Radio Receiver Design

Basic designs

Crystal radio

Main article: Crystal radio receiver

A crystal set receiver including a antenna, a variable inductor, a cat's hair, and a capacitor.

Benefits

Simple, easy to make. This is the classic design for a clandestine receiver in a POW camp.

Drawbacks

Insensitive, it needs a very strong RF signal to run.

Poor selectivity, it frequently just has actually only one tuned circuit.

Direct amplification

Main article: directly amplifying receiver

The straight enhancing receiver contains the input radio frequency filter, the radio frequency amplifier (enhancing radio signal of the tuned station), the detector and the sound frequency amplifier. This design is basic and reliable, however much less sensitive than the superheterodyne (explained below).

Reflectional

Main short article: reflectional receiver

The reflectional receiver includes the single amplifier that amplifies very first radio, and afterwards (after detection) sound frequency. It is easier, smaller and consumes less power, but it is also relatively unpredictable.

Regenerative

Main short article: Regenerative circuit

The Regenerative circuit has the benefit of being possibly really delicate, it utilizes positive feedback to enhance the gain of the phase. Many valved sets were made which utilized a single stage. However if misused it has the fantastic potential to cause radio interference, if the set is adjusted mistakenly (too much feedback made use of) then the detector phase will oscillate so causing the interference.

Regenerative Receiver Schematic

Tuned radio frequency

Main short article: Tuned radio frequency receiver

the RF disturbance that the local oscillator can produce can be controlled with using a buffer phase in between the LO and the Detector, and a buffer or RF amp phase between the LO and the antenna.

Direct conversion

Main short article: Direct-conversion receiver

In the Direct conversion receiver the signals from the aerial pass through a band pass filter, and an amplifier before reaching a non-linear mixer where they are mixed with a signal from a regional oscillator which is tuned to the carrier wave frequency of an AM or SSB transmitter. The output of this mixer is then passed with a low pass filter prior to an audio amplifier. This is then the output of the radio.

For CW morse the regional oscillator is tuned to a frequency somewhat different from that of the transmitter to make the gotten signal audible.

Benefits

Simpler than a superhet

Better tuning than an easy crystal set

Drawbacks

Less selective than a superhet with regard to strong in-band signals

A broader bandwidth than an excellent SSB communications radio, this is since no sideband filtering exists in this circuit.

Superheterodyne

Main article: Superheterodyne receiver

Right here are 2 superheterodyne designs for AM and FM respectively. The FM design is a low-cost design intended for a broadcast band household receiver.

A schematic of a superhet AM receiver. Keep in mind that the radio has a AGC loop.

For single conversion superheterodyne AM receivers made for mediumwave and longwave the IF is frequently 455 kHz.

A schematic of a basic inexpensive superhet FM receiver. Note that the radio lacks a AGC loop, which the IF amplifier has an extremely high gain and is driven into clipping.

For numerous single conversion superheterodyne receivers created for band II FM (88 - 108 MHz) the IF is frequently 10.7 MHz. For TV sets the IF tends to be at 33 to 40 MHz.

FM vs. AM

To make a good AM receiver an automatic gain control loop is important; this requires great design. To make a good FM receiver a huge number of RF amps which are driven into restricting are needed to develop a receiver which can benefit from the capture result, among the most significant benefits of FM. With valved (tube) systems it is more expensive to make active stages than it is to make the very same number of phases with strong state parts, so for a valved superhet it is simpler to make an AM receiver with the automatic gain control loop while for a solid state receiver it is simpler to make an FM system. Thus even while the idea of FM was understood before World War II its use was uncommon since of the expense of valves - in the UK the government had a valve holder tax which motivated radio receiver designers to utilize as few active phases as possible, - but when solid state parts became offered FM began to obtain favor.

Automatic gain control

Main short article: Automatic gain control

Additional reading

Radiocommunication handbook (RSGB), ISBN 0-900612-58-4

References

^ Cheney, M., Uth, R., & & Glenn, J. (1999). Tesla, master of lightning. New York: Barnes & & Noble Books. Page 71.

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