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16717Re: HUM_FORUM: Re: VLF interesting info discovery!

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  • sandnella
    Mar 1, 2013
      Good article Jim......Last year, a low frequency experimental radio enthusiasts was posting on this forum.  He was trying to steer the group away from radio waves.  When I called him out.....he denied being on other web sites having to do with " Experimental Radio"....Then he dropped off this forum.  Strange isn't it ? 
      I personally think the Hum hearing has to do with location on the planet.  I moved away from my Hum.  I can never go home again.

      From: Jim <w4jbm@...>
      To: humforum@yahoogroups.com
      Sent: Fri, March 1, 2013 6:06:18 AM
      Subject: HUM_FORUM: Re: VLF interesting info discovery!


      McGreevy is, simply put, one very, very smart and very, very active
      radio experimenter. His BBB-4 receiver is fairly easy to build, uses
      readily available parts, and does a good job. The one thing I would say
      is that the "earth sounds" tend to be totally swamped by man-made noise
      unless you get out in the open with no powerlines or homes within a
      quarter to a half mile. NASA used to have an earth sounds receiver you
      could listen to on-line but it hasn't been working in some time. (There
      are recordings at the NASA site, you can google it and find the site.)

      McGreevy also was involved in deploying some very low-power beacons on
      shortwave. A nightlight is typically around 4 watts and he used powers
      more like 1/10 of a watt. Conventional wisdom would be that something
      like that might be heard sporadically a few dozen miles away. In fact he
      was the inspiration for a group of PiFERs. (LowFERs are "Low Frequency
      Experimental Radio" enthusiasts and hobiest who focus on frequencies
      below 500 kHz or so and PiFERs are "Pirate Frequency Experimental Radio"
      enthusiasts who deploy solar powered "pirate" [unlicensed] beacons
      around the country. A few years back I logged low-power PiFER beacon
      from the Pacific Northwest here in Atlanta--something a lot would argue
      was a fluke, except I did it for several mornings over a two week period
      with decent reception.)

      One thing I will say about low frequency radio is that reception tends
      to be noticeably better in the winter when the leaves are off the trees.
      Most low frequency signals attenuate quickly through foliage. They
      operate higher in frequency, but anyone who is interested in learning
      more about low frequency radio should google NDB or "non directional
      beacons". These are low-power transmitters used at airports and is kind
      of a vintage "direction finding" technology. In theory they should only
      be heard a few dozen miles away also, but I (and many others) have
      logged NDBs from hundreds and thousands of miles. (I can regularly
      receive the Caribbean and Canada as well as many beacons in the mid-West.)

      The Longwave Club of America is another resource. (Low frequency means
      you have a "long wavelength" while higher frequencies become
      "shortwave"--this is kind of dated terminology in terms of radio
      frequencies today but came into use well before the second world war.)

      I actually think the "whistlers" may have something to teach us about
      some cases of the hum--they are believed to be caused by the radio
      wave-front caused by a lightning strike "colliding" with itself coming
      from different directions after traveling around the world each way. In
      engineering terms this would be "multi-path hetrodyning". A similar
      effect could occur with audio waves or even shifts in atmospheric
      pressure. There was some discussion about peoples perception of the hum
      as they climbed to higher altitudes that would be consistent with some
      kind of "audio multi-path hetrodyning".


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