frequency standard from color TV signal?

[Ancient_Hacker]

IIRC there are very accurate signals in your basic color TV off the
air signal. Now the question is it the 3.58 MHz color subcarrier or
is it the 3.545... color burst? What about the 4.5MHz sound
subcarrier? And how accurate are they?

Any info appreciated.

 

[martin griffith]

IIRC there are very accurate signals in your basic color TV off the
air signal. Now the question is it the 3.58 MHz color subcarrier or
is it the 3.545... color burst? What about the 4.5MHz sound
subcarrier? And how accurate are they?

Any info appreciated.

http://msl.irl.cri.nz/services/time/
Seems pretty good, I assume NTSC is similar, but if your video comes
via digital and gets converted to composite video in the STB, all bets
may be off. And the way analogue Txs are being shut down in favour of
digital.....

Have a browse at SMPTE, they may even have the specs for free


martin

 

[[email protected]]

in the old days, when transcontinental microwave was the feed from NY
or LA to the station, things were excellent, timing being generated
by a network's master cesium clock. Now each station gets a digitized
fiber feed and its ran through a buffer, so unless for some reason
that station decides to have a rubidium master clock for its timing
chain, your probably screwed.

some smaller countries still use microwave and things are good, but in
the us and mainland europe, its on a station by station basis. Big
stations (NY,LA,chicago) probably have a decent clock.

Steve Roberts

 

[Don Bowey]

in the old days, when transcontinental microwave was the feed from NY
or LA to the station, things were excellent, timing being generated
by a network's master cesium clock. Now each station gets a digitized
fiber feed and its ran through a buffer, so unless for some reason
that station decides to have a rubidium master clock for its timing
chain, your probably screwed.

some smaller countries still use microwave and things are good, but in
the us and mainland europe, its on a station by station basis. Big
stations (NY,LA,chicago) probably have a decent clock.

Steve Roberts

Most multiplexing today is SONET. Network sync traceable to Stratum 1 is
available from the multiplexer.
Don

 

[Richard Henry]

http://msl.irl.cri.nz/services/time/
Seems pretty good, I assume NTSC is similar, but if your video comes
via digital and gets converted to composite video in the STB, all bets
may be off. And the way analogue Txs are being shut down in favour of
digital.....

Have a browse at SMPTE, they may even have the specs for free

martin

Any time standard that depends on transmission through the atmosphere
must deal with the variabilities of the medium. Unless your receiver
is in direct line of sight from the transmitter, the effective length
of the transmission channel is not constant.

 

[[email protected]]

IIRC there are very accurate signals in your basic color TV off the
air signal. Now the question is it the 3.58 MHz color subcarrier or
is it the 3.545... color burst? What about the 4.5MHz sound
subcarrier? And how accurate are they?

Any info appreciated.

The color sub-carrier and the colorburst refer to the same frequency
in NTSC. 3.579545 MHz.

 

[Tom Bruhns]

IIRC there are very accurate signals in your basic color TV off the
air signal. Now the question is it the 3.58 MHz color subcarrier or
is it the 3.545... color burst? What about the 4.5MHz sound
subcarrier? And how accurate are they?

Any info appreciated.

The nominal colour subcarrier frequency for NTSC is 315/88 MHz; you
can do some multiplication and division and get to one of the
"standard" reference frequencies like 10MHz = colour subcarrier *
176/63 = c.s.c.*2^4*11/(3*3*7). The FCC tolerance is +/-10Hz, last I
knew; heaven only knows under deregulation. Though stations MAY
broadcast it with very high accuracy, they may not, too. And if you
get your signal via cable, be aware that cable companies have a habit
of moving channels around. Even if the signal is in the same channel
it was broadcast in, there is no guarantee it will be synchronous with
the broadcast signal.

If you want an accurate frequency standard, why not use an ovenized
10MHz crystal oscillator? If that's not good enough, why not
discipline it with the 1 pulse per second from a GPS receiver?

Cheers,
Tom

 

[Tom Bruhns]

Any time standard that depends on transmission through the atmosphere
must deal with the variabilities of the medium. Unless your receiver
is in direct line of sight from the transmitter, the effective length
of the transmission channel is not constant.

This is true, and technically even if you are receiving your signal
line-of-sight, there's variation due to changes in atmospheric
pressure and humidity, for example. I believe you can find some good
information on the accuracy to expect for off-the-air reception of WWV/
WWVB/WWVH on various frequencies, on the NIST website. A few years
ago I was playing with how accurately I could calibrate a good oven
standard from WWV's sky wave from Colorado to the Seattle area, and
found that using FFT techniques I was able to consistently do better
than they suggested, but not reliably better than about one part in
10^8, as I recall. That took some understanding of how and when the
propagation path experiences the most change.

Cheers,
Tom

 

[GregS]

This is true, and technically even if you are receiving your signal
line-of-sight, there's variation due to changes in atmospheric
pressure and humidity, for example. I believe you can find some good
information on the accuracy to expect for off-the-air reception of WWV/
WWVB/WWVH on various frequencies, on the NIST website. A few years
ago I was playing with how accurately I could calibrate a good oven
standard from WWV's sky wave from Colorado to the Seattle area, and
found that using FFT techniques I was able to consistently do better
than they suggested, but not reliably better than about one part in
10^8, as I recall. That took some understanding of how and when the
propagation path experiences the most change.

I think orginally, the live TV shows had direst feeds and the carriers were more accurate.
I used to run NASA timming at the Goldstone Apollo site, back when they
actually had ground stations before the TDRS satillite. The sky waves were pretty
radical. We used loran to monitor drifting. Were pretty close to Colorado, but still
a lot of drift. I usd to cal my frequency counter with the stations Cesium clock
using the basic 5Mhz sent around the station.

greg

 

[martin griffith]

This is true, and technically even if you are receiving your signal
line-of-sight, there's variation due to changes in atmospheric
pressure and humidity, for example. I believe you can find some good
information on the accuracy to expect for off-the-air reception of WWV/
WWVB/WWVH on various frequencies, on the NIST website. A few years
ago I was playing with how accurately I could calibrate a good oven
standard from WWV's sky wave from Colorado to the Seattle area, and
found that using FFT techniques I was able to consistently do better
than they suggested, but not reliably better than about one part in
10^8, as I recall. That took some understanding of how and when the
propagation path experiences the most change.

Cheers,
Tom

one of my favorites is
http://www.rt66.com/~shera/index_fs.htm


martin

 

[GregS]

I think orginally, the live TV shows had direst feeds and the carriers were
more accurate.
I used to run NASA timming at the Goldstone Apollo site, back when they
actually had ground stations before the TDRS satillite. The sky waves were
pretty
radical. We used loran to monitor drifting. Were pretty close to Colorado, but
still
a lot of drift. I usd to cal my frequency counter with the stations Cesium
clock
using the basic 5Mhz sent around the station.

I think the WWV signals were only good enough to tell what second you were on.
The Collins digital equipment had battery backup, and there was Rubidium and
crystal backups. Of, course the Cesium was a crystal oscillator.
There seemed an unwritten backup, anyone with a good wristwatch.

greg

 

[Richard Henry]

This is true, and technically even if you are receiving your signal
line-of-sight, there's variation due to changes in atmospheric
pressure and humidity, for example. I believe you can find some good
information on the accuracy to expect for off-the-air reception of WWV/
WWVB/WWVH on various frequencies, on the NIST website. A few years
ago I was playing with how accurately I could calibrate a good oven
standard from WWV's sky wave from Colorado to the Seattle area, and
found that using FFT techniques I was able to consistently do better
than they suggested, but not reliably better than about one part in
10^8, as I recall. That took some understanding of how and when the
propagation path experiences the most change.

My first experience with this was about 1980 while testing some oven-
controlled oscillators by comparing to a bench frequency standard that
received a reference signal from WWVB. One night I was testing late
in the day, and as the sun wnet down my numbers wandered all over the
place. The next day I showed the results to my boss and he had a good
laugh at my ignorance.

 

[[email protected]]

Shera is the granddaddy of all the reflock boards,

but if you want something simple and fast, start with a jupiter gps
board (~20$ US) from ebay


and go here:

http://mysite.verizon.net/n1jez/

Jupiter boards output a 1 pulse per second signal and a 10Khz signal

Steve Roberts

 

[martin griffith]

On 17 Apr 2007 13:14:05 -0700, in sci.electronics.design

Shera is the granddaddy of all the reflock boards,

but if you want something simple and fast, start with a jupiter gps
board (~20$ US) from ebay


and go here:

http://mysite.verizon.net/n1jez/

Jupiter boards output a 1 pulse per second signal and a 10Khz signal

Steve Roberts

Not Found
The requested URL /n1jez/ was not found on this server.

Any about theShera Grandad, I've never quite followed
P2 on the pdf

"Interestingly, it is desirable to have the
frequency of U7 drift slightly rather than
being synchronized with the VCXO. A
slight random drift averages out the ±1
count ambiguity that is inherent in any
pulse-counting device.

My measurements indicate that the simple phase-measuring
circuit I use is consistently accurate to 2 or
3 ns (for a 30-second measurement), while
without drift, the resolution would be lim-
ited to 42 ns. "

Do you have a simple explanation?




martin

 

[Mike Monett]

one of my favorites is
http://www.rt66.com/~shera/index_fs.htm

martin

Yes, a very good one.

That is one of many places where the Binary Sampling technique can
dramatically improve the accuracy and speed of sampling noisy data.

For a description, see "Noise-Rejecting Wideband Sampler" at:

http://www3.sympatico.ca/add.automation/sampler/intro.htm

The same technique works in software as well as hardware. A delta
value (dv) is selected appropriate for the signal. The system is
initialized by averaging, then storing the result in the current
value (cv).

At each sample time, the raw input signal is measured and compared
to the current value (cv).

If the raw signal is greater than the current value, the current
value is incremented by the delta value, otherwise it is
decremented:

if (raw > cv) then
cv := cv + dv
else
cv := cv - dv

This allows the software to track the signal much better than
conventional averaging techniques allow. The reason is the magnitude
of the large amplitude noise spikes are not included in the result,
only the direction.

Since random noise has zero mean, the system will track the mean of
the signal much more accurately than averaging techniques allow.

The same software can also perform a moving average on the acquired
output signal. A simple moving average filter is a very fast method
since each sample requires one addition, one subtraction and one
division. This can easily be done in integer math, so inexpensive
microprocessors and PIC's can be used.

A single stage acts as a low-pass filter with a cutoff floor of
about -13 dB. Cascading 4 filters provides a gaussian response with
a floor of about -60dB. This is in addition to the filtering
provided by the Binary Sampling technique.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://members.spsdialup.com/[email protected]/index.htm
SPICE Analysis of Crystal Oscillators:
http://members.spsdialup.com/[email protected]/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automation/sampler/intro.htm

 

[martin griffith]

Yes, a very good one.

For a description, see "Noise-Rejecting Wideband Sampler" at:

http://www3.sympatico.ca/add.automation/sampler/intro.htm

ouch, my head hurts.... thxs


martin

 

[MassiveProng]

IIRC there are very accurate signals in your basic color TV off the
air signal. Now the question is it the 3.58 MHz color subcarrier or
is it the 3.545... color burst? What about the 4.5MHz sound
subcarrier? And how accurate are they?

Any info appreciated.

http://www.smpte.org/standards/

 

[MassiveProng]

IIRC there are very accurate signals in your basic color TV off the
air signal. Now the question is it the 3.58 MHz color subcarrier or
is it the 3.545... color burst? What about the 4.5MHz sound
subcarrier? And how accurate are they?

Any info appreciated.

http://www.novia.net/~ereitan/NTSC_overview.html

 

[MassiveProng]

Most multiplexing today is SONET. Network sync traceable to Stratum 1 is
available from the multiplexer.
Don

Or DWDM (Dense Wave Division Multiplexing)

Sun is coming out with a 10Gb/s link set, and some nebulous startup
is claiming 100GB/s capability.

 

[MassiveProng]

My first experience with this was about 1980 while testing some oven-
controlled oscillators by comparing to a bench frequency standard that
received a reference signal from WWVB. One night I was testing late
in the day, and as the sun wnet down my numbers wandered all over the
place. The next day I showed the results to my boss and he had a good
laugh at my ignorance.

Instead of your gear, YOU were affected by sunspots. :-]