"Richard Fry" wrote in message
...
"Frank" wrote
At 1000 m, between a height of zero meters, and 1000 m
the field strength is in the range of 5 mV/m peak. (i.e. including
ground wave). Not sure why the calculation does not agree
with Richard Fry's analysis, but may be due to the fact that
NEC computes ground losses for the surface wave.
____________

At the bottom of this post is a link to another analysis, this time using
NEC-2 with the input assumptions of my first "spreadsheet" approach.

It shows a field of 84.12 mV/m at 1 km for 1 kW of radiated power.
Adjusting that 1 km field that for the power reduction to 50 watts brings
it to 18.8 mV/m -- which is in close agreement with my spreadsheet value
of 18.5 mV/m.

NEC-2 cannot deal with buried radials, but the 1 km NEC-2 field as
calculated here for a perfect ground can be plugged into the applicable
FCC propagation curves to show the groundwave field for a given distance,
frequency and conductivity, as I did in earlier post. Repeating those:

Field Strength Radius
0.500 mV/m 10.3 miles
0.250 mV/m 15.5 miles

In another post, Frank, you wrote "With 50 W input the peak E-field at
1000 m is 62.9 mV/m (44.5 mV/m RMS). At 24 km the E-field is 2.2 mV/m
(1.5 mV/m RMS), at ground level, and 2.0 mV/m (1.4 mV/m RMS) at 10,000 m
elevation. These results appear to be very close
to Richard Fry's analysis, though not sure why there is a 6 dB
difference."

I think you were looking at my first post, where I guesstimated 6 dB
ground loss for a 24 km path, and showed 0.773 mV/m there.

The (much) more accurate FCC approach shows only 0.25 mV/m for a 24 km
path with 2 mS/m conductivity, and the difference between that and your
1.5 mV/m is 15.6 dB -- rather significant.

I don't know for sure what explains all this, but it is interesting to
consider.

http://i62.photobucket.com/albums/h8...adiatorNEC.gif

RF

Calculating space wave plus surface wave at 24 km, at ground
level, NEC shows 0.79 mV/m peak (0.55 mV/m RMS). I used
a ground conductivity of 2 mS/m and relative permittivity 4.
The vertical tower was modelled with 3/8" dia. aluminum, neglecting
the actual lattice structure. I have not added the capacity hat.
I used eight 200 ft radials 3" below ground, also 3/8" aluminum
(6063-T832 alloy).

The input impedance is 6 - j 1008, and I am driving it with
4.1 kV peak (50 W). Don't understand why I am getting
different results than the FCC method at 0.25 mV/m. This
analysis does assume a lossless matching network, where
practical systems would show 3 or 4 dB of additional loss.

Frank