Dear Wim PA3DJS:

How I wish that I could read Dutch. However, in looking over all of
your work, it continually occurred to me that much of the base of English
comes from Northern Nederland.

I looked at the first table on page 20 of your work. The information so
intrigued me that I ran almost the same information through NEC4, which does
well with antennas close to the ground. I assumed: a center frequency of
3.6 MHz, a horizontal half wave dipole slightly adjusted to be resonant at
3.6 MHz at each height, the use of Cu wire 2 mm in diameter, and earth with
a sigma of 0.01 and a relative dielectric constant of 15. This is what I
found without too obsessive an amount of tweaking:

The data is in this order:
height of the dipole in meters
the real part of the dipole's impedance in ohms
(the phase angle of the impedance was kept under 2 degrees)
the approximate SWR=2 BW in a 50 ohm system in kHz
the total apparent loss of the system in dB
(this is found by integrating gain in all directions)
the peak antenna gain in dBi

4.2 38.1 125 6.25 2.0
5.8 37.7 120 4.31 4.1
8.3 42.1 130 2.59 5.8
10.4 49.0 140 1.81 6.5
15 66.5 145 1.04 6.9
20.8 85.7 125 0.7 6.5

Most of my results are close to your results. It is interesting to know if
I used the same assumptions. Please let me know.

I encourage you to consider translating your work, or at least parts of it,
into English.

73, Mac N8TT
--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Wimpie" wrote in message


Hello Rick,

At 100 miles distance, the TOA is almost vertical (maybe 75 degr), so
with respect to signal strength, it is practically impossible to
detect whether the antennas are broad side. Because of the distance,
ground wave propagation loss is far higher with respect to NVIS
propagation loss under these circumstances.

One would mention polarization of the waves going up and down. I
would not matter about this. These low frequencies are strongly
affected by faraday rotation. On the way up and down, the polarization
rotates several times and several wave fronts do exist.

While you transmit (nearly vertical) with linear polarization, the
down coming wave may have a strong circular component.

With respect to the radiation pattern, you are right, the differences
in pattern are minimal below 30 feet. However the overall efficiency
is strongly depended on antenna height and soil properties. I did some
simulation and practice. I made a short document of it (for JOTA
porpuse), however the document is in Dutch Language (http://
www.tetech.nl/divers/NVISantenneNL1.pdf). Maybe you can get some
useful info out of it. At low heights, much power is dissipated into
the ground (resulting in a useful bandwidth).

Best Regards,

Wim
PA3DJS