[TowerTalk] 4 square for 80

[Jim Brown]

Mike,

I don't always subscribe to "do what the mfr says" philosophy, but in 
this case, you've gotten solid engineering advice. I'd say take it!  
Engineering and science are NOT a matter of opinion, nor of popular 
vote. Once you've gotten that good advice, say thank you and start 
building it!

One observation though about ALL vertical TRANSMITTING antennas. In 
general, the PERFORMANCE of horizontal antennas is NOT affected by the 
quality of the soil (although their feedpoint Z strongly depends on 
height and soil quality), but the PERFORMANCE of vertical antennas is 
STRONGLY affected by soil quality.  I suggest that you study the antenna 
planning tutorials/applications notes on my website.  My QTH, in 
mountains where the "soil" mostly rocks with a thick layer of "duff" 
(droppings from redwoods laying on top) is quite poor, except during the 
winter when our 70 inch annual rainfall makes that top layer fairly 
conductive. So verticals don't work for me -- my only vertical antennas 
are for 160M, where any practical horizontal antenna is too low to be 
good at low angles. I've tried verticals on 80, 40, and 30M, and they 
had terrible efficiency.

So -- take Tim's comparison of 4-squares for the higher bands with a 
Yagi at 50 ft with that in mind -- that is, compare his ground with yours.

Another important point about radials. Their function is to SHIELD the 
field produced by the antenna from the lossy soil, so that return 
current for the antenna flows in low resistance copper rather than lossy 
soil. BUT-- current in radials couples inductively to the soil, so 
current flows in the soil, burning TX power. The equivalent circuit of 
the radial adds a resistor in series with it.

Power is I squared R; as more radials are added, the current divides 
between them, while the R in each radial remains the same (if 
identically installed and the soil is the same under each). SO -- as we 
double the number of radials, we reduce the power in the radials by 
half. THAT'S why more radials are better, and that's why 16-32 radials 
is the point of diminishing returns. (Note that I'm not saying that the 
efficiency improves by 3 dB, but that the loss in the soil is reduced by 
3 dB).

As we RAISE our radials, there is less coupling with the earth, and it 
takes fewer radials to keep the ground loss low.  N6LF has done a LOT of 
excellent work on this, and published it in QEX and on his website. It's 
well worth the time to study it thoroughly.

When thinking about the effect of soil, there are two.  First is the 
loss in the radials, and we have control over that. We can put more 
copper in/on the ground, or we can elevate radials. And we can use 
K2AV's FCP if we don't have room for radials. The second effect is the 
loss in the far field where the first reflection combines with the 
direct wave from the antenna to form the vertical pattern. The strength 
of that reflection is strongly dependent on the soil, and that is NOT 
under our control.  THAT'S how sea water makes verticals work so well, 
and ONLY in the direction where there's sea water.

73, Jim K9YC

  On Thu,9/22/2016 2:12 PM, Tim Duffy wrote:
> Having engineered 4 square antenna systems (successfully) for over 25 years
> - I was the advising engineer to Rod on your project. I was very careful to
> make sure Rod had all of his facts correct before giving you advice.
>
> You asked for advice on your project and we gave you the straight engineered
> scoop - with tons of experience. We do not want you to go through lots of
> work only to find out a system you proposed does not work correctly. You
> might get various other guidance from others, my advice is be careful.