be
reasonable
In the USA, you can receive various signals from NIST transmitters (10 MHz "exactly" is one, I think). However, you must be aware of ionospheric effects that can cause an apparent frequency shift near sunrise and sunset.
be
reasonable
In the USA, you can receive various signals from NIST transmitters (10 MHz "exactly" is one, I think). However, you must be aware of ionospheric effects that can cause an apparent frequency shift near sunrise and sunset.
market
setting.
could be
Traceable"
reasonable
A few ideas:
1) If 1Hz is OK (your frequency counter would have to be able to do gating measurement), then a GPS receiver with a 1Hz reference output will beat almost any other reference available.2) You can get used Rubidium standards on eBay, that will get you
10^-11 Many Rubidium standard can also be locked to a 1Hz GPS reference.3) There have been a few projects over the years which extract the
15.625KHz (I think for PAL) frequency from a TV set. The theory being that the reference used by the Tv station is of rubidum quality or better. This was a standard way to calibrate frequency counter kits in the past, at least here in Australia, I don't know about the US and NTSC.5) Hire a Rubidium standard for a day.
4) Don't bother tweaking your frequency counters, the drift of their (presumably) non oven controlled crystal with temp is going to be all over the place anyway :->Dave :)
market
setting.
could be
Traceable"
reasonable
A few ideas:
1) If 1Hz is OK (your frequency counter would have to be able to do gating measurement), then a GPS receiver with a 1Hz reference output will beat almost any other reference available.2) You can get used Rubidium standards on eBay, that will get you
10^-11 Many Rubidium standard can also be locked to a 1Hz GPS reference.3) There have been a few projects over the years which extract the
15.625KHz (I think for PAL) frequency from a TV set. The theory being that the reference used by the Tv station is of rubidum quality or better. This was a standard way to calibrate frequency counter kits in the past, at least here in Australia, I don't know about the US and NTSC.5) Hire a Rubidium standard for a day.
4) Don't bother tweaking your frequency counters, the drift of their (presumably) non oven controlled crystal with temp is going to be all over the place anyway :->Dave :)
There are many inexpensive, so-called "atomic clocks" in the mass market which AIUI use something like the NIST radio sites to do the time setting. Is it possible to hack into one of these and extract a signal that could be used for calibration of instruments. I'm not looking for "NIST Traceable" but just something to calibrate a bunch of frequency meters to a reasonable standard.
TIA Norm
No.
The "atomic clocks" just recieve the time from NIST a few times a day... to the nearest second. Not the kind of signal to calibrate any instrument to.
be
reasonable
The stations in question are WWV (10Mhz) and WWVH (15Mhz) as far as I know. WWV broadcasts from Fort Collins, Colorado, and WWVH is based in Honolulu, Hawaii if I recall correctly. They at least used to be on other frequencies as well. Mostly good for setting a watch by. They broadcast a tone every second, and a different one on the minute. I have a piece of equipment somewhere in my garage that uses their signal to generate a timing output to control something else (designed for traffic control I think)
WWV frequencies are 5, 10, 15 and 20MHz; transmit grequencies are based on the standard they keep, but transmission path effects can cause received variations which tend to average out. There is encoded info at the end of every minute and i think more info at each hour; perhaps the NIST website has info concerning that coding.
A lloonngg time ago, I read that the most accurate frequency reference that is readily available is the 3579545 Hz color subcarrier oscillator in a TV when it is receiving (phase-locked to) a color video signal. The reasoning was that the subcarrier generated back at the network was NIST-traceable so the local oscillator would be too. I don't know if this still applies given current distribution methods for cable signals but it might still apply for over-the-air transmissions.
I've never actually tried it myself... poking around inside a live TV has never been my cup of tea.
-- Tim Hubberstey, P.Eng. . . . . . Hardware/Software Consulting Engineer Marmot Engineering . . . . . . . VHDL, ASICs, FPGAs, embedded systems
Here is one in the $250 to $350 range:
Try this:
I keep meaning to build an updated version with a CPLD replacing the 74HC logic.
Leon
I think WWV was originally set up for mariners, who need accurate time to do celestial navigation.
For those of you interested in celestial navigation or observing the heavens, the WWV signal also contains (or used to contain) information about sub-second discrepancies between clock time and celestial time. Celestial time is what you would use to look-up or calculate coordinates of celestial bodies.
When the discrepancy becomes large enough, leap seconds are inserted or removed. Thus, UTC (fka GMT) is never more than a second off of almanac time. The sub-second discrepancies are reported by using a slightly different tone for the seconds following the exact minute.
Also, there are (or used to be) synthesized-voice, ocean-weather reports for various parts of the ocean at various times on WWV. Winter weather reports for the high-latitude North Pacific are particularly sobering.
--Mac
setting.
be
Traceable"
reasonable
Generally, no. However it may be that the carrier frequency used on one or more of the transmitters is deliberately of a high accuracy. This is the case in the UK, where the Rugby LW transmitter (60KHz), is warranted to have an accuracy to 2parts in 10^12. The WWVB broadcast from Fort Collins in the USA, is I think certified to a similar standard.
Best Wishes
Use the carrier of a radio or TV station. These are usually very stable.
-- Reply to nico@nctdevpuntnl (punt=.) Bedrijven en winkels vindt U op www.adresboekje.nl
No, the atomic clocks use the WWVB VLF transmitter running at 60 kHz.
Try Atmel for the receiver ICs, originally from Telefunken.
The modulation is in the NIST publications 432(?). It's on their web site. Or in _Reference Data for Radio Engineers_.
Mark Zenier snipped-for-privacy@eskimo.com Washington State resident
setting.
Traceable"
That looks quite doable but I have a question. Where would you get the composite video input? Is a composite output of a normal TV set tuned to, say, a broadcast channel sufficient?
Norm
If your frequency counter has a 1 MHz or 10 MHz oscillator output, or you can use it to measure a separate 1 MHz or 10MHz crystal oscillator, then you can use a shortwave radio and mix a little of the oscillator (or a harmonic of the oscillator) in with the shortwave WWV signal. I use 10MHz WWV.
The mixing is an art form - while receiving a healthy WWV signal, wind a piece of wire connected to the oscillator around the telescopic antenna on your shortwave receiver. You have to get similar amounts of both signals. When you have similar proportions, you will hear a tone ranging from a beep down to a growl. Tune the oscillator so the growl becomes a slow pulsing whoosh. The frequency of the whoosh is the difference between the WWV and oscillator frequencies. For a simple oscillator or counter, you can get the difference down to 1 cycle quite easily - that is 1 in 10 million. A simple oscillator / counter can't hold that accuracy for long, but it can hold 1 in a million for minutes, and 1 in 100000 over months.
This is a practical way to get your frequ meter adjusted. The phase shift due to shortwave propagation is not an issue at around the 1 cycle beat note - in fact can do 1 cycle in 10 seconds on WWV here in Australia !
Roger
be
reasonable
Yes. Most UK TVs output composite video on the SCART connector, usually for connection to a VCR.
Leon
-- Leon Heller, G1HSM http://www.geocities.com/leon_heller
which one? I have three, and there are probably a dozen more....
Cheers Terry
The one with the title _Reference Data for Radio Engineers_, from ITT/Howard W. Sams.
In the Eighth Edition, (_Reference Data for Engineers :Radio, Electronics, Computers,..._), it's in Chapter 1, in the subchapter titled "Standard Frequencies and Time Signals".
Mark Zenier snipped-for-privacy@eskimo.com Washington State resident
well.
As opposed to the one with the title "reference data for radio engineers" by Federal Telephone And Radio Corporation
Cheers Terry
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