frequency standard from color TV signal?

[Octavio]

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.

Color burst is just a... burst of subcarrier signal where the phase is
synchronized with that subcarrier for the picture frames involved. I don't
quite remember exactly but the burst phase is offset by 90 degres with the
subcarrier phase in NTCS, the correct phase can be obtained with a simple,
ajustable RC network in the TV set, the old famous TINT control.The short
term precision of the phase is the important factor in television to get
correct colors in the following picture frames.
Long time frequency accuracy may not be interesting.

Octavio

 

[Michael A. Terrell]

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.

Most analog NTSC signals are sent through a frame store at the
transmitter site to clean up the sync, and to clean up any switching
errors. The color burst is regenerated, and must be within +/- 10 Hz of
3,579,54.54545 Hz. This setup was already common 20 years ago.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[rebel]

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

IMHO the downside of the Shera system is the long conditioning times to get a
decent accuracy. For many applications the Jupiter-based references will give
an acceptable result within seconds of the GPSr achieving lock, due to the
higher reference frequency..

I built a 10MHz reference on that basis, and it spends its days turned off
because I know it achieves its ultimate performance within three minutes of
turn-on. A very similar unit can be seen at
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm

 

[martin griffith]

IMHO the downside of the Shera system is the long conditioning times to get a
decent accuracy. For many applications the Jupiter-based references will give
an acceptable result within seconds of the GPSr achieving lock, due to the
higher reference frequency..

I built a 10MHz reference on that basis, and it spends its days turned off
because I know it achieves its ultimate performance within three minutes of
turn-on. A very similar unit can be seen at
http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm

That's quite nice, had a quick browse through the Navman OEM site
(dreadful). I couldn't find any GPS modules with 10KHz out, any
pointers?


martin

 

[rebel]

That's quite nice

My version was actually a rework of a TV-derived unit I had built earlier, which
used 7812.5 Hz as the ref from the 10MHz xtal (half PAL line). Replaced the
divider chain and threw out the sync separator in favour of the 10k from the
Jupiter, and it ran straight off. It was only later I saw Miller's unit, and
learned that I had reinvented yet another wheel.

I actually , had a quick browse through the Navman OEM site
(dreadful). I couldn't find any GPS modules with 10KHz out, any
pointers?

They (Jupiters) pop up from time to time on ebay.

Since the Rockwell->Conexant->Navman transfer, the Navman people have gone Sirf
and lost the 10k in the process.

There's a fair bit of doco out there on "Jupiter GPS".

 

[Tam/WB2TT]

Most analog NTSC signals are sent through a frame store at the
transmitter site to clean up the sync, and to clean up any switching
errors. The color burst is regenerated, and must be within +/- 10 Hz of
3,579,54.54545 Hz. This setup was already common 20 years ago.

Put this together with what Tom says, and you can get 3.579545454 * 88 / 315
=1 MHz, exactly. At one time it was claimed that on live network programs
the frequency accuracy of the color burst was on the order of 10E-11. What
you do is to divide the color burst frequency by 315, and then multiply it
by 88 in a 1 MHz crystal controlled phase locked loop. Only problem with
this is that it is goiung away in 2009.

Tam

 

[Michael A. Terrell]

Put this together with what Tom says, and you can get 3.579545454 * 88 / 315
=1 MHz, exactly. At one time it was claimed that on live network programs
the frequency accuracy of the color burst was on the order of 10E-11. What
you do is to divide the color burst frequency by 315, and then multiply it
by 88 in a 1 MHz crystal controlled phase locked loop. Only problem with
this is that it is goiung away in 2009.

I'm familiar with the frequency conversion but as a former NTSC TV
broadcast engineer, I've seen a framestore at every transmitter site
since the late '80s. That reduces your accuracy to roughly 10 MHz, +/-
27.93 Hz.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Tam/WB2TT]

I'm familiar with the frequency conversion but as a former NTSC TV
broadcast engineer, I've seen a framestore at every transmitter site
since the late '80s. That reduces your accuracy to roughly 10 MHz, +/-
27.93 Hz.

I can't remember exactly, but I think the article I was referring to was
probably from the early or mid 80s. So much for progress.

Tam

 

[Brandon D Cartwright]

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

Do you imagine that by cutting and pasting a primer you'll fool folk
into thinking you are capable of answering the guy's questions?

What a sad freak.

 

[Michael A. Terrell]

I can't remember exactly, but I think the article I was referring to was
probably from the early or mid 80s. So much for progress.

The color burst was never intended to be used as an external
frequency standard. OTOH, the framestore/proc amp cleaned and stabilized
the video before transmission, and did improve picture quality.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[MassiveProng]

Do you imagine that by cutting and pasting a primer you'll fool folk
into thinking you are capable of answering the guy's questions?

What a sad freak.

**** off. I use ultra stabilized 10MHz reference modules everyday,
and they are followed up by 100 PPS pulse trains.

 

[Don Bowey]

**** off. I use ultra stabilized 10MHz reference modules everyday,
and they are followed up by 100 PPS pulse trains.

(he says while beating his chest, glad he got past that one without being
cornered into having to say anything technical)

 

[joseph2k]

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

1 pps may well be way to slow to be useful. Sure it will eventually get
there, maybe in days. Only 86,400 ticks in a whole 24 hour day. Sure you
can use deltas etc., but the result "real"?

 

[Gary Tait]

@b75g2000hsg.googlegroups.com:

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.

That is if you want accurate clock time.

For just an accurate frequency reference, you only need receive a signal
soerced from a cesium beam reference