Topband: DX Conditions

[Jim Brown]

On 12/20/2024 7:36 AM, Mark Lunday wrote:
> I was watching on my waterfall  and DL8LAS would go from unreadable to Q5 copy and then disappear again in 10 seconds.

This is the fading which back when AM radio was all there was was called 
"selective fading, and on VHF/UHF FM is called "picket fencing" when a 
mobile station is involved. No matter the frequency, it is the result of 
the transmitted signal arriving at the receiver via more than one path 
(usually two), and thus with different travel times. Phase is directly 
related to time, so the phase difference between the two arrivals is 
continuously rotating over the full 360 degrees. When the two arrivals 
have close to zero phase difference, the station is loud, when close to 
180 degrees the station is weak. The weaker the station becomes, the 
closer the two arrivals are to the same strength. The greater the 
difference in the distance of the two paths, the faster the fading. 
Likewise, the higher the frequency band, the faster the fading.

73, Jim K9YC