84 I don't trust the calibration of my instruments? What can I use tocheck them?
Description
This article is from the Antique Radios And Phonographs FAQ, by Hank van Cleef vancleef@netcom with numerous contributions by others.
84 I don't trust the calibration of my instruments? What can I use tocheck them?
There is a good frequency standard available for free: WWV, which
broadcasts on 5, 10, and 15 Mhz. If you have a signal generator with a
crystal calibration oscillator, you can tune in WWV on a shortwave
receiver, tweak the crystal tank circuit, and have a fairly good
reference to WWV for other frequencies----though it's a long stretch
from 5Mhz to 455 Khz. Fresh dry batteries generally are fairly close to
their nominal voltages, and an automobile battery that is fully charged
is a first cut "standard" 12.6 volts. Accurate voltages above that are
hard to find in the basement workshop. Ohmmeters tend to be wildly
inaccurate, but you can measure a bunch of resistors of different values
to get "somewhere near."
(Faq editor note: other countries have frequency-standard time
stations; if someone familiar with them could E-mail me the information,
I will include it here).
The rule of thumb is that two-figure accuracy is readily achievable, and
more than what is needed for service work. However, if you are using
flea-market test equipment, it may have been discarded or surplussed
because it could not be calibrated, or may not have been checked and
calibrated for thirty or forty years.
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