[TowerTalk] 80 Meter yagi question

[Jim Brown]

On 10/11/2017 3:33 PM, Grant Saviers wrote:
> So height is very important for horizontal antennas on 80m. IMO (from 
> my QTH) it is not worth the trouble for a rotatable 80m antenna below 
> 110' or so.  They really start to work at 1/2 WL, 130'. Every 10' 
> higher is noticeable.  Modeled them all and NEC concurs. 

That is one of the important conclusions of the applications note I 
posted earlier in this thread. That work is based on NEC modeling for 
"flatland" and my on-air experience confirms it. For low angle paths, 10 
ft is worth 0.9 dB between 40 ft and 130 ft. Going from 67 ft (quarter 
wave) high to 133 ft (half wave) is worth 6 dB. The same math applies on 
40M, so divide heights by 2. Above a half wave, the curve flattens out, 
so going from a half wavelength to 3/4 wavelength adds about 3 dB.

EU is about 500 miles closer to you than me (S of San Francisco), but 
more of your path is through the AU zone. I do find that I can work the 
stronger EU stations SP around their sunrise, and also long path a bit 
after my sunrise. A few years ago during ARRL DX, I worked three Ukraine 
stations within a hundred miles or so of each other on successive 
mornings. Later, I studied the path with DXAtlas and saw that it was 
grey line.

73, Jim K9YC