A squelch circuit is disclosed that distinguishes between noise impulses and valid packets of data transmitted over a transmission line such as a twisted pair media within a local area network. The squelch circuit converts supplied data into a stream of positive and negative pulses and detects a sequence of positive and negative pulses quantified in time based on prior knowledge of the characteristics of a valid packet of data and permits the supplied data to pass if it has the characteristics of a valid packet of data or prohibits the supplied data from passing if it does not have the characteristics of a valid packet of data.

The invention comprises a digital detector used in a paging system. This detector has reference levels, against which the received signal is compared with a digital comparator (11). The reference levels can be changed with an updating logic (12), if changes are observed in the levels of the received signals. The detector may also compensate for differences between individual FM detectors.

The present invention relates to process for encoding and transmitting information wherein data, digitalized speech, image, or documents, optionally in colour, are encoded by multilevel combination code with multilevel code elements into a signal, in particular represented by period duration of said signal and/or by a different number of periods in connection with amplitude levels of said signal whereby an amplitude level is used as redundance or quasi level for an identification of code combinations. In the case of digital encoding of the information of a sequence of similar code elements, similar code words, similar lines with associated code words in the sequence are combined in such a way that the number of the sequences are provided in code. The processes may be adapted in such way that the half tones of telefax on the transmitting side are either directly provided with a quantification value of the half tones, preferably according to the run length principle, and thereafter transmitted in a multilevel code, and that, at the receiving end, means are foreseen that after decoding convert the signal into pixels according to a dither process. By using these kinds of processes, transmission times are shortened and bandwidths are reduced.

A private local area network (LAN) is created for use with a variety of transmission media for the purpose of exchanging data preassigned addresses, and control signals according to simplified protocols. The LAN members can consist of any combination of computers, electronic devices or terminals adapted for intercommunication via microprocessor-based modems which are capable of performing either master or slave functions within the LAN in accordance with their individual software designations. Each modem operating on the LAN has the capability of filtering analog noise, detecting/blocking digital data errors, operating within a wide range of appropriate line impedances, and both transmitting and receiving digital data at rates in the neighborhood of 85 kbaud in the form of frequency, or tone, bursts according to a hybrid ASK/FSK data encoding an transmission scheme. That encoding/transmission scheme consists of the selection of one frequency, or tone, to be both transmitted and received for a duration equivalent to no more than one-half the bit period of a "1" and of the selection of a second frequency to be both transmitted and received for a duration equivalent to no more than one-half the bit period of a "0".