RF power amplifier

A RF amplifier is a device for electrically amplifying the power of an electrical signal,

typically, but not exclusively, radio frequency signals.

An RF power amplifier is a type of electronic amplifier used to convert a low-power radio-

frequency signal into a larger signal of significant power, typically for driving the antenna of

a transmitter. It is usually optimized to have high efficiency, high output Power(P1dB)

compression, good return loss on the input and output, good gain, and optimum heat

dissipation.

rf is a single tuned amplifier . Its functions are :-

1.improves selectivity ( i.e rejection of unwanted signal) , so that it prevents heterodyning which

results in interference frequency.

2. improves image frequency rejection

3. improves sensitivity ( gain of amplifier )

4.improves coupling of receiver with antenna .

5. improves signal to noise ratio.

6. reradiation of local oscillator through receiver antenna is prevented

RF Amp Devices

The primary device responsible for the signal enhancement is known as a triode, or a

diode with one added part--a control grid. The control grid affects on the electric

charge flows through the diode, and by applying small voltage variations in the

current passing through, the triode can make large changes in the strength and

behavior of the current.

Of course, this is a very basic description of the process: modern RF amplifiers

employ entire circuit boards to make sure the signal is given maximum strength with

as little signal distortion as possible. Today, these amplifiers are used no only in radio

towers, walkie-talkies, and specialized communication devices, but also in every cell

phone and cell phone tower.

Service Data Chart For Troubleshooting the RF Amplifier Stage

Symptom Abnormal Reading Possible Cause

RF Stage

Inoperative

Plate voltage = 0. Other

voltages normal

Open primary (L4) of interstage transformer T-2.

Open plate resistor R-4.

Plate de-coupling capacitor C-4 shorted

Screen voltage = 0. Other

voltages normal

Screen by-pass capacitor C-14 shorted.

Screen resistor R-14 open

All voltages normal Check for short in gang tuning capacitor C-2.

Defective tube

Cathode high Open cathode resistor R-1

Cathode voltage = 0 Shorted cathode by-pass capacitor C-1

Dead tube

Weak signal All voltages normal Weak tube.

Check for open winding (L1-L2) on antenna

transformer T-1.

Open plate by-pass capacitor C-4.

Open AVC by-pass capacitor C-30.

RF stage out of alignment

Oscillation All voltages normal Open screen by-pass capacitor C-14.

Tube shield not making good ground

connection.

Noisy operation All voltages normal Open or corroded antenna transformer T-1.

Open AVC by-pass capacitor C-30.

Corrosion in the interstage transformer T-2.

Defective tube.

Defective gang tuning capacitor C-2 (check for

grounding wipers making poor contact).

Dirty trimmer capacitor C-2A

Poor tone

quality

All voltages normal Shorted AVC by-pass capacitor C-30.

Ground waves

In physics, a surface wave is a mechanical wave that propagates along the interface between

differing media, usually two fluids with different densities. A surface wave can also be an

electromagnetic wave guided by a refractive indexgradient. In radiotransmission, a ground wave is a

surface wave that propagates close to the surface of the Earth

Ground waves refer to the propagation of radio waves parallel to and adjacent to the surface of the

Earth, following the curvature of the Earth. These surface waves are also known loosely as the

Norton surface wave, the Zenneck surface wave, Sommerfeld waves, and gliding waves.