Re: Grid Dip Oscillator
Reply To: vonpostel-at-prodigy-dot-net
Sent: Saturday, November 22, 1997 6:22 PM
To: Tesla List
Subject: Re: Grid Dip Oscillator
Tesla List wrote:
> From: Anderson's Publishing[SMTP:andersons-at-geeky1.ebtech-dot-net]
> Sent: Thursday, November 20, 1997 7:55 PM
> To: tesla-at-pupman-dot-com
> Subject: Grid Dip Oscillator
> I was looking through the first issue of "On The Air!" magazine, a
> magazine for ham radio, and saw an article on building a device called a
> grid dip oscillator(or a drain dip oscillator). Has anyone any >experience
> Anderson's Publishing
Most commerical GDOs if not all, could be used as wave meters.
James Millen Co. made a GDO with a complete set of coils giving a
coverage down to about 100 kHz or so. The oscillator was of the Colpitts
type with a micoamp. meter in the grid circuit It could also be used as
a "wave" meter.
The General Radio Co. made a "precision" wave meter with a frequncy
range of 16 kHz to 50 MHz and an accuracy of plus or minus 0.25%. GR
used a set of seven coils to cover the full range of their Type 724-B
Precision Wavemeter selling for $295 in 1954. They and Millen used a
straight-line-frequency variable capacitor. This permits approximately
linear variation in frequeny with scale setting.
I found the GDO useful when I needed know the resonant or anti-resonant
frequency of an LC circuit. It was also used to determine the tunning
range of a circuit. As a wavemeter it was used to neutralize the grid
to plate capacitance of triode RF amplifiers.
Neither the GDO nor the Wave Meter give precise information, but they
are useful when either bulding equipment or operating it. As a GDO it
will tell you approxamately where your TC should operate. As a wave
meter it will give you an indication of the actual operating frequency.
You can use a wavemeter as an elemetary field strength meter giving an
idea of the effect of the last change you made.
The book, "Radio Instruments and Measurements", Circular C74, National
Bureau of Standards, edition of 1924, reprinted 1937 used to be
available from the U.S. Government Printing Office. You should be able
to get it from your local library. It contains most of the equations,
practices, and techniques used in the design and measurement at the
frequencies employed by Tesla. To quote "The most generally useful
masuring instrument at radio frequencies is the wave meter."
My opinion is that the GDO is a wave meter updated by the vacuum tube
and then by solid state devices. As such, it has a place in the coilers
bag of tricks. It is a simple device which should repay careful
construction and calibration.