Re: [IRCA] Reviewing SDR Recordings & Western DX Questions

[Barry McLarnon <bm@xxxxxxxxxxxxxxxx>]

On 01/12/2014 02:45 PM, Russ Edmunds wrote:
>   <<Since my primary interest is in Western US stations, I
>   assume that sunset is going to be the most productive for
>   me, correct? >>
>
> Not necessarily. I routinely can hear KOA-850 here on the car radio around local sunrise here
> on an all-darkness path on my car radio.
>
> With western DX as your objective, sunrise might actually be better for you.

Agreed.  Around sunrise, there can be a nice "western window" of 
opportunity.  Think of it in terms of ionospheric propagation: skywave 
is greatly attenuated during the daylight hours due to ionization of the 
D layer, which essentially forms a curtain between the earth's surface 
and the E and F layers that support skywave.  As the sun rises in the 
east, this curtain is being drawn above you from east to west.  This 
means that low-angle skywave signals arriving from west of you are 
suffering much less D-layer absorption than signals arriving from other 
directions, since the latter must penetrate portions of the D layer that 
are already being illuminated and ionized by the sun's rays.

Of course, stations to the west of you at this time are probably still 
on their night facilities, so the window mainly applies to western 
stations that send some signal in your direction at night, but are 
normally covered up by other stations.  And sometimes the window 
persists long enough that you can catch them after they switch to day 
facilities.  A classic example for me was the one and only time I heard 
KWTL-1370 in North Dakota (1020 miles west of me), in November 2008, at 
0900 EST, more than two hours past my local sunrise, when they powered 
up to their 12 KW day power.

Barry

--
Barry McLarnon  Ottawa, ON

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