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Switchable line powered modem

  • US 4,578,533 A
  • Filed: 02/17/1984
  • Issued: 03/25/1986
  • Est. Priority Date: 11/03/1980
  • Status: Expired due to Term
First Claim
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1. A telephone modem comprising:

  • a modem transmitter subsystem operative in response to data from a source to provide modulated data signals to the telephone line;

    a modem receiver subsystem operative to provide data signals derived from signals received on the telephone line including a filter selectively providing in response to a mode control signal, a band-pass characteristic in one of two operating frequency bands and selectively providing in response to said mode control signal, a band-rejection characteristic in the other of the two operating frequency bands wherein the selected band-pass characteristic includes a range of frequencies exclusive of the band-rejection characteristic range of frequencies; and

    control means operative to select either of two frequency bands for transmission and reception and for providing the mode control signal,wherein said receiver subsystem filter comprises a switchable feedback network band-pass filter providing in response to said mode control signal, a predetermined band-pass characteristic having at least one relative signal amplitude peak in the one of two frequency bands of interest, and a simultaneous band rejected characteristic having at least one relative signal amplitude notch in the other of two frequency bands of interest,wherein the filter circuit feedback network includes switch means which alter the feedback network topology to provide the selection of band-pass and band-reject characteristic from among the particular frequency bands of interest.

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