Hi Jay a steady increase in the apparent reflection height ....or the
waveguide width depending on which model you use? Its not a lot different to
the higher vlf or eveb LF bands. A pi/2 phase shift requires a change in
height of about 12kn for a single hop but at your range it is probably only
4km which is quite possible. Particularly after a geomagnetic event I have
seen steady increases like this as the precipitated electrons recombine (I
think) but an event may not actually be necessary. Nice plot !!

Alan G3NYK

----- Original Message ----- 
From: <[email protected]>
To: <[email protected]>
Sent: Wednesday, April 14, 2010 1:04 PM
Subject: LF: VLF...alpha long selective fade?


> Been monitoring / plotting the alpha stations over the past couple weeks
while working to improve
> the VLF receiving setup. The following very slow 'selective fade' has been
seen every night that
> I've looked (4 times) so it's not a one off occurrence. Anyone care to
speculate on what would cause
> this?
>
> Full screen here: http://www.w1vd.com/capture/alphafade1.jpg . Condensed
version as an attachment.
>
> Jay W1VD  WD2XNS  WE2XGR/2
>