High Frequencies in Computer CPUs

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    Computer Frequencies
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Discussion Overview

The discussion revolves around the question of why high frequencies (1GHz-3.8GHz) of computer CPUs do not interfere with television signals received via aerials, particularly in the context of VHF and UHF bands. Participants explore the differences in frequency usage between computer processors and television signals, touching on concepts of electromagnetic radiation and signal power.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the gigahertz rating of a computer CPU refers to the number of calculations per second, while the gigahertz for television refers to electromagnetic waves being received.
  • Others argue that the gigahertz in computers and televisions is fundamentally the same, with the main difference being the power of the signals emitted.
  • A later reply questions the assertion that the gigahertz ratings are equivalent, suggesting that a poorly shielded computer could indeed interfere with other electronic devices.
  • Some participants clarify that a computer's GHz rating refers to its clock frequency, while operations per second are measured in FLOPS, indicating a distinction between frequency and computational capability.
  • There is a discussion about whether wireless telephones receive electromagnetic radiation similarly to televisions, with some asserting that they do, while others express confusion over the nature of the signals involved.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the relationship between CPU frequencies and television signals, with no consensus reached on the fundamental nature of the gigahertz measurements or their implications for interference.

Contextual Notes

Some statements reflect uncertainty about the definitions and implications of gigahertz in different contexts, as well as the conditions under which interference might occur. There are unresolved questions regarding the specifics of signal modulation and reception in various devices.

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Hi Everyone,

I just joined the forum and would like to extend a big hello to everyone! I had a look around the forum and it's a treasure trove of information. Congrats to everyone...

I have a question that my father keeps asking and I don't know the answer to this one:

Why don't the high frequencies (1Ghz-3.8Ghz) of computer CPUs interfere with signals from aerials for television? ie, watching TV in the same room on the VHF and UHF band. The aerial would be on the roof.

Anyone know why this might be the case? :shy:
 
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Welcome to the forum, refreshments are available in the back... and watch out for the Evo :P

Anyhow, as for your question, the "gigahertz" your computer talks about is different from the "gigahertz" a television is using. A television is receiving electromagnetic waves that are measured in hertz. When your TV receives a 5gigahertz signal, it is receiving an electromagnetic wave in the air that is also 5gigahertz.

A computer, on the other hand, rates the speed of its processors in hertz as well but not for the same process. 3,000,000,000 hertz (3ghz) means that the processor is making 3,000,000,000 calculations every second. It is not giving off any radiation at 3GHZ like a television is from the CPU.
 
Pengwuino said:
Welcome to the forum, refreshments are available in the back... and watch out for the Evo :P

Anyhow, as for your question, the "gigahertz" your computer talks about is different from the "gigahertz" a television is using. A television is receiving electromagnetic waves that are measured in hertz. When your TV receives a 5gigahertz signal, it is receiving an electromagnetic wave in the air that is also 5gigahertz.

A computer, on the other hand, rates the speed of its processors in hertz as well but not for the same process. 3,000,000,000 hertz (3ghz) means that the processor is making 3,000,000,000 calculations every second. It is not giving off any radiation at 3GHZ like a television is from the CPU.

Couldn't have said it any better, Pengwuino :smile:.
 
I am sorry Penquin, you are entirely wrong. The Gigahertz in a computer is EXACTLY the same as Gigahertz in a telephone or any other broadcast device. The single difference is power. The signal from a computer is very low power.

Now, if you have ever taken the time to open your computer you may notice the copper fingers which surround the open side. The purpose of these is to provide a EM tight enclosure. If you do not have a good enclosure you CAN have interference with other electronic devices.
 
Thank you!
 
Pengwuino said:
Welcome to the forum, refreshments are available in the back... and watch out for the Evo :P

Anyhow, as for your question, the "gigahertz" your computer talks about is different from the "gigahertz" a television is using. A television is receiving electromagnetic waves that are measured in hertz. When your TV receives a 5gigahertz signal, it is receiving an electromagnetic wave in the air that is also 5gigahertz.

A computer, on the other hand, rates the speed of its processors in hertz as well but not for the same process. 3,000,000,000 hertz (3ghz) means that the processor is making 3,000,000,000 calculations every second. It is not giving off any radiation at 3GHZ like a television is from the CPU.
Really 3GHz is the frequency of the clock of the computer. Most operations use several clock cycles and a 3GHz computer makes considerably less than 3 billion calculations by second.
And I agree with Integral that a poorly shielded computer could interfere with communications if it is near enough.
 
Integral said:
I am sorry Penquin, you are entirely wrong. The Gigahertz in a computer is EXACTLY the same as Gigahertz in a telephone or any other broadcast device. The single difference is power. The signal from a computer is very low power.
Now, if you have ever taken the time to open your computer you may notice the copper fingers which surround the open side. The purpose of these is to provide a EM tight enclosure. If you do not have a good enclosure you CAN have interference with other electronic devices.

which is one reason they want you to turn them suckers off in the airplane.
 
Pengwuino said:
The "gigahertz" your computer talks about is different from the "gigahertz" a television is using. A television is receiving electromagnetic waves that are measured in hertz. When your TV receives a 5gigahertz signal, it is receiving an electromagnetic wave in the air that is also 5gigahertz.

A computer, on the other hand, rates the speed of its processors in hertz as well but not for the same process. 3,000,000,000 hertz (3ghz) means that the processor is making 3,000,000,000 calculations every second. It is not giving off any radiation at 3GHZ like a television is from the CPU.
vs.
Integral said:
You are entirely wrong. The Gigahertz in a computer is EXACTLY the same as Gigahertz in a telephone or any other broadcast device. The single difference is power. The signal from a computer is very low power.
Now, if you have ever taken the time to open your computer you may notice the copper fingers which surround the open side. The purpose of these is to provide a EM tight enclosure. If you do not have a good enclosure you CAN have interference with other electronic devices.
Penguino is right! The GHz in a computer is how many calculations per second its microprocessor can do, whereas a TV's GHz has to do with the electromagnetic radiation.

A Hz is simply 100 cycles per second.
 
Integral said:
I am sorry Penquin, you are entirely wrong. The Gigahertz in a computer is EXACTLY the same as Gigahertz in a telephone or any other broadcast device. The single difference is power. The signal from a computer is very low power.

Wait, so a telephone is receiving e/m radiation just like a television's reciever picks up broadcast signals (mind you, not cable TV, just normal broadcast bunny ears tv type signals)? I mean if we're talking about cable tv then yes you are right, however I don't understand how you are right if we are talking about broadcast signals from local stations wirelessly (like how a radio works).
 
  • #10
Mk said:
vs.
Penguino is right! The GHz in a computer is how many calculations per second its microprocessor can do, whereas a TV's GHz has to do with the electromagnetic radiation.
No, GHz is the frequency of the clock. Operations per second is flop (floating point operations). A computer able to do one billion operations per second would be labelled as 1 Gflop. Each operation needs, in general, several cycles of clock to be performed.
A Hz is simply 100 cycles per second.
No, 1 Hz is 1 cycle per second.
 
  • #11
Mk said:
A Hz is simply 100 cycles per second.
1 hz is 1 cycle per second
 
  • #12
SGT said:
No, GHz is the frequency of the clock. Operations per second is flop (floating point operations). A computer able to do one billion operations per second would be labelled as 1 Gflop. Each operation needs, in general, several cycles of clock to be performed.

I thought it was the other way around, each cycle could do multiple operations...
 
  • #13
Pengwuino said:
Wait, so a telephone is receiving e/m radiation just like a television's reciever picks up broadcast signals (mind you, not cable TV, just normal broadcast bunny ears tv type signals)? I mean if we're talking about cable tv then yes you are right, however I don't understand how you are right if we are talking about broadcast signals from local stations wirelessly (like how a radio works).
A wireless telephone receives EM radiation exactly as a radio or television receiver. The information (sound or video) modulates a high frequency carrier (hundreds of kHz in AM radio, tens of MHz to a few GHz in FM radio, television and cell phones). The signal is demodulated at the receiver in order to recover the information.
 
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  • #14
SGT said:
A wireless telephone receives EM radiation exactly as a radio or television receiver. The information (sound or video) modulates a high frequency carrier (hundreds of kHz in AM radio, tens of MHz to a few GHz in FM radio, television and cell phones). The signal is demodulated at the receiver in order to recover the information.

I assume he meant a wired telephone or else i would have expected him to say "cell phone".
 
  • #15
Pengwuino said:
I assume he meant a wired telephone or else i would have expected him to say "cell phone".
Even in a wired phone, your voice is digitized and mixed with the voices of other people by modulating a high frequency carrier.
And most people now use cordless phones. In a cordless phone, the base receives the incoming signal and uses it to frequency modulate a carrier and transmit it to the handset. The carrier frequency goes from several hundreds of MHz to a few GHz.
 
  • #16
Yah but a television is receiving radio waves floating around in the air while wired telephones and computers are sending electronic signals through a wire/silicon track.
 
  • #17
The Hz rating of a Cpu tells you how fast the CPU clock is and not how many operations per second that CPU does. The operations per second has a relationship to the clock speed but also depends on the number of transistors the CPU has.

Anyway basically the clock speed depends on the physical constraints the manufacture of the chip imposes. That is the time taken for the chip to complete one cycle of its computation (which generally takes more than one) is limited by how far apart the resistors etc are because it takes a finite time to send an electrical signal down a particular path.
 
  • #18
Pengwuino said:
Yah but a television is receiving radio waves floating around in the air while wired telephones and computers are sending electronic signals through a wire/silicon track.
The current in a wire moves according to an electric field and the moving electrons generate a magnectic field, so in a wire, in the air or in vacuum we have allways a varying electromagnectic field.
 
  • #19
Pengwuino said:
Wait, so a telephone is receiving e/m radiation just like a television's receiver picks up broadcast signals (mind you, not cable TV, just normal broadcast bunny ears tv type signals)? I mean if we're talking about cable tv then yes you are right, however I don't understand how you are right if we are talking about broadcast signals from local stations wirelessly (like how a radio works).
I do not have a cell phone but I do have older technology 900Mhz portable phones. These are so common that I do not even consider an old fashioned hard wired phone. To communicate with the base station my phone broadcasts a weak 900MHz signal.

What ever speed your computer is operating at, mine is ~2GHz, that clock rate must be an actual signal produced by the motherboard. It is an electromagnetic signal carried mainly by the traces on the motherboard but it is impossible to constrain that frequency to the conductors alone. There will always be some power in electromagnetic radiation surrounding the conductors. This signal is essentially broadcast. It is a very weak signal but a signal none the less.
 
  • #20
Well I'm talking about the old old old phones that are actually hard wired into the wall :D
 
  • #21
Pengwuino said:
Well I'm talking about the old old old phones that are actually hard wired into the wall :D

Even an old fashioned hard wired Telephone must produce some EM around the wires carrying the signal. It is not in the GHz or perhaps even in the RF range, but it is there. Keep in mind that ALL conducting wires are surrounded by a magnetic field. If the signal the wire is transporting is changing then so is the surrounding magnetic field. A changing magnetic field implies EM radiation. The frequency of the EM radiation will be determined by the frequency content of the signal on the wire. This is basic, inescapable physics.
 
  • #22
Clock speed vs CPU speed has become quite a marketing game. See for instance

http://www.computeruser.com/articles/daily/12,84,1,0801,03.html

Back in 2001, AMD changed its CPU model numbering to reflect performance levels as opposed to actual clock speeds.

From an Electromagnetic interference standpoint, the speed of the clock signal is probably not going to be as important as the speed that the bus operates at, as the clock would feed only one pin on the CPU, and the bus would feed long wires which radiate better.

As of this writing, the current speed demons are the AMD Athlon XP 3200+ and Intel Pentium 4 3.0GHz. The 3200+, based on the AMD's Barton core, is a 2.2GHz CPU that runs on a 400MHz FSB, features 512K of L2 cache, and is built on a 0.13-micron copper fabrication process. Intel's 3.0GHz CPU operates on an 800MHz, quad-pumped FSB, and features 512 KB of full-speed L2 cache and is built on 0.13-micron technology.

It is quite true that a CPU has to be shielded to avoid interference with TV's. The fast rise-times of signals in CPU's allow them to radiate multiple harmonics of the fundamental frequency. Problems with interference are not unheard of in the real world - sometimes this is due to poor shielding on the CPU, sometimes it's due to the TV being sensitve to signals outside the broadcast band range.

For completeness, I ought to look up the TV broadcast bands, but I have to run to the store before they close.
 
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