Carrying this line of thought to the business end of things, 12 ohms /
75 ohms = 16% of the voltage from your transmitted signal will be
across the antenna and 84% of the voltage being dissipated in dirt.
Assuming that you are transmitting 100 watts and have a perfect
lossless feedline, and since the same current flows at the base of the
antenna as at the entrance to the "ground" system, you are only
transmitting 16 watts off of the antenna and dissipating 84 watts
somewhere in the dirt. Any loss in the feedline just makes it worse.
As in just about all sparse radial systems using commercial lengths
intended for commercially dense radial systems, the very few radials
plus ground rod, or other misc radials wastes most of the power sent
to the system by forcing the counterpoise current through the dirt,
either by direct connection, or by induction.
First design issue of any 160m antenna is always what to do about the
dirt. When you've figured that out, you can start worrying about the
wire. And in measuring SWR, an SWR that is consistent across the band
means that the fixed resistance of the dirt has swamped the
measurement with loss, AKA dummy load.
I am assuming that what you meant by "disconnect the ground from the
antenna" was removing the connection to a ground rod. If you meant
disconnecting the rod AND the radials, then you have a coax problem.
If you meant disconnecting the radials, then the radials are
completely all and your shield connection is effectively a ground rod
and that is entirely resistance.
73, Guy.
On Wed, Nov 30, 2011 at 3:48 PM, DAVID CUTHBERT <telegrapher9@gmail.com> wrote:
> The radiation resistance of your antenna is 12 ohms.
>
> The 1.5:1 VSWR tells us the base resistance is either 33 or 75 ohms. The
> ground loss resistance is either 21 or 63 ohms. The radiation efficiency is
> either 36 or 16 percent.
>
> The low VSWR over the band (1.8 to 2 MHz?) points to the base resistance
> being 75 ohms.
>
> Dave WX7G
> On Nov 30, 2011 1:28 PM, "james soto" <kp2bh@yahoo.com> wrote:
>
>> Hello friends,I am experimenting with an inverted L for 160. the antenna
>> is about 132 ft long with about 45 to 50 ft vertical and the rest
>> horizontal.i have about 4 radials connected direct to the antenna and one
>> wire connecting to other radials that use to belong to another vertical
>> antenna not in use now. at this time i have work south ,central and north
>> america but i have not work any europeans as yet. the wsr is pretty ok 1.5
>> across the band . i disconnect the ground from the antenna and i don see
>> any difference in swr at all. my question is do leaving the ground wire
>> disconnected from the ground rod improve the reception? any ideas are
>> wellcome.
>>
>> ps i also have a 1/2 wave dipole for 160 at 60 ft high and running in all
>> kind of shapes ( no space for long antennas) and my reception is better
>> with the inverted L.
>>
>> thanks and 73's
>>
>> de kp2bh / kp2dx jimmy
>> _______________________________________________
>> UR RST IS ... ... ..9 QSB QSB - hw? BK
>>
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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