propagation1

Theoretically, the strongest DX signals arrive and depart our antennas at low angles, typically, between 2 and 8 degrees. The reason for this is that the closer the signal is to the horizon when it leaves the antenna, the less ground-to-ionosphere hops it has to make. Remember, each time the signal hops, it looses energy to the ionosphere and the Earth. This absorption varies with frequency, terrain continuity and D-layer absorption ( daylight paths ) to name a few.

It's difficult to get the main-lobe of an antenna to radiate as low as 2 degrees on HF, but luckily for us, even relatively low antennas transmit and hear a significant amount of RF energy at those low angles. How much energy depends on antenna height and surrounding terrain. The closer we can get the main-lobe of our antennas ( where the gain is ) to "scoop-up" these low-angle signals, the better the Dx performance.

Now that we've got that out of the way - your G5RV at 40 feet would have it's main-lobe at approximately 25 degrees elevation at 14Mhz. At 5 degree angles, the gain of the main-lobe has dropped-off considerably (about -10db ). Below 5 degrees, the antenna is still hearing Dx, but with diminishing signal strength.

You could set the minimum radiation angle parameter higher to reflect this, but, by doing this, your telling the software that your antenna is "deaf" when signals arrive at these angles which isn't the case - the antennas hearing is weak, but not deaf!

The best approach is to expect lower Dx signal strengths for lower antennas, but leave the factory default at 1.5 degrees so you don't miss an opportunity to work any DX path.

When all is said and done, there are ALLOT of tall-tower and multi-element DX stations on the air and there is always the opportunity to work Dx, and plenty of it, with the other guys station doing most of the work!

The "above average" HF station can radiate enough low-angle signal to make-up for where your antenna is lacking. He may be running a 5 element Yagi on 20 meters at 75 feet which would certainly out-perform a low dipole or vertical from the same QTH. If you cut-off the signals arriving at angles lower than 5 degrees, the software will indicate that the opening to say "Big-Gun Sam in Japan" would not take place : ) You know this would be false because your log-book has plenty of Dx in it!

On the other hand, with 40 and 80 meters it would make allot of sense to up the minimum radiation angle for Dx signals because the main-lobe take-off angle, at those frequencies, would be 45 degrees and above with a low antenna. The software's predicted signal strengths would give better real-world figures when the minimum radiation angle is at a more realistic 20 degrees on 80 and 10 on 40 meters.

The W6EL software predicts HF path openings and signal strengths based on resonant dipoles in free-space, not above ground. So, these antennas would hear signals at 0 degrees just as well as they would at 90 degrees. In other words, with the software's imaginary dipole antenna, all take-off angles are covered with the classic 2dbi gain and the lack of influence from the ground so there's no way to manipulate the antennas take-off angle. In the real world, things are different - height does matter ( sounds like another saying, but we won't go there ).

One more thing - the ionospheric model used in HF propagation software is statistical in nature. It uses the average sunspot numbers or 10cm flux to predict what USUALLY happens at HF frequencies for a specific time of year at a specific time of day. It can't account for chordal hops, ( strong HF signals that skirt the ionosphere without refracting back to earth for long distances) ionospheric anomalies, ( equatorial bulge ) enhanced ionospheric density due to a sudden burst of solar energy which increases the maximum usable frequency, and so on.

With that said, the software's predicted band openings and relative signal strengths are surprisingly accurate in most cases.

I hope this helps. If you have any questions, I'd be happy to add to the chaos ( hi ).