Re: [wsjt-devel] Frequency calibration - use of AM broadcasts
On 06/07/17 20:58, Joe Taylor wrote: > Richard -- > > On 7/6/2017 3:48 PM, 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? >> >> 73, >> Richard G4DYA > > As described here > http://www.physics.princeton.edu/pulsar/K1JT/FMT_User.pdf > my experience has been that (at least in NA) the carriers of big-city AM > broadcast stations are "on frequency" to within better than 1 Hz. > > It's always best to over-determine your fitted calibration line by using > more independent calibrators than the minimum necessary. Then you can > reliably identify outliers, and remove them from your analysis. Well the experiment I've just done certainly bears that out. Using a K3S + GPSDO + audio spectrum analyser, I've just measured about several stations near me and most were within 1 Hz. The others, except one, were all within 3 Hz. The booby prize goes to BBC Radio Stoke on 1503 kHz, which was 9 Hz low. Still in spec though. 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
Re: [wsjt-devel] Frequency calibration - use of AM broadcasts
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
Re: [wsjt-devel] Frequency calibration - use of AM broadcasts
Richard -- On 7/6/2017 3:48 PM, 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? 73, Richard G4DYA As described here http://www.physics.princeton.edu/pulsar/K1JT/FMT_User.pdf my experience has been that (at least in NA) the carriers of big-city AM broadcast stations are "on frequency" to within better than 1 Hz. It's always best to over-determine your fitted calibration line by using more independent calibrators than the minimum necessary. Then you can reliably identify outliers, and remove them from your analysis. -- 73, Joe, K1JT -- 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
Re: [wsjt-devel] Frequency calibration - use of AM broadcasts
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. 73 Bill G4WJS. -- 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
Re: [wsjt-devel] Frequency calibration - use of AM broadcasts
When I was working in BC, and later when looking at stations with an HP precision frequency measuring instrument, I regularly saw errors less than one Hz on the MF broadcast band with major US stations. 73, Jim K9YC On 7/6/2017 12:48 PM, 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? -- 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
[wsjt-devel] Frequency calibration - use of AM broadcasts
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? 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
