Receiver circuit

High-pressure float valves plus handset throttle valves for some flooded and low-pressure receiver circuits. 

Optical receiver noise can arise partly from fundamental photon noise and partly from thermal noise in the receiver circuit. For CO2 detection, it was assumed that the optical receiver was an extended InGaAs detector, followed... 

So, one important lesson is that the receiver circuit must be sampled often enough to make the pattern recognizable. The Nyquist theorem tells us that in order for a computer to determine the frequency (Av,) of each component of the wave function by this method, it must acquire at least two points... 

After B, is turned off, each nonzero component of M in the x y plane (that is, precessing in the xy plane) gives rise to an induced rf signal (which is a summation of all contributing precessional frequencies) in the receiver circuit. This exponentially decaying FID sig-... 

A home-built solid-state NMR spectrometer with stochastic excitation has been described. An overview of the instrument has been given and the control unit and the module for the pulse generation have been described. A static probe with crossed coils for the transmitter and receiver circuits and the data processing part of the spectrometer software have been presented. Several examples of NMR measurements have been shown, including selective excitation in solids and the acquisition of static solid-state NMR spectra with a spectral width of up to 185 kHz. 

The fact that the echo decays very nq>idly in the time domain leads to a problem common in solid-state NMR work the appearance of a pulse feedthrong . This artifact results from the recovery of the receiver circuits and a ringdown of the transmitter and probe circuits after the high-power excitation pulses. To reduce this problem a pulse sequence used to eliminate ringdown in quadrupolar echo NMR was employed [10]. In this sequence, the phase of the tc/2 and the n pulses of the Hahn-echo sequence are varied in such a way that the arti cts add destructively and are essentially eliminated. 

J. L. Engle, "Low-noise broadband transmit/receive circuit for NMR," J. Magn. Resonance 37, pp. 547-549 (1980). 

What makes NMR such a unique analytical technique NMR uses the very weak interaction between a nucleus and the rest of the universe. The interaction between the magnetic moment of a nucleus and the RF field of an NMR pulse/receiver circuit is extremely weak of the order hundreds of MHz versus several eV for optical spectroscopy (500 MHz corresponds to about 2 peV). At first glance, this seems to be an enormous disadvantage as, for an equivalent sample mass, NMR has a much lower signal-to-noise ratio relative to many other spectroscopic techniques. However, the weak interaction also yields extremely high resolution. The weak interaction isolates the nucleus from external perturbation for long periods relaxation times of the order of seconds are common and, conversely, line widths can be less than 1 Hz. Small changes to the environment at an NMR-active nucleus can be detected and identified. Most other analytical techniques are burdened with broad Hne widths. 

Receiving Circuit Power Supply Data Retrieval Data Processing Output Stage... 

In either case, the generating toroid is energized from a source of a stable ultrasonic frequency, typically 20-50 kHz. The pickup toroid is connected to a receiving circuit that measures the current induced through the secondary winding. The current is then amplified and displayed on a meter or transmitted to a strip chart recorder or computer. The output is a... 

For more discussion of receiver design and examples of practical receiver circuits, the reader is referred to the ARRL Handbook (ARRL, 1994). 

As with the DSB receiver, achieving coherent detection requires a local oscillator in-phase with the transmitter oscillator. This can be done by transmitting a pilot signal, using a phase-locked loop (PLL) in the receiver circuit, or by simply tuning the local oscillator for the best output signal. 

---