A field experiment that transmits a full bandwidth of C-band satellite downlink signals over 35 km of 1.3-μm single-mode fiber was demonstrated. The major requirements of this analog fiber-optic link for video transmission, including system linearity and carrier-to-noise ratio, were experimentally characterized. Assessment of the system performance was based on measurement of video signal quality. A complete system analysis is given and the results agree well with the measured data.

A 1.3-&#181;m 35-km fiber-optic microwave multicarrier transmission system for satellite earth stations

The present invention relates to the improved demodulation system which improves the noise characteristics for the demodulation of a wideband television FM signal. A variable bandpass filter (8), the center frequency and the bandwidth of which are controllable, for improving C/N, is inserted at the output of a reference bandpass filter (7) in an FM signal path. The bandwidth of the variable bandpass filter (8) is controlled so that said bandwidth is wide when the input carrier level is high, and said bandwidth is narrow when the input carrier level is low. The center frequency of the variable bandwidth filter (8) is controlled so that said center frequency follows to the instantaneous frequency of the color sub-carrier component (3.58 MHz). Said color sub-carrier component is derived by a narrow-band bandpass filter (10) coupled with the output of said discriminator (9) for controlling the center frequency of the variable bandpass filter (8).

High-sensitivity fm signal demodulation system.

The demodulator combines a conventional frequency discriminator with a bandpass filter for removing the noise which is present from the band occupied at a given instant by the modulated signal. The center frequency of the bandpass filter is controlled in dependence on the instantaneous frequency of the modulated signal and its bandwidth bu is controlled in dependence on the instantaneous width of the band occupied by the modulated signal.

FM Demodulator with variable bandpass filter

A rectangular waveform signal reproducing circuit for electronic musical instruments which is composed of a first charge-discharge circuit having a relatively small charge time constant and a relatively large discharge time constant for charging and discharging positive components of a monophonic signal, a second charge-discharge circuit having a relatively small charge time constant and a relatively large discharge time constant for charging and discharging negative components of the monophonic signal, first comparing means for comparing the monophonic signal with the output from the first charge-discharge ciruit to produce a first compared output representing that the level of the former is larger than that of the latter in the positive direction, second comparing means for comparing the monophonic signal with the output from the second charge-discharge circuit to produce a second compared output representing that the level of the former is larger than that of the latter in the negative direction, and a flip-flop having first and second input terminals respectively supplied with the first and second compared outputs to produce a rectangular waveform signal having the fundamental period of the monophonic signal.

Rectangular waveform signal reproducing circuit for electronic musical instruments

A noise reduction circuit for a video signal, comprises a feedback type comb filter in which an output video signal of a delay circuit which delays a video signal by one or two horizontal scanning periods, is fed back to an input side of the delay circuit through a feedback path, and an equalizer circuit coupled in series with the feedback type comb filter. The feedback path comprises a highpass or bandpass filter circuit and a coefficient multiplier which are coupled in series. The equalizer circuit has a frequency characteristic complementary to an envelope characteristic in a frequency characteristic of the feedback type comb filter.

Noise reduction circuit for a video signal

A tunable oscillating limiter threshold extension demodulator capable of demodulating video and other wide band width FM signals is described. A steering signal is generated to tune the oscillating limiter in response to the video output signals from an FM discriminator to which input signals from the oscillating limiter are applied. The steering signal is generated so as to be in proper phase relationship to track the frequency of the FM signal for modulating frequencies within certain critical regions and is reduced in amplitude over another region where proper phase relationship is not achievable because of unavoidable delays in the system. The steering signal generating circuit may be provided by a filter having a phase response characteristic such that the total phase lag of the system is small at the low frequency end of the band width and about 360° at the high frequency end of the band width. The filter presents substantial attenuation (in the form of a notch) in the frequency region of the band width where the phase delay may be about 180° and would otherwise provide improper oscillating limiter steering action. In the case of color television signals, for example, significant spectral components of the signal, specifically the components due to the sync and equalizing signals are present in the low frequency end of the signal band width while the significant color or chromatic subcarrier spectral component is at the high frequency end of the signal band width. Accordingly, when applied to tune the band pass filter of the oscillating limiter the frequency to which the oscillating limiter is tuned is caused to substantially match the instantaneous frequency of the color television modulated FM signal at the frequencies of these significant components and the noise threshold in terms of the minimum signal to noise ratio which the demodulator can operate properly is thereby improved.

Threshold extension fm demodulator apparatus for wide band width fm signals

For a frequency-modulation relay link carrying television, a simple general form is suggested for the relationship between baseband signal-to-noise ratio and the ratio of carrier power to noise power density applied to the receiver discriminator. The bandlimiting, emphasis, and weighting functions prescribed by various standards are characterized by effective noise bandwidths with respect to triangular noise.

FM Television Signal-to-Noise Ratio

An improved circuit for producing two square wave electrical signals in relative phase-quadrature from an input sine wave whereby the amplitude and relation of the two output square waves do not vary with either the frequency or amplitude of the input sine wave. In one embodiment, the input sine wave is split into positive and negative rectified signals, and each signal then is used to produce intermediate signals which have a first and second output level and which change that level each time the potentials of the positive and negative rectified signals are equal. These intermediate signals are applied to logical devices to cause production of the output square wave signal in quadrature. An averaging and level shifting circuit is employed to shift the DC bias of the rectified signals so that the output signals are in quadrature.

Lorimer Clayton

Papers

Threshold extension fm demodulator apparatus for wide band width fm signals

FM Television Signal-to-Noise Ratio

Quadrature square wave generator