Calibration Signal from Observatory?

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mesfet

Joined: 04 Jan 2002
Posts: 155
Helped: 1

11 Mar 2003 17:16 Calibration Signal from Observatory?

Hi all,

I heard that people in Japan and USA can utilize the signal sent out by observatories so as to calibrate their clock or watch. I wonder if it is really the case? I just know the signal is in ASK format. Anyone have the details of the signal? Frequency, power......etc. Also, any suggestion on the demodulation circuits?

Thanks a lot.

mesfet

flatulent

Joined: 19 Jul 2002
Posts: 4856
Helped: 292
Location: Middle Earth

11 Mar 2003 17:36 several sources

Several countries have standard frequency and time transmissions in the VLF band. One frequency is around 60 kHz and another is around 77 kHz. There is a time code amplitude modulated on the signal at about a 10% level. There are several commercial products made by Zeit, Oregon Scientific, and La Crosse that have clocks set by these signals.

Here is a link to the WWVB format http://www.boulder.nist.gov/timefreq/stations/wwvbtimecode.htm

mesfet

Joined: 04 Jan 2002
Posts: 155
Helped: 1

11 Mar 2003 17:44

Hi flatulent,

Thank you for your information. At 60khz or 70khz, how can the signal be transmitted out? Also, how to receive such a low frequency signal. Very interesting!!

mesfet

flatulent

Joined: 19 Jul 2002
Posts: 4856
Helped: 292
Location: Middle Earth

11 Mar 2003 18:00 low antenna efficiency

The antennas have low efficiency but the ground wave loss is very low. The site I gave you has photos of their antenna farm.

Receivers for this use ferrite loaded loop antennas and phase locked loop synchronous detectors.

g86

Joined: 21 Jan 2003
Posts: 208
Helped: 4
Location: On top of antenna :))

11 Mar 2003 18:20 Re: Calibration Signal from Observatory?

Days are coming to make all systems syncronous Mad

. Already softweres are available which can sinc the computer time with an atomic clock linked to different time servers. I dont know about the signal you are talking about but it seems very interesting. Are they similar to GPS clock sinc pulses?

Exclamation

mesfet wrote:

flatulent

Joined: 19 Jul 2002
Posts: 4856
Helped: 292
Location: Middle Earth

11 Mar 2003 19:59 history

The history of these stations goes back many years. At first they were used for standard frequency references. They were on 2.5, 5, 10, 25, 20 and 25 MHz in the HF band. They had voice announcements of the time and one second tic sounds. One problem with them was the variable dealy time caused by the singal path to the E and F layers always changing distance.

Then the lower frequency stations were set up. They were more accurate because the ground wave signals were almost ideal constant delay time from the transmitter. All of these stations around the world are run by government depatments, usually the standard weight and measurement departments.

The GPS time marks is a newer source of time information. It has the possibility of even more accuracy because distances are well known and the travel time of the radio signal can be subtracted out. Also, the wider bandwidth will allow smaller errors from pulse rise times being smaller.

FANT

Joined: 27 Feb 2002
Posts: 333
Helped: 9

11 Mar 2003 21:28

In Germany there is a station DCF 77 that transmits a time mark received in all central Europe and in some parts of southern Europe.
In all Europe you can find some clocks with a 77 KHz receiver that receives and synchronize the time with this transmission; the price is very cheap ( about 40/50 Euro ) and the reception is assured even inside buildings.
GPS is more stable and accurate, we use it to syncronyze different receivers at different locations at the same time mark.
You can find easily receivers with a 1 second time mark very accurate.
Garmin GPS 35 has a 1 pps time pulse out.

Mandi

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