ka3jjz
Wiki Admin Emeritus
Some of you that have gotten (or will be getting) SW rxs from Santa may not realize that hearing HF broadcasts - whether we're talking broadcast, Utility, hams, ect.- are dependent on having a path between where you are and what you want to hear. In a broad sense, (and yes, this is highly generalized), propagation between 2 points on the globe is possible when;
a. Both you and the target are in daylight, and the freq is above 10 mhz or so (somewhat lower in the winter)
b. Both you and the target are in darkness, and the freq is below 10 mhz
c. You are in local sunset, while the target is experiencing dawn -or-
d. The opposite condition exists - you are at local sunrise, and the target is experience sunset.
Conditions c and d are very generally referred to as gray line, and due to the fact that the ionsphere is is a state of flux (due to either the loss of, or the acquiring of sunlight), DX on certain bands between the 2 points is possible for a period of time. There has been numerous very technical articles written on the subject, and this description only scratches the very surface of the subject.
How do you know when this is happening? There are several tools now available to allow you to actually view a Mercator map which shows sunrise/sunset times all over the planet. Probably among the best known is GeoClock; something I found out about some time ago, and has attracted some European interest is a screen saver called Sunclock. I've added these utilities to the propagation sections of the SWL and utility wikis.
Some of the more powerful HF receiver control packages such as SWLog and Ergo contain built in utilities for calculating paths between 2 points. These can be found on the Strong Signals software page links found in both of the wikis mentioned above.
There have been numerous articles and books written on the subject of propagation and solar effects. Don't feel bad if you think that it's a lot of information to absorb, because it is. But getting an even basic understanding of the subject will allow you to begin to understand how and why you hear something on hf...
or don't.
73s Mike
a. Both you and the target are in daylight, and the freq is above 10 mhz or so (somewhat lower in the winter)
b. Both you and the target are in darkness, and the freq is below 10 mhz
c. You are in local sunset, while the target is experiencing dawn -or-
d. The opposite condition exists - you are at local sunrise, and the target is experience sunset.
Conditions c and d are very generally referred to as gray line, and due to the fact that the ionsphere is is a state of flux (due to either the loss of, or the acquiring of sunlight), DX on certain bands between the 2 points is possible for a period of time. There has been numerous very technical articles written on the subject, and this description only scratches the very surface of the subject.
How do you know when this is happening? There are several tools now available to allow you to actually view a Mercator map which shows sunrise/sunset times all over the planet. Probably among the best known is GeoClock; something I found out about some time ago, and has attracted some European interest is a screen saver called Sunclock. I've added these utilities to the propagation sections of the SWL and utility wikis.
Some of the more powerful HF receiver control packages such as SWLog and Ergo contain built in utilities for calculating paths between 2 points. These can be found on the Strong Signals software page links found in both of the wikis mentioned above.
There have been numerous articles and books written on the subject of propagation and solar effects. Don't feel bad if you think that it's a lot of information to absorb, because it is. But getting an even basic understanding of the subject will allow you to begin to understand how and why you hear something on hf...
or don't.
73s Mike
