In article , doug doug@doug wrote:
Ken Smith wrote:
In article m,
Too_Many_Tools wrote:

I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?


For frequency, you can use WWV. You need:
A short wave radio with an audio output.
Perhaps an audio filter tuned to about 1KHz.
A generator you wish to calibrate near the WWV frequency.
A frequency counter that is not too far off.

Procedu
Tune in WWV.
Put wire on generator and set it to WWV-1KHz
Listen for tone and move stuff around until it sounds good.
Feed tone into the filter.
Place the counter on the output of the filter.

The number on the counter is X Hz away from 1KHz when the generator is XHz
off from WWV-1KHz.



This works if you only need about 1 part in a million.

One PPM is enough for almost all the test equipment you will find on
places like ebay.

You can do better if you average over longer periods.

[.....]
just use it for the timebase all the time. Alternately, use a Rb
source. They were also used in cell sites and are available easily.
They cannot move more than about a part in 100 million and they make
excellent time bases for frequency counters.

I thing someone messed up a decimal. You just made a Rb clock 100 times
worse that WWV.




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forging knowledge

Ken Smith wrote:
In article , doug doug@doug wrote:

Ken Smith wrote:

In article m,
Too_Many_Tools wrote:


I have a well stocked test bench at home containing a range of analog,
digital and RF test equipment as I am sure most of you also do.

Well the question I have is how do you handle the calibration of your
equipment? What do you use for calibration standards for resistance,
voltage, current and frequency?


For frequency, you can use WWV. You need:
A short wave radio with an audio output.
Perhaps an audio filter tuned to about 1KHz.
A generator you wish to calibrate near the WWV frequency.
A frequency counter that is not too far off.

Procedu
Tune in WWV.
Put wire on generator and set it to WWV-1KHz
Listen for tone and move stuff around until it sounds good.
Feed tone into the filter.
Place the counter on the output of the filter.

The number on the counter is X Hz away from 1KHz when the generator is XHz
off from WWV-1KHz.




This works if you only need about 1 part in a million.


One PPM is enough for almost all the test equipment you will find on
places like ebay.

You can do better if you average over longer periods.

[.....]

just use it for the timebase all the time. Alternately, use a Rb
source. They were also used in cell sites and are available easily.
They cannot move more than about a part in 100 million and they make
excellent time bases for frequency counters.


I thing someone messed up a decimal. You just made a Rb clock 100 times
worse that WWV.



No. One part in 100 million (10^-8) is 100 times better than wwv
(10^-6). There is lots of excellent equipment on ebay that can take
advantage of this level of accuracy. The main point is that you do
not have to think about it very often. The low cost counters that have
uncompensated or poorly compensated timebases are basically useless for
any serious work. The other nice part about the high stability
references is that you can distribute it to all the synthesizers on your
bench and everything is coherent.
Of course it depends on what you do. For my ham work, one ppm is fine.
I do other work where the Rb source is not good enough.

In article , doug doug@doug wrote:
Ken Smith wrote:
In article , doug doug@doug wrote:

A mistake go read it if you want.

No. One part in 100 million (10^-8) is 100 times

Yes, I misread the statement.

[....]
uncompensated or poorly compensated timebases are basically useless for
any serious work.

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
59.9Hz, I don't think you would mind.


The other nice part about the high stability
references is that you can distribute it to all the synthesizers on your
bench and everything is coherent.
Of course it depends on what you do. For my ham work, one ppm is fine.
I do other work where the Rb source is not good enough.

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




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forging knowledge