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RE-: Grid Dip Oscillator (fwd)
---------- Forwarded message ----------
Date: Sat, 29 Nov 1997 16:03:00 GMT
From: Robert Michaels <robert.michaels-at-online.sme-dot-org>
To: tesla-at-pupman-dot-com
Subject: RE-: Grid Dip Oscillator
Together, each of you have half of the story partially
correct.
Firstly -- there are no longer any "Grid-Dip Oscillators" in
practical terms. The last one of these went out of
style about the time John F. Kennedy was President.
The modern incarnation of this instrument uses transistors
(or integrated circuits). Ergo, no "grid". So - let us not
mislead the gullible - I'd hate to be responsible for
having some young'un laughed-out of the electronics shop.
Second - Any righteous Dip Oscillator (note correct term-
inology) can be used as an active or passive device.
As an =active device= it generates a signal and is used
to test =passive circuits=. Its meter =dips= when
power from it is absorbed by the circuit under test.
Howsoforever - in any self-respecting and proper Dip
Oscillator it is possible to turn off the signal. The
instrument thus becomes a =passive device= and is used
to measure =active circuits= . It this use it is
effectively a wavemeter. Its meter peaks when it absorbs
power.
Note how the meter response differs in each situation: It
dips when on frequency as an active device (Dip Oscillator).
It peaks when on frequency as a passive device (wavemeter).
- - - - - -
While I have your rapt attention: (and strictly not to
mislead the young'uns):
Dip Oscillators are rude and crude, rough and ready,
handy-dandy, quick and dirty, fast and frivolous devices.
There are much better and more precise ways to obtain the
same measurements. Their main value is in their
portability - not their precision.
In a transistor oscillator - note: no grid - there is also
no "dip" either. The meter reading peaks on max. power
absorption by the passive circuit.
Hosoforeverbethatasitmay -- the reading is inverted by
additional circuitry, so it actually does dip in the
practical, working commercial instrument. This, I guess,
for historical reasons, so as not to mislead the old'uns.
Not young, or old, but maybe
a little dippy -- in
Detroit, USA
Robert Michaels
TL>From: Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
TL>Subject: Re: Grid Dip Oscillator
TL>On Monday, November 24, 1997 2:25 PM Edward V. Phillips
TL>[SMTP:ed-at-alumni.caltech.edu] wrote;
TL>> ...To quote "The most generally useful masuring instrument
TL>> at radio frequencies is the wave meter.""
TL>A wave meter is not the same as a grid dip meter, a wave meter is a
TL>calibrated variable tank circuit with a detector across the tank circuit
TL>and requires the circuit you are measuring to be active, by contrast a grid
TL>dip meter is an active device that allows you to measure and tune resonant
TL>circuits that are not active or powered ie you can measure the resonant
TL>frequency of an isolated Tesla coil secondary.