Robert11 wrote:

Hi,

New at this.

Just want to be sure that I have this correct -

"In general," listening is better in daylight hours Above 10 MHz, or so.

And, in the evenings, below 10 MHz,

Is this correct ?

Thanks,
B.


Yes. The sun produces more free charged particles in the ionosphere. That gives
two effects.

First, low frequencies (like MW) are reflected by charged layers all day. Somewhere
in the shortwave band is a frequency high enough so it doesn't reflect; the more
charged the ionosphere, the higher this frequency needs to be. Higher frequencies
than this cutoff proceed into space and don't return.

So in the day, more and more frequencies are reflected, from low to some high frequency
cutoff.

Second, charged particles take energy from the wave, and reradiate it a quarter cycle
later (which is how charged particles refract the waves in the first place, and
enough refraction constitutes the reflection). In picking up energy, the particles
move, and if the atmosphere is dense enough, they collide with the air and give up
their energy unreradiated. This means that the wave loses energy and disappears.
``Attenuation.''

Low frequencies move the particles more, and so encounter attenuation before high
frequencies.

The sun charges up lower denser layers of the ionosphere, and soon MW waves, which
would reflects if they continued, instead get absorbed first by the newly charged
lower levels. Higher frequencies still make it through to reflection.

Thus : absorption kills off low frequencies in the day, even though they always
reflect.

Reflection adds newly-reflected high frequencies in the day.


So, in the day, go to higher frequencies; in the night, go to lower frequencies.

An X-ray event, if severe enough, will charge up enough of the ionosphere so that
everything is absorbed, and it's called a radio blackout, meaning distance radio.
--
Ron Hardin


On the internet, nobody knows you're a jerk.