[cma-l] Propagation effects

[Ian Hickling]

There are four separate phenomena here and I've done a lot of work on this in the past - mainy with TV signals in Band I and III.The E layer (and also the even higher F layer) in the upper atmosphere become ionised by sunspots and other phenomena and act in a reflective/refractive manner.Sporadic (i e unpredictable) E propagation tends to last quite a long time - sometimes for days - and signals can be received very strongly over large distances.F-layer propagation is much rarer and can extend thousands of miles - such as conveying TV signals across the Atlantic.
The signals bursts which flash and disappear in seconds are caused by meteor scatter - where a very short-lived ionised track is generated by a decaying meteor.It's possible then to receive a series of signals from different sources on the same frequency (or indeed television channel) within just a few seconds as the "mirror" moves across the sky.
Tropospheric ducting (or "trop") is caused by temperature inversion.Static cold air over the Earth's  surface develops a warm upper layer from the Sun's heat and this acts like a tunnel, causing remote signals to curve back down to the surface.Hams often refer to all this erroneously as "lift".
In fact - it's exactly the reverse - as it involves a downward rather than upward movement.

Ian Hickling
Partner

Office: 01635 578435  (7am-11pm UK time)Carphone: 07530 980115 (only responds when driving)6 Horn Street, Compton, NEWBURY, RG20 6QS

From: tlr at gairloch.co.uk
To: cma-l at mailman.commedia.org.uk
Date: Fri, 31 Jul 2015 10:16:49 +0100
Subject: Re: [cma-l] Funky SX and the Lille tranmitter








Yes, as you say, it can work both ways - we 
also got a QSL request email from a DXer in Sweden who'd picked up our 
106.6 broadcasts.
 
Alex

  ----- Original Message ----- 
  From: 
  vwradio at aol.com 
  
  To: cma-l at mailman.commedia.org.uk 
  
  Sent: Friday, July 31, 2015 8:42 AM
  Subject: Re: [cma-l] Funky SX and the 
  Lille tranmitter
  
When we get stations coming in strongly 
  from places like Spain - that's usually caused by sporadic-E. It's a 
  phenomenon where signals bounce off ionized clouds and can last minutes or 
  just seconds. Last month I heard a station from Morocco on FM stronger than 
  our local Heart in Dorset sitting in my car. This is different from the 
  tropospheric effect where French stations start coming in loud and clear. 
  Works both ways though - we got a report of being heard in Sweden on 92.3 via 
  sporadic E. 
  

  The wonders of radio propogation. Nothing you can do about it.

  

  Steve


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Telephone: Office 01202 820003 Studio 01202 
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