Showing papers on "Co-channel interference published in 1976"

Systems and methods for determining radio frequency interference

Abstract: The presence, frequency and amplitude of radio frequency interference superimposed on communication links originating from a terrestrial region and including a relay in a geostationary spacecraft are determined by pointing a narrow beam antenna on the satellite at the terrestrial region. The level of noise radiated from the region, in a predetermined frequency band of interest, to the antenna is measured at a terrestrial station that is usually remote from the region. Many of the measurements are performed in each of a plurality of frequency bands across the spectrum. Calibrating radio signals having a plurality of predetermined EIRP's (Effective Isotropic Radiated Power) and frequencies in the spectrum are transmitted from the region through the spacecraft narrow beam antenna back to the station. At the station, the levels of the received calibrating signals are separately measured for each of the frequency bands and EIRP's. In response to comparisons of the measured amplitudes of like frequencies of the calibrating signals and noise, the presence, frequency and amplitude of sources of radio frequency interference originating from the region are determined.

Narrow-band radio communication system

Abstract: Ultra-narrow-band system for communication between a transmitter device and a receiver device provided by locking both to a carrier signal from a radio broadcast station and synthesizing a precise local frequency at each device as a preset multiple of the frequency of the carrier. Such a system is usable in a multi-station alarm and status communication system including a multiplicity of independent radio alarm transmitters whose various carrier frequencies are different from but phased locked to a local radio broadcast station, and a central alarm receiving station which employs a corresponding multiplicity of synchronous detectors. The detectors each have associated with them a synthesized local oscillator source which is also phase-locked to the same radio broadcast station used by the alarm transmitters. Both the alarm transmitters and the central receiver are thereby accurately referenced to a readily available local frequency source (the broadcast station). As a consequence, very narrow-band radio circuits may be employed and the receiver and transmitter bandwidth may be accurately matched to the information content of the alarm and status signal source to achieve high signal-to-noise ratio reliable transmissions. The disclosed apparatus is relatively immune to intentional or unintentional interference and will burn-through most conventional transmissions which may be transmitting on the same radio channel at the same time, without unduly bothering those other unrelated transmissions.

Crosstalk Loss Requirements for PCM Transmission

Abstract: We present in this paper a unified approach to the crosstalk interference problem arising in PCM transmission on paired cables. For bipolar signaling, and three types of commonly used channel shaping, viz., cosine, raised cosine, and Gaussian, we present the minimum average near-end crosstalk (NEXT) and far-end crosstalk (FEXT) loss requirements at any transmission rate as a function of repeater spacing and number of interfering pairs so as to meet a desired error rate objective. This will aid in indicating if new cables need to be developed for a proposed rate of transmission or, for a given cable, the error margin available for degradations other than crosstalk can be readily determined. Extension to other coding schemes is indicated, and crosstalk compatibility is examined for mixed T systems, such as T1 , T1C , and T2 . Graphical results are presented to readily aid in system design of any T carrier with repeater spacings up to 70 dB.

Radio receiver having co-channel interference operated squelch

Abstract: FM-radio receiver having an audio amplifier stage, provided with switching means, and a squelch circuit which is coupled to the output of the receiver demodulator, this squelch circuit comprising two circuits which are constructed in such a manner that one circuit produces at an early stage an output signal when co-channel interference occurs whereas the other circuit produces an output signal which controls said switching means and which occurs only at an impermissible signal/noise ratio and/or an impermissible degree of co-channel interference.

A Prediction Model for Ship-Generated Intermodulations

Abstract: The need f o r a c c u r a t e , f a s t , i n t e r f e r e n c e f r e e and r e l i a b l e communication systems i s e v e r i n c r e a s i n g . The uses o f e l e c t r o m a g n e t i c spectrum f o r a m ul t i tude o f purposes such as radar , n a v i g a t i o n , f i r e c o n t r o l , e l e c t r o n i c warfare and e l e c t r o n i c countermeasures impose se v e r e spectrum p o l l u t i o n problems. These pose p a r t i ­ c u l a r d i f f i c u l t i e s on l i m i t e d "real e s t a t e " systems such as naval v e s s e l s , a i r c r a f t and space v e h i c l e s . A l l . o f th e s e uses r eq u ire antennas which r a d i a t e and r e c e i v e e l e c t r o m a g n e t i c energy on l i m i t e d "real e s t a t e s . " T h is , in t u r n , causes s e v e r e e l e c t r o m a g n e t i c i n t e r f e r ­ ence problems. One such i n t e r f e r e n c e problem i s the n o n l i n e a r g e n e r a t e d in term o d ula t io n products (IMP).

Selectivity Requirements to Eliminate Adjacent Channel Interference on Multi-Channel Catv Systems

Abstract: TV receiver and transmitter characteristics required for the elimination of visible adjacent channel interference effects are discussed. The interference mechanisms involved are explained. Effects caused by the upper adjacent channel signal are different in nature from those of a lower adjacent channel signal. It can be shown that the suppression of upper channel interference needs little extra effort, if any, in the receiver, but calls for special care in designing the VSB filter response at the transmitter (or headend modulator). To eliminate interference from the lower adjacent channel, however, the receiver selectivity has to meet requirements which are more stringent than those for the upper adjacent channel.