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# Obtaining Frequency Shifts

IP.com Disclosure Number: IPCOM000097649D
Original Publication Date: 1961-Mar-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 23K

IBM

## Related People

Fowler, AB: AUTHOR

## Abstract

Photoconductors R1, R2, R3, etc. are utilized for effecting measurable frequency shifts in an oscillator when one or more of the photoconductors are illuminated.

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Obtaining Frequency Shifts

Photoconductors R1, R2, R3, etc. are utilized for effecting measurable frequency shifts in an oscillator when one or more of the photoconductors are illuminated.

The frequency of oscillation in an oscillator is a function of the resistance in the circuit. Here the resistance is a set of resistors in parallel in which one fixed resistor R0 is low enough in value for the oscillator to oscillate stably at a frequency F0. Photoconductors R1, R2, R3 are chosen such that their dark resistances are much larger than R0. Also, their illuminated resistances are sufficiently low to shift the frequency enough to be detected but not enough to cause the circuit to change its operating mode. The effect of illuminating one of the photoconductors is detected as a frequency shift by suitable measuring devices.

If R1, R2, R3 are made so that R1 not equal to R2 not equal to R3 then the photoconductor illuminated is identified by the resultant frequency. If two are illuminated at once then the two illuminated are identified if R1 + R2 not equal to R1 + R3 not equal to R2 + R3. This may be extended so that any combination of the photo conductors can be identified.

Another method uses a single linear photoconductor and different levels of illumination from one or more sources in which the particular level of illumination is determinable by measuring the resulting frequency of the oscillator.

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