Bob W7LR asked
>What does the propagation curve look like between 1.8,
>1.99, and 3.5 ?
>
That's an interesting question, and it involves how refraction,
absorption, and polarization change with frequency. Noise would also
have to be considered.
One way to gain some theoretical insight into this question is to do a
ray trace (using a program that takes into account the Earth's magnetic
field and electron-neutral collisions) over a simple one-hop path. The
result of this exercise for a 1257 km path in darkness in winter at
solar minimum gives the following results (these results do not address
polarization, though).
freq elev angle absorption
1.82 13.5 deg 10.84 dB
1.99 13.2 deg 8.8 dB
3.52 22.5 deg 1.52 dB
This theoretical analysis of a simple path, along with considering
noise, suggests 1.99 MHz could have a noticeable advantage over 1.82 MHz.
Some real-world measurements would indeed be helpful to assess this
analysis.
Carl K9LA
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