[Lowfer] Embattled E-Probe

[Bill Ashlock]

Ed,

Thanks for the input. Comments below.

>My antenna is a 50 foot Hygain "Hightower", tapering from the ground to
>the top in such a way as to minimize the radiation resistance.  (Not as
>much current toward the top as in a uniform wire or mast.)

I think I understand that your tree situation was the reason for designing 
the taper but actually in a treeless environment you want to increase the 
radiation resistance by reducing the taper in current with height as much as 
possible, with the use of a top hat of maximum size. Unfortunately when 
trees are within 20 ft, increasing the top size has the reverse effect.

>It originally was installed between two large old oak trees, whose trunks
>were less than 20 feet from the tower and whose tops went way above it.
>The capacitance of this antenna is about 450 uufd, and the effective
>series resistance of the ground plus the antenna was of the order of 40
>ohms, a lousy combination but all I can manage with the base between the
>house and nearby driveway and our dry soil.  Every year we'd have the
>trees pruned and the resistance would go down a bit until the foliage
>grew back as it will with California live oaks.  About four years ago
>both trees died of "California oak root disease) and were removed.  The
>resistance went down from about 40 ohms to less than 30, indicating a
>significant loss due to the trees.  So , they were indeed "sucking up"
>energy, although only by a dB or so.  I can certainly tell the
>difference in antenna current for a given final power input.

Very interesting. I'm thinking that with 450pf you should see a lot less 
than 30 ohms if all the 'tree effect' is gone (assuming a reasonably good 
ground system). Are there additional trees?

>I don't use the antenna in resonance for receive so don't know what
>effect the tree was having on reception.

On receiving your vertical isn't effected nearly as much by the trees as for 
TX since you are well into a atmospheric 'noise limited' situation with 
loads of excess signal plus noise. Giving up 6db or so wouldn't be noticed 
from a signal-to-noise standpoint.

Bill A

PS: Hate to mention it but while the two oaks were alive you had a good TX 
loop environment.

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