6 ms·

The missing word is 'efficiency'. To TRANSMIT a radio signal (and here we don't differentiate between AM, FM, PM or any of the other ways of modulating a radio

The missing word is 'efficiency'. To TRANSMIT a radio signal (and here we don't differentiate between AM, FM, PM or any of the other ways of modulating a radio wave) most efficiently and most cheaply the antenna must be tuned to the signal's frequency/wavelength. To RECEIVE a radio signal, while it's most efficient to have the antenna tuned to the signal's frequency/wavelength, it's mostly not as convenient to do so. If the antenna only picks up 20% of the possible signal, so what? As long as enough signal is received for you to listen to, that's all that matters. (In some cases, where we're not needing portability, like permanent radio-receiving stations we usually do see tuned antennas in use.)

JKCalhoun 5y ago
Yeah, that was how I understood radio. An antenna picks up all radio signals, but it does a much better job of picking up frequencies that are "resonant" with it (based, I had assumed on length alone — it sounds though like I may have been under-informed in this regard). The coil + tuning capacitor (the tank?) is the adjustable filter that selects the frequency from the antenna we want to "tune in to". As you say, crappy antenna will still get something.
- martyvis 5y ago
  Richard Feynman gets very excited about this very fact, that at any point it has ALL of the radio waves, amongst other electromagnetic radiation, that just has to be tuned in or focussed on. https://youtu.be/FjHJ7FmV0M4 https://youtu.be/FjHJ7FmV0M4
  - simonblack 5y ago
    that at any point it has ALL of the radio waves, Which is where the Software-Defined Radio comes into its own. https://en.wikipedia.org/wiki/Software-defined_radio https://en.wikipedia.org/wiki/Software-defined_radio
- ngcc_hk 5y ago
  The issue would then be if the most resonant one is not the one you want, that would be a noise you have to filtered. Whilst practicality mean we can’t be optimal due to size, is it a major matter. Can the filter be efficient or make efficient by electronic. At least in 70s when radio listening is peak, the antenna is key to good reception.
  - simonblack 5y ago
    if the most resonant one is not the one you want, that would be a noise you have to filtered. Which is where the tuned-circuits of the radio's front-end come into play. In a sense the locations of the tuned circuits are not especially critical, in that the tuned-circuit filtering can be at the antenna itself, at the radio-frequency amplification front-end stage, or even at the intermediate-frequency amplification stage. In really good radios you would find tuned-circuits in all of those locations to increase the level of wanted signals and the attenuation of unwanted signals.

JKCalhoun 5y ago

Yeah, that was how I understood radio. An antenna picks up all radio signals, but it does a much better job of picking up frequencies that are "resonant" with it (based, I had assumed on length alone — it sounds though like I may have been under-informed in this regard). The coil + tuning capacitor (the tank?) is the adjustable filter that selects the frequency from the antenna we want to "tune in to". As you say, crappy antenna will still get something.

martyvis 5y ago
Richard Feynman gets very excited about this very fact, that at any point it has ALL of the radio waves, amongst other electromagnetic radiation, that just has to be tuned in or focussed on. https://youtu.be/FjHJ7FmV0M4 https://youtu.be/FjHJ7FmV0M4
- simonblack 5y ago
  that at any point it has ALL of the radio waves, Which is where the Software-Defined Radio comes into its own. https://en.wikipedia.org/wiki/Software-defined_radio https://en.wikipedia.org/wiki/Software-defined_radio
ngcc_hk 5y ago
The issue would then be if the most resonant one is not the one you want, that would be a noise you have to filtered. Whilst practicality mean we can’t be optimal due to size, is it a major matter. Can the filter be efficient or make efficient by electronic. At least in 70s when radio listening is peak, the antenna is key to good reception.
- simonblack 5y ago
  if the most resonant one is not the one you want, that would be a noise you have to filtered. Which is where the tuned-circuits of the radio's front-end come into play. In a sense the locations of the tuned circuits are not especially critical, in that the tuned-circuit filtering can be at the antenna itself, at the radio-frequency amplification front-end stage, or even at the intermediate-frequency amplification stage. In really good radios you would find tuned-circuits in all of those locations to increase the level of wanted signals and the attenuation of unwanted signals.