[Menu]>[Application]>[Ultra High Accuracy Digital Clock]>[Production]
The color burst signal ( 3.579545MHz ) in the television picture signal is used to obtain exact time.
The method of the TV signal may differ by the country. Therefore, the method that I introduce here is sometimes not able to be used in your country.
In the color television signal of the NTSC method the information of the color ( color phase, saturation degree ) goes to be sent by the color signal carrier. However, there is not a color sub carrier in the carrier wave.
The color sub carrier makes on the side of the television set. And, the frequency and phase of the the color sub carrier must be same rigidly with the one that is a broadcasting station.
Therefore the color sub carrier of 8 or 9 cycles is being inserted to 'Horizontal back porch' of the picture signal.
This signal is called the color burst signal.
'Horizontal back porch' is the period of time between the end of the horizontal synchronous pulse and the active TV picture. The TV picture is depicted by the electron beam that moves to horizontal. Only when the beam moves right from left the picture is depicted. Because the beam that moves left from the right is offensive to the eye the electron beam is switched off during horizontal blanking region.
the color television signal
( NTSC )
Also, the broadcasting station sometimes carries out network broadcast with other broadcasting stations. Accuracy of color burst signal becomes very important because the color has differed when this color burst signal deviates.
The accuracy of the frequency of the color burst signal is as follows according to the '10MHz standard frequency oscillation kit' data of 'Akizuki Denshi Tsusho Ltd.'.
In the case of the NHK head office, it is 1 x 10-12 of accuracy by using the cesium oscillation device that is the 1st standard device.
Also, in the case of key office of the commercial broadcast, it is 1 x 10-11 of accuracy by using the rubidium oscillation device that is the 2nd standard device.
10-12 of accuracy are the accuracy that goes wrong 1 second in one trillion seconds. It assumed to go wrong 1 second in 31,688 years, because 1 year is 31,557,600 seconds. It is the accuracy that even 10-11 go wrong 1 second in about 3,000 years.
Is this correct?
The leap year is been about 59 seconds in the second on a day. It is a little below 2.5 seconds in one hour. When the length on one day is decided 59 seconds seem to have been the range of an error.
The clock that makes it this time does not synchronize to the TV signal when TV broadcast is not carried out. Also, there is the error of PLL. Therefore, it does not become to the above kind of accuracy.
The error of PLL depends on the comparative accuracy of the phase comparator and control performance of VCO( How fast is that able to carry out the revision of frequency by the control voltage from the comparator ).
The picture signal can also obtain from the picture signal output terminal( Yellow pin connector ) of the television set.
I used a small television tuner to get it.
There are several kinds of small television tuner.
The cheaper thing is able to purchase with 500 to 1000 price of the yen( 4 US$ to 8 US$ ) in Akihabara Tokyo Japan.
Although the picture signal that obtained from the tuner inputs to the PLL oscillator, there is a little affinity.
As picture output is connected through the buffer amplifier in the manual of the tuner it is entered.
It does not synchronize well, although the input level to the PLL oscillator seems low in this method.
Thereupon, I connected directly through capacitor( Electrolytic capacitor was used ) without using the buffer amplifier.
Although if the appropriate buffer amplifier is made it is good, even if it connects only with capacitor the fine result appeared. I am using like that.
VHF/UHF television tuner unit
|BU||:||UHF selection ( 13 - 62ch )
|VT||:||Voltage tuning terminal
|BH||:||VHF selection ( 4 - 12ch )
|BL||:||VHF selection ( 1 - 3ch )
|AGC||:||AGC input ( connected the inside unuse )
|B||:||Power supply input DC12V
|8||:||AGC output ( connected the inside unuse )
|11||:||AFC output ( connected the inside unuse )
The voltage of the tuning is 28V in specification. Because the power supply becomes needed especially I used the power supply of 12V.
All the broadcasting stations do not need to able to be selected because it is not to see TV broadcast. If it is able to receive a broadcasting station of somewhere it is good.
In the case that there is not the broadcasting station that is able to receive it finely in the range of 12V, making the voltage high even other broadcasting stations need to try to select.