rf

[m3vuv]

just a quicky question,When does ac get classed as rf?,is it when the frequency is above the threshold of hearing,ive often wondered but never seen it explained anywhere,cheers paul m3vuv 73.

[cdev]

If we go by the standard decade means of breaking down parts of the EM spectrum, I would say 30 KHz, 30-300 KHz might be VLF.

[rhb]

When it is used for communication might be a better definition given the use of 3-30 KHz  for submarine communications.

[Waldmann]

Well I'd say that generally when we talk about radio frequency (RF) we talk about few kHz and above. Typically 30 kHz and above.
So yes, it's about a certain threshold of frequency of electromagnetic oscillation.
60 Hz out of your wall is not RF.

[ElectronicCat]

I guess the lowest frequency someone might commonly come across that could be described as 'RF' is longwave AM radio which can be down at around 100-200kHz, although lower than that is possible for communications (with submarines for example).

Personally though I would only really consider things RF engineering above the point where special PCB layout considerations are required (around 20-50MHz) and above which frequencies are more commonly used for wireless communications. A simple DC-DC converter might have a switching frequency of hundreds of kHz-single digit MHz and a hobbyist without much experience might be able to use a microcontroller on a breadboard with an 8/16MHz crystal and an SPI communication bus at several tens of MHz without any knowledge of experience of RF, and it could reasonably be expected to work fine. I have met some old crusty engineers who laugh off anything under a couple of GHz as 'low frequency' though, so I suppose it all depends on who you ask .

[awallin]

30-300 KHz might be VLF.

see table here: https://en.wikipedia.org/wiki/Radio_frequency
kHz with a small 'k' please 

[vk6zgo]

"RF" is just a convenient label for those ac signals we radiate on purpose for communications purposes.
If we took it in mind to radiate 50Hz, we could, but it would be unwieldy in the extreme, due to the enormous lengths required for resonant antennas.(A half wave dipole would be about 3000km long).

Actually, we do radiate a lot of 50 & 60Hz, inadvertently, from our power networks.

We could postulate very large sentient beings from outer space, to whom antennas for such frequencies would be a nice, convenient size.
They might receive noise from our power networks, but not notice our "RF" outputs.

[rhb]

"RF" is just a convenient label for those ac signals we radiate on purpose for communications purposes.
If we took it in mind to radiate 50Hz, we could, but it would be unwieldy in the extreme, due to the enormous lengths required for resonant antennas.(A half wave dipole would be about 3000km long).

Actually, we do radiate a lot of 50 & 60Hz, inadvertently, from our power networks.

We could postulate very large sentient beings from outer space, to whom antennas for such frequencies would be a nice, convenient size.
They might receive noise from our power networks, but not notice our "RF" outputs.

That's a really interesting point.  The radiated power from the electrical grid is probably a few orders of magnitude greater than  conventional RF.  And a 3000 km antenna in orbit would not be hard.  The local noise cancellation problem would like be challenging though.

I wonder if the SETI crowd has considered that?

[xyrtek]

just a quicky question,When does ac get classed as rf?,is it when the frequency is above the threshold of hearing,ive often wondered but never seen it explained anywhere,cheers paul m3vuv 73.

Paul,

Interesting question for sure.

Because you can radiate very low frequencies and the threshold of hearing has nothing to do with it, you are going to have to define RF.

However if by any chance you are referring to RF in the Radio Waves context (to be radiated), here in the U.S, anything above 9 kHz is considered Allocated Radio Spectrum.

[TheUnnamedNewbie]

For me, the idea of 'RF' is related to wavelength - when you are dealing with transmission-line effects and such, you are dealing with RF. Hence, when working with discretes, RF can go down to pretty low frequencies (down to a few kHz when working on very large installations with large arrays and long transmission lines). When working on-chip, even a few GHz might not really appear as RF (unless you design the LNA or output buffers, where you might have to transmission line effects into account).

I don't know many people working on 5 GHz digital integrated circuits who consider themselves doing RF...

[tggzzz]

For me, the idea of 'RF' is related to wavelength - when you are dealing with transmission-line effects and such, you are dealing with RF. Hence, when working with discretes, RF can go down to pretty low frequencies (down to a few kHz when working on very large installations with large arrays and long transmission lines). When working on-chip, even a few GHz might not really appear as RF (unless you design the LNA or output buffers, where you might have to transmission line effects into account).

I don't know many people working on 5 GHz digital integrated circuits who consider themselves doing RF...

Inside such a chip it is analogue and distributed digital (i.e. no single clock domain). Outside the chip it is analogue and microwave RF.

[rsjsouza]

I always made the distinction based on the type of wave regardless of the frequency involved.

If it is designed to produce mechanical waves through a transducer such as a loudspeaker, ultrasonic sensor, mechanical delay lines, sonar, etc. it is not Radio Frequency.

Otherwise, whenever the intention is to have a "transducer" that sends electromagnetical waves through a medium (ether, eire, waveguide), that is Radio Frequency.