# Does AC make frequencies?

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Do AC motors/generators make frequencies since it alternates, it should be an oscillation or a frequency?

I'm curious if Tesla used AC generators/motors to do high frequency stuff and is that frequency similar to sound frequency or even the frequency of everything?

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Yes, you can get EM radiation from motors. It’s usually seen as interference, or noise.

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19 hours ago, DARK0717 said:

Do AC motors/generators make frequencies since it alternates, it should be an oscillation or a frequency?

Motors and generators are, effectively, the opposite of one another, although there are many types of each.

You apply a voltage (possibly AC) to a motor and it turns. In some types of motors the rate at which it turns depends on the frequency of the AC voltage.

In the case of a generator, when it is made to turn then an AC voltage will be generated, with the frequency depending on the speed of rotation.

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I'm curious if Tesla used AC generators/motors to do high frequency stuff and is that frequency similar to sound frequency or even the frequency of everything?

I have no idea what Tesla used, but it should be easy to find out. (Although made more complicated by the existence of Tesla motor cars!)

His AC electrical distribution system used 60 Hz (the frequency still used in the USA). This would be a very low hum if converted to sound.

His resonant coil worked at over 50kHz (https://en.wikipedia.org/wiki/Tesla_coil#Oscillation_frequency) which, if it were sound, would be beyond the range of human hearing.

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Alternators have been used at radio transmitters, long ago, between spark-gap and vacuum valves. What ol' Nikola did, I ignore it.

They had big numbers of pole pairs relatively prime at the rotor and the stator, so that for a given rotation frequency, the stator and rotor poles that just began to overlap passed quickly from one pair of elements to an other. Well done.

While this scheme is efficient at removing the current components at low frequencies, it doesn't amplify the desired radio frequency, it only keeps it. So the field at the pole edges had to be very sharp, with edges at the metal and a very thin airgap.

Imagine 100m/s rotor speed, difficult enough then: 1mm transitions in the field could produce AC current with strong components up to roughly 2*10µs or 50kHz, reaching the LW. But any pole length over 1mm was waste, producing components at lower frequencies removed by the relatively prime scheme. Poles 1mm long would have been more efficient but impossible to produce.

I had thought at modernizing the alternator. Silicon can rotate at 500m/s, with patterns and gaps few 10nm small. The alternator could be electrostatic rather than electromagnetic. The achievable frequency is the same as the read throughput of a mechanical disk drive, that is, 200MB/s=2Gb/s would achieve 1GHz energy conversion - or rather less for a significant power hence facing area. But magnetrons do that better.

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Thank you very much

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• 2 weeks later...
On 12/26/2018 at 10:06 AM, Enthalpy said:

Alternators have been used at radio transmitters, long ago, between spark-gap and vacuum valves. What ol' Nikola did, I ignore it.

They had big numbers of pole pairs relatively prime at the rotor and the stator, so that for a given rotation frequency, the stator and rotor poles that just began to overlap passed quickly from one pair of elements to an other. Well done.

While this scheme is efficient at removing the current components at low frequencies, it doesn't amplify the desired radio frequency, it only keeps it. So the field at the pole edges had to be very sharp, with edges at the metal and a very thin airgap.

Imagine 100m/s rotor speed, difficult enough then: 1mm transitions in the field could produce AC current with strong components up to roughly 2*10µs or 50kHz, reaching the LW. But any pole length over 1mm was waste, producing components at lower frequencies removed by the relatively prime scheme. Poles 1mm long would have been more efficient but impossible to produce.

I had thought at modernizing the alternator. Silicon can rotate at 500m/s, with patterns and gaps few 10nm small. The alternator could be electrostatic rather than electromagnetic. The achievable frequency is the same as the read throughput of a mechanical disk drive, that is, 200MB/s=2Gb/s would achieve 1GHz energy conversion - or rather less for a significant power hence facing area. But magnetrons do that better.

Fascinating! Recently, I looked up the theory of Magnetron operation, as I had studied it in the early '60s as a Technical School student. The poles, basically axial keyholes in the I.D. of a cylindrical chunk of conductive non-ferrous material, copper commonly I think, form a tuned  resonant circuit in which the pole faces form the capacitive plates, the poles the inductor. To me, simple-minded, this concept seems to border on original design madness. Yet, it works quite well.

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