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I'm a noob regarding radio: do I understand it correctly that low frequency radio signals can more easily be used with more solid carriers while higher frequenc

by _def 5y ago

I'm a noob regarding radio: do I understand it correctly that low frequency radio signals can more easily be used with more solid carriers while higher frequencies allow more/faster bandwidth? (I'm totally oversimplifying here)

williamtwild 5y ago
Yes
ajsnigrutin 5y ago
You need bandwidth to transfer more data (there is a theoretical limit of how much data you can transfer at a given bandwidth with a given signal to noise ratio). The lower you go with frequencies, the larger antennas you need (quarter wavelength is usually the minimum... for FM radio (around 100MHz) it's 75cm which is very realistic length for a car or a house radio... at 14mhz (ham radio freq), it's 5.3 meters, which is still doable if you live in a house, and at 1.8MHz (another ham band) is ~40 meters, which is hard.. going lower is even harder, and special "tricks" are needed. The second problem is the bandwith itself... some wifi equipment supports bands up to 100MHz of width (to simplify, you use all the frequences from eg. 5.1GHz to 5.2GHz), and if you want to stay at low frequencies, it's impossible to create such a wide band, because the antenna sizes are so different at 1MHz and 101MHz, the propagation is different, etc., so usually you're stuck with narrower bandwiths at lower frequencies (and of course, many of the low frequencies are already in use.. eg for fm radio). But generally yes, higher the frequency, more directly (in a straight line) it goes, and you get more losses in stuff between the transmitter and receiver.
- TedDoesntTalk 5y ago
  Can the antennas be coiled to achieve a long length while not being strung , for example, 40 meters? I recall car antennas that used to have coils long ago.
  - namibj 5y ago
    There are coil antennas, but they work magnetically. The 40m straight wire works electrically. The key difference is that the electric antenna interacts with more of the wave, so it's stronger in the far-field, while the magnetic antenna interacts more localized. The latter is why/how NFC works at 13 MHz (23 m wavelength) with an antenna that fits on a credit card.
  - ajsnigrutin 5y ago
    Not really, atleast not the classic designs and if you want to transmit. You can bent them a bit, but the total lenght has to be around the quarter wavelength
  - bigiain 5y ago
    Old school 27MHz CB radios would have 1/4 wave antennas 2.75m tall. In practice, for vehicle mounted use, they'd almost always have bottom or centre coils to allow overall lengths down in the 1.5-2m sort of range, with compromises accepted there for practicalities and convenience. Fixed base stations would often use a "proper" 2.75m antenna though.
- _def 5y ago
  Thanks!
brk 5y ago
Generally speaking, yes. With RF there are a handful of encoding methods, but in very simple terms binary 1's and 0's correspond to the high/low peaks of the frequency. Higher frequencies can therefore transmit data faster because you have more "peaks", and opportunities to encode data per interval of time. Higher frequencies have less power in terms of ability to travel a great distance or through materials. It is very much like audible sounds, you can hear bass notes from someone playing music far away, but you'll lose the highs and then the mids after a relatively short distance. One of the many tradeoffs in RF networks is trading range for throughput.
- zild3d 5y ago
  > but in very simple terms binary 1's and 0's correspond to the high/low peaks of the frequency This is AM, "Amplitude Modulation" Wiki has some good articles on other modulation techniques https://en.wikipedia.org/wiki/Amplitude_modulation https://en.wikipedia.org/wiki/Amplitude_modulation
- _def 5y ago
  Oh the comparison with audible sounds is brilliant, thank you.
colechristensen 5y ago
Bandwidth, literally the width of the band. Don’t think of it as transmitting at one frequency but a range between two, a band. Information rate depends on the width of the band. For example wifi uses 20, 40, or 80 MHz bands. Easy when your signal is around 2.4 or 5 GHz. But you can’t do that at 100 Hz or 100 kHz or 100 MHz because… well the numbers aren’t big enough. You could have a funny radio that transmitted from 1 to 80 MHz, but you wouldn’t say your signal was “at” 100kHz. That make sense?
- _def 5y ago
  Yes thank you!

by _def 5y ago

williamtwild 5y ago

Yes

ajsnigrutin 5y ago

You need bandwidth to transfer more data (there is a theoretical limit of how much data you can transfer at a given bandwidth with a given signal to noise ratio). The lower you go with frequencies, the larger antennas you need (quarter wavelength is usually the minimum... for FM radio (around 100MHz) it's 75cm which is very realistic length for a car or a house radio... at 14mhz (ham radio freq), it's 5.3 meters, which is still doable if you live in a house, and at 1.8MHz (another ham band) is ~40 meters, which is hard.. going lower is even harder, and special "tricks" are needed. The second problem is the bandwith itself... some wifi equipment supports bands up to 100MHz of width (to simplify, you use all the frequences from eg. 5.1GHz to 5.2GHz), and if you want to stay at low frequencies, it's impossible to create such a wide band, because the antenna sizes are so different at 1MHz and 101MHz, the propagation is different, etc., so usually you're stuck with narrower bandwiths at lower frequencies (and of course, many of the low frequencies are already in use.. eg for fm radio). But generally yes, higher the frequency, more directly (in a straight line) it goes, and you get more losses in stuff between the transmitter and receiver.

TedDoesntTalk 5y ago
Can the antennas be coiled to achieve a long length while not being strung , for example, 40 meters? I recall car antennas that used to have coils long ago.
- namibj 5y ago
  There are coil antennas, but they work magnetically. The 40m straight wire works electrically. The key difference is that the electric antenna interacts with more of the wave, so it's stronger in the far-field, while the magnetic antenna interacts more localized. The latter is why/how NFC works at 13 MHz (23 m wavelength) with an antenna that fits on a credit card.
- ajsnigrutin 5y ago
  Not really, atleast not the classic designs and if you want to transmit. You can bent them a bit, but the total lenght has to be around the quarter wavelength
- bigiain 5y ago
  Old school 27MHz CB radios would have 1/4 wave antennas 2.75m tall. In practice, for vehicle mounted use, they'd almost always have bottom or centre coils to allow overall lengths down in the 1.5-2m sort of range, with compromises accepted there for practicalities and convenience. Fixed base stations would often use a "proper" 2.75m antenna though.
_def 5y ago
Thanks!

brk 5y ago

Generally speaking, yes. With RF there are a handful of encoding methods, but in very simple terms binary 1's and 0's correspond to the high/low peaks of the frequency. Higher frequencies can therefore transmit data faster because you have more "peaks", and opportunities to encode data per interval of time. Higher frequencies have less power in terms of ability to travel a great distance or through materials. It is very much like audible sounds, you can hear bass notes from someone playing music far away, but you'll lose the highs and then the mids after a relatively short distance. One of the many tradeoffs in RF networks is trading range for throughput.

zild3d 5y ago
> but in very simple terms binary 1's and 0's correspond to the high/low peaks of the frequency This is AM, "Amplitude Modulation" Wiki has some good articles on other modulation techniques https://en.wikipedia.org/wiki/Amplitude_modulation https://en.wikipedia.org/wiki/Amplitude_modulation
_def 5y ago
Oh the comparison with audible sounds is brilliant, thank you.

colechristensen 5y ago

Bandwidth, literally the width of the band. Don’t think of it as transmitting at one frequency but a range between two, a band. Information rate depends on the width of the band. For example wifi uses 20, 40, or 80 MHz bands. Easy when your signal is around 2.4 or 5 GHz. But you can’t do that at 100 Hz or 100 kHz or 100 MHz because… well the numbers aren’t big enough. You could have a funny radio that transmitted from 1 to 80 MHz, but you wouldn’t say your signal was “at” 100kHz. That make sense?

_def 5y ago
Yes thank you!