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RF Trapping Precision Analog Filter

IP.com Disclosure Number: IPCOM000089034D
Original Publication Date: 1977-Sep-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Olsen, FW: AUTHOR

Abstract

Commercially available solid state relays have internal RF oscillators that provide a source of RF interference for any analog instrumentation that may use them. Since each relay has its own oscillator and since its frequency may be anywhere within specified limits, any combination of two or more of these relays held on at a time can produce RF interference well beyond the specified limits due to the sums and differences (beats) of the individual oscillators.

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RF Trapping Precision Analog Filter

Commercially available solid state relays have internal RF oscillators that provide a source of RF interference for any analog instrumentation that may use them. Since each relay has its own oscillator and since its frequency may be anywhere within specified limits, any combination of two or more of these relays held on at a time can produce RF interference well beyond the specified limits due to the sums and differences (beats) of the individual oscillators.

The present circuit is a special RF absorption circuit that absorbs the interfering oscillators fundamentals without the requirement of filtering out the beats. This filter consists of series resonant L-C traps parallel connected in two groups with resonant frequencies tuned so that one group has every odd sequence progressive frequency from low to high in the band to be rejected and the other group has the even sequence. The two groups are isolated from each other by a resistor or choke.

The circuit shown is for 3 MHz to 8 MHz relays.

The frequency spacing is derived from the selectivity of the individual series traps separately.

The second group is tuned to the zero absorption frequencies of the first group when the higher frequency trap becomes capacitive and the next lower frequency trap becomes inductive.

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