Propagation Primer Part 1: Beyond the Numbers

[KL7AJ]

Many new hams...or at least hams new to H.F. are mystified or intimidated by solar forecasts. Although solar numbers are important, they fail to take into account local variables....most importantly local MAGNETIC variables. In fact, most propagation software totally ignores the Earth's magnetic field, which only lends to the confusion.

The Earth's magnetic field does two major things, which cannot be ignored. Solar numbers do nothing to address these issues.

#1) Magnetic fields create non-reciprocal propagation paths.
#2) Magnetic fields invalidate the great circle "path of least resistance."

At moderate latitudes, these factors are often not noticed....at high latitudes they become all-important factors in H.F. Propagation.


Next up...... X and O modes. a condensed version of my QST article "Gimme an X, Gimme an O, What's that spell? Radio"

Stay tuned!


Eric

[N7SMI]

You've introduced the problem of magnetic fields very well. So how do you account for this?

I'm upgrading from a vertical to a beam very soon, so suddenly what was previously just "propagation" will soon be "propagation paths" to me as I'll want to know where to point the thing. There's no question that a good chunk of the populated world (Europe, Africa, Southern Asia) lies on the other side of the magnetic pole for most of us here in the Northern US.

[KL7AJ]

You've introduced the problem of magnetic fields very well. So how do you account for this?

I'm upgrading from a vertical to a beam very soon, so suddenly what was previously just "propagation" will soon be "propagation paths" to me as I'll want to know where to point the thing. There's no question that a good chunk of the populated world (Europe, Africa, Southern Asia) lies on the other side of the magnetic pole for most of us here in the Northern US.

I hope you got to read my March QST article, "Three Wrong Assumptions about the Ionosphere." I mention the importance of asking the distant station if you're pointed the right direction for best reception on HIS end! It may not be what gives YOU the strongest received signal!

Eric

[KL7AJ]

Forgot to mention. The magnetic field not only makes the Absorption non-reciprocal, but it also makes the azimuth skewing (departure from Great Circle direction) non-reciprocal! It can get pretty radical up here!

Eric

[N7SMI]

I hope you got to read my March QST article, "Three Wrong Assumptions about the Ionosphere."

I did. And just reviewed it again. And your X's and O's article. Excellent pieces. Now that I realize that this is what you are referring to, most of my questions have been answered.

I mention the importance of asking the distant station if you're pointed the right direction for best reception on HIS end!

This doesn't work particularly well if you're trying to bust a pile-up to some remote location. You'd need to know the optimal direction (and perhaps, as you note, elevation as well) before you start transmitting. It seems that this delta in azimuth is likely too complex to simply calculate based on ionospheric and magnetic conditions, and that typical beam width is probably wide enough that it doesn't matter too much for most of us, but it's still a very interesting problem to think about.

[KL7AJ]

I did. And just reviewed it again. And your X's and O's article. Excellent pieces. Now that I realize that this is what you are referring to, most of my questions have been answered.



This doesn't work particularly well if you're trying to bust a pile-up to some remote location. You'd need to know the optimal direction (and perhaps, as you note, elevation as well) before you start transmitting. It seems that this delta in azimuth is likely too complex to simply calculate based on ionospheric and magnetic conditions, and that typical beam width is probably wide enough that it doesn't matter too much for most of us, but it's still a very interesting problem to think about.

Hee hee! No, a pileup wouldn't be the place to try this out...but for nice DX ragchchewint it should make an interesting topic of discussion!

Eric

[N7SMI]

How consistent and stable would the affects of magnetic fields be on propagation? In other words, if the time of day and ionospheric conditions were essentially the same, would you expect the same azimuth delta from day to day? If not, and if there's no way to really calculate the magnetic effects, it seems there's not much to apply here except "sometimes the great circle bearing isn't always the best, so slew right or left a bit to see if receive conditions improve."