Calibration Of Electronic Equipment In The Home Workshop

I've seen that discussed elsewhere, and although it would take me a week to find the particulars, (1) the frequency can be off as much as 10 Hz by FCC standards, (2) from what I've read it's frequently off by more than that, even on network feeds, (3) IIRC they don't even use the good clocks on the networks any more, (4) NIST clocks are going to be a couple of orders of magnitude better than the best a network would buy for the purpose of meeting FCC regulations, (5) IIRC the frequency should actually be 3,579,545.454545454545..... Hz, and (6) Doppler shift on the incoming television signal could potentially cause the subcarrier frequency to vary up and down.

I don't think the oscillator on a PIC would be good to 2ppm absolute accuracy even with a very good xtal, unless you FIRST calibrate it against something that has already been calibrated, therefore it doesn't get you far. It will however be good enough to calibrate your scope since that would only need 1% or so, and any old crystal should achieve that, even with a fairly primitive oscillator. For frequency calibration, your best bet is to receive an off-air standard, for example GPS or in many countries there are low frequency standard transmissions (50kHz, 60kHz, 77.5kHz or others, look up which ones are available in your country). It is quite feasible to build your own receiver for these. These transmitters are maintained to a higher accuracy than any piece of hardware that a hobbyist could afford (e.g. 2 parts in 10^12).

Chris

A mistake go read it if you want.

Yes, I misread the statement.

That depends a lot on your definition of "serious". There are lots of things where just being within 100PPM is more than good enough. RS232 is ok up to 5% error. If the so called 60Hz in your motor home was actually

A lot of them have worse short term noise than a good OCXO.

In article , snipped-for-privacy@abuse.gov (known to some as Jim Yanik) scribed...

Unfortunately, according to their product list, they have discontinued ALL their O-Scope calibration products.

However, that's not necessarily the end of the world, as it were. This simply means that there is a better chance of such showing up on the surplus market, which consequently creates a much better chance of my finding something useful. ;-)

Thanks.

"Bee's Knees"?? Was that before or after the "Cat's pajamas"?

Check.

On Thu, 1 Mar 2007 06:43:01 -0600, "Anthony Fremont" Gave us:

Huh?

Bwuahahahahahahaha! Hilarious!

On Thu, 1 Mar 2007 19:39:00 +0000, Clint Sharp Gave us:

For audio? absolutely. It had nothing to do with the DVD player's clock. There are several industry standard tones provided, and the disc replaced hardware TV test generators for years.

It carries DTS and THX certified content.

That is the current reference standard for MPEG, if you know who they are. That's good enough for me. I can verify the setup of my FPD, and I can setup my stereo with the audio diagnostic and setup section.

Hey, chucko! He didn't give a GPS source. You don't get to change the scene, pal! A subsequent poster mentioned a GPS setup.

Go back and read.

Yep, didn't you know that scope you are using is only a few % accurate on the vertical scale?

Hardly, it would be perfectly adequate for the job actually.

Dave :)

On Thu, 01 Mar 2007 16:32:18 -0600, clifto Gave us:

So there!

On 1 Mar 2007 23:53:14 -0800, "David L. Jones" Gave us:

You guys must be behind the times.

On 1 Mar 2007 23:53:14 -0800, "David L. Jones" Gave us:

Wrong. That could easily leave the scope over 6% off.

It takes a much finer source to calibrate a device than the final accuracy of the device being calibrated, dipshit.

Yeah, maybe you should do some reading.

In message , MassiveProng writes

So varying the reference clock of a DVD player doesn't affect the pitch of any tones played back off a disk? OK. I wondered because it does on a CD player.

K, so it's a good for setting up home theatre equipment at the very least

Not personally, but I may have heard of them in passing.

FPD?

Hey 'pal' I didn't try to change the scenario, I just speculated that a GPS source would be better.

No need, I read that post, that's why I mentioned it. Turn down the aggression a notch or two, I only asked a question and speculated that there might be a better way.

Not in this case. If he used a meter with 0.5% accuracy on DC volts then he could check and adjust his scope's vertical scale to the same 0.5% accuracy.

And if you start crapping on about the tolerance of the resistor chain adding up etc, then you haven't thought about this one hard enough...

Dave :)

My 6000 series Agilent is not behind the times, and it's only +/-2% accurate on the vertical scale. A good analog scope like say the Tek2465 is only 2% as well.

Perhaps those two are the exception huh? Care to post some links to prove otherwise? I could post until the cows come home scopes that are no better than a few % accurate on the vertical scale.

Dave :)

On Fri, 2 Mar 2007 18:19:08 +0000, Clint Sharp Gave us:

Flat Panel Display.

You ain't too sharp, Sharp.

On Fri, 2 Mar 2007 18:19:08 +0000, Clint Sharp Gave us:

There's no doubt it would be better for RF frequency locks. Since we use them at work, I have no doubts about their capabilities.

Audio though? Most of the respondents referred to audio spectrum frequencies.

On 2 Mar 2007 13:06:24 -0800, "David L. Jones" Gave us:

If you set a scope up with 0.5% accurate source validator, the scope will NOT have that accuracy level. It will ONLY have that accuracy level at that set point, and that is even questionable.