Re: AM Radio Receiver based on Spin Exchange Relaxation Free mechanism
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Posted by Mike Kaliski on July 5, 2007, 6:19 am
Please log in for more thread options The simplest answer is no. The reason is that you specify 'distant'. The strength of a magnetic field decays rapidly with distance and for most practical purposes, 800 metres would be a maximum typical detection range for man made magnetic fields as opposed to natural fields like the earth's magnetic field. Man made fields can be many times thousands of times stronger than the earth's magnetic field at a local level, but the field strength decays rapidly as you move away from the source. A friends father experimented with a factory machinery control system using induction coils a foot long and about 8 inches in diameter wound with thousands of turns of thin copper wire. The maximum reliable communication distance with this set up was only 200 yards. This was 35+ years ago and detection techniques have improved considerably. The reason for the experiment was to try and develop a control system that could work in the presence of very high strength RF fields. This was superceded by the development of fibre optic cabling which was not susceptible to RF pickup. Communication using the magnetic field element of electromagnetic waves is best demonstrated by the 'molephone' devices used to communicate with cavers underground. See the following link for details and try googling cave rescue, underground communications, and molephone for more links. http://www.scavalon.be/avalonuk/technical/radio1.htm Squids and other highly sensitive magnetic field detectors can be used to detect the most minute distortions or changes in the earths magnetic field but are not suitable for communications use. It is possible to build a magnetometer at home that is so sensitive that it will pick up disturbances in the earth's magnetic field caused by solar activity for less than $100. This is not however going to be capable of receiving and demodulating 150kHz radio signals. It doesn't really matter what frequencies you want to receive, 44kHz, 150kHz, 150MHz or what the modulation method is, a diode (or two) and a tuned circuit are essentially at the heart of all receiving and demodulating systems. They are cost effective, reasonably efficient and they work. Why would you want to spend a million dollars to receive signals that can be picked up (probably a lot better) on a ten dollar consumer radio? Modulation methods, frequencies and bandwidths are chosen by commercial broadcasters to meet specific demands, e.g. limited bandwidth available for broadcasting, high fidelity music broadcasts, high efficiency powerful signals that can punch through interference, etc, etc. The basic rule is to get the job done as cheaply, efficiently and as quickly as possible. Mike G0ULI | |||||||||||||||||||||||||||||||
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Posted by on July 5, 2007, 9:25 pm
Please log in for more thread options <snip>
> Agreed, static magnetic fields tend to decay rapidly as you move away
> from them. However, alternating magnetic fields continue to propogate > by generating alternating electric fields of the same frequency. These > alternating electric fields, in turn, generate alternating magnetic > fields. The cycle keeps repeating. Nonsense as stated. You have no understanding of the differences between: 1. A magnetic field 2. An electric field 3. An electromagnetic field. -- Jim Pennino Remove .spam.sux to reply. | |||||||||||||||||||||||||||||||
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Posted by John Larkin on July 12, 2007, 11:52 am
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On Fri, 06 Jul 2007 01:25:02 GMT, jimp@specsol.spam.sux.com wrote: >
><snip> > >> Agreed, static magnetic fields tend to decay rapidly as you move away
>> from them. However, alternating magnetic fields continue to propogate >> by generating alternating electric fields of the same frequency. These >> alternating electric fields, in turn, generate alternating magnetic >> fields. The cycle keeps repeating. >
>Nonsense as stated. No, it's just a qualitative restatement of Maxwell's theorems. Changing e-field makes H-field, changing H-field makes e-field, and they toodle off into the sunset at the speed of light. John | |||||||||||||||||||||||||||||||
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Posted by Rich the Philosophizer on July 12, 2007, 1:29 pm
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On Thu, 12 Jul 2007 08:52:24 -0700, John Larkin wrote: > On Fri, 06 Jul 2007 01:25:02 GMT, jimp@specsol.spam.sux.com wrote:
>>
>><snip> >> >>> Agreed, static magnetic fields tend to decay rapidly as you move away
>>> from them. However, alternating magnetic fields continue to propogate >>> by generating alternating electric fields of the same frequency. These >>> alternating electric fields, in turn, generate alternating magnetic >>> fields. The cycle keeps repeating. >>
>>Nonsense as stated. >
> No, it's just a qualitative restatement of Maxwell's theorems. Changing > e-field makes H-field, changing H-field makes e-field, and they toodle off > into the sunset at the speed of light. Exactly. The Yin calls forth the Yang, and in their cosmic dance, they create Manifestation. ;-) Cheers! Rich -- For more information, please feel free to visit http://www.godchannel.com | |||||||||||||||||||||||||||||||
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Posted by Jeff Liebermann on July 6, 2007, 1:25 am
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>Radio waves are made up of electric and magnetic fields.
Yep. >Couldn't the Spin Exchange Relaxation Free Magnetometer receive the
>magnetic portions of AM radio waves at the carrier frequencies I >described? If not, why? Nope. 1. The range of the magnetic field is limited. For example, you're not going to bounce (errr... refract) a magnetic fields off the ionosphere. 2. Magentometers use very big coils. Very big coils have lots of inductance. Resonant circuits with lots of inductance tend to resonate at very low frequencies. Figure on maybe 30Hz being the highest frequency detectable by a magnetometer. Most roll off even earlier to avoid 60Hz power line pickup. 3. Magnetometers are expensive. You're proposing using one as a replacement for a 5 cent silicon diode detector. If the technology doesn't get to you, the accountants will. >Agreed, static magnetic fields tend to decay rapidly as you move away
>from them. However, alternating magnetic fields continue to propogate >by generating alternating electric fields of the same frequency. These >alternating electric fields, in turn, generate alternating magnetic >fields. The cycle keeps repeating. Rubbish. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 | |||||||||||||||||||||||||||||||
>
> Can the Spin Exchange Relaxation Free Magnetometer be used to receiver
> distant AM radio signals in which the carrier frequency is 150 KHz?
> What if the carrier frequency is 44.1 KHz [for the same reason CDs use
> a 44.1 KHz sample rate]? 40 KHz?
>
>
> Thanks a bunch,
>
> Radium
>