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Problems generate, create qr codes none with .net projects Web application Problem 5.1. So Denso QR Bar Code for .

NET metimes two multipliers, two phase shifters, and an adder are used to build a mixer that has only one output band (a so-called single-sideband mixer). The design for an upper sideband mixer, for example, follows directly from the identity: cos RF L:O: t cos RF t cos L:O: t sin RF t sin L:O: t : Draw a block diagram for a circuit that carries out this operation. Problem 5.

2. The diode ring switching mixer also works when the L.O.

and RF ports are interchanged. Explain the operation in this case. Problem 5.

3. Show that the diode ring switching mixer will work if the L.O.

frequency is one-third of the nominal L.O. frequency.

This is sometimes done for convenience if this 1 L:O: frequency is readily available. Find the conversion gain (loss) for this 3 situation. Why would this scheme not work if the L.

O. frequency is half the nominal L.O.

frequency Problem 5.4. Consider a situation where two signals of the same frequency but with a phase difference, , are separately mixed to a new frequency.

Suppose identical mixers are used and that they are driven with the same L.O. signal.

Show that the phase difference of the shifted signals is still . Problem 5.5.

In RF engineering, considerable use is made of the trigonometry identities cos(a+b) = cos(a)cos(b) sin(a)sin(b) and sin(a+b) = sin(a)cos(b)+cos(a)sin(b). Prove these identities, either using geometric constructions or using the identity ejx = cos(x)+j sin(x)..

CHAPTER Amplitude and frequency modulation Modulation mean s variation of the amplitude or the phase (or both) of an otherwise constant sinusoidal RF carrier wave in order that the signal carry information: digital data or analog waveforms such as audio or video. In this chapter we look at pure amplitude modulation (AM) and pure frequency modulation (FM). Historically, these were the first methods to be used for communications and broadcasting.

While still used extensively, they are giving way to modulation schemes, mostly digital, some of which amount to simultaneous AM and FM. The simplest form of AM is on/off keying. This binary digital AM (full on is a data 1 and full off is a data 0 ) can be produced with a simple switch, originally a telegraph key in series with the power source or the antenna.

The first voice transmissions used a carbon microphone as a variable resistor in series with the antenna to provide a continuous range of amplitudes. With AM, the frequency of the carrier wave is constant, so the zero crossings of the RF signal are equally spaced, just as they are for an unmodulated carrier. The simplest FM uses just two frequencies; the carrier has frequency f0 for data zero and f0 + f for data one.

FM is usually generated by a VCO (voltagecontrolled oscillator). For binary FSK (frequency shift keying), the control voltage has only two values: one produces f0 and the other produces f0 + f. FM broadcasting uses a continuous range of frequencies; the instantaneous frequency is determined by the amplitude of the audio signal.

With FM, the amplitude of the carrier wave signal is constant. Figure 6.1 shows an unmodulated carrier wave, an AM-modulated wave, an FM-modulated wave, and a wave with simultaneous AM and FM modulation.

Phase modulation is a type of frequency modulation, since frequency is the time derivative of phase. Amplitude and frequency (or phase) exhaust the list of carrier wave properties that can be modulated. The fractional bandwidth of RF signals is low enough that if one zooms in on a stretch of several cycles, the waveform is essentially sinusoidal and can be described by just its amplitude and frequency.

Schemes such as single-sideband suppressed carrier (SSBSC), double-sideband.
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