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A SIMPLE METHOD FOR MAGNETIC TAPE RECORDING OF BIOELECTRIC POTENTIALS,
UNIVERSIDAD DE LA REPUBLICA MONTEVIDEO (URUGUAY) INSTITUTO DE NEUROLOGIA
A system was built which includes a pre-amplification by means of one channel of a Grass IIID Electroencephalograph, a modulator with a 1N34 germanium diode biased in parallel with the 3 terminal available at the control panel of the IIID, a recorder Ampex model 601, 7 12 insec, full-track, a demodulator of the peak-detection type using a series diode 1N34 and an RC circuit with a time-constant of about 10 msec. The carrier generator was a Grass S4 Stimulator which has an output impedance of 250 ohms and supplies a rectangular wave of a frequency of 2 kcsec and a duration of 0.25 msec, with an amplitude of about 1V. In spite of a marked valley in the amplitudefrequency curve at about 35 csec, it was not necessary to install a high pass filter between the modulator and the recorder. However, to obtain the frequency characteristic required by the International Federation of EEG Societies, it would be necessary to put in series a condenser of about 500 pF between the modulator and the recorder. It was also found that the system works without the positive clamp, owing, perhaps, to a high frequency deformation of the carrier square wave as well as to the fact that modulation was not very pronounced. Author
Pub. in Electroencephalography and Clinical Neurophysiology (Canada) v13 p800-2 1961 (Copies available only to DDC users).
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