# Frequency standard - Page 4

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Re: Frequency standard

"Alan Peake"

**   Yawn ........

So now the dopey ass finally tells us he was testing a diesel gene.

........  Phil

Re: Frequency standard
Depends on how accurately you want to measure the mains frequency. Last
time I did this (in SA), the mains drifted by +/- 1.5 Hz with a period
of about 20 minutes. Your 2 MHz crystal should be good enough for that.
Alan

Suzy wrote:

Re: Frequency standard

Hey Suzy what about using a phase locked loop?
Since you're mainly looking at frequency shifts of a faily short
duration a phase locked loop should be able to give you an indication of
the frequency shift if you have it heavily damped.

Elmo

Re: Frequency standard

I remember trying to measure variations in mains frequency 30 odd
years ago.

All I can say is you will need a very accurate measuring kit.

While I can't remember what the accuracy of the xtal we used was, I do
remember we could measure _no_ variation from 50Hz at any time. the
result was a big surprise to us at the time, I do remember that.

By and large the 50Hz mains could be used as a frequency standard in
it's own right, both short and long term.

I really doubt that total load affects frequency in any meaningful way
as you apparently believe from your website.

But measure away, who am I to stop a seeker of knowledge! :)

Ross

Re: Frequency standard

"RMD"

** Can be done very easily  -  if you have a stable sine generator with fine
tune and a basic CRO and frequency counter.

Just set up a lissajous pattern, with a ratio of 20 to 1,  on the CRO
creen  -   then tweak the audio gen frequency to get the pattern stationary.
Read the generator frequency off the counter.

When it is 1000 Hz,  the AC supply is 50 Hz.

When it is 1005Hz,  the AC supply is 50.25 Hz.

** Ditto.

Bout as useful as reading tea leaves.

However,  an AC voltmeter will tell you if the load in your local area is
unusually heavy or light at some given time.

......   Phil

Re: Frequency standard

Any cheap frequency meter with reciprocal measurement will be able to
measure it just fine.

Dave.

Re: Frequency standard

Good Lord! Unadulterated sense!  How erratic (down, Phil, I did not say
erotic). Yes, I can see that measuring voltage on a continuous basis might
be a help, but only as far as the variations go, as we are all at the end of
a finite line and must suffer not only from that but the seemingly random
supply system settings at the nearest sub or zone... Why, though is the UK
meter site irrelevant? Is that not showing one of the symptoms of overall
system imbalance? For example, how do you explain the meter showing a drop
at heavy load times (eg TV advert breaks)? I am really interested in this,
and was all agog waiting for the answer to put me straight in place of which
I got Phil's anti-women rantings...   Sigh...

Re: Frequency standard

Think it was EA that ran a project for a TV derived frequency
reference around 15 years ago.

They claimed atomic clock accuracy, since that's what most, if not
all, of the commercial channels used to derive their horizontal sync.

I used one as a reference for a frequency counter, with good results,
up until our TV went digital (I'm on Optus satellite TV).  Presumably
it would still work on ground based analogue transmissions (which I
don't get).

It was available as a kit IIRC.

--
John H

Re: Frequency standard

Jim Rowe based it on a simple circuit I submitted as a Circuit and
Design Idea. ;-)

Re: Frequency standard

!5 years ago?  TV stations tend to use a frame store at the transmitter
to clean up switching glitches, and they regenerate the color sync with
a cheap crystal, typically four times the color burst.  These are
accurate to about 10 hz.  Prior to that, live network feeds were run
from Rubidium frequency standards.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
We've slightly trimmed the long signature. Click to see the full one.
Re: Frequency standard

Thanks for the info, Michael.
Back then, Jim Rowe got the Australian Commonwealth Scientific and
Industrial Research Organisation (CSIRO) to do some precise measurements
of his TV-derived frequency standard.
They found that all the networks were very accurate, but a couple
were super-precise.  Maybe it's all different now and GPS is the way to go?

Bob

Re: Frequency standard

Strange considering Telstra maintained the Australian frequency standards at
the time, not the CSIRO.
Telstra has now given it away, but last I heard the CSIRO was not
interested. Didn't want to spend the money (the same reason Telstra gave it
away)

go?

Well the ABC-2 clock was running 1 hour and five minutes fast, (compared to
AEDT and their programs) most of Sunday morning. I wouldn't have too much
faith in them any more :-(

MrT.

Re: Frequency standard

GPS is the way to go now for sure.
Even Rubidium references come up cheaply on eBay these days.

Dave.

Re: Frequency standard

It may have taken longer for the frame store equipment to migrate
from type 'M' NTSC in the US to other countries. Want to have some fun?
Try synching two different brands of frame store to the transmitter
site's sync generator for live programming from two other cities. A one
degree phase shift was visible on air.

GPS derived 10 MHz lab standards are common these days.  There was a
construction article on a website to convert a surplus rack mount cell
phone base station GPS receiver into a low cost lab standard.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
We've slightly trimmed the long signature. Click to see the full one.
Re: Frequency standard

Saw something like that at:
http://home.teleport.com/~oldaker /

petrus bitbyter