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A discussion on the opening of ILR at Lots Road


Lots Road Power Station.

Lots Road Power Station in Chelsea, London once supplied electricity to the London Underground. It is also well-known in broadcasting circles for being the MF transmitter site for the new commercial stations, Capital Radio and LBC when they opened in 1973, until their main site at Saffron Green became available in 1975. It was later the MF relay for the long wave version of BBC Radio 4 until this service was moved to Crystal Palace.

Here mb21 contributors discuss their recollections of the launch of Independent Local Radio at Lots Road.

The Clothesline

Robert Preedy was intrigued to see the Lots Road mast on the mb21 Transmission Gallery and the subsequent sloping wire at Crystal Palace that carries Spectrum 558. He mentions that Capital and LBC were the first on the "clothesline" at Lots Road in 1973, but wonders how the IBA was able to claim the original 557kHz as a UK frequency. At the time it blotted out Veronica, but that hardly justifies its London use.

As the MW low end carries a fair way, he questions why Capital/Sunrise/Premier Radio now lumbered with expensive electric bills by being at the MW high end? The Lots Road site provided London wide coverage, and it appeared to be a very simple solution - or is it a very complex equation?

Martin Watkins replied that the official chapter and verse is in here IBA Technical Review 5 particularly pages 9 and 10 (although the whole of that planning document is fascinating - at least to those of us around at the time).

As far as he knew, 557 kHz and 719 kHz were some of the first negotiated non-UK frequencies, a process which didn't really happen until the late 1960s when the first "more supple" approaches to the Copenhagen plan started to emerge, whereby by mutual negotiation, and on the basis of non-interference, countries could bilaterally choose to share certain frequencies at low power. But we were still in an era of high engineering standards and fixed "plans",and having acquired 1546 and 1151 kHz from the BBC the IBA were damned well going to use them, and install state of the art equipment and radiators so to do.....

However, 557 kHz was pretty good and went miles and miles in the daytime.... 719 kHz was less good, and to this day the night time coverage of Radio 4 from Crystal Palace is reduced by continental interference.

Martin suggests that 557 kHz - whilst a good stop gap - wouldn't have been entirely suitable as a general ILR frequency precisely because its use for local radio is negated by its huge carrying power over land....

What he does remember reading was that 557 kHz caused no end of problems for the BBC at the Albert Hall (or maybe it was the Festival Hall) as it seemed to be particularly good at getting into the microphone cabling, even though of course all that was of the balanced type.

Siting and transmitters

Glyn Roylance : Although the low end gets better ground wave coverage than the high end, I think the actual transmitter site at Lots Road has a lot (no pun intended!) to do with it. Firstly it's right next to the river which is going to help get a great earth. Secondly I was told that the aerial system actually used the earthing system of the power station. So although the radiating element was rather humble, taken as a package this site has a big advantage as a MF transmission site over a bit of scrub land near Hounslow.

I have some insight on the Spectrum era as I was a humble Broadcast Engineer at IBA Croydon at the time. I'll never forgot the day when my boss, the TMM told us we had to install a new service operating at 558kHz at Lots Road. "But that's co-channel with Caroline" I bleated. "Yes" said my boss and he gave me the impression that it was a deliberate choice - I got the impression though it was not the IBA's choice, but came from somewhere rather higher up! Maybe the motivating factor was that it would mean, probably for the first time, that "the men in suits" could say Caroline was interfering with legal stations. Some while earlier I recall the BBC had "bottled it" and not launched BBC Essex on 558 because Laser was on there at the time.

I recall the original licenced power was around 500w, but my boss being a cunning guy bought-in a Redifon BT100 unit. This is a solid-state transmitter capable of 1000w. These units were quite unusual at the time and a bit feared by the engineers as they had a delicate reputation compared to the big old Marconi valve jobs. Unsurprisingly when commissioned it barely got past the end of the road before copping interference from Caroline. Quickly we were asked to go back and double the power but that did not help much.

My boss then commandeered another BT100 from the IBA training college at Seaton, Devon. I then moved onto other projects, but I believe they eventually got up to 8 transmitters and probably quite a few kW of power. My boss also requisitioned a big 300w Harris FM transmitter as a pragmatic solution to get Spectrum an un-interfered service (on 100 or 101 MHz I recall), but the "powers that be" seemed determined for a show-down and would not allow him to use it. At the time I lived in Penge. Turn your radio one direction you had Spectrum, turn it at right angles and you had Caroline virtually perfectly. In the car the interference from Caroline would start around the start around Abbey Road and get gradually worse on the M1 until Caroline was dominant around Luton.

Then the interference from Spectrum faded and Caroline was perfect from around Daventry and northwards. After a while they put a second MF service on for Spectrum (990kHz?). I can't remember the exact order of events thereafter, but Caroline's mast came down, they moved to 576 and eventually were towed in during a storm by the British authorities. Bah humbug!

Lots Road 'clothesline' aerial
mb21 Transmitter Gallery
Photo: Philip Rayner.

Sean Cooper commented: You are quite correct re. Spectrum's second frequency being 990kHz, and from what I understand and remember, this was only a temporary measure due to Spectrum threatening the powers that be (the IBA?) with legal action due to them licensing 558kHz when they knew Caroline occupied the frequency and would cause interference.

I have a vague memory regarding the 990kHz system - AISTR, a tee antenna was strung between 2 lighting pylons at one of the London football clubs (Fulham FC comes to mind, although I might be wrong).

Martin W: Absolutely fascinating Glyn - thank you - I remember the situation well (as a listener to Caroline). I duly complained to Peter Baldwin about the situation, a belligerent man even on paper. Of course he was quite right to say that one station was licensed and the other not, but as I pointed out one had a huge audience and the other a few thousand non-English speaking folk.

The only thing I would say was that use of 576 kHz for Caroline was before the demise of Laser - as soon as Laser failed Caroline moved to 558 kHz, so that must have been before Spectrum. Certainly the mast at Caroline came down soon after the October 1987 hurricane (about a month afterwards) and eventually Caroline used 819 kHz, although I think that was more to do with the fact that 963 kHz became hopeless for them when the new 600 kW tx at Pori came into use; prior to that Finland had only used about 50 kW on that frequency.

Roger Piper : I understand that the IBA had huge problems finding a suitable site for MF for which planning permission was obtainable. It's rumoured that they failed at Saffron Green, too, and in desperation approached the government of the day at ministerial level with what was essentially a polite ultimatum of if you don't override the local authority the London ILR MF services (which were the primary services in those days, band II FM having a minority audience) won't happen.

As the flagship ILR stations any avoidable delay in Capital and LBC's on air dates was unthinkable and a temporary site was needed. Capital provided a 24/7 service from day one so use of the allocated frequency of 1546kHz (later 1548kHz) at a temporary site would have prevented aerial power testing at the permanent site, so a temporary frequency was needed. In those days the MF band was electrically fairly quiet in most areas and 557kHz from Lots Road was widely audible daytime, including in the Birmingham area. Lots Road continued broadcasting on 557kHz, in parallel, for a number of months after Saffron Green was commissioned. Capital soon built up a pretty good idea of Lots Road's coverage from the locations of listeners phoning in for requests, quiz show participation etc. Ray Hills, former IBA Assistant Director of Engineering, informs me that the "clothes line" was the brainchild of the late Les Lester, a previous BBC PID engineer who was recruited by IBA after his retirement as he was known to be a "guru" in MF matters. He adds:

"The Redifon BT100 was a transmitter designed for marine DF stations and actually manufactured just across the river at the Redifon factory in Wandsworth. I recall an early visit, together with the late Derek Chambers - then Head of the HQ group developing the ILR stations, to talk with Carl Den Brinker, their Chief Engineer. I can't remember how many we bought but as I recall the majority of the MF stations were fitted with the well proven Marconi 1kW with valves (tubes?) in the output, for which we were given a very attractive price to get the business. Provision of all ILR transmitting facilities was the responsibility of Derek's group, part of a Department within my bailiwick, although we made use of station staff to help with installations around the country."

Michael recalls: Caroline and Radio Luxemburg eased the pains of A-level maths homework more than I can say. I had to make a frame-aerial to separate the blighters... And RTL( King Rosko et al)ignited my interest in French and German, which eventually took me to Heidelberg and beyond...

Glyn : Yes Sean - now you say it, it was Fulham FC. I recall they kept that second frequency (and presumably the extra power at Lots Road) for a long time after the demise of Caroline 558. I understand the original intention when the Ross Revenge was built the mast was designed for 558 but for some strange reason they launched on 963.Just imagine how the 50kW would have got out if they'd used it on 558! I've been told by the time they did use 558 and 576 they rarely had more than 5kW...

Robert P: What comes through clearly is the BBC intransigence over site sharing and releasing frequencies - thereby causing planning delays, and colossal running costs for the Independent stations forever cast at the high end. Curious as well is how the BBC managed to conjure up 585 for BBC Scotland around Dumfries, when this was the main frequency for Austrian public radio. Veronica/Caroline on 557 and its temporary use for ILR casts a subtle difference to the accepted facts about "blotting out the pirates". Rather odd that Ofcom is now proposing low power community radio on 648 - and the more feasible Orfordness frequency of 1296 is currently being tested at high power by Babcocks. Is 1296 licensed for domestic UK broadcasting? Once again thanks for unravelling the fading story of Lots Road.

Mark Carver: I'm not sure that was the case, the IBA often had different technical requirements for the MF transmitters for ILR. The directional arrays pushed far more signal far more efficiently into the big cities. Compare Langley Mill near Birmingham, with the Beeb's miserable effort for MF from Sutton Coldfield (take a look at Ray Cooper's account of that on mb21). Of course, eventually, the BBC joined the IBA at Langley Mill.

The BBC did allow site sharing for MF, where it was appropriate for the IBA. Plymouth, Exeter, Bristol, Teeside, Stoke, Bournemouth, Canterbury, Leicester, all spring to mind.

As far as FM was concerned, the IBA led the way, mixed polarisation, and the use of Croydon for Capital and LBC. The Beeb at that time were using Wrotham for BBC London (and polluting the south coast with its signal. Again, later the Beeb saw sense and relocated to CP in 1980.

Alwyn Seeds: I can't let this thread conclude without recalling my developing experience of electromagnetic compatibility issues, courtesy of Lots Road.

At that time I had a "Texan" kit built 20W + 20W amplifier. This design took little account of such issues and used a 748 op-amp as a disc amplifier. In my student bed-sit off Wandsworth Common this detected BBC1 VHF sound and frame buzz from Crystal Palace wonderfully. I solved this with a common-mode cancelling ferrite transformer/filter on the back of the DIN input socket. The Crystal Palace problem was not unknown in professional circles- I treasure a recording of Messiaen's La Nativite du Seigneur, made in St Paul's Cathedral, that has the bizarre accompaniment of the Saturday tea-time football scores clearly audible in the quiet passages.

Later I moved up-market in bed-sits to Chelsea, just along the road from Quentin Crisp. There Capital romped in from nearby Lots Road, this time picked up on the amplifier speaker leads. I had to modify the power amplifier feedback loops considerably to eliminate it. A bit of wire, diode and multimeter registered the signal strongly. I agree with correspondents that access to the earthing system and riverside location were probably key to the Lots Road station success.

Roger: I can't resist adding a post script to that on the general subject of broadcast related EMC issues. In the early days of Capital Radio the OB mixing desk in use was prone to picking up and demodulating strong MF and HF signals. The Royal Albert Hall was close to Imperial College's amateur radio club station, G5YC, which was picked up well on the desk. Capital's chief engineer at the time, Gerry O'Reilly, had to politely ask them not to operate during recordings and fortunately they kindly agreed to cooperate.

Dave Thickett: I remember doing a night shift at Lots Road with Dave Brian, a quite exceptional antenna engineer from the IBA. The night shift was to install the combiner to allow the BBC service to be added to the already radiating IBA service (although it could have been the other way round), I was the representative of the BBC. From memory, the system didn’t achieve the impedance bandwidth on the lower frequency after the combiner was added but we had to go ahead and switch on the service anyway as there was no way to modify the earth or antenna in time for the service date. This must have been in the late 80's.

From memory, there was a separate cabinet for the combiner and matching circuits in the centre of the chimneys in an enclosed compound to stop anybody getting their hands onto the vertical wire, I'm pretty sure the antenna earth was a copper tape going from the cabinet to a stake hammered into the mud of the river bank, and that there were some coax cables going back to the transmitters inside the power station a few hundred metres away.

See also :

   mb21 Transmission Gallery : Lots Road
   Features article : Saffron Green
  Why was 1973 the year UK radio changed forever? (BBC)


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