equation that describes the cost-benefit of long-wave broadcasting, i.e.:

worthwhileness equation

W = Worthwhileness of Long-Wave Broadcasting
C = Total cost of providing the service
A = Audience
LW = Long Wave
Tot = Total

As long as W>0 as A(FM) increases it continues to be worthwhile to broadcast on long-wave as the cost of providing the service is greater than the cost of doing the same thing using FM.

The cost of providing an FM service - C(FM) - is not constant, and will increase with the audience served, and not in a linear fashion either. The final few audience will cost significantly more than the first few. This is because stations which only serve small, sparse communities tend to be more costly (per person) than ones serving densely packed areas.

The cost of providing the LW service - C(LW) - however, is largely constant regardless of how many people listen to it.

It's therefore possible to draw a graph of the cost per person - C/A - of the FM audience and the cost per person of the long-wave audience, as the FM audience increases.

long wave fm graph

The figures used in the graph above are illustrative only. They assume that:
  • The cost per person of providing an FM service increases by a factor of 10 between the first and the last person served;
  • The cost per person of providing the long-wave service is initially only a third of that of providing the same service on FM.
Based on these assumptions, it is not until the FM audience reaches almost 90% of the population that the cost per listener of FM is less than that of providing the same service on long-wave. As FM coverage becomes more widespread, it is this factor that is causing many broadcasters to cease long-wave transmissions (the BBC has a plan to end its long-wave service too, though there is no date set for the closure yet).

Of course there are many other factors to take into account, in particular the difference in service quality between FM and long-wave, and the proportion of receivers that have a long-wave function. There are thus other factors that will hasten the end of long-wave as FM coverage increases. The same could largely be said for medium-wave where arguably, the problems of night time interference make it even worse off than long-wave (though more receivers have it).

long waveWireless Waffle reported back in 2006 on the various organisations planning to launch long-wave services, not surprisingly none of them have (yet) come to fruition.

There is, however, one factor in favour of any country maintaining a long-wave service (or even medium-wave for that matter), and it's this: simplicity. It is possible to build a receiver for long-wave (or medium-wave) AM transmissions using nothing more than wire and coal (and a pair of headphones) as was created by prisoners of war.
Prisoners of war during WWII had to improvise from whatever bits of junk they could scrounge in order to build a radio. One type of detector used a small piece of coke, which was a derivative of coal often used in heating stoves, about the size of a pea.

After much adjusting of the point of contact on the coke and the tension of the wire, some strong stations would have been received.

If the POW was lucky enough to scrounge a variable capacitor, the set could possibly receive more frequencies.

In the event (God forbid) of a national emergency that took electricity (such as a massive solar flare), it would still be possible for governments to communicate with their citizens using simple broadcasting techniques and for citizens to receive them using simple equipment. Not so with digital broadcasting! Ironically, most long-wave transmitters use valves which are much less prone to damage from solar flares than transistors.

So whilst long-wave services are on the way out in Russia and elsewhere, it will be interesting to see whether the transmitting equipment is completely dismantled at all sites, or whether some remain for times of emergency. Of course if every long-wave transmitter is eventually turned off, there is some interesting radio spectrum available that could be re-used for something else... offers on a postcard!
1 comment ( 2225 views )   |  0 trackbacks   |  permalink   |   ( 3 / 580 )

Where next for radiomicrophones?signal strength
Monday 16 December, 2013, 23:10 - Broadcasting, Spectrum Management
Posted by Administrator
It wasn't that long ago that Wireless Waffle was discussing the need for spectrum for programme making and special events (PMSE). At the time we were considering how the needs of the burgeoning demand for radio spectrum for the Eurovision Song Contest would be met. Most radiomicrophones currently operate in the UHF television band, in the gaps between transmitters. These gaps (which are there to protect neighbouring television transmitters from interfering with each other) are also being eyed by the wireless broadband and machine-to-machine community amongst others and have been given the moniker 'white space' (though one person infinitely more learned in these things believes they should correctly be considered 'grey spaces' as they aren't as white as you might believe).

tv squashedThere are also moves afoot to squash television broadcasting into even less spectrum to make way for more mobile broadband. At present the spectrum from 470 to 790 MHz is generally available (40 channels - channels 21 to 60). The new plans involve using the spectrum from 694 MHz upwards for more mobile broadband leaving the terrestrial television broadcasters with just 28 channels (channels 21 to 48). And at the moment, there is no guarantee that there won't be further erosion of the UHF television band for other uses.

If TV use is squashed into less spectrum, there will be less 'grey space' available for radiomicrophones, or for anyone else for that matter. To make matters worse, the tuning range of most radiomicrophones (and similar devices) is very limited and each time they are forced to change frequency, new equipment needs to be bought. Of course, this is good news for manufacturers such as Sennheiser and Shure, but is bad news for the end users.

The need for spectrum for radiomicrophones and other PMSE uses is recognised at an European level in the Radio Spectrum Policy Programme (RSPP) article 8.5 of which states:
Member States shall, in cooperation with the Commission, seek to ensure the necessary frequency bands for PMSE, in accordance with the Union's objectives to improve the integration of internal market and access to culture.

So what can be done? Are PMSE users to be left as the nomads of the radio spectrum, packing down their camps, wandering across the desert and re-assembling their tents in a new area every 3-4 years? Or is there a long(er)-term solution that would allow them to lay solid foundations and put down some bricks?

For many years, a band at 1785 - 1800 MHz has been available for wireless microphone use, but only for digital microphones (see CEPT Report 50). Almost no use has been made of the band and the views of Audio-Technica illustrate why this is the case:
The frequency range [1800 MHz] is not really suited for wireless microphones, as the higher frequencies (i.e. shorter wavelengths) create more body absorption and shadow effects due to the directivity, etc. The use of these frequencies will only work adequately when there is a line of sight and a short distance between the transmitter and the receiver.

alesha microphoneUsing diversity reception (already commonplace in radiomicrophone equipment) and careful antenna placement, there is no reason why the 1.8 GHz band could not prove useful. But one of the other problems with this band is that radiomicrophones are not well suited to using digital technology. To send audio digitally, it must first be converted from analogue to digital. For 'high quality' audio, this would yield a 'raw' data rate of at least 512 kbps, if not more - and more like 1 Mbps by the time error correction is added in. If we were to try to transmit this data in the 200 kHz channels that microphones currently use, we would have to use a high-order modulation scheme (such as 8-PSK or 16 QAM) and this causes problems because:
  • transmitters need to be linear meaning they draw more power and would drain batteries much more quickly;
  • higher-order modulation schemes require decent signal-to-noise levels and thus higher powered transmitters;
  • it takes time to encode and decode complex modulation schemes.
It is this latter point that is perhaps the Achilles Heel of the system. The delay between words being spoken, and the sound coming out of the PA system has to be very small. If it is not, problems of lipsynch soon occur (e.g. the speakers lips are out of synch with the sound you hear). A delay of only a few 10s of milliSeconds is usually regarded as the largest tolerable.

This means that the other way in which digital systems use spectrum efficiently is also a no-go. Compressing the data (e.g. using a compressed audio format such as mp3 instead of the raw digitised audio) also takes time - generally longer than the time taken to transmit the signal digitally. And so we reach an impasse: compressing the audio to use less spectrum takes too long, and transmitting the raw data uses more spectrum than their analogue counterpart and involves a number of other trade-offs. All this means that digital radiomicrophones, whilst slowly being developed, tend to offer no better performance than analogue versions (and at much higher cost).

But the fact is, that if the radiomicrophone industry does not make some strides towards adopting higher frequencies or more spectrum efficient modulation techniques, it might find itself without enough spectrum in which to operate.

So where could microphones go? There are a whole host of frequencies which are currently assigned at a European level by CEPT for radiomicrophone use (as per ERC Recommendation 70-03, Annex 10). These include:
  • 29.7 - 47 MHz - manufacturers claim that these frequencies are not ideal as they are too noisy and antennas are too large (fussy lot aren't they)
  • 174 - 216 MHz - VHF band III - mostly occupied by TV broadcasting and DAB radio
  • 470 - 790 MHz - the aforementioned UHF band that is now being squeezed
  • 863 - 865 MHz - licence exempt and shared with other devices
  • 1785 - 1805 MHz - 'too high'
The UHF band accounts for over three quarters of the available spectrum, so if it is lost, where next for the radiomicrophones? How's about:
  • 1215 - 1350 MHz - mostly an aeronautical radar band but shared with many other uses and therefore presumably sharable with others
  • 1350 - 1400 MHz - low capacity fixed links and some mobile services
  • 1492 - 1518 MHz - more low capacity fixed links - and already proposed in ERC 70-03 but available in a tiny amount in the UK only
  • 1675 - 1710 MHz - a downlink band for meteorological satellites but not heavily used - sterilisation zones around official downlink sites would protect professional users
If the big guns (Sennheiser, Shure, Audio-Technica, AKG) refuse to find a way to use higher frequencies, perhaps the time is right for one of the small guys to. You can bet your bottom Renminbi that if they don't, some enterprising Chinese company will!

china wins microphone
2 comments ( 4135 views )   |  0 trackbacks   |  permalink   |   ( 3 / 779 )

<<First <Back | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | Next> Last>>