Who noticed this, and in 1936 he proposed a practical FM system.

FM broadcasting in United States began 1939 but suffered a setback in 1944 when its frequency allocation was abruptly shifted from?

At the beginning, we observe that only three parameters of a carrier wave can be change or modulated in order for it to carry information namely?

In FM, carrier amplitude remain constant, while the carrier frequency is changed by the modulating signal.

The amount of change in carrier frequency produced by the modulating signal is called

The most important advantage of FM or PM over AM is the possibility of

𝑓𝑠𝑖𝑔 𝑡 = 𝑓𝑐 + 𝑘𝑓𝑒𝑚(𝑡)

An AM modulator has kf= 30 kHz/V and operates at a carrier frequency of 175 MHz. Find the output frequency for an instantaneous value of the modulating signal equal to:

a. 150 mV

𝛿 = 𝑘𝑓𝐸m

changing the amplitude of a carrier sine wave generated extra frequencies called

The simplest way of generating FM is through the use of

𝑘𝑝 = Φ /𝑒m

Interference from high frequency noise can be minimized by boosting the amplitude of the highfrequency modulating signal prior to modulation.

The effect of pre-emphasis circuit can be reversed using de-emphasis circuit by passing the received signal though a RC low-pass filter.

The frequency where pre-emphasis and de-emphasis begins – Occurs at the frequency where Xc , or XL equals R.

Advantage of FM over AM

An angle modulation in which the frequency of the carrier is varied directly by the modulating signal.

The carrier is generated by LC or crystal oscillator circuits.

is used to change the capacitance of an LC tank.

The frequency of LC oscillators will vary with temperature changes, variations in circuit voltage and other factors.

• Is a circuit that uses a transistor amplifier that acts like either a variable capacitor or an inductor.

An indirect method of generating FM using crystal oscillator for a frequency stability with a phase modulated buffer stage.

Simplest form of tunedcircuit frequency discriminator

Also known as Round-Travis Detector

Also known as the Center-Tapped or phase shift discriminator • Looks like a ratio detector but instead of third winding, a choke is used.

Variation of the Foster Seeley discriminator which includes an amplitude limiter which improves the limiting action. • Provide a greater level of noise immunity

Also called coincidence detector •

Extracts the original information signal from the composite IF waveform by multiplying two quadrature (90o out of phase) signal.

Widely used in FM building block

First practical receiving device called

was consist of tube with metal filing through which the

RF and DC signal pass through

Coherer was first used by?

Is a measure of the signal strength required to achieve a given signal-to-noise ratio

Is the ability to reject unwanted signal at frequencies different from that of the desired signal.

Q=XL/R

Determine the upper-half frequency of a class C amplifier having lower half power frequency of 4.75 MHz, a resonant frequency of 5 MHz and a circuit Q of 10.

A TRF receiver is to be designed with a single tuned circuit using a 20 H inductor. Calculate the capacitance range of the variable capacitor required to tune from 535-1605 kHz.

– Another way of specifying selectivity

Occurs when the frequencies generated are multiples of the fundamentals

when frequency components of the original signal mix in a nonlinear devices, creating sum and difference

– Time delay which can be translated to phase shift that increases linearly with frequency.

A receiver must operate over a considerable range of signal strength

– Occurs when two signals with slightly different frequencies and very different power levels are applied to the antenna simultaneously.

Other term for Blocking

A receiver has a sensitivity of 0.75 V and a blocking dynamic range of 80 dB. What is the strongest signal that can be present along with a 75 V signal without blocking/desensitization taking place?

The tendency of the receiver to receive signals at frequencies to which it is not tuned.

A second input frequencies that produces the same output frequencies

– Defined as the ratio of voltage gain at the input frequency to which the receiver is tuned to gain at the image frequency.

An AM broadcast receiver has an IF of 455 kHz, tuned to a station 590 kHz. Use high side injection.

a. Find the image frequency

For a receiver with IF, RF and local oscillator frequencies of 455 kHz, 630 kHz and 1085 kHz, respectively, determine:

a. image frequency

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• Combination of mixer and local oscillator

– is a linear fixed-frequency tuned amplifier, found in the IF stage of a superheterodyne radio receiver.

An IF transformer operates at 455 kHz. The primary circuit has a Q of 40 and the secondary has a Q of 30. Find

a) the critical coupling factor

Drift was reduced through the use of ?

• tuning of transformers to slightly different frequencies

– Used to automatically adjust gain of signals

– circuit that is used to decrease gain

– circuit used to increase gain

Disables the receiver audio in the absence of the signal

The simplest way to deal with noise pulses is simply to use ?

is a circuit that cuts electronics pulses

– This filter can be tuned to the frequency of the interfering carrier, greatly attenuating it and avoiding the audible whistle.

– Designed to indicate signal strength for comparison and to aid in tuning the receiver and sometimes in adjusting antenna.

– Can perform half duplex or full duplex transmission

– A measure of the effectiveness of FM limiting