[Milsurplus] Shade-Tree Scope Calibration

[David Stinson]

Shade-Tree Scope Calibration at RF.

IMHO, a properly-functioning scope is
the First member of the "Holy Trinity"
of test equipment-
The Scope, The Meter
and The ZM-11 Bridge, Amen.

But a scope is only as good as the
calibration and linearity of it's
vertical amplifiers.  One can use a
variable voltage supply and see if the
amplifier agrees with what it says, but
who's to say the supply is properly cal'ed?
Improperly calibrated test equipment
can have you chasing your tail for days.

For checking the scope at DC input,
perhaps a 300V supply feeding the top
of a Zener stack, then stepping down the
stack, checking agreement at each step?
Can someone recommend a Zener family
with closer tolerances than most?

Well and good for DC, but how about
"where the rubber meets the road"
at RF?  An old vertical amp in a Tek scope
might be spot-on at DC or 60 Hz, but that's
no promise of how it behaves at 4 or 7 MC.

So here's the question:  You don't have
the NIST-certified standards available
and you aren't going to take a 2nd mortgage
to get them.  You need to scope a transmitter's
output and read the PTP voltage so you can
calculate the true power output in Watts,
then use that to calibrate a Wattmeter.
I have three or four Wattmeters around here
and none of them agree with each other.
One Drake is connected to a Johnson Viking II
with AM 270 V PTP output and the meter says
the carrier is only 45 Watts.... Uhhh, no...

So, if you calibrate your scopes at RF,
how do you do it?

TNX OM ES 73 DE Dave AB5S


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