Looking back at 1981 and the reception of BBC TV audio on 41.5 MHz in Texas

First of all, let's set the scene for a bit of context.

The original TV system in the UK was known as 405-line and was in use from 1936 to 1985. The lowest TV channel was B1 with the video carrier being on 45.0 MHz.

One unusual feature of this system was that the audio was AM and this was 3.5 MHz lower than the video carrier i.e. 41.5 MHz for Channel B.

Pat Dyer, WA5IYX was a very active TV DXer and logged many TV station over the years. Back in November of 1981 after the peak of solar cycle 21, he managed to hear the TV audio on AM on 41.5 MHz from several transmitters in the UK at his home in San Antonio, Texas.

The distance was about 7500kms and was most likely multi-hop F2 propagation.

Pat is now unfortunately silent key but he did send on the recording to Hugh Cocks, a long time TV DX-er himself and now living in the south of Portugal.

The audio can be heard below. See below the video for a description from Hugh.

Hugh writes... "He sent me the recording many years ago, I can't see it on his own channel so thought it was a good idea to post it on YouTube. There are very few 405 line TVDX recordings in existence.

Mainly BBC 1 from the Divis , Northern Ireland 405 line VHF transmitter on 41.5 MHz.

The Recording starts at 1738 UTC where the regions run separate promos. Divis dominates, around 30 seconds in 'Nationwide' can be heard which is almost certainly from the London area Crystal Palace transmitter on the same frequency.

At least one other signal is there too, maybe from Wales or Scotland or Redruth in Cornwall.

After 90 seconds or so they all combine to transmit the national news from London,

The rumbling/varying tone in the background at times is the beating together of the AM(amplitude modulated) audio carriers which are on fractionally different frequencies.

405 line VHF transmissions finished in early 1985."

Example of BBC TV signal at 45 MHz being heard in South Africa

The BBC recently released this old television clip from 1949 explaining how an amateur radio station in Cape Town, South Africa had received TV signals from the UK.

#OnThisDay 1949: England and South Africa were linked through the magic of radio. pic.twitter.com/BpTODBlaRZ

— BBC Archive (@BBCArchive) October 6, 2019

The map below shows the path which is about 9,700kms or 6,000 miles...

The TV transmitter mentioned in the video was a 405 line transmission from Alexandra Palace in North London. This was vertically polarised with a power of 500 kilowatts (ERP?).

This TV signal had a video carrier on 45.0 MHz and a sound carrier down at 41.5 MHz.

The reception report in 1949 was near the peak of solar cycle 18. As can be seen from the chart below, that was a really good sunspot cycle and conditions were probably excellent on all the HF bands and well up into the low VHF region.

The most likely mode of propagation at 45 MHz was probably multi-hop from the F2 layer in the ionosphere. The maximum usable frequency was probably above 50 MHz so the signals on 45 MHz should have been very good.

It's likely however that with a video signal spread out over three and a half megahertz, the picture was probably very distorted and constantly changing. It should have been possible however to have very good reception of the sound on AM on 41.5 MHz with a dedicated radio receiver.

The radio contact shown in the clip between G8IG in England and ZS1PK in Cape Town, South Africa was probably on 28 MHz AM (note the beam at the start of the clip).

The South African station mentioned that signal were better when things were calm which might infer some sort of tropo ducting. That is unlikely to have been the case as it was very probable that all propagation was via the ionosphere and the weather conditions would have no impact.

All the same, it's an interesting example of early low band VHF TV reception.