Topband: propagation differences

[Carl K9LA]

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