[time-nuts] Cutler NAA on 24.0kHz....
CollinG at navcanada.ca
Wed Aug 13 09:12:38 EDT 2014
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:
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
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at 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.
On Aug 12, 2014, at 10:25 PM, Brian, WA1ZMS <wa1zms at 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! ;- )
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