On Sat, 13 Feb 2010 10:45:37 -0500, "Ralph Mowery"
wrote:

The horizontal channel was
fed with an oscillator of around 2000 to 2500 Hz.

From link previously offered:
The frequency at which the protons precess is directly proportional to the strength of the earth's magnetic field. This is the Proton Gyromagnetic Ratio, equal to .042576 Hertz / nanoTesla. For example, in an area with a field strength of 57,780 nT (such as my home), the frequency of precession would be approximately 2460 Hz.

73's
Richard Clark, KB7QHC