Droitwich 198 kHz Radio 4

[Albert H]

The clueless BBC have decided to close down the 198 kHz Radio 4 Long Wave transmitter next year. This is a really stupid decision, since the 198 kHz frequency is traceable to the National Physical Laboratory, and is accurate to thirteen digits. I've used it as a standard for years, since it's usually easier to receive than the MSF 60 kHz transmitter (even though the MSF accuracy is ~10 times better!).

I've used it - divided down - as the timebase for Medium Wave transmitters for years. I even modified my original homebrew standard signal generator from receiving the old 200 kHz signal (more easily divided to something useful) to handle the 198 kHz frequency when it was changed in the late '70s!

The 198 kHz signal also carries its own radio data - a bit like a slow version of RDS - and there's an interesting paper on decoding it (and what it's used for) at https://www.nxp.com/docs/en/application-note/AN1597.pdf which includes details of how to build your own decoder!

There is an online petition at https://chng.it/LMbdTQJ4DV to keep the 198 kHz rig going. If you have the slightest care for our radio heritage, please sign it!

[Gigahertz]

Done!

I often drive around the Yorkshire Dales for work and when other AM/FM/DAB broadcast don't work in the Van I often have 198KHz on in the back ground.

Have know it to be a suitable for off air referance but never used it like.

[radionortheast]

I wonder why it's a timing signal, they can't keep it going because of that can they?! they need a new pocket watch

[Albert H]

Way back, the Long Wave Radio 4 was on 200 kHz, ad was also traceable to the National Physical Laboratory. It was really useful to have a carrier that was so frequency accurate (and stable) - several million times better than you could achieve with a crystal (even in an "oven").

Unfortunately, in 1988 the BBC bowed to EBU pressure and moved the transmitter off 1500m (200 kHz) to the new 198 kHz frequency to fit in with the 9 kHz channelling that was being adopted throughout Europe. This required modification to the timebase of my frequency counter!

I divided the off-air 198 kHz by 99, and ran a voltage-tuned oscillator (in a 7046 PLL IC) at 200 kHz. I divided the 200 kHz by 100 and compared with the divided down 198 kHz and this steered my 200 kHz oscillator to the exact frequency. I then used the phase-locked 200 kHz for the timebase for my frequency counter and signal generators. The only problem with this set-up was that the lock-up time could be dreadfully slow - it could take several minutes from switch-on to "locked" indication - especially with the slow data messing about with the signal!

The reason for the accuracy of the carrier frequency was that it was intended to provide a frequency standard throughout northern Europe.