4 ms·

I’m somewhat confused. I’ll admit that I’m not very familiar with super high frequency radio, but isn’t the difference at least 200 MHz, approximately 10 times

I’m somewhat confused. I’ll admit that I’m not very familiar with super high frequency radio, but isn’t the difference at least 200 MHz, approximately 10 times larger than the entire FM radio spectrum? Doesn’t out-of-band emission stop being a problem at that much separation? Or should we look at it relative to the base frequency? edit: For what it's worth, I found this paragraph from the FCC last year: https://www.federalregister.gov/d/2018-14806/p-20 https://www.federalregister.gov/d/2018-14806/p-20 It sounds like they're saying "we don't know if this will be a problem yet, but be prepared to limit emissions in 23.6-24ghz range because we might require it at some point". Also, paragraph 9 of the same document has the actual band limits (with a special requirement) if anybody is interested: > The 24 GHz band consists of two band segments: The lower segment, from 24.25-24.45 GHz, and the upper segment, from 24.75-25.25 GHz > any mobile or transportable equipment capable of operating in any portion of the 24 GHz band must be capable of operating at all frequencies within the 24 GHz band, in both band segments

borkt 7y ago
"At the high end of the electromagnetic spectrum, signals travel over a band of 10 million trillion Hz (that is, 10^22Hz). This end of the spectrum has phenomenal bandwidth, but it has its own set of problems. The wave forms are so miniscule that they're highly distorted by any type of interference, particularly environmental interference such as precipitation. Furthermore, higher-frequency wave forms such as x-rays, gamma rays, and cosmic rays are not very good to human physiology and therefore aren't available for us to use for communication at this point." Not the best analysis but I'm working. Basically like any other metric, as the frequency increases the space between peaks and valleys decreases and it becomes harder to determine/separate from others 30hz to 230hz is much easier to tell the difference than 15khz to 15.2khz if you want to listen to audio tones. Once you get to microwaves this becomes of course much more difficult. http://www.informit.com/articles/article.aspx?p=24687&seqNum=4 http://www.informit.com/articles/article.aspx?p=24687&seqNum...
- oceliker 7y ago
  To me, this analysis sounds more about the interference with physical objects (like how 2.4ghz can pass through walls easier than 5ghz). It doesn't seem to be about interference with other radio emissions? > 30hz to 230hz is much easier to tell the difference than 15khz to 15.2khz if you want to listen to audio tones That's definitely true for humans, but I don't think it necessarily applies to radio signals in general (though it does make sense at first glance).
ummonk 7y ago
It should definitely be looked at relative to the base frequency.
staticfloat 7y ago
While bandwidth is typically measured in absolute Hz difference due to the spread directly relating to the amount of information-carrying capacity, when you are actually generating signals many things scale with carrier frequency. The way most of these signals are being generated is through an "information signal" (usually referred to as a modulator) being created within your device, then moved up in frequency by combining it with a "carrier signal". This separation allows the information signal's properties (such as bandwidth, modulation scheme, bitrate/Hz, etc...) to be more-or-less independent from the physical characteristics of propagation, which will be more strongly related to the carrier signal's properties (e.g. water absorption, reflection/transmission off of/through materials, etc...). However, no process is perfect, and although we would like to generate perfect signals, we can't. Distortion appears in multiple parts of this pipeline, both in the generation of the low-frequency modulator and the high-frequency carrier. Distortion typically comes from "linear" components not being perfectly linear and thereby generating harmonics of the signal passing through them. In the case of the modulator, this splatters signal energy up and down the spectrum on the order of the bandwidth of the modulator, but in the case of the carrier it does so on the order of the carrier frequency. This is all a matter of degree and depending on the application may not be that big a deal, but it definitely must be addressed for high-density communications equipment like cell networks. All transmitters have filters at multiple stages of their signal processing chains, both lowpass filters that filter the modulator before it's mixed with the carrier signal to boost it up in frequency, as well as bandpass filters that ensure the output stays within the bounds it's meant to be; but these filters only do so much and they can be expensive to create (as they can have rather fine physical tolerances) so everybody is always just playing the "do the best job we can for the least money" game. Luckily, most transmitters are also connected to antennae that provide a convenient filtering on the output (they only resonate at the frequencies they transmit at) which helps for specialized systems that only operate at a single transmit frequency, but for something like 5G is less helpful, due to the many channels it supports, causing the antenna to necessarily support a wide range of frequencies.

borkt 7y ago

"At the high end of the electromagnetic spectrum, signals travel over a band of 10 million trillion Hz (that is, 10^22Hz). This end of the spectrum has phenomenal bandwidth, but it has its own set of problems. The wave forms are so miniscule that they're highly distorted by any type of interference, particularly environmental interference such as precipitation. Furthermore, higher-frequency wave forms such as x-rays, gamma rays, and cosmic rays are not very good to human physiology and therefore aren't available for us to use for communication at this point." Not the best analysis but I'm working. Basically like any other metric, as the frequency increases the space between peaks and valleys decreases and it becomes harder to determine/separate from others 30hz to 230hz is much easier to tell the difference than 15khz to 15.2khz if you want to listen to audio tones. Once you get to microwaves this becomes of course much more difficult. http://www.informit.com/articles/article.aspx?p=24687&seqNum=4 http://www.informit.com/articles/article.aspx?p=24687&seqNum...

oceliker 7y ago
To me, this analysis sounds more about the interference with physical objects (like how 2.4ghz can pass through walls easier than 5ghz). It doesn't seem to be about interference with other radio emissions? > 30hz to 230hz is much easier to tell the difference than 15khz to 15.2khz if you want to listen to audio tones That's definitely true for humans, but I don't think it necessarily applies to radio signals in general (though it does make sense at first glance).

ummonk 7y ago

It should definitely be looked at relative to the base frequency.

staticfloat 7y ago

While bandwidth is typically measured in absolute Hz difference due to the spread directly relating to the amount of information-carrying capacity, when you are actually generating signals many things scale with carrier frequency. The way most of these signals are being generated is through an "information signal" (usually referred to as a modulator) being created within your device, then moved up in frequency by combining it with a "carrier signal". This separation allows the information signal's properties (such as bandwidth, modulation scheme, bitrate/Hz, etc...) to be more-or-less independent from the physical characteristics of propagation, which will be more strongly related to the carrier signal's properties (e.g. water absorption, reflection/transmission off of/through materials, etc...). However, no process is perfect, and although we would like to generate perfect signals, we can't. Distortion appears in multiple parts of this pipeline, both in the generation of the low-frequency modulator and the high-frequency carrier. Distortion typically comes from "linear" components not being perfectly linear and thereby generating harmonics of the signal passing through them. In the case of the modulator, this splatters signal energy up and down the spectrum on the order of the bandwidth of the modulator, but in the case of the carrier it does so on the order of the carrier frequency. This is all a matter of degree and depending on the application may not be that big a deal, but it definitely must be addressed for high-density communications equipment like cell networks. All transmitters have filters at multiple stages of their signal processing chains, both lowpass filters that filter the modulator before it's mixed with the carrier signal to boost it up in frequency, as well as bandpass filters that ensure the output stays within the bounds it's meant to be; but these filters only do so much and they can be expensive to create (as they can have rather fine physical tolerances) so everybody is always just playing the "do the best job we can for the least money" game. Luckily, most transmitters are also connected to antennae that provide a convenient filtering on the output (they only resonate at the frequencies they transmit at) which helps for specialized systems that only operate at a single transmit frequency, but for something like 5G is less helpful, due to the many channels it supports, causing the antenna to necessarily support a wide range of frequencies.