Yes, agree with everything you say. I have measured my ground conductivity
as 50 mS/m, so it is possible I used that figure to arrive at the results.
Much of Alberta and Montana have very high ground conductivity in the order
of 15 - 40 mS/m (Reference Data for Radio Engineers, 6th ed, pp 30-7, 30-8).
I must admit to being fixated on super high Q inductors to minimize matching
network losses. Your figure of 1.6 dB loss with a Q of 1000 -- based on a
1.5 Ohm resistance is of course correct. Just the same I plan to model the
vertical, as described in the original post, and see what I get for various
soil conditions, and the loss effects of some typical Qs. I know it has all
been done before, but enjoy doing it just for fun.
Frank Meredith (VE6CB)
"Roy Lewallen" wrote in message
...
The input resistance of 1.5 ohms you quote implies an extremely good
ground system. I suspect that very few people, particularly ones putting
up such a short vertical for 160, have the room for that elaborate a
system. As ground loss increases, the fractional loss caused by the
inductor decreases. So I don't agree with your blanket statement that an
inductor with a Q of 1000 will lose that fraction of the power. It
might, if a person had an extremely elaborate ground system, but not
otherwise.
Incidentally, although 30% power loss sounds impressive, it'll reduce
the signal less than 1.6 dB.
So it won't be worthwhile for most people to make heroic efforts to
produce extremely high Q loading inductors. (And, even if they can make
one with a Q of 1000, it would have to somehow be suspended well above
the ground and away from other conductive objects in order to retain
that sort of Q.)
Roy Lewallen, W7EL
Frank wrote:
"Roy Lewallen" wrote in message
...
Frank wrote:
Also the series inductor should have a very high Q for 160 m. A Q of
1000
will loose about 30% of your power.
Can you tell us how you calculated this? How much ground loss did you
assume?
Roy Lewallen, W7EL
I have run a number of NEC models (NEC-Win Pro), for ground mounted
verticals with a radial system, using the Sommerfeld/Norton ground
models
(usually in the range of: Sigma = 0.02 S/m Er = 17) -- although not for
the
specific dimensions indicated. My models would be approximately 0.001
wavelengths above ground (as per Cebik: Basic Antenna Modeling). The
input
impedance calculated is of the order of 1.5 - j1500. From these data it
is
relatively trivial to estimate the required Q of a series inductor.
I have been very interested in such antennas, but have never actually
gotten
around to building -- just modeling! If the original poster is
interested,
I would be very happy to model the specific dimensions.
Frank Meredith (VE6CB)
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