[Lowfer] Embattled E-Probe

[Ed Phillips]

Bill Ashlock wrote:
> 
> 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.

	The remark about taper of my tower was meant to be sarcastic, not an
indication of stupid design on my part!  I know very well that the thing
is a lousy VLF radiator but that's all I had and all I had space for (no
guys).  The tower was assembled in pieces and then each section was
raised with great difficulty until the whole stack was complete.  I've
often looked at the top of the tower and wished I had some way to get up
there and install some top loading to increase the current up there. 
Only way I know would be to rent a crane which could span the distance
from the street, which is about 100 feet to where the tower sits.  By
the way, in years past I helped several locals put up guyed TV masts and
they all worked better than my tower!  At least 6 dB greater signal for
the same power input.
 
> >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?

	Who has a good ground?  Except where irrigated soil here is dust dry
down a few inches, and furthermore it's full of rocks - alleuvial fan
from the nearby San Gabriel mountains.  Six foot ground rods driven in
by hydraulic boring (hose at the top) show several hundred ohms between
them!  I do have a 2" copper water main coming in from the street and
extending into the back yard.  About 150 feet total and I'm tied to
that.  Best ground I can get and seems to work OK on HF.  No other trees
close; house three feet to the north and driveway about 10 feet to the
south.

> >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.

	I understand and agree.  The thing is tall enough that tuning doesn't
improve the S/N and that's why I don't bother.  The noise is mostly
local domestic garbage and I very seldom hear QRN.

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

	No room for a loop; you'd have to see the available space.  I envy guys
who room to install a good vertical over soil with good conductivity and
then add frosting to the cake by running out a large system of radials. 
No way here!!!!

Ed