Topband: Skywaves from Monopole Surface Waves

[Paul Christensen]

The measured MW data looks compelling and agrees with the NEC surface wave analysis.  Even accounting for frequency disparity between the BC band and 160m, low angle field strength remains robust.

Rich, what is the station's operating frequency and approx. soil conductivity?  Doubters may think the station's antenna is located along a coastal salt plane to get these strong low angle measurements.

Paul, W9AC



Sent from my iPhone5

On Oct 7, 2012, at 5:42 AM, "Richard Fry" <rfry at adams.net> wrote:

> Guy Olinger wrote:
>> I find it curious that some of those that so insist on
>> standing-man-with-meter in affairs regarding performance of antennas are
>> willing to accept a considerable logical reach on "upward launching" of
>> ground wave without the appropriate metric **at altitude**.  ...  But I got
>> no proof, no measurements, no RBN, no ad-hoc reasonable comparisons.
> 
> It should be noted that no research or data is available to support the theory that currents carried by buried radial wires propagate off the open ends of those wires to travel through the earth, and produce the "standing-man-with-meter" groundwave field measured miles away from a vertical monopole.
> 
> Also it should be noted that base-insulated/driven vertical monopoles using elevated radial systems having no physical contact with the earth can produce the same groundwave fields as if 120 x 1/4-wave buried radials were used in place of the elevated radials.  How would such remote earth currents be present when using elevated radials having no contact with the earth?
> 
> As to the absence of measured data stated in the quote above, below with his permission is a quote from a broadcast consultant acquaintance of mine who has made helicopter measurements of the elevation
> patterns of MW monopoles.  These data below were taken using a helicopter at a horizontal distance of 2.8 km from the monopole, showing the fields existing at elevation angles of zero to about 3 degrees above the horizontal plane.
> 
> This path length is short enough so that earth conductivity has little bearing on the measured fields, but not so short that the intrinsic, ~cosine-shaped elevation pattern of a 1/4-wave monopole will significantly affect the fields at those measured elevations.
> 
> It will be seen from the data that no "notch" exists in the fields radiated by the monopole at elevation angles of 3 degrees and less, as expected by some when considering only the far-field patterns shown by MoM (NEC) software, and in antenna textbooks.
> 
> That low-angle radiation can reach the ionosphere to produce a skywave,
> under the right conditions.   That skywave can be very useful to hams
> using vertical monopoles, even though its existence may not be
> recognized.
> 
> QUOTE
> 
> Helicopter Vertical Calibration
> 
> To check for variations in field intensity due to elevation above ground, we
> hovered over one location and rose from the ground at 50-foot intervals to
> 500 feet.  Location #12 on the 230° radial was used (non-directional mode),
> and the data as presented below shows no significant effect.  Measurements
> taken for this report were done at an average elevation of 500 feet and the
> calibration of the meter takes the vertical factor into account.
> 
> Height above ground      Field Intensity       Variation from 0 feet
> 0                                  56 mV/m                    (Ref.)
> 50                                   56                          +0.0 mV/m
> 100                                  56                           +0.0
> 150                                  55                            -1.0
> 200                                  55                            -1.0
> 250                                  55                            -1.0
> 300                                  55                            -1.0
> 350                                  54                            -2.0
> 400                                  54                            -2.0
> 450                                  54                            -2.0
> 500                                  54                            -2.0
> 
> Averages:               54.91 mV/m               -1.09 mV/m (-1.99%)
> 
> END QUOTE
> 
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