Propagation Question Re AM or PM State ?

[BOBRR]

Hello,

Was wondering about this:

It's generally agreed, I think, that propagation in general
is better in the "Daytime" above 12 MHz or so, and in the "Evening" below that.

Does this refer to, e.g., where the:

Transmitter is ?
Receiver is ?
Or both should have the same "condition" ?

Thanks,
Bob

 

[ka3jjz]

As a very general rule, both the transmitter and receiver should be in the same daylight condition for propagation to work. This is because the F1/F2 layers of the ionosphere are needed for frequencies above 10 Mhz to propagate. This is due to solar radiation.

However at night the 2 F layers merge and become one. Then the lower frequencies will propagate. These frequencies are heavily attenuated by the D layer, and during the day, only short distances are possible here

If the sun is very active, as it was in the 80s, daylight propagation would continue until several hours into the night, due to heavy increases in solar radiation. I can remember hearing Tahiti on 19 meters as late as 02 UT. That was when I was living in your neck of the woods....Mike

 

[BOBRR]

Hi,

Thanks.
I was never certain if both trans and receiver should have the same condition.

Good info; clearer for me, now.

Best regards,
Bob

 

[Boombox]

It's dependent on the prevalence of daylight or nighttime between the transmitter and the receiver -- and then you've got the 'grey line', which is the zone where it's dawn or dusk at either location.

 

[majoco]

Boombox said:

and then you've got the 'grey line', which is the zone where it's dawn or dusk at either location.

I disagree, the 'grey line' is a ring around the world that is dawn or dusk at the same time. I often track the late afternoon dusk line here in NZ and it passes over southern Europe's dawn - catching the ham callsigns on 80 and 40 metres from Greece (not many) over Italy (heaps), France, Spain a few Portuguese then.... nothing!

On the map you can see the gray line over NZ, bottom right passing over Japan and over the Northern poles and down through Northern Germany, France, Spain and Portugal. It's shown as a sharpish line on the map but in fact it may be about an hour wide.