Cutler NAA on 24.0kHz....
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
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 wa1zms@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
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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-bounces@febo.com [mailto:time-nuts-bounces@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 wa1zms@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
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Indeed according to the tracor 900 manual you could get to -11th in 24
hours best case. Further comment was NAA is CS as of 1976! The 900 indeed
has a semi simple op amp adapter thing that reduces or gets rid of the MSK.
Though I have read the description and details it makes no sense as to how
it gets rid of the shift. (Quite curious magic)
The manuals quite a good read at 52 pages a lot of detail. Further all of
the unit could be built again its all simple technology or concepts adapted
to more modern methods.
The only gotcha as time nuts goes is it ain't NIST. Nor is there time and I
don't care about time I simply want an alternate frequency reference.
Here at Boston I can hear it in my fillings. :-) I could also hear LORAN C.
My type of pipe.
By the way Paul/Ziggy was also after me on NAA to consider it.
I had discounted it because of the lack of info and totally unclear how to
get rid of the FSK. MSK is FSK just with a very narrow shift. Also the
effects of the fsk on the carrier. Hmmm glad I am typing this.
It may be that the mark or the space is indeed exactly the true carrier and
that op amp circuit is notching out the shifted carrier. I will bet thats
the trick!
Regards
Paul
WB8TSL
On Tue, Aug 12, 2014 at 10:25 PM, Brian, WA1ZMS wa1zms@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
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and follow the instructions there.
NAA actually is above and below 24KHz. That said I suspect that the system
simply averages the MSK out of the loop by the filter TC of the PLL.
There are numbers of propagation papers on NAA.
Paul
WB8TSL
On Fri, Aug 15, 2014 at 3:09 PM, paul swed paulswedb@gmail.com wrote:
Indeed according to the tracor 900 manual you could get to -11th in 24
hours best case. Further comment was NAA is CS as of 1976! The 900 indeed
has a semi simple op amp adapter thing that reduces or gets rid of the MSK.
Though I have read the description and details it makes no sense as to how
it gets rid of the shift. (Quite curious magic)
The manuals quite a good read at 52 pages a lot of detail. Further all of
the unit could be built again its all simple technology or concepts adapted
to more modern methods.
The only gotcha as time nuts goes is it ain't NIST. Nor is there time and
I don't care about time I simply want an alternate frequency reference.
Here at Boston I can hear it in my fillings. :-) I could also hear LORAN
C. My type of pipe.
By the way Paul/Ziggy was also after me on NAA to consider it.
I had discounted it because of the lack of info and totally unclear how to
get rid of the FSK. MSK is FSK just with a very narrow shift. Also the
effects of the fsk on the carrier. Hmmm glad I am typing this.
It may be that the mark or the space is indeed exactly the true carrier
and that op amp circuit is notching out the shifted carrier. I will bet
thats the trick!
Regards
Paul
WB8TSL
On Tue, Aug 12, 2014 at 10:25 PM, Brian, WA1ZMS wa1zms@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
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.
On Fri, Aug 15, 2014 at 03:09:23PM -0400, paul swed wrote:
I had discounted it because of the lack of info and totally unclear how to
get rid of the FSK. MSK is FSK just with a very narrow shift. Also the
effects of the fsk on the carrier. Hmmm glad I am typing this.
It may be that the mark or the space is indeed exactly the true carrier and
that op amp circuit is notching out the shifted carrier. I will bet thats
the trick!
MSK is a kind of continuous phase differentially coded PSK in
which the carrier phase smoothly shifts either EXACTLY plus 90 degrees
or EXACTLY minus 90 degrees in EXACTLY one symbol time - in the MSK
variety of PSK the transmitted carrier phase never stays the same as the
it was the last symbol time. When transmitting steady mark there are a
series of these shifts plus 90 degrees (hi frequency mark) one after the
other, and when transmitting steady space there is a series of minus 90
degree shifts.
Obviously a steady negative phase shift is what is produced by
a signal below a center "carrier" frequency and a steady positive
phase shift by one above that frequency. Thus the isomorphism with
filtered FSK.
Effectively a QPSK (multi-arm Costas type) tracking loop should
be able to track a MSK signal just as if it was a filtered QPSK signal
with only 90 degree and minus 90 phase shifts each symbol time and generate
a phase continuous recovered carrier.
--
Dave Emery N1PRE/AE, die@dieconsulting.com DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in
celebration of what could have been, but wasn't and is not to be now either."
David
Yes I have seen various comments and documents describing MSK that way.
But have to say the tracor 900 does not use that method to establish a
reference.
Its a few opamps perhaps one side acting as a phase delay summing with the
original and hitting a BPF. all of that running at 100Hz center frequency.
Through this magic the 900 could use NAA as a phase tracking reference.
Its as if its a classic phase doubler. The documentation almost speaks to
that.
Its seriously simple.
Regards
Paul.
WB8TSL
On Fri, Aug 15, 2014 at 4:31 PM, David I. Emery die@dieconsulting.com
wrote:
On Fri, Aug 15, 2014 at 03:09:23PM -0400, paul swed wrote:
I had discounted it because of the lack of info and totally unclear how
to
get rid of the FSK. MSK is FSK just with a very narrow shift. Also the
effects of the fsk on the carrier. Hmmm glad I am typing this.
It may be that the mark or the space is indeed exactly the true carrier
and
that op amp circuit is notching out the shifted carrier. I will bet thats
the trick!
MSK is a kind of continuous phase differentially coded PSK in
which the carrier phase smoothly shifts either EXACTLY plus 90 degrees
or EXACTLY minus 90 degrees in EXACTLY one symbol time - in the MSK
variety of PSK the transmitted carrier phase never stays the same as the
it was the last symbol time. When transmitting steady mark there are a
series of these shifts plus 90 degrees (hi frequency mark) one after the
other, and when transmitting steady space there is a series of minus 90
degree shifts.
Obviously a steady negative phase shift is what is produced by
a signal below a center "carrier" frequency and a steady positive
phase shift by one above that frequency. Thus the isomorphism with
filtered FSK.
Effectively a QPSK (multi-arm Costas type) tracking loop should
be able to track a MSK signal just as if it was a filtered QPSK signal
with only 90 degree and minus 90 phase shifts each symbol time and generate
a phase continuous recovered carrier.
--
Dave Emery N1PRE/AE, die@dieconsulting.com DIE Consulting, Weston,
Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole -
in
celebration of what could have been, but wasn't and is not to be now
either."
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