[TowerTalk] Terrain Modeling (was choke on vertical dipole)

[vk3od at yahoo.com]

I had a similar situation with Hygain 204BA's, one at 30ft and one on a separate tower at 65 feet.
TA explained it, although I was not on a massive downward drop, the slight gradual terrain drop seemed to help. The 30ft Yagi was always equal and many times better on numerous paths. Numerous DX stations would not believe that a 30ft high 204BA beat the higher antenna.

What is also interesting is that when you run you station antennas and compare them to similar higher yagis in VOACAP, the online VOA prop tool. On numerous paths the path reliability from 30ft is essentially the same for the same type of antenna and a 10 metre high antenna might have a 10% less path reliability versus a 200ft high. A single high 200ft antennas shows only a slight advantage when the band opens and closes. I cant generalize for everyone's location, however from my location the path reliability remains essentially the same and a antenna at 70 to 82ft has the same path reliability as a 200ft high single Yagi using the same sunspot number. I have tried all the different models in VOACAP including using angles below 3 degrees.

https://www.voacap.com/hf/

The antenna comparison for path reliability is in the Point to Point drop down menu.

73
Craig
VK3OD

"Comparing the 50' 20M Yagi to the 80' Yagi is fascinating. Both Yagis have the 
same boom length; the 50' one is 3 elements on 20 and the 80' one is 4 elements 
on 20. MOST OF THE TIME THE 3 ELEMENT AT 50' BEATS THE 4 ELEMENT AT 80'."