In message , "Dave Plowman (News)"
writes
In article ,
David Looser wrote:
"Don Pearce" wrote

The GPO line that fed the main London medium wave Home Service
transmitter had a pretty dreadful rolloff, which the Beeb engineers
used to limit the frequency response offered to the transmitter. At
some point the line was changed to a better one and all of a sudden
the medium wave service was going out to about 12kHz. After a few
months this was noticed, and a lowpass filter was put in.

Can't remember the exact dates, I'm afraid, but it was while John Peel
had his Top Gear programme on Sunday afternoons.

Sounds like an urban legend to me. Do you have any evidence that this
extraordinary claim is true?

I was told the land line to Brookmans Park used for R2 (light prog) on
247? metres was originally installed for pre-war TV sound which was
'advertised' as being of better quality than radio. And had about double
the bandwidth of a normal circuit.
All that came from a BBC lines person in the '60s. FWIW. After I asked why
my Quad AM tuner sounded so much better on R2 than other AM stations.
There was also something else about the 247 wavelength which allowed the
BBC to broadcast a wider bandwidth than some of the other frequencies
allocated to them.

On lower frequencies, aerials have lower (absolute) bandwidth -
especially if they are loaded to resonate them. The same goes for tuned
circuits (in the transmitter, matching, diplexing etc). I might be
wrong, but I believe that the audio from the LW transmitter on 200 (now
198) kHz is affected (reduced) by the aerial RF bandwidth (as is the
audio phase response), and some pre-emphasis is needed. I'm not sure if
such effects are significant on the MW but, potentially, the 247m signal
(around 1.2MHz) could be wider than the 909kHz.
--
Ian