Each year during the Antarctic Midwinter, the BBC World Service broadcast a special programme called the ‘Antarctic Midwinter Broadcast’. The programme is specially broadcast for the around 40 scientists and support staff of the British Antarctic Survey who are enduring the harsh polar midwinter.
The first Midwinter Broadcast was in 1955, meaning that this years broadcast marked the 70th anniversary of this unique programme. To mark the occasion, King Charles III sent a message as part of the broadcast, which was transmitted on the 21st July.
But why am I telling you this?Some of you may remember a talk given to the club on Zoom last year by friend of DARC, Matt Porter G8XYJ, titled ‘a Day in the Life of a Shortwave Broadcast Engineer’. Well Matt was on duty at the only remaining shortwave transmitter site in the UK, namely Wooferton on the evening of Saturday 21st July, and he wrote:“An evening shift for me today! Making sure that the BBC World Service Mid-Winter Antarctica Special on 12065kHz is transmitted from Woofferton, Shropshire, UK to all those working for the British Antarctic SurveyVery proud to be part of this!”As you can see from the pictures attached, the Croatian built RIZ Sender (Transmitter) number 96 was used for the broadcast on 12.065.000 MHz.
Matt messaged me with the following information about the type of transmission used.Matt said, ” It was at 250kW AM for tune up, then when on air, it changes to AMCAM compandingThis works that when you have modulation, the carrier drops by 6dB whilst the sidebands are high, then when there is silence the carrier returns to 250kwBasically, when they’re speaking, you are getting PEP of 250kw as the carrier drops by 6db to 62.5kw, bug ten sidebands means that you times that by 4 to get 250kwIt’s all about energy savingIf it was 250kw carrier all the time, you would be pushing 1MW at peak “A recording of the 2025 Antarctic Midwinter Broadcast can be found at:voice https://www.bbc.co.uk/programmes/w3ct7zyv
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