On 06/07/17 20:56, Bill Somerville wrote: > On 06/07/2017 20:48, Richard Lamont wrote: >> Is it a good idea to use AM broadcast transmitters as a frequency >> standard when the regulatory tolerance (ITU and many countries) for such >> transmitters is ± 10 Hz? Is that good enough for the purpose? > > Hi Richard, > > I would expect many to be at least GPS locked. Droitwich 198kHz is > rubidium atomic clock locked at less than 10e-11 Hz per day accuracy! > At least until they run out of transmitting valves.
Droitwich 198 kHz is GPS-locked and/or rubidium - not sure which. Always used to be the latter. But many broadcast transmitters just use free-running crystal drives. They are not designed to be standard frequency stations, and there's usually no business case for the broadcaster to take on that role. In the UK, the tolerance is tighter in synchronised groups (two stations carrying the same programme). Otherwise the 10 Hz rule applies. It's in the Ofcom broadcast specification. 10 Hz is sufficient to ensure that the beat from a weak co-channel carrier is no more than 20 Hz and thus sub-audible. For the broadcaster's purpose, that is sufficient. 73, Richard G4DYA ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ wsjt-devel mailing list wsjt-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/wsjt-devel
