I can't speak in absolute terms with respect to current stability, however, they have always been very stable being locked to rubidium or cesium standards.
Another interesting twist with the VLF transmitters are the TACAMO transmissions by flying aircraft. They transmit on a couple of different frequencies and can be quite strong in North America and most likely also are as stable as any of the large Navy land based transmitters. However, if you observe these transmission you will note a relative phase shift as the aircraft circles while transmitting. You can see the effect visually in this image: https://www.dropbox.com/sh/ahvgr4sekcgg99s/zZCqDbxJ02#lh:null-ve3gtcVLFgrab20140803_174500.jpg The TACAMO transmission is the bright vertical line centered around 17.8 KHz, the "wavy" pattern is caused by the relative phase shift of the transmission. Interestingly, NAA on 24.0 KHz, NLK on 24.8 Jim Creek WA, and NLM 25.2 LaRouse ND all seem to be off the air, likely for their extended preventative maintenance. The program Spectrum Lab has built in functions for making phase measurements MSK signals but I have never done anything more than play around with that feature. Might be an interesting experiment to try and use one of the shore based VLF transmitters as a short term secondary reference. I suggest short term as these transmitters usually go off the air once a week for regular maintenance. If you would like to try and receive any these transmitters, it can be done with nothing more than sound card which can sample at least 2x your desired target and a long wire antenna plugged into the MIC input. Unfortunately the common 48KHz sampling sound cards are just not quite enough if interested in the 24KHz or higher signals. I use a USB EMU-PRE sampling at 192KHz and a 23 foot whip antenna on the roof. Cheers, Graham ve3gtc -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Paul Davis Sent: August-12-14 11:12 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Cutler NAA on 24.0kHz.... According to a document I just found (<http://tf.boulder.nist.gov/general/pdf/1743.pdf>) it would seem that the naval transmitters are at least .05 10e-9. I don't imagine they have gotten worse since that was published (1967!). So maybe not quite as good as WWVB (which was then spec'ed at .02 10e-9) but probably still useful. But no time code of course. The least common multiple of the two is also 120 khz. Food for thought. Paul On Aug 12, 2014, at 10:25 PM, Brian, WA1ZMS <wa1...@att.net> wrote: So does anyone know what frequency stability NAA has as of today? When I fire-up my VLF RX converter they are so loud I'd hate to live near the site. One might be able to hear it with silver fillings in their teeth while eating a lemon! ;- ) -Brian, WA1ZMS This electronic message, as well as any transmitted files included in the electronic message, may contain privileged or confidential information and is intended solely for the use of the individual(s) or entity to which it is addressed. If you have received this electronic message in error please notify the sender immediately and delete the electronic message. Any unauthorized copying, disclosure or distribution of the electronic message is strictly forbidden. NAV CANADA accepts no liability for any damage caused by any virus and/or other malicious code transmitted by this electronic communication. Le présent message électronique et tout fichier qui peut y être joint peuvent contenir des renseignements privilégiés ou confidentiels destinés à l’usage exclusif des personnes ou des organismes à qui ils s’adressent. Si vous avez reçu ce message électronique par erreur, veuillez en informer l’expéditeur immédiatement et supprimez le. Toute reproduction, divulgation ou distribution du présent message électronique est strictement interdite. NAV CANADA n’assume aucune responsabilité en cas de dommage causé par tout virus ou autre programme malveillant transmis par ce message électronique. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
