Topband: Daylight QSO's during the SP

Carl K9LA k9la at
Mon Dec 31 15:47:07 EST 2007

Chas N5UL said:

> I worked F6IRA/p at 2325Z on the 29th. My local sunset
> followed at 2355Z. The next DX I heard (and worked) was
> CT1JLZ at 2356Z.

I believe many will agree that this is not an uncommon scenario - 
especially in the winter months with high solar zenith angles (the Sun 
is low on the horizon).

What's important is where the electromagnetic wave encounters the D 
region, and the elevation angle involved. A low elevation angle wave 
will spend more time in the D region, whereas a high elevation angle 
wave will pass through quickly with less absorption.

If a low elevation angle was involved in N5UL's QSOs, then it would 
start encountering the D region roughly over central Kansas - about 
where the terminator is at 2325 UTC on Dec 29 along the path from N5UL 
to F. The path being in daylight from N5UL to the terminator is not the 

The other possibility is a ducted signal coming out at a high elevation 
angle. The high angle would likely be due to the pronounced tilt in the 
ionosphere on the N5UL end.

Carl K9LA

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