Discussion in 'General Electronics Discussion' started by brinks, Mar 2, 2017.

1. ### brinks

16
0
Dec 16, 2013
radio waves are produced with AC current. So where do you get AC current from a battery (direct current) operated radio. Also in any AC source their must b a moving part in the system cause AC is produced with movement from a wire or a magnet.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,490
2,832
Jan 21, 2010
You get AC from an oscillator. No moving parts required.

Strictly speaking when you say radio I assume you mean radio transmitter, although most receivers contain oscillators too.

AC comes from more than steam powered generators.

CDRIVE likes this.
3. ### brinks

16
0
Dec 16, 2013
Thanks again Steve! Ok oscillator no moving parts. Creating it with feedback ?

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,490
2,832
Jan 21, 2010
You could say that.

5. ### davennModerator

13,812
1,945
Sep 5, 2009
there's just one example of an RF oscillator circuit ......

Dave

6. ### hevans1944Hop - AC8NS

4,606
2,151
Jun 21, 2012
That is just one way to produce AC. The purpose of an oscillator circuit is to convert DC into AC of appropriate amplitude, wave shape, frequency, and power. There are many circuits available to do this. But all electronic oscillators have two things in common: an amplifier circuit with sufficient gain (amplification) to overcome losses, and positive feedback from the output of the amplifier to its input. The devil is in the details, which can be quite complicated. You need to decide what you are going to DO before you can determine HOW to do it.

In the latter part of the 19th Century, and somewhat into the early part of the 20th century, rotating machinery was used to generate quite powerful low-frequency radio waves for communications purposes. The invention of the triode vacuum tube revolutionized the manner in which electronic oscillators with no moving parts were used to generate radio waves.

The invention of the linear and reflex klystrons, and the resonant-cavity cross-field magnetron during WWII, and later the cross-field amplifier, extended "solid state" no-moving-parts radio oscillators and amplifiers into microwave frequencies. Then came the mid 20th Century semiconductor revolution with tunnel or Esaki diodes, Gunn diodes, and exotic gallium arsenide heterojunction bipolar transistors that virtually eliminated vacuum-tube based oscillators for all but the highest microwave frequency applications.

Note that vacuum tubes still reign supreme at most microwave frequencies requiring significant amounts of power: magnetrons, traveling-wave tubes (TWTs), backward wave oscillators (BWOs), and megajoule free-electron lasers (FELs) have extended power radio oscillators to vacuum ultraviolet wavelengths and beyond to low-energy gamma rays. The only "moving parts" in these devices are electrons, albeit with the help of magnetic fields to direct and control their motion.

duke37 and (*steve*) like this.

16
0
Dec 16, 2013
Thank you

8. ### duke37

5,364
771
Jan 9, 2011
The classic oscillator consists of a tank resonant circuit with power added to make it resonant and power taken out to feed the driver. The gain of this loop must be exactly one which needs to be set for low distortion. See AGC - automatic gain control.

There are many variations of the oscillator circuitry, look up Colpitts, Hartley or Clapp for some of the most common types.