Technical Topics > Propagation
So you think you are are beginning to understand propagation?
Josh:
So much par up there it melted the shuttles kite string that one time.
https://rationalwiki.org/wiki/STS-75_incident
jasonRF:
--- Quote from: NQC on December 16, 2021, 1225 UTC ---Hey All,
FASCINATING INFO !!!
I read along time ago( a bit fuzzy now) about ULF /whistler/ sferics being "conducted" down "tubes" in the magnetosphere and actually getting a measure of natural AMPLIFICATION from incoming solar radiation ,so far , the only known example of NATURAL radio amplification (??).
I also just read /printed a Hardcore Dx Medium Wave Propagation article by KN4LF, good stuff there.
de N1NQC
--- End quote ---
Yup - the whistlers are essentially guided along one of the Earth's magnetic field lines, and can bounce back and forth between the hemispheres. It is possible to estimate the integrated electron density along the propagation path by looking at the shape of the whistler in a frequency-time spectrogram of ground-based measurements of these waves. Some researchers at Stanford mapped out the plasmasphere using these kinds of measurements before their work was corroborated by later spaceborne measurements (I want to say back in the 1950s or 1960s, and cannot recall the researchers name!).
There are actually a bunch of different instabilities in plasmas that cause waves to grow. Most of the naturally produced plasma waves in the ionosphere and magnetosphere start out as thermal noise that is amplified by these instabilities (whistlers generated by lightning are a notable exception). Some of these plasma waves are electromagnetic, while some are so-called 'electrostatic' waves that have a negligible magnetic component. A couple of decades ago I was in graduate school studying these kinds of waves using instrumentation on spacecraft. I've been fascinated by the ionosphere and magnetosphere for a long time, so it is kind of weird that I am just now getting interested in shortwave!
jason
UncleJohn:
--- Quote from: jasonRF on December 28, 2021, 1635 UTC ---
--- Quote from: NQC on December 16, 2021, 1225 UTC ---Hey All,
FASCINATING INFO !!!
I read along time ago( a bit fuzzy now) about ULF /whistler/ sferics being "conducted" down "tubes" in the magnetosphere and actually getting a measure of natural AMPLIFICATION from incoming solar radiation ,so far , the only known example of NATURAL radio amplification (??).
I also just read /printed a Hardcore Dx Medium Wave Propagation article by KN4LF, good stuff there.
de N1NQC
--- End quote ---
Yup - the whistlers are essentially guided along one of the Earth's magnetic field lines, and can bounce back and forth between the hemispheres. It is possible to estimate the integrated electron density along the propagation path by looking at the shape of the whistler in a frequency-time spectrogram of ground-based measurements of these waves. Some researchers at Stanford mapped out the plasmasphere using these kinds of measurements before their work was corroborated by later spaceborne measurements (I want to say back in the 1950s or 1960s, and cannot recall the researchers name!).
There are actually a bunch of different instabilities in plasmas that cause waves to grow. Most of the naturally produced plasma waves in the ionosphere and magnetosphere start out as thermal noise that is amplified by these instabilities (whistlers generated by lightning are a notable exception). Some of these plasma waves are electromagnetic, while some are so-called 'electrostatic' waves that have a negligible magnetic component. A couple of decades ago I was in graduate school studying these kinds of waves using instrumentation on spacecraft. I've been fascinated by the ionosphere and magnetosphere for a long time,
so it is kind of weird that I am just now getting interested in shortwave!
jason
--- End quote ---
Don't Forget To Bring Your Aluminum Hat! ::)
NQC:
Aluminum lets through too much of the bad energy used to read my thoughts.
I've gone over to a pure copper hard hat now :) !
Josh:
You need ferrous materials to block rf best, a viking helmet would be a good start.
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