What Are the Limits of Frequency and Current for Wireless Device Antennas?

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Discussion Overview

The discussion revolves around the limits of frequency and current for wireless device antennas, exploring theoretical and practical constraints related to transmission and reception. Participants consider aspects of electromagnetic theory, antenna design, and the implications of frequency and current on efficiency and performance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how low a frequency and how high a current a wireless device can transmit, referencing radio frequencies and the generation of current in antennas.
  • Another participant suggests consulting the electromagnetic spectrum chart to understand the boundaries of radio signals.
  • It is proposed that while there are no theoretical limits to frequency and current, practical limits exist based on transmitter power and antenna size.
  • A participant mentions that a low-frequency transmitter could theoretically deliver high currents, but practical limitations arise from the size of the antenna required.
  • Concerns are raised about the implications of coiling antennas, including increased inductance and resistance to changes in current, which may affect signal amplitude.
  • Discussion includes the concept of tuning circuits to specific frequencies and the potential practical limits on capacitance in such circuits.
  • Another participant notes that while the number of turns in a coil affects how the antenna is driven, it does not necessarily improve efficiency.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement regarding the theoretical limits of frequency and current, with some asserting that practical constraints exist while others emphasize the absence of theoretical limits. The discussion remains unresolved on several technical points.

Contextual Notes

Participants mention various assumptions, such as the relationship between antenna size and efficiency, the impact of inductance on signal transmission, and the financial implications of achieving high capacitance. These factors contribute to the complexity of the discussion.

mtanti
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I have a weird question I think... I'de like to know how low a frequency and how high a current can a wireless device transmit.

eg, radio frequency is over 1000s of Hz, can it be much lower than that?When you receive a radio signal to an antenna, a small current is generated which is interpreted as sound. How high can that current be?

If there's no limit to the amperage generated at the receiving end, how can you calculate it?
10x!
 
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well, just check the electromagnetic spectrum chart, somewhere higher or lower, it won't be a radio signal anymore.
 
It's not a weird question at all.

There are no limits. But there are practical limits. For example, if you start
off by saying that you have a 1 MegaWatt transmitter, then you can determine
how large your antenna has to be if you fix the frequency in order to achieve
a certain efficiency.

You can make a 0.00001 Hz tansmitter and deliver billions of amps through
the antenna. Just not on the Earth because the planet is too small to hold the
antenna.
 
re

low frequency antenna don't have to be a long piece of wire, you can have large coil of wire that when unwound is just as long.
 
what said:
low frequency antenna don't have to be a long piece of wire, you can have large coil of wire that when unwound is just as long.

I'm not an electrical engineer, so this is partly a question. It seems to me that coiling the antenna would give it a higher inductance, and therefore a higher resistance to change in current. Doesn't that limit the amplitude of the signal you can transmit/receive?

Also, I was thinking about the frequency of the receiving circuit. From what I've heard, you "tune" to a specific frequency by creating a circuit that has a natural frequency at that of the desired radiation, creating a resonance. Might there be practical limits to the natural frequency of this circuit? How large can one make a capacitance in practice?
 
The area of the coil would have to go up in order for it to be an efficienct radiator.
The number of turns won't make it more effieicient but it would change the way
you would drive the antenna. Look up "Radiation Resistance" to discover how.

The practical limit on capacitance is set by your budget. Bill Gates could
afford many many Farads.
 

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