Radio wave quality at night

Discussion in 'Wireless & RF Design' started by jaygatsby, Dec 17, 2012.

  1. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
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    I remember hearing that satellite links could be noisier in warm or cold weather, I forget which. And I used to have a point to point wifi bridge that spanned a couple of meters, that would drop out every night. That was solved by replacing the whip antennas with directional antennas.

    My question: does cold weather, warm weather, humidity, etc. affect the radio signal strength or SNR?

    Thanks
    J
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    You had to use directional antennas to get a link working that only spanned a couple of meters? Unless these were uncommonly low power links, there was probably something else going on.

    Yes, radio propagation is affected by all kinds of things. Generally, the warmer things are the more electrically noisy they are. There is generally more sun-induced interferrence during the day then at night. Humidity and moisture, either in the air or condenced on the antenna, can have significant impacts in certain RF bands, particularly microwave bands, because of resonant adsporbtion peaks. The list goes on and on.
     
  3. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
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    Correction: couple of hundred meters.
     
  4. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
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    What might have made it drop out at night? This was in the desert...

    I thought I remembered from satcom school something about sat links being noisy at night, i always thought it was from attenuation due to denser air or something like that.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    It is misleading to think of EM waves having different degrees of "quality". They are all essentially the same. What you are referring to is called propagation. This is the study of things that either attenuate or propagate EM waves, primarily as a function of frequency.

    The thing which makes HF (3-30 MHz) attractive for long range communications is the ability of the D, E, and F layers of the ionosphere to reflect EM waves arriving at a certain angle of incidence back toward the Earth. It is known that at night the F-layer separates in to a pair of sublayers at different altitudes. This leads to two different ranges where communication is possible with dead spots in between. For example I might be able to talk to people at a range of 1100-1300 miles and to people from 2750-2950 miles, but I can't talk to anybody across town, in between the two ranges, or farther away than 2950 miles.

    As we move into the VHF (30-300 MHz) range it is the transparency of the ionosphere that makes these frequencies attractive for space communication.

    There are also propagation modes that come and go, seemingly at random, called "Tropospheric Ducting" and "Sporadic E-skip"

    In the UHF (300-3000 MHz) range is where atmospheric scattering plays an increasing role due to the typically narrow beamwidths of the antennas.

    The higher you go in frequency the more challenging it is raise the power of the transmitted signal and the more difficult it is to focus the power of the signal and make it propagate where you want it to go and amplify it when it gets there.
     
    Last edited: Dec 17, 2012
  6. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
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    What about the LOS wifi shot that went out at night? The quality changed, as im SNR, due to presumably something about the atmosphere

    Thanks
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    It was just explained.

    At night the local area you are in contains not only the all the local radio and Television transmissions, but also those which cannot be received during daylight hours. The spectrum becomes more densely populated, or it can also be said to be more 'noisy'.
     
  8. Bouval

    New Member

    Dec 16, 2012
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    There is dew, even in the desert.
    .
     
  9. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
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    Ok, thanks. But aren't frequencies that would propogate differently or further at night much lower than those in my ISM wifi range? Would they still interfere?

    Thanks
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    Any strong nearby RF signal will desensitize a receiver even if the interference is well outside the receiver's passband. It will make your receiver essentially deaf.
     
  11. tinamishra

    New Member

    Dec 1, 2012
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    Nice information is shared here. But If you mean brief surf, the response is that the reduced part of the ionosphere dissapears at night so brief trend alerts then jump off a higher part of the ionosphere and can journey further. Stereo part of the electro-magnetic variety . Stereo surf are separated up into groups by regularity. I think in night time other unusual frequencies reduces so we can listen the radio at mid night much better.
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    Is it just me, or does every one of tinamishra's posts seem like almost random, perhaps even computer generated, babble that is only passingly connected to the discussion? Maybe it is just an english-as-second language issue, but the syntactic strructure seems too good and the semantic content too poor for that to be likely.
     
    Papabravo likes this.
  13. Papabravo

    Expert

    Feb 24, 2006
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    It has the look and feel of a mechanical fuzz phrase generator.
     
  14. jaygatsby

    Thread Starter New Member

    Nov 23, 2011
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    Yes but he echos what posters in this thread say: that the issue of nighttime problems with my signal are due to ionosphere effects. My specialty is not radio, though I spent several years as a technician in it, but I think that the 2.4 GHz ISM band is not going to be interfered with by this. I think that the problem is an issue of night time air density or moisture refraction in the microwave range.
     
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