[NLRS] Link -- New phase-modulation WWVB signal

[S. Earl Jarosh]

I miss the old days of slide rulers when hundredths resolution was good
enough for the most part.......


S. Earl Jarosh, N0HZ
Twin City FM Club President
Cell:  612.868.1313
Off:   763.545.3275
Home:  763.546.7897
Fax:   763.546.7897
earl at jarosh.org 
www.tcfmc.org
 
 Twin City FM Club 


 
-----Original Message-----
From: nlrs-bounces at mailman.qth.net [mailto:nlrs-bounces at mailman.qth.net] On
Behalf Of Dr. Gerald N. Johnson
Sent: Tuesday, March 12, 2013 9:57 PM
To: Donn, WA2VOI
Cc: nlrs at mailman.qth.net
Subject: Re: [NLRS] Link -- New phase-modulation WWVB signal





On 3/12/2013 7:46 PM, Donn, WA2VOI wrote:
> According to the NIST web pages, they're a little better than that, 
> though they do acknowledge the difficuties of 60KHz work. :-)
>
> "The antennas are spaced 857 m apart. Each antenna is a top loaded 
> monopole consisting of four 122-m towers arranged in a diamond shape. 
> A system of cables, often called a capacitance hat or top hat, is 
> suspended between the four towers. This top hat is electrically 
> isolated from the towers, and is electrically connected to a downlead 
> suspended from the center of the top hat. The downlead serves as the 
> radiating element.
>
> As the length of a vertical radiator becomes shorter compared to 
> wavelength, the efficiency of the antenna goes down. In other words, 
> it requires more and more transmitter power to increase the effective 
> radiated power. The north antenna system at WWVB has an efficiency of 
> about 50.6%, and the south antenna has an efficiency of about 57.5%.
> However, the combined efficiency of the two antennas is about 65%. As 
> a result, each transmitter only has to produce a forward power of 
> about 54 kW for WWVB to produce its effective radiated power of 70 kW."

I'm sure I have that data here somewhere. But it will take another year to
find it once I start looking for it.

I have used WWVB and used to use WWVL to check my in house standard. I did
it short time and I could see either random walk in my standard, variations
in propagation time, or I figured movement of the vertical wire radiator in
the wind. It might have been random variations in my test set up also.

What I did was with a TRF receiver tuned to 60 kHz, I put that on the scope
vertical (Tek 475) and I triggered the scope sweep with 100 kHz from the
standard (Manson Labs, double oven, 5 MHz 5th overtone crystal in a sealed
glass tube about the size of a 6146). The sine wave 60 kHz signal with 100
kHz trigger gives the appearance of three power line phases. I selected a
crossing of two sine waves and followed it across the scope, only when they
were at high power part of each second. That way I maximized my S/N. When I
got the standard tweaked so the crossing stayed within 100 ns for 15 minutes
I figured I had it as good as I could do because the crossing was then
wandering randomly in that 100 ns. That's 1.1x10-10, as good as an
oscillator rated for 10-9 per day aging gets for such a short term
measurement.

It might have been better to have used the local standard's output for the
horizontal sweep to take scope triggering out of the measurement, but then
it would have been much harder to figure the error having to look for drift
of a major fraction of that 100 kHz cycle lasting 10 microseconds (10,000
nanoseconds). That standard has a 1 MHz output too which might have given
some help but the scope sweep made it much easier to measure the amount of
drift.

I now have an HP 10811 oscillator without battery back up and I warm it up
before using it with my microwave counter, but I have not checked it with
WWVB or GPS. I am content with pretty good, say a part per 10 million which
it should do unless savaged and I've not had to argue frequency that close
in my life so I'm in a don't really care all that much. I'm not going to set
up to run the station from that high quality frequency standard when I have
a tuning dial on the IF.

At 60, kHz QRM from NTSC TV sweep is a big problem and sometimes harmonics
from arcs on the AC power line appeared to contribute considerable QRM.

More conventional VLF frequency standard techniques use a phase locked loop
with about a 10 hour time constant, maybe longer so the twice an hour phase
shifts used on WWVB for identification don't kick the local standard out of
lock. So I presume phase shift keying as proposed won't mess up those
either. Though that way it can take a week to get a standard on frequency so
they can plot the received phase and detect the ID shifts and detect when
aurora is on the way. The VLF propagation shifts considerably several hours
before aurora arrives. At the Iowa frequency standard maintained by W0PFP at
ISU (dismantled when he retired early) it too three 6' tall racks of
equipment to perform that function.

I wonder how well the clock handles the known QRM sources when its based on
the binary coding and the amplitude shift keying.

73, Jerry, K0CQ
>
> Basic clock is <1x10-12. Compensating for path delay allows UTC to 
> <100usec. Not too bad, actually, for consumer use (i.e., $20 clocks).
>
> 73 Donn
> WA2VOI/0
>
>

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