Practical Radio-Frequency Handbook docx

[...]... consist of a pyrolytically deposited film of carbon on a ceramic rod, with pressed-on end caps Initially, the resistance is a few per cent of the final value: a spiral cut in the film is then 2 Practical Radio-Frequency Handbook made automatically, to raise the resistance to the designed value Higher power or higher stability requirements are met by other resistor types using spiralled films of tin oxide... combination (a) Series parallel (also works for impedances) (b) The star–delta transformation (also works for impedances, enabling negative values of resistance effectively to be produced) 4 Practical Radio-Frequency Handbook In a piece of metal an outer electron of each atom is free to move about in the atomic lattice Under the action of an applied EMF, e.g from a battery, electrons flow through the conductors... of ten cycles per second or 10 Hz, t indicating elapsed time in seconds † N750 indicates a tempco of capacitance of –750 parts per million per °C: NP0 indicates a nominally zero tempco 6 Practical Radio-Frequency Handbook I I ω ICE V C V (a) I ω V V L ELI I (b) Figure 1.4 Phase of voltage and current in reactive components (a) ICE: the current I leads the applied EMF E (here V) in a capacitor The origin... relative permeability Thus B = µ0µrH Stated more fully, φ/A = µ0µrF/l so that: φ= F l /( µ 0 µ r A ) The term l/(µ0µrA) is called the reluctance S of the magnetic circuit, with units of 8 Practical Radio-Frequency Handbook amperes/weber, and is analogous to the resistance of an electric circuit The magnetic circuit of the toroid in Figure 1.5e is uniform If it were non-uniform, e.g if there were a semicircular... = S + jωC At a given frequency, a resistance and a reactance in series Rs and Xs behaves exactly like a different resistance and reactance in parallel Rp and Xp Occasionally, it may be 10 Practical Radio-Frequency Handbook Rwp Llp Rws Lls Rc Lm Perfect transformer (a) Ip Ea Ll Ip ′ Rw Is EpB Rc Es RL Lm (b) Figure 1.6 Transformers (a) Full equivalent circuit (b) Simplified equivalent circuit of transformer... factor) of the inductor at that frequency Capacitors also have effective series resistance, but it tends to be very much lower than for an inductor: they have a much higher Q So in this 12 Practical Radio-Frequency Handbook Curve no Constant voltage input Voltage output Current output into open circuit into short circuit vo vi vi 1 vo vi jωT 1 + jωT vo vi 1 1 + jωT R io vi io io vi 5 io vi 1 1 + jωT... band is obtained with critical coupling; if the coupling is greater than this, the pass band will become double-humped, with a dip in between the peaks Where the coupling between the two 14 Practical Radio-Frequency Handbook tuned circuits is by means of their mutual inductance M, the coefficient of coupling k is given by k = M/√(LpLs) = M/L if the inductance of the primary tuned circuit equals that of... temperature is required, but the warm-up time or power requirements of an oven are unacceptable, a temperaturecompensated crystal oscillator (TCXO) can be used Here, temperature-sensitive 16 Practical Radio-Frequency Handbook (2.0) [1.146] 1R (1.0) [1.303] (1.0) [1.303] c c 1R (Butterworth) and [Chebychev 0.25 dB] Low-pass filters, third order, cut-off frequency 1 rad/s, Z0 = 1 ohm, C in farads, L in henrys... the net current in the load is the sum of the incident and reflected currents, = 1 – 0.5 = 0.5 A The net voltage across the load is increased (or decreased) in the same proportion as the 20 Practical Radio-Frequency Handbook current is decreased (or increased), so the net voltage across the load is 150% and varies along the line between this value and 50% of the incident voltage The ratio of the maximum... At λ/8 from an open circuit, the current leads the voltage by 90°, i.e at this point an o/c line looks like a capacitance C with a reactance of 1/jZ0 At λ/4, C = ∞ (b) The Smith chart 22 Practical Radio-Frequency Handbook loci of constant VSWR, the centre of the chart representing unity VSWR and the edge of the chart a VSWR of infinity Distance along the line from the load back towards the source can .