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Groups > sci.physics > #533995
| From | Thomas 'PointedEars' Lahn <PointedEars@web.de> |
|---|---|
| Newsgroups | sci.physics |
| Subject | Re: long antenna |
| Date | 2015-11-18 22:56 +0100 |
| Organization | PointedEars Software (PES) |
| Message-ID | <4736856.kWDMch3Bm0@PointedEars.de> (permalink) |
| References | <d82a6d99-39d1-4eb7-9aa0-4ed38641537a@googlegroups.com> <n2fsm5$ms8$1@speranza.aioe.org> |
Odd Bodkin wrote: > On 11/17/2015 12:42 PM, RichD wrote: >> During my workout yesterday, I attached a 3 meter >> extension to the earphone cord of my radio, as I >> wanted to place it at a distance. >> The cord is the antenna. >> >> I was indoors, where the reception is usually crummy. >> I figured the longer line should improve performance, >> right? No! The reception was barely decipherable. >> >> Can anyone explain the physics here? > > Yeah, it's pretty simple. The earphone is attached to an OUTPUT of the > radio. The only valuable place to stick an antenna is on an INPUT to the > radio. Wrong. > Signals-->||-->Tuner-->Amplifier-->Analog driver-->||-->Earphones > <----------- Radio -------------------> > > See where the antenna goes? Not only is your answer wrong, you also missed the point of the question. As the OP indicated, earphone (also: headphone) cords contain wires which can serve as antennas. [They certainly do with smartphones (from where I know the technology): Once you have plugged the headphones into the smartphone, you can start a radio app to tune in to FM (frequency modulation) radio channels (*without an Internet connection*). [0] It stands to reason to use the same technology elsewhere.] How does radio, how does an antenna work? Radio is based on the transmission and reception of radio waves carrying information piggybacked on them through modulation of them. Radio waves are electromagnetic (EM) waves with frequencies from ca. 3 kHz to 300 GHz. [1] EM waves can be understood as self-propagating waves of self-inducing electric and magnetic fields. [2] An electrical current in an conductor creates a magnetic field (MF) around it (Ørstedt, 1820; see: electromagnet). If it is an oscillating current, the result is an oscillation in the surrounding MF, which induces an oscillating electric field (EF) which creates an oscillating MF and so on, propagating through space: an EM wave. So far for the transmitter, at the radio station. Also, a change in the MF around a conductor, such as a wire, induces a current in it (Faraday, 1831). [3] In particular, with a radio receiver, “when radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor” (Hertz, ca. 1880). [1] AIUI, a conductor serves best as an antenna (either for transmission or reception of radio waves) if its electrical resonance frequency matches approximately the frequency of the radio waves to be received. [4] The electrical resonance frequency f₀ of a conductor is given by the angular frequency ω₀ = 1∕√(LC) where L is the inductance and C is the capacitance of the conductor, and ω₀ = 2πf₀, so that f₀ = ω₀∕2π = 1∕(2π√(LC)). [5] The inductance of a coaxial cable [6a] is L = µ₀l∕2π ln(R₂∕R₁) where µ₀ – vacuum permeability l – length of the cable R₂ – half of the thickness of the cable (also a₁, outer radius) R₁ – half of the thickness of the conductor (also a, inner radius). [6b] The capacitance of a coaxial cable is C = 2πεl∕ln(R₂∕R₁) where additionally ε is (absolute) permittivity (ε = ε_r ε₀, whereas the relative permittivity ε_r depends on the material, and ε₀ is the vacuum permittivity). [7a][7b] So both the inductance and the capacitance of a conductor increase with length, which means that its electrical resonance frequency decreases with length. Or, IOW, since wavelength λ = c∕f, where f is frequency, “Antennae length is proportional to the wavelength of reception.” [0] Therefore, the longer line does _not_ improve reception quality of a particular radio channel (its station transmitting at a particular frequency) to begin with. I also think that the longer the line the more likely that there is interference, i.e. alternating, partially canceling electrical currents induced at different points of the cable as the (peak of the) radio waves can hit the cable at those points at different times, and interference from other sources. Finally, electrical resistance of a conductor R = ρl∕A, where ρ is the material-dependent electrical resistivity and A is the cross- sectional area, is proportional to the length l of the conductor [8], so the signal that reaches the tuner should become weaker as the cable length increases. However, I understand that there are also traveling wave antennae that are nonresonant, like random wire for receiving shortwave radio. [9] So it appears to depend on the frequencies that one wants to receive. I would like someone with experience in radio technology to add their expertise here. And please, CMIIW. PointedEars ___________ [0] <https://www.quora.com/How-headphones-work-as-an-Antenna-to-play-FM-radio-channels-on-Mobile-phones-Why-mobile-companies-doesnt-install-the-same-inbuilt-Antenna-on-phones-to-be-able-to-play-FM-without-the-headphones> [1] <https://en.wikipedia.org/wiki/Radio> [2] <https://en.wikipedia.org/wiki/Electromagnetic_radiation> [3] <https://en.wikipedia.org/wiki/Electromagnetic_induction> [4] <https://en.wikipedia.org/wiki/Antenna_(radio)#Antenna_types> [5] <https://en.wikipedia.org/wiki/RLC_circuit> [6a] <https://en.wikipedia.org/wiki/Coaxial_cable> [6b] <https://en.wikipedia.org/wiki/Inductance#Self-inductance_of_simple_electrical_circuits_in_air> [7a] <https://en.wikipedia.org/wiki/Capacitance#Capacitance_of_simple_systems> [7b] <https://en.wikipedia.org/wiki/Permittivity> [8] <https://en.wikipedia.org/wiki/Electrical_resistance_and_conductance#Relation_to_resistivity_and_conductivity> [9] <https://en.wikipedia.org/wiki/Antenna_(radio)#Traveling_wave> p. -- Q: How many theoretical physicists specializing in general relativity does it take to change a light bulb? A: Two: one to hold the bulb and one to rotate the universe. (from: WolframAlpha)
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long antenna RichD <r_delaney2001@yahoo.com> - 2015-11-17 10:42 -0800
Re: long antenna Odd Bodkin <bodkinodd@gmail.com> - 2015-11-17 12:46 -0600
Re: long antenna Poutnik <poutnik4nntp@gmail.com> - 2015-11-17 20:10 +0100
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-17 20:28 +0000
Re: long antenna benj <nobody@gmail.com> - 2015-11-17 16:59 -0500
Re: long antenna Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-18 22:56 +0100
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-18 16:57 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-18 23:15 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-18 20:42 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-19 05:29 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-19 08:54 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-19 18:44 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-22 15:32 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-22 23:16 +0000
Re: long antenna HVAC <mr.hvac@gmail.com> - 2015-11-19 06:59 -0800
Re: long antenna benj <none@gmail.com> - 2015-11-19 20:02 -0500
Re: long antenna benj <none@gmail.com> - 2015-11-19 01:36 -0500
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-17 13:28 -0600
Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-17 14:04 -0800
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-17 22:35 +0000
Re: long antenna benj <nobody@gmail.com> - 2015-11-17 19:28 -0500
Re: long antenna Timo <timo@physics.uq.edu.au> - 2015-11-17 17:18 -0800
Re: long antenna RichD <r_delaney2001@yahoo.com> - 2015-11-24 11:39 -0800
Re: long antenna benj <none@gmail.com> - 2015-11-24 15:12 -0500
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 09:21 -0600
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 10:05 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 20:05 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 18:39 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-27 01:46 +0000
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 19:55 +0000
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-24 20:04 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-24 16:33 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-24 22:58 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 09:11 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 19:42 +0000
Re: long antenna "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2015-11-26 11:57 -0800
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 14:52 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 21:12 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 18:58 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-27 01:37 +0000
Re: long antenna benj <none@gmail.com> - 2015-11-26 23:45 -0500
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-27 01:01 -0600
Re: long antenna "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2015-11-26 23:31 -0800
Re: long antenna benj <nobody@gmail.com> - 2015-11-27 11:34 -0500
Re: long antenna "Ross A. Finlayson" <ross.finlayson@gmail.com> - 2015-11-27 09:58 -0800
Re: long antenna benj <nobody@gmail.com> - 2015-11-27 11:46 -0500
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-28 16:42 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-28 22:58 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 07:46 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-30 19:01 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 14:12 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-30 20:43 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 17:41 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-12-01 00:15 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 20:23 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-12-01 06:21 +0000
Re: long antenna benj <none@gmail.com> - 2015-11-30 15:22 -0500
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-30 20:48 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 17:16 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-30 23:52 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-30 19:59 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-12-01 02:16 +0000
Re: long antenna benj <none@gmail.com> - 2015-11-30 19:20 -0500
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-27 18:53 +0000
Re: long antenna benj <none@gmail.com> - 2015-11-25 00:08 -0500
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-25 06:13 +0000
Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-18 16:25 -0800
Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-19 16:08 -0800
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-20 00:40 +0000
Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-20 15:51 -0800
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-21 00:34 +0000
Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-21 14:37 +0000
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-21 19:32 +0000
Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-22 14:50 +0000
Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-22 11:27 -0800
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-22 19:44 +0000
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-22 19:40 +0000
Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-23 14:13 +0000
Re: long antenna benj <none@gmail.com> - 2015-11-23 13:00 -0500
Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-24 13:20 +0000
Re: long antenna benj <none@gmail.com> - 2015-11-24 13:40 -0500
Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-25 13:44 +0000
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-23 18:47 +0000
Re: long antenna jmfbahciv <See.above@aol.com> - 2015-11-24 13:20 +0000
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-24 19:49 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-24 16:36 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-24 23:00 +0000
Re: long antenna gilber34 <fafa@invalid.com> - 2015-11-26 16:17 -0600
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-26 23:35 +0000
Re: long antenna benj <none@gmail.com> - 2015-11-20 20:58 -0500
Re: long antenna benj <none@gmail.com> - 2015-11-19 20:09 -0500
Re: long antenna "nuny@bid.nes" <Alien8752@gmail.com> - 2015-11-24 12:51 -0800
Re: long antenna benj <none@gmail.com> - 2015-11-25 00:01 -0500
Re: long antenna "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-25 15:36 -0800
Re: long antenna jimp@specsol.spam.sux.com - 2015-11-25 23:51 +0000
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