[Aavso-sid-list] Too close, too far?

[ChrisAtUpw at aol.com]

In a message dated 20/02/2006, samouce2 at netscape.com writes:

A couple of  questions:
Q.  How close is too close to avoid the VLF ground  wave?
Q.  How far is too far not to receive the reflected VLF  signal?



Hi Dusty,
 
    How long is a piece of string?
    For a rough guide see _http://mariottim.interfree.it/_ 
(http://mariottim.interfree.it/)  and  click on 'A DCF77 Radio Clock Receiver'. The ground wave 
strength  depends on the terrain between you and the transmitter. Flat terrain 
 and water both help. Mountains tend to be obstructive.
    In answer to your questions, I would guess a  minimum distance of about 
500 km and a maximum distance of 2,500 km (without a  'skip'). I have received 
DCF77 at 2000 km perfectly well during the day, on  the far side of a mountain 
range. The things which muck up reception are  thunder storms and more 
especially local RFI - including radiation from PC  monitors.
    
    Hope this helps,
 
    Regards,
 
    Chris Chapman
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