Does it still amaze you that radio works?

Discussion in 'Wireless & RF Design' started by KL7AJ, Dec 23, 2015.

  1. KL7AJ

    Thread Starter AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    An S-9 H.F. signal arriving at the input terminals of a shortwave receiver has on the order of 25 PICOWATTS of power. Down at the noise threshold, the signal is on the order of a few dozen FEMTOWATTS.

    After half a century I am still intrigued by the fact that you can slosh a few electrons up and down a coat hanger and be heard thousands of miles away. If this still doesn't amaze you, you have no soul.

    Eric
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,544
    2,369
    Another amazing feat is the capability of a Satellite station that can keep in sync with my Dish!.
    On the other end of the spectrum was Rugby Radio, conceived in 1910 to transmit to anywhere in the British Empire and later to communicate with a submarine a couple of fathoms anywhere under water.
    The normal working voltage of the aerial was 165,000 volts r.m.s. and the current at the base of the aerial was about 750 amps. The earth system consisted of an open network containing about 120 miles of copper wire buried a few inches in the ground and occupying a space of 1600 feet wide under the length of the aerial.:cool:
    Max.
     
  3. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,908
    2,168
    Lost my soul a long time ago.:)
     
    absf likes this.
  4. Willen

    Member

    Nov 13, 2015
    138
    12
    It feels like I have multiple souls, every part and everything related to electronics amazes me horribly! :)
     
    atferrari likes this.
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,045
    3,811

    Could you calculate the wattage of the signal coming from the Rosetta spaceship flying next to the comet for the past 13 months.

    http://www.space.com/27697-rosetta-comet-landing-full-coverage.html
     
  6. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,908
    2,168
    http://blogs.esa.int/rosetta/2014/08/05/tracking-the-spacecraft-following-a-comet/
    What amazes me is not radio but how our radio signals are so distinctly human in their nature that we can resolve them from naturally generated signals at levels below the noise level. Our signals are differ from most natural signals by being neither random or regular. The generation of deterministic signals with changing patterns is the sign of intelligent communication. When we want to hide our radio signals we mimic nature with deterministic randomness that looks like noise unless you have the key, So maybe what we think is space radio noise is intelligent communication between beings, we just lack the proper key to decode it.
     
    Last edited: Dec 30, 2015
    sailorjoe likes this.
  7. BR-549

    Well-Known Member

    Sep 22, 2013
    1,987
    388
    That's find for secure signals, but what about a beacon. How do you get someones attention?

    You broadcast on an unnatural frequency. Right smack dab between the 1st and 2nd energy levels of the H atom. Any intelligent life will investigate that.

    However I would not recommend it. Even though I don't believe in alien life, I could be wrong.

    Life is predatory.
     
    nsaspook likes this.
  8. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    763
    Nice to hear someone still using those units. thumbsup.gif Last time I did, it was maybe 20 or 25 years ago, if not more.
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,789
    945
    Can you fathom the archaic units of furlongs per fortnight?

    Yeah. Neither can I. :)
     
  10. KL7AJ

    Thread Starter AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    I LOVE your term "deterministic randomness." I've always asserted that what we call noise is only "random" because we don't have the processing power to decode all the wave parameters at once...such as phase, direction of travel, polarization, etc. Nature abhors random.
     
  11. KL7AJ

    Thread Starter AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    I still measure wavelength in cubits. :) (MY cubit happens to be exactly half a meter, which is quite convenient for paying out dipole wires. :) )
     
  12. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,908
    2,168
  13. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    763
    It is measured with the middle finger extended?

    I know that in a pinch I can estimate measurements using de distance between my thumb and little finger with my hand open and flat (gives between 21 and 22 cm).
     
  14. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,908
    2,168
    We are limited in our of 'decoding' of random noise sources by two operational factors that constrain us.
    1. No FTL communication in signal locality. The measurements we take are constrained by time to the past not present. In practical systems this limits our resolution.
    2. Predictability of outcomes. The assumption that one can predict the outcomes of all possible measurements. In practical systems this limits our accuracy.

    These limit the classical computability of determinism at some scale. We can only measure to see probabilities, not the exact nature of the source function. If it is impossible to signal faster than light then it is impossible to predict the outcomes of all experiments even if there is some underlying hidden model causing randomness that is deterministic. So for us nature is random (the uncertainty principle/perfect predictability) at the quantum scale.

    Perfect predictability is the one nut we can't crack.
     
    Last edited: Jan 1, 2016
  15. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,805
    833
    After converting to metric, my finger span is between 22 and 23cm (9"). My stride is 5 feet. A US Dollar bill is 6" long...
     
    atferrari likes this.
  16. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,805
    833
    Are you familiar with cellular automata theory. There are systems defined by simple rules, that produce randomness. See Wolfram and Rule 30. So underlying models can produce randomness.
     
  17. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,908
    2,168
    I'm not saying physical models can't be random or look random at the limits of our technology. I'm saying there are limits to our ability to compute (reversibility) true randomness or even Chaos at some scale. Rule 30 is described as chaotic so small changes in the initial conditions can create events that look random due to our inability to perfectly predict outcomes.
     
  18. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,805
    833
    I did not mean to imply that you believed models could not be random or look random. I was just presenting cellular automata theory (CAT) as an example of a model that produced randomness. As you mentioned and I agree, there are limits to our ability to compute true randomness or even understand random events. Supposedly, a good source of randomness is atmospheric noise. See http://random.org/
     
  19. nsaspook

    AAC Fanatic!

    Aug 27, 2009
    2,908
    2,168
    Sure, cellular automata theory is one method of many to generate a 'Pseudorandom' number in a computer. Some are cryptographically secure and can be used to secure radio and communications in general. The streams generated from cellular automata methods like rule 30 (as a PRNG function) are not as there is a correlation and fault attack to reverse the Stream Cipher and recover the secret initial conditions.
    http://mathworld.wolfram.com/RandomNumber.html
     
    Last edited: Jan 1, 2016
Loading...