Dave, K1ZG writes:
I READ YOUR INFO RE THE ROHN 25 TOWER SPECS FOR 160M >VERTICAL. I
WASN'T SURE THAT A 12.5" DIAMETER IS THE PROPER >EFFECTIVE DIAMETER FOR
THE ROHN 25. I THOUGHT MOST PEOPLE >USED 8" FOR MODELLING PURPOSES. HOW
WOULD THE CHANGE IN
EFFECTIVE DIAMETER AFFECT YOUR CALCULATED VALUES FOR A >SHUNT-FED TOWER?
========================
Decreasing the models from 12.5" diameter to 8" yields:
# of Tower Gamma Gamma Capacitor
Sections Height Height Capacity Voltage
------------ ----------------- ------------ -------------
--------------
9 87' 4-1/2" 83' 77 pF 5044
10 97' 1" 72' 105 pF 3712
11 106' 9-1/2" 57' 6"' 155 pF 2515
12 116' 6" 39' 9" 263 pF 1477
13 126' 2-1/2" 26' 10 497 pF 783
14 135' 11" 35' 6" 465 pF 837
15 145' 7-1/2" 50' 3" 320 pF 1214
Compared to the 12.5" models, the most significant fact is that the gamma
height must be reduced by about 4 feet in the 8" models. Reducing the
gamma spacing from 24" to 14" in the 8" models yielded very close to the
same values obtained in the 12.5" models.
My two 72' tower widths taper from 30" at the base to 18" at the top.
Modeling them (along with the HF beams at 75') using the actual tower
width as the conductor diameter yields exactly the same gamma height &
spacing and capacitance values oblained in the real world (I've never
measured the voltage).
If anyone ever uses the values I've presented, I'm sure they'll initially
be in the ballpark.
73 es DX, de Earl, K6SE
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