[R-390] Ramblings on Calibration - was: HP 8640B

Thu Apr 7 15:10:54 EDT 2005

Yes that is the process. It does it to 0.1 Hz and does the calculations
internally to display the Rx frequency. Not as nice as a phase lock
system, but on a long haul HF path, not a bad process. I am using the HP
3586.

Lester Veenstra
Senior Engineering Program Manager
Intelsat General
6550 Rock Springs Drive, Suite 450
Bethesda Maryland, 20817
+1-301-571-1212
e-mail: lester.veenstra at intelsatgeneral.com

-----Original Message-----
From: Cecil Acuff [mailto:chacuff at cableone.net] 
Sent: Thursday, April 07, 2005 3:04 PM
To: Veenstra, Lester; Roy Morgan; r-390 at mailman.qth.net
Subject: Re: [R-390] Ramblings on Calibration - was: HP 8640B

Les,

    What are you doing reading the beat note with the levelmeter?  I
have a 
dedicated WWV receiver just haven't figured out how to use it as a 
reference.  It receives WWV selectable from 2.5 through 20 or 25 
Mhz...whatever the top is.

I noticed my WWVB clock stopped sync'ing here a couple months ago after
2 
years of flawless service.  Put a new refrigerator in and changed the
washer 
and dryer...that's all that has changed around here.  I figured I have 
disturbed the signal somehow.  I have tried several other locations in
the 
house and no joy.  Put it outside overnight and it works fine...bring it

back in and it won't sync.

Cecil...
----- Original Message ----- 
From: "Veenstra, Lester" <Lester.Veenstra at intelsatgeneral.com>
To: "Roy Morgan" <roy.morgan at nist.gov>; <r-390 at mailman.qth.net>
Sent: Thursday, April 07, 2005 1:30 PM
Subject: RE: [R-390] Ramblings on Calibration - was: HP 8640B

By the way Roy, since my Rb standard dropped out of internal sync (one
of many items on the "soon" to be fixed list, I find that the Selective
Level meter, counter mode in 20 hZ bw, does a very nice job of keeping
track of my local standard vs WWV at 20 mhz (propagation willing) to
within better than 0.5 Hz. Still not as good by a long shot from those
GPS disciplined sources surplused from the Cellular industry, but it
keeps me "glowing"
     Les

Lester Veenstra
Senior Engineering Program Manager
Intelsat General
6550 Rock Springs Drive, Suite 450
Bethesda Maryland, 20817
+1-301-571-1212
e-mail: lester.veenstra at intelsatgeneral.com

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net] On Behalf Of Roy Morgan
Sent: Thursday, April 07, 2005 10:44 AM
To: r-390 at mailman.qth.net
Subject: [R-390] Ramblings on Calibration - was: HP 8640B

At 04:54 PM 4/6/2005, John Lawson wrote:
>On Wed, 6 Apr 2005, Cecil Acuff wrote:
>
>>choked when he told me what it (calibration) would cost.  Wanted
$800.00.
>   However - it is possible that the cal lab might offer a "limited
cal"
> or a "reference only" cal -

John, Cecil, and others,

(From the great cal lab in the sky... err... Gaithersburg - NIST, though
I
don't do anything of that sort in my job here....)

Here are some ramblings about the topic of calibration:

On "Accuracy of Measurements":
   The expensive cal labs have three or four things we normally don't:
1)
Fancy, specialized equipment to do the calibrations with  2) Reference
standards "traceable to NIST" which costs them to keep current  3) Well
worked out, "accepted" and proven procedures  4) Trained, experienced
people to do the work

For example, in the measurement of frequency, as done in the calibration
of
a signal generator, the lab might well have a satellite-connected local
frequency standard that is continuously monitored for drift and
error.  This thing is part of a system that does the monitoring, allows
for
periodic higher-level calibration, reports it's condition, and provides
suitable output frequencies for use in calibrating other
equipment.  Nowadays it's unlikely that such a frequency standard it
actually sent to NIST for calibration because satellite transfer methods

exist.  This establishes the "traceable" nature of that measurement.
The
procedures used in frequency measurements are probably not too
complicated,
but if you were to get a signal generator calibrated, you will be paying

them to have a trained, experienced technician carry out the
measurements
according to the established procedures.

Measurement of frequency is easy out to 10^-12 or so, but that kind of
accuracy in voltage and power measurement is not feasible.  A check of
the
manual specs on the HP 8640 will show that the accuracy for output level
is
far lower than for the frequency.

On "Why do we do this?"
   Some folks like John, KB6SCO, are responsible in an organization to
make
sure things are correctly calibrated. The organization's goals and
customers require it and he has a full time job making that happen.  Few

Amateur radio stations need such calibration.  Some Amateur radio folks
WANT to know that their equipment is calibrated correctly.  If a
frequency
counter is a little bit off, they won't like it, but a customer's
crucial
communications links won't degrade or fail.  Some of us just like to
mess
with measurements and enjoy knowing our equipment is working right.  For

example, a while ago I got a General Radio Precision Capacitance Bridge
that joins a similar inductance bridge here.  I don't yet know if they
are
working right, but I expect to check them whenever I can.  I have no
earthly reason to measure inductors or capacitors to 0.05 percent!

On "What can we do about all this?"
   For many of us, doing it at home is a fine thing.  Getting an
instrument
and an invoice for a big amount back from a Cal Lab is likely not in our

future.

   At home we can check frequency counters and generators with very
small
errors.  Receiving the WWVB signals at 60 kc is the start of a system
that
gets you well within the specifications of most oscillators found in
frequency counters and generators.  For a couple hundred dollars you can

buy a standard oscillator (surplus from the cell phone industry, as I
understand it) that is extremely accurate.

Measuring resistance, inductance, and capacitance is a bit more
complicated, but you can find reference standards at hamfests or on the
web
that will make a start at a set of known values.  As you dig into the
methods of measuring these values you will begin to understand the value
of
the setup and the methods you use and how they affect the results.  It
takes a small table full of inductance standards to calibrate a high
accuracy inductance bridge, and these things have sold at fests and
auction
sites for $300 apiece and more.

Measuring voltage is even tougher at home.  Systems to measure voltage
to
high accuracies is very complicated, often involving shielded rooms,
calorimetric methods, quantum physics based references, and so on.
Voltage
reference instruments can be had on the used market the would be quite
useful to check our DMM's however.

Careful web searching will reveal a lot of good information about
electronics calibration.  The Agilent web site has interesting reading.
For
example, I recently found a publication on Tips for Making Accurate
Measurements or some such title.  Any one of the setup diagrams in that
one
included at least $50,000 worth of their equipment, so it wasn't all
that
useful.

The NIST website, www.nist.gov, has lots of papers and reports but you
have
do dig for them (the search engine is terrible!) and you'll read about
methods and techniques impossible anywhere but a national calibration
laboratory in many cases.  (How many of us have a cryogenic system
capable
of cooling a Josephson junction array to four degrees Kelvin?)

I think there are many things we can do in our basement workshops to
both
check the accuracy of our equipment, and give us many happy hours of
time
at the bench.  If you want to know whether your R-390A is hearing 1
microvolt or nothing lower than 50, you have a shot at it.  If you need
to
know that your signal generator is giving you one half microvolt to
three
decimal places, you probably have a ways to go.

In the meantime, do have fun, and tell the rest of us about what you are
up to.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan at nist.gov --

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