[Antennas] 30 Meter Ground plane

[Charles Greene]

Dan and All,

I never tried a 30 meter vertical, but I built a 20 meter portable vertical 
with 2 elevated radials.  I tried the radials both at 2' and at 7'; it 
required quite a bit of retuning with radials at 7' by adjusting the length 
of the radials to get it resonated from its tuning when the radials were at 
2'.  In both cases the impedance was 50 ohms, which means that there are 14 
ohms of loss in the ground.

I first put it up and lengthened the radiator to about 19' and tuned the 
radials to resonance.  I lengthened the radiator so that it would function 
as an OCF antenna.  Shorter radials and a longer radial should have raised 
the impedance.  It did; to 65 ohms.  So I shortened the radial and 
lengthened the radials until it was resonant again and the impedance was 50 
ohms.  It had the dimensions of an ordinary vertical, with the radiator 
about 234/f.

Adding 2 more radials would have improved the efficiency somewhat.  Over 6 
radials, you get diminishing improvement in efficiency for each pair.  So 
for a fixed installation, 6 radials is a good choice.

I also modelled it using EZNEC.  I couldn't figure out what was going on, 
as the model said the impedance should have been 36 ohms. EZNEC doesn't 
model grounds very well.  So I contacted Roy Lewallen who said I should add 
some resistance in series with each of the radials until the model and 
actual results agreed.  I did, and the efficiency of the antenna using 
EZNEC was about 36/50 or 72%,  All that means is that there was about 14 
ohms of ground loss.

IAt 03:44 PM 2/25/2004, you wrote:

>>At 07:36 AM 2004-02-25, W3HKK@aol.com wrote:
>>>Tilting the radials at 45 degrees will raise your feedpoint to about 52 ohms
>>>but it also raises your angle of radiation making it somehwat less effective
>>>for dx but better for  1000-2500 mile distances.
>>
>>I did a quick model with EZNEC and drooping the radials barely changes 
>>the angle of radiation.
>>[snip]
>>73, N6RY
>
>That's correct. Drooping and/or increasing the number of the radials does 
>little to change the takeoff angle. That (the takeoff angle) is determined 
>by the ground condition out to several wavelengths from the antenna.
>
>73, K6MHE
>
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