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A double-tuned transformer from a radio receiver intermediate-frequency amplifier with its screening can removed. A double-tuned amplifier is a tuned amplifier with transformer coupling between the amplifier stages in which the inductances of both the primary and secondary windings are tuned separately with a capacitor across each.
One of the windings of the transformer had a variable capacitor connected across it to make a tuned circuit. A variable capacitor (or sometimes a variable coupling coil called a variometer) was used, with a knob on the front panel to tune the receiver. The RF stages usually had identical circuits to simplify design.
The coupling transformer has to have a turns ratio of 1:1.41 ± 3.0 percent. The resistors R both have to have a value of 0.75 Zo ± 2.0 percent, where Zo is the characteristic impedance of the bus at 1 MHz. Figure 10: Data bus interface using direct coupling
Perfect coupling implies infinitely high core magnetic permeability and winding inductance and zero net magnetomotive force (i.e. i p n p − i s n s = 0). [3] [c] Ideal transformer connected with source V P on primary and load impedance Z L on secondary, where 0 < Z L < ∞. Ideal transformer and induction law [d]
The coupling factor is defined as: , = where P 1 is the input power at port 1 and P 3 is the output power from the coupled port (see figure 1). The coupling factor represents the primary property of a directional coupler.
Created Date: 8/30/2012 4:52:52 PM
Note, , the reactance in parallel, has a negative reactance because it is typically a capacitor. This gives the L-network the additional feature of harmonic suppression since it is a low pass filter too. The inverse connection (impedance step-up) is simply the reverse—for example, reactance in series with the source.
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