Author Archives: radiohead

Finding an FM Frequency



We are often told by Ofcom that “there are no available FM frequencies” in an area. We find this an unfortunate situation which can often seem impossible to address. Yet life is seldom that simple, as with all things in life it depends upon what assumptions we use, and what engineering solutions we consider. Here at ABC we contest that in most situations we can find a technical solution to such an assertion. Although we admit that, in the limit, things may be difficult and such solutions may not always be economically or practically viable. But in most situations we can suggest a realistic solution.  IF the regulator is willing to consider it.

We recommend a three-step approach:

1. Assess frequency availability in general, following Ofcom guidelines
2. Verify clear frequencies locally on a radio in several locations or driving around in the target area
3. Analyse the best frequencies in detail, assessing interference from and to other radio services

Step 2 can be done by anyone, steps 1 and 3 need to be done by a radio engineer with access to the right tools.

The ABC Approach

Here at ABC we have recently developed a method to perform step 1 that is very similar to the approach demonstrated by Ofcom in a meeting a couple of years back.  But we believe it has an important enhancement. We believe there is an inherent weakness with the Ofcom approach, because their initial frequency scan is performed from the local broadcast site. By nature the broadcast site is in an elevated location, so it will tend to exaggerate incoming interference compared to the typical listener location.  Real listeners are normally in a town/city centre, low down and amongst building clutter.  We don’t care if sheep on the hillsides get interference!

The ABC approach considers a realistic location in the centre of the target coverage area. We then consider incoming signals from EVERY licenced FM signal in the UK using the latest Ofcom database.  We also take account of first adjacent, second adjacent and +/- 10.7MHz signals as specified in Ofcom recommendations.  Of course we also consider transmit aerial height, aerial pattern and receiver aerial height.  Oh and we factor-in the (controversial to some) Ofcom/ITU protection ratios.  The result is an understanding of the total interference environment in an area, as opposed to on-site snapshot frequency scans that can only be done in a limited number of locations.

Our Results

Our results are displayed as a chart to aid selection of an appropriate frequency.  When all the rules are factored in,we’re often surprised how many of the 205 possible channels get ruled-out from use.  For example see below example for the city of Gloucester – a relatively “quiet” area for FM spectrum (click to enlarge):

Chart showing FM spectrum utilisation in Gloucester

The red columns are channels that we rule-out by Ofcom’s +/- 10.7MHz rule.   Ideally, for full protection a channel we would have a total signal power less than the lower blue line, although the upper line is acceptable for Community radio according to Ofcom rules.  Using this tool we can show that although the spectrum is fairly busy, there are still several potential frequencies.

The Next Step

If we choose 95.4, we can check the feasibility using ABC’s Frequency Viewer tool here:

Map showing utilisation of 95.4 MHz and adjacent channels

This tool indicates that the closest co-channel interferer is Radio Berkshire, but with only 500w at 25m height.  It also displays potential adjacent channel interferers – in the map above we have clicked on one and see that it is Radio Nottingham from Fishpond Hill with 1kW on 95.5.

The Final Stage

Using this information, combined with local drive-round surveys, the next step would be to perform a detailed interference analysis with the most significant surrounding radio services. This involves modelling the “Source” and “Interferer” transmitter in detail in a coverage modelling tool.  Then we’d calculate for every pixel (normally 9 million) whether or not the required Ofcom protection ratio was met.

This last stage involves significant effort, but it is worth the effort – we’ve successfully used this approach to challenge Ofcom’s preliminary allocation and secure double the power for a station!

ABC have over 25 years experience in this sort of analysis – contact us for more information!


ABC Wins Nationwide FM Contract


Map of Middle EastAssociated Broadcast Consultants are proud to announce that we recently won a contract to deliver a nationwide FM network plan for a major economy in the Middle East.  Our Teir 1 client chose ABC to assess the technical and financial feasibility of utilising their existing sites portfolio to host the network.

Work started at the end of 2015 and was completed today.  The delivered feasibility study provided three alternative deployment plans, with further options on transmitter vendor – Nautel or Broadcast Warehouse.  In addition a complete set of Bill of Materials was provided catering for each category of sites, a Total Network Cost Model, and ABC’s unique interactive online “Coverage Explorer” tool.  This tool permits the customer to explore the planned coverage in detail using the power of Google mapping API’s.  They can compare network plans, and switch individual sites on and off to see how much coverage each provides.  We believe this gives our customers powerful and unique insights into their network plans.

If you think ABC can help with your radio network engineering, then Contact Us!


Is Radio 1 Ten Times Better than Commercial Radio? – FM Spectrum Consumption in the UK


It’s a deliberately provocative title – “Is Radio 1 Ten Times Better than Commercial Radio?”  That is to say, does it deserve to be able to use 11 times the FM spectrum resource per listener than Commercial radio?  We could equally have asked:-

  • Is Radio Cymru fourteen hundred times better than Community radio?”  or
  • “Is BBC Radio 3 twice as good as Classic FM?”

These questions stem from an analysis we have done of the way our FM radio spectrum is consumed in the UK.  All things being equal, then approximately the same amount of this precious resource called “spectrum” should be consumed for each listener.  But as we will see, things are far from equal.

FM Spectrum Profligacy?

We’ve long harboured a suspicion that the BBC consumes an inordinate amount of FM spectrum in the UK.  Particularly for local radio there seem to be numerous examples of excessively high powered transmitters on massive hills with huge masts.   This gives a wonderfully strong and reliable signal, but an unfortunate side-effect is that they effectively sterilise that frequency over huge areas of the country – preventing it from being re-used for other services – hence the “no frequencies available” response that many new services get from Ofcom.   One such example is Holme Moss, half a kilometre above sea level atop the Pennines.  It broadcasts three “BBC Local” services from a further 168m up its mast at powers of 4000-5600 watts.  It’s rather bizarre sitting in your student flat in Manchester being able to receive a clear stereo signal for Radio Leeds and Radio Sheffield – cities the other side of the Pennines.  What a waste of FM spectrum resources!

Facts & Figures

But maybe this is an isolated example and we have a distorted view?   We need facts and figures to properly look at this.  So we set-about getting some facts and figures – using the latest Ofcom FM database, and the Q12015 RAJAR figures.

To start at the beginning.  There are three key factors that determine how much FM resource any particular station, or group of stations consumes:

  1. How many transmitters are used for the service/s
  2. The power (ie: watts or kilowatts) of those transmitters
  3. The height of the transmitting antennas above the area they are covering

In the UK there are 205 available FM channels for FM services.  The Ofcom database indicates that there are 1918 licensed FM transmitters using those channels – meaning that on average each channel is re-used 9.4 times up and down the country.   In actual fact some channels are re-used more than this, and some substantially less (see our previous analysis).

The power of these transmitters ranges from 0.05 Watts to 125,000 Watts, and they are broadcast from sites ranging from 1 to 1097 metres above sea level with masts from 3 to 305 metres in height.  Each transmitter (presuming it is stereo) uses approximately one quarter of a MHz of radio spectrum.

To compare the FM spectrum consumption of each transmitter, we chose the unit MHz-Watt. That’s not MHz per Watt – its MHz times Watts.  Just like your electricity meter measures your consumption in Watt-Hours.

As an illustration a service that uses three transmitters of 0.5,1 and 2 kWatts to deliver its service consumes (0.5+1+2)x1000/4 = 875MHz-Watts of FM spectrum (the 4 is because each transmitter uses one quarter of a MHz of spectrum to deliver a stereo service)

Note:- We also tried MHz-Watt-Metres but found that although it changed the figures, it did not significantly change the results.  Use of Metres would also have led to difficult questions – should it be the height of the mast, or the height above sea level, or both combined?  In actual fact whichever metres figure was used it did not change the outcome.  

The Results

So analysis of the Ofcom database yields this top-line result of how our UK FM spectrum resources are consumed.  In short BBC consumes 81%, Commercial Radio consumes 18% and Community Radio consumes only 0.06%.

Watt-MHz utilisation of UK FM services

We can split that down and look at some of the detail – it turns out that BBC Local services do not consume nearly so much spectrum as we had imagined (8.9% versus 8.1% for local commercial services).

Watt-MHz utilisation of UK FM services

If we tried an imaginary scenario where all national services vacated the FM band the split would look like this.  Community radio at last starts to become visible, but would still be tiny.

Watt-MHz utilisation of UK FM services

But of course this does not tell the whole story because it does not factor in how many listeners each station has.  Perhaps the Community Radio share of the FM cake is so small because they have so few listeners?  And vice versa for the BBC national stations?   So now we use a new metric to also take into account each station’s Reach (000’s) as declared in the Q1 2015 RAJAR results.  The unit is Watt-MHz/Reach 000’s.

Watt-MHz per 1000 listeners of UK FM radio services

The result you will see is both surprising and unsurprising.  Radio Cymru consumes most FM spectrum per listener (1123 Watt-MHz per 1000 listeners) – but considering the low population density, and difficulty of Welsh terrain, then this does not seem very surprising.   The consumption per listener of Local vs National radio is interesting – no doubt driven by geographic/population targets for national stations that don’t apply for local services?   The stand-out figure has got to be Community Radio though at only 0.8 Watt-MHz per 1000 listeners.  Admittedly it uses the “Other Radio” RAJAR figure which may over-estimate their share – but even if it over estimates their share by 4 times, Community Radio still consumes half the amount of FM spectrum per listener as BBC and Commercial local radio – and as you will see – 1400 times less per listener than Radio Cymru!


Small Scale DAB Demo


If after 8 weeks you are getting impatient waiting for Ofcom to announce a decision on the successful Small Scale DAB applicants, we thought this video of our Small Scale DAB demonstration might distract you for a while!  Don’t forget to hit the [ ] icon bottom right to view it full screen.  Apologies for the slight sibilance – it’s not Roger Shcott narrating – it seems to be an artefact caused by YouTube’s transcoding!


Small Scale DAB Applications are in!


Ofcom logo

…and they’re off!   Ofcom has published all 51 Small Scale DAB trial applications.   Martin Steers has rather usefully plotted them on a map.

Rather strangely, this map indicates there were no applications received from Wales or Northern Ireland – so it seems this will be an exclusively English and Scottish affair! [Edit – since writing we now can see Hollywood FM BFBS on the map in Northern Ireland!]

The vast majority of applications appear to be from radio stations – thus indicating that Small Scale DAB might follow a different model from National, Regional and Local DAB which embedded a clear demarcation between DAB Multiplex providers (Muxco etc) and programme providers.   However it appears there are some potential “mini-Mux-operators” in the mix – including who are known to be very active in the Open Digital Radio development community.  ODR is the organisation that has developed, and continues to develop the open-source software through which these trials will be delivered. small scale DAB trialMore than one of the applicants (eg: and Seaside Radio) indicate that they already have operational DAB transmission chains.  This suggests a high state of readiness and must surely increase Ofcom’s confidence that they can deliver operational Muxes within the target 12 weeks from licence award.  We know from our own experience building a DAB transmission chain using the ODR tools that it is not so straightforward as FM, but ultimately achievable, and very reliable once completed.

It is heartening to see Radio Caroline in the mix on both of the above applications – it seems certain that Small Scale DAB will deliver much-needed variety to the DAB airwaves – even for old anoraks like us!

It is interesting to see Celador radio in the list of applicants, despite them already being present on existing “big scale DAB”.  Maybe they see this as a negotiating lever with their current Mux providers, or even a serious alternative?   Or perhaps just a pragmatic way to cost-effectively get a DAB presence for all of their stations.

More interesting still is to see UKRD on the list who already operate 3 “big scale DAB” mux’s.   We wonder whether Ofcom will welcome and encourage such interest, or perceive it as a potential blocking move from an incumbent!


Ofcom Small Scale DAB trial – Too Small?


Basic CMYKWith their latest announcement it is now official – the previous Ofcom Low-Cost DAB trial has seamlessly morphed into a “Small-Scale DAB” trial.   This is an important difference that will impact (negatively) on many radio stations’ commercial viability.

The key difference between FM and DAB is the concept of a DAB multiplex – which combines several stations that take a finite (roughly 7 times more, and no less) amount of radio spectrum more than a single stereo FM station – even if only one station is carried.  Put that the other way – in a “small scale” area we need 7 stations to fill the small-scale-DAB multiplex just to break-even with what is technically possible with FM. That’s fine as long as the rules of the DAB game  permit an adequate coverage area to capture 7 stations.  Yet Ofcom are imposing an arbitrary limit of 100w which in many situations is unlikely to encompass 7 commercially-viable radio stations.

Two respondents to their consultation expressed concern at the arbitrary 100w limit set in the document was not congruent with the parallel Ofcom requirement of:

  • 100w maximum effective radiated power
  • no larger than 40% of the local commercial DAB Mux area.

The latter seemed a reasonable compromise to protect the monopoly incumbents (if really necessary?), whilst the former is an arbitrary power limit that does not make sense compared to the second point (ie: the lower the power permitted the more the transmitters required = £cost).

The Ofcom response was “it is not necessarily the case that allowing a higher power will in all cases reduce the number of transmitters needed” – which answers a question which was not asked!  (hint – sometimes a power above 100w will reduce the number of transmitters needed!)

As far as we understand the DAB infrastructure in the UK is currently provided by a monopoly provider (Arqiva) – a company which claims an EBITDA (profit) margin of 51% – substantially higher than traditional regulator targets like mobile phone companies.  Say no more.

The original low-cost DAB concept trialled by Ofcom offered a potential route to break this monopoly and lower the cost of entry for a new tier of broadcasters.    Their offer to supply equipment for the trial is to be applauded.

Yet in parallel we have a trial licence that is likely to seamlessly morph into the permanent licence regime that handcuffs small broadcasters in a similar way to the current Community Radio Licences – Is it impertinent of us to ask why we have such arbitrary power limitations on this wonderful new concept?


DCMS Community Radio Consultation Response – Part 2


Well finally the DCMS have responded!  Up and down the country community radio station managers are celebrating the decision with magnums of Pol Roger champagne, while small commercial stations contemplate the rapid demise of their business…

We jest of course, but you’d be forgiven for believing us if you had read RadioCentre’s comments on Radio Today!

In reality it’s all a bit of a damp squib as we predicted in our post on Monday.   By DCMS’s own admission (in their Impact Assessment) it is actually a “Modest Change”.  You can see for yourself in their document and on other radio news websites.   Community radio currently has a 0.7% share of radio advertising in the UK (source Ofcom Communications Market report 2014). If all CR stations take 100% advantage of the new £15k advertising ability it will increase to around 1.4% – hardly earth shattering.   In reality though many community stations will use the new “disregard figure” to reduce the considerable time and effort they currently spend raising funds through non-radio means.

And it is also likely that community radio’s share of the radio advertising market is actually increasing the market size.  After all, how many big advertisers have you heard on your local community radio station?  The reality is that these small radio stations with 25watt transmitters run by part-time volunteers attract a different tier of advertisers who cannot afford to advertise on commercial stations.

So in effect today’s announcement from the DCMS is preserving the status quo and nudging it slightly in favour of the community stations.  In the Government’s mind there seems to be a clear divide between community radio and commercial radio, so they have sought to preserve the regulations that ensure no blurring of the lines.

There are a couple of interesting points buried on page 12 of the DCMS impact analysis:-

  1. Community stations will have to request (and pay to apply) to use the new DCMS rules: “where stations will want to take advantage of new conditions a small cost would be incurred by a station to meet Ofcom’s administrative and resource costs – to cover application form, guidance note, assessment and decision”
  2. Perhaps if community stations maintain the pressure there is scope to review the £15k “income disregard” limit over time without waiting for slow legislation: “the income disregard figure will fall to Ofcom to review, on an annual basis, to ensure it retains its worth and benefit to the community radio sector. It should be noted it will be possible for the income disregard figure to be adjusted either up down or to remain unchanged”

We wonder what the radio landscape could have looked like if the DCMS had recommended Option 4 in their Impact Assessment (and learned how to spell!) “4. Full deregulation – Not considered as it would turn community radio into commercial radio undermining wider policy goals. Option 2 is the prefered option.”   A renaissance in local commercial radio could be just the tonic that Radio in the UK needs!

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DCMS Community Radio Consultation Response


DCMS Department for Culture, Media and Sport logoGetting on for a year after it was published the DCMS Community Radio consultation response is finally about to be available.   On the cusp of its publication we thought we’d stick our necks out and review what’s at stake.  We reserve the right to update this post in the coming days!

Just in case you cannot remember, it asked for opinions on four key questions:

  1. The lifting of the restriction on community radio stations preventing them from taking any income from on-air advertising or sponsorship if they overlap with a commercial radio licence whose coverage area includes 150,000 adults or fewer.
  2. On the restrictions preventing community radio stations from taking more than 50% of their annual income from on-air advertising and sponsorship, if they remain appropriate, and what, if any changes, are justifiable.
  3. On the case for further licence extensions for community radio stations in the event of a decision to implement a radio switchover.
  4. On improving the effectiveness of the Community Radio Fund.

Associated Broadcast Consultants responded to the consultation last year.   Our response probably won’t win us many friends in the Commercial radio sector, but we like to believe it was considered and balanced:-

  1. Of course the advertising restrictions with overlapping small commercial stations should be scrapped.  Heck, if you are worried by the threat from a band of part-time volunteers running a not-for-profit venture, then actually you’ve got bigger things to worry about!   In any case, many of these so-called small stations are actually the local outlet for one of the semi-national radio brands like Heart or Breeze.   It’s akin to saying Oxfam aren’t allowed to sell clothes if there is already a Next shop on the High Street!
  2. Of course the 50% funding rule should be scrapped.   The main business of a Community Radio station should be producing good radio, not scratching about running cheese and wine parties, jumble sales etc to diversify funding away from advertising.  If this rule applied to newspapers then we wouldn’t have the Metro free newspaper to read on the way to work.
  3. Licence extensions – should be judged upon the merit/track record of the station and the scarcity (or not) of FM frequencies in the area
  4. Community Radio Fund is a dangerous distraction.  It risks breeding a dependency culture, and due to its lottery nature cannot be relied upon for stable business planning.  We suggested scrapping the fund and using the funds released to set-up a national advertising agency for the community stations.  Hopefully over time this would become self-funding.

It remains to be seen what the actual response will say in the coming days.  Our guess is that the incumbent broadcasters will win some concessions, but also they will throw a few changes in to try and keep the community radio broadcasters quiet, whilst also alluding to the potential of “Low Cost DAB”.


Raspberries, Steroids and Low Cost DAB


On the horizon there is a real possibility that digital radio broadcasting in the UK could become affordable….

TODROID-U3he picture on the right is of a small yet powerful Linux computer called the ODroid.  It was described yesterday by Martin James (Manager of Broadcast Radio) at Ofcom as “like a Raspberry Pi on steroids”.

It is smaller than a pack of playing cards, yet it is this hardware that they were using to demonstrate the potential of Low Cost DAB at Riverside House yesterday.   It seems incredible, but this diminutive device was being used to encode 6 audio streams into MP2 (the current codec of choice for DAB in the UK) and then multiplex them together into a DAB multiplex suitable to be fed to a Band III transmitter modulator.   Thus for around $65 plus some free open-source software it seems possible to produce a mux signal equivalent in many ways to that generated by professional DAB Mux equipment costing tens of thousands of pounds.

And it seemed pretty stable too.  Rashid Mustapha (low cost DAB guru at Ofcom) demonstrated the lack of impact by failing on of the programme streams (by pulling the plug!).  The other five streams on the Mux happily carried on – as demonstrated on a domestic DAB radio set alongside the demo equipment.

Of course more is needed to transmit DAB – not least a modulator (to turn the Mux bistream into a radio signal), an amplifier (to amplify!) a filter (to remove any sprogs generated in the amplification stage) and an antenna plus some kind of tall structure to mount it on.  All this does not come cheap, but then again, compared to the cost of carriage on existing commercial Mux’s, it is not expensive either.

Nor should we forget the cost of links – the important lines that get programme services from different stations to the little ODroid Mux box, and potentially a broad link from the output of the little Mux box up to the transmitter site.  Yet here too there are low cost alternatives to current approaches.  Trials indicate that the internet is stable enough for individual programme feeds.  And for the big link between Mux and transmitter there are affordable digital microwave links available.   Intruigingly also Ofcom hinted at the possibility of using on-channel repeaters.  This means the mux could be connected to a low power transmitter at a suitable host location (possibly one of the radio stations hosted on the Mux), and then this signal could be received, amplified and re-transmitted from a big hill giving wide area coverage.

Low cost DAB spectrum analyser

Spectrum Analyser showing the Low Cost DAB signal

There is still a long way to go.  The current stage is very much prototype.   The next stage is a trial next year for which Ofcom recently issued a consultation (see post below).

It will be interesting to see how this low-cost DAB concept develops, and how incumbent DAB Mux operators  will react.  Hopefully there is room in the UK Broadcast industry for both “Gold Plated” and “Low Cost” DAB.