Jeff: Last week we began an item on the history of the 648 kHz mediumwave channel in the UK, which has been researched and written up by Radio Caroline chief engineer Alan Beech. Today we continue with Ray reading Alan’s article, which was published in both the BBC engineering journal ‘Signal’, and on the Radio Caroline website.
Ray: Thanks, Jeff.
In the late 1970’s the BBC was using 648 kHz on its 500 kW Aspi 1 transmitter at Crowborough in Sussex, near the south coast of England, for the BBC World Service for Europe. But, the transmitter was 40 years old, and coverage from that site into continental Europe was not optimal. So…
Offshore (2)
The search was now on for a new site to house a new transmitter and antenna to provide BBC European coverage as the Cold War continued to escalate. It is said that Mr Bernard Bale, an engineer in the BBC World Service Schedule and Frequency Management Department, had suggested a certain technically suitable location to the powers-that-be, as he was aware that the RAF and USAF had vacated an apparently-failed over-the-horizon-radar facility in eastern England.
On the coast of Suffolk, or more precisely, a few hundred yards off the coast of Suffolk, is a spit of land known as Orford Ness, used as a secret military area during both world wars and during the 1960’s until the mid-1970’s to house an experimental joint UK/US missile tracking radar system. Code-named ‘Cobra Mist’, the site was no longer required by the Ministry of Defence and now the BBC, in conjunction with the Foreign Office, made plans to redeploy it. The 1296 kHz 500 kW European multi-language service from Crowborough was transferred there first in 1979 using ORF-2A and ORF-2B transmitters at 250 kW each, combined on to a six-tower array producing a bearing of 90⁰.
BBC World Service for Europe on 648 kHz was first broadcast from Orfordness on a test transmission basis in 1979 using a 1965-vintage 50 kW Continental Electronics 317C transmitter during the hours of daylight into a simple two-mast directional array. Compared to Aspi 1, results were so encouraging that the full 24/7 service was established there from September 1982 until March 2011 using ORF-1, an AEG-Telefunken 600 kW transmitter. The antenna system was an array of five in-line towers; this array directed the signal into a south-easterly 110⁰ beam from the UK, giving an effective radiated power to the target area of over 3 MW.
A reserve antenna was provided for the 648 kHz service together with a reserve 180 kW Doherty transmitter (ORF-3) that had been transferred from Crowborough. This antenna was a new design and consisted of a 200-foot top-loaded omnidirectional, half-folded dipole; the top-loading was adjusted in both angle and length at commissioning, so that the feed-point impedance was 50 Ω; this approach negated the need for an antenna tuning unit.
Although mostly in English, programmes in German and French were also aired at times, particularly in the early 1990’s as East and West were united and the Iron Curtain came down.
BBC QRT
The BBC service on 648 kHz was terminated in March 2011, followed by the 1296 kHz then DRM-only service some months later for a number of reasons – financial savings, lack of interest in international radio, listener migrations to online and digital listening and upcoming major capital investment to replace the ageing equipment. At the end of transmissions, the site was operated by Babcock Communications on behalf of the BBC and Foreign and Commonwealth Office.
A temporary RF reprieve
It was during the period that the 648 kHz service was silent, and before the operating licence was withdrawn, that there was an unfortunate coincidence of fires and system failures at several principal Dutch transmitter sites. They were taken off-air within hours of each other in late July 2011, thus depriving a significant amount of the population of The Netherlands of almost any domestic radio broadcasting. It was deemed to be such an important event that arrangements were put in place between the Dutch and UK Governments to broadcast NOS Radio 1 (the Dutch equivalent to BBC Radio 4) from Orfordness using ORF-1 to provide instant total coverage to the country. Radio 1 is deemed by the Dutch Government to be the national emergency communications channel, in much the same way as Radio 4 is in the UK. These transmissions came to an end on 22nd September 2011 when regular services were again restored from within Holland.
And so, on that date, 648 kHz from Orfordness finally fell silent…. and the licence to use the 648 kHz frequency was withdrawn by Ofcom in 2012. Eventually, Ofcom declared the frequency would be made available for new community radio stations and licence applications were invited by them in late 2016.
Then, on 22nd May 2017, Ofcom announced that Radio Caroline had been offered a licence and a few days later allocated the 648 kHz channel, but the power granted was only 1 kW. Several transmission sites were considered, but after protracted negotiations with the current site owners, it was agreed that Radio Caroline could also broadcast from the same Orfordness site previously used by the BBC, although they would have to provide their own transmitter.
Thanks to a donation from a supporter in Switzerland, a 2½ kW solid-state Canadian Nautel ND2.5 transmitter was obtained and installed, feeding what had been the reserve omnidirectional antenna at Orfordness. So, on 22nd December 2017 – 648 was back on: but now at minus 599 kW compared to before! Here’s Johnny Lewis on Radio Caroline, opening procedings at 7am live from the station’s Radio Ship, the MV Ross Revenge:
Although nominally a ‘clear channel’ across north-western Europe, 648 kHz is by no means quiet. Radio Caroline is fortunate in that no other station in the UK has (so far) been granted permission to use the channel, so even with a modest output of 1 kW, the signal provided ‘anorak’ DX-grade reception at some considerable distance from the transmission site during the daytime.
There is little chance that any neighbouring countries will also be allocated the channel which is an added benefit. However, there are stations in Spain (which was well outside of the BBC’s directional beam), Slovenia and possibly Bulgaria on this frequency. Spain and Slovenia are both active and put a reasonable signal into the UK at night – though with slow and deep fades. The Bulgarian station may well be defunct. As Slovenia and Bulgaria both lie within the main beam of the former BBC transmission, it is quite possible that transmissions were introduced deliberately during the Cold War to provide night-time disruption to the BBC service. Other stations to which 648 kHz is allocated are in Libya (also believed to be inactive) and a 2 MW station in Saudi Arabia. Although the latter is many miles away, it will at times put a signal into Northern Europe. None of these transmissions cause problems within the primary coverage area of Radio Caroline, but they do limit the extent to which the signal can be heard around Europe at night-time.
In July 2021, Ofcom increased the licensed ERP for Radio Caroline to 4 kW, agreeing to an expansion of the primary coverage area to include the counties of Suffolk, Essex, Kent and East Sussex. To implement this increased power authorization, the station acquired a Harris DX25 transmitter previously installed in The Netherlands, which has been used as the primary transmitter since November 2021.
Following a successful fund raising campaign in 2022, an array of solar panels was installed at Orfordness with the capability to provide double the level of power needed for the 648 kHz transmitter. Thus, during daylight hours, the excess power generated is exported back to the grid, with the net result that the cost for electricity to operate the transmitter is now zero.
A subsequently requested increase to 16 kW has not yet been granted by Ofcom, but station spokesman Peter Moore said:
“Other major radio stations including the BBC have been ceasing or cutting back their AM radio services due to high energy costs.
“We have taken the opposite tack by making our own electricity. Indeed, we wish to increase our AM power, installing extra panels if and when a power increase is granted in the future, while helping the planet just a little. Maybe others will follow our example.”
European listeners who have a pre-1978 radio with stations marked on the dial, will find ‘Third’ or ‘BBC R3’ marked at 464 m. 1950-era dials may have this marked as ‘Daventry’. This is where one can find Radio Caroline today on 648 kHz, and the station also uses the frequency one weekend each month for its Radio Caroline North service, again relayed live from their radio ship the MV Ross Revenge, which lies at anchor in the middle of the River Blackwater near Bradwell in Essex.
And, we thank Alan Beech, chief engineer with Radio Caroline, for his research into that very interesting history of the use of 648 kHz in the UK.
Wavescan is an international DX program, researched and written in Indianapolis by Dr. Adrian Peterson and in Los Angeles by Ray Robinson. Wavescan is produced in the studios of WMRI Shortwave in Okeechobee, Florida, by Jeff White.
The program frequently covers radio stations aboard ships. These reports are documented here.
