time difference / atmosphere

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AlphaFive

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Here is a question that occupies my mind at times. I have the most basic understanding that for a low frequency transmission (anything well below 30Mhz.) to travel it's longest distance, the best atmospheric conditions would generally be after dark, and cold...
With that most basic understanding, the question arises, as to who should have the cold and dark? The transmitter, or the receiver? Say, it is 4:00 a.m. EDT in New York City, someone has their fantastic receiver up and functioning. But, it is 10:00 in the morning in Norway, the sun is well up for the day. For the transmission to be successfully received, will the sun being out in Norway negatively affect the transmission? Or, does the fact the receiver is still in the cool darkness overcome that hardship at the transmission site?
Help my simple mind grasp this concept. Thank you.
 

ka3jjz

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The temperature really has nothing to do with HF propagation, but the seasons on the other hand certainly do. Activate your Flash player and study this presentation...

Propagation Primer - Flash Movie by AE4RV

Now how and when you hear a station is determined by a lot of factors; but perhaps the easiest to understand is the sunrise / sunset connection. As a general rule - there are exceptions to this that are a bit more complex to understand, and I'll get to that in a moment - for stations above roughly 10 Mhz, both stations need to be in daylight; below that, both stations need to be in darkness.

The exceptions? The most common one is the one that happens every day. If the station you want is approaching dusk, and you're approaching dawn, there is a short window - from where we are, it lasts roughly 10-15 mins - where the ionosphere is in flux. Even tho your target station is dark, and you are approaching light, there is a small chance you might hear them; but as I mentioned, it doesn't last long. The opposite condition is also true.

There are a number of other variables - activity on the sun causing disruptions in our ionosphere, for example - but these are, by far, the easiest to understand

Mike
 

AlphaFive

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atmosphere

Thank you very much for the information. I genuinely appreciate it. I have my first receiver set up coming in August. I am really looking forward to learning as much as I can. Take care.
 
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