abc@BRL-TGR.ARPA (09/12/84)
From: Brint <abc@BRL-TGR.ARPA> >re-Re: wavelength vs size of antenna >My AM radio is about 1/3000 the size of the wavelengths that it >receives. -- >Gene E. Bloch (...!nsc!voder!gino) And it receives a 50,000 watt signal probably no more than 10-15 miles away! Brint <abc@brl> ----- End of forwarded messages
gino@voder.UUCP (Gino Bloch) (09/18/84)
## >re-Re: wavelength vs size of antenna ## >My AM radio is about 1/3000 the size of the wavelengths that it ## >receives. -- ## >Gene E. Bloch (...!nsc!voder!gino) ## And it receives a 50,000 watt signal probably no more than 10-15 ## miles away! ## Brint ## <abc@brl> Pocket radios can receive signals from kilomiles away (I've seen [heard] it). Especially 50KW clear channel, of course. What power will USN use? Five watts? More? -- Gene E. Bloch (...!nsc!voder!gino)
rcd@opus.UUCP (Dick Dunn) (09/18/84)
> >re-Re: wavelength vs size of antenna > > >My AM radio is about 1/3000 the size of the wavelengths that it > >receives. >... > And it receives a 50,000 watt signal probably no more than 10-15 miles > away! Nice misinterpretation of both intent and facts. Oh, sure, it's true that the little radio will receive the 50Kw signal 10 miles away. It will also receive a 1 Kw station 20 miles away--a factor of 100-200, but who's counting? The interesting fact is that the same little radio can, under some circumstances, receive a 1 Kw signal from 1000 miles or more. My point (lest I be misconstrued as well as >> (Gino)) is that you really DON'T need an antenna that's a large fraction of a wavelength; you just have to work on it a little harder. It means that you might not be able to use $5 AM radio technology in your underwater ELF receiver. -- Dick Dunn {hao,ucbvax,allegra}!nbires!rcd (303)444-5710 x3086 ...Never offend with style when you can offend with substance.
dnc@dartvax.UUCP (David Crespo) (09/29/84)
i am curious about how antennae reception works, in light of the recent discussion on the subject...what i guess happens is that the changing field (transmitted) innduces the electrons in the metal to act as if there (oopss) were a voltage, etc., so that the ac current in the radio is then the signal. of course, I am not really sure how this carries the information, i.e. am not sure how this gets tied into carrier waves (fm), or how the tuner (lrc circuit--resonance, ho!) can tell the main frequency(oscillations) from the modulations about that frequency (is the frequency (i.e. 1010WINS on your radio dial) an average frequency?) , and more to teh point, what ARRE the limits on antennae, size, shape, materials, construction, direction....also, what are the effects of the medium in which the waves pass...what are the determining factors: conductivity, dielectricity, resistance, capacitance, inductance, salinity, pH, law of averages, density, temperature, pressure, (volume?), specific gravity, (gee this is fun), reluctance, dissenting opinion, homogeneity, reynold's number, young's modulus, serendipity, esp: salt water vs. fresh, i think the thought about the antennae size may have been a "misapplication" of the reasoning that comes up around diffraction and the relationship between the size of the wave and the object (hole in a diffraction grating)... the hole must be about the size of the wave for diffraction to occur (light as a wave), versus the other wtwo cases (shadows and insignificance). what is the coupling between the electr field and the antennae...is that the question? anyhow....this is all to much, fun, that is, but for the person out there, wherever you are, looking for + or -i terms on your feynman graph to propagator terms in your ahamiltoninan, the following towo books on field theory and particle physics contains sketches and derivations of these factors... first...Introduction to Particle Physics, by Omnes at Orsay 2nd.....Particles and Fields , by Lurie also, there is a recently published book called something like Quarks and Leptons:an Introduction, but author is at best, forthcoming. I mean, i have to go back to where I saw it, not that it was written before its time, or in vilation of causality, though that would bne a book indeed apropriately written. dnc over and out