Meachom Bridge Oscillator

Meachom Bridge Oscillator with circuit

The Meacham bridge oscillator, illustrated in figure 1460, provides the greatest frequency stability of any vacuum-tube oscillator yet devised, but the region of maximum frequency stability is limited to the lower frequencies because of the increased effect of the 8cray circuit capacitances when the frequency becomes greater than a few hundred kilocycles per second. The oscillator is of the crystal-stabilized type employing tuned circuits. At frequencies above 1000 kv the effect of the stray capacitance is sufficient to reduce the stability to a point where little is to be gained by the use of the Meacham

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Crystal Oscillators

Oscillators with Crystals Having Two Sets of Electrodes

The original crystal oscillator devised by Dr. Nicolson, as well as a number of the earlier crystal oscillators tested by Dr. Cady, employed crystals with, effectively, two pairs of electrodes. The basic circuit is shown in figure 1-156. The re quired phase inversion of, the amplifier output voltage is provided by the crystal unit operating at a mode for which the polarities of the plate and grid terminals with respect to ground are 180 degrees out of phase. The circuit shown operates the crystal unit very

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The superposition theorem

This tutorial is superposition theorem. The superposition theorem states:
 
‘In any network which is made up of linear resistances & containing more than 1 source of e.m.f., the resultantcurrent flowing in any branch is the algebraic sum of the currents that would flow in that branch if eachsource was considered separately, all other sourcesbeing replaced at that time by their respective internal resistances.’

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SIGNAL-TO-NOISE RATIO

We can express the amount of noise present in a signal in many different ways. We need not usually the absolute power of the noise, but the power of the noise relative to the power of the signal itself is important. Keeping this reason in view, one of the most commonly used ways of expressing the amount of noise is the signal-to- noise power ratio. A ratio of two powers is most conveniently stated on the decibel scale. As the power is directly proportional to voltage squared, the signal-to- noise ratio is defined as:

In equation shown above, vs is the rms signal voltage and vn is the rms noise voltage. The equation has the standard form that is used for expressing a ratio of powers in decibels.

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