On 12/17/2020 1:27 PM, Roger Kennedy wrote:
I do take offence at people suggesting that I am somehow lying about the
results I have always had with a 160m Dipole at 50ft !
I don't see where anyone is saying you're lying, Roger.
In terms of people doing their own DIRECT comparisons against a
Vertical at
the same QTH, I believe the problem is that the Dipole is usually above (or
near) a decent Radial system. That will have the effect of lowering the
Antenna, and therefore making it only fire at very high angles.
A radial system would be only a small part of the story for a horizontal
wire, potentially reducing loss in the soil under the antenna; the major
contribution of height is formation of the pattern from the reflection
in the far field.
A Dipole that is above poor ground, and without any wires underneath it, I
believe will "think" it's much higher
The property that aligns with that thinking is the Skin Depth at the
frequency of interest. W8JI has noted that can be in the range of 60 ft
(don't recall the specific numbers he cited -- it's a long time since I
read it). I haven't studied the relationship between soil conductivity
and skin depth.
, and probably therefore be more
efficient at lower radiation angles.
The strength of the first reflection increases with increased soil
conductivity. The shape of the resulting vertical pattern depends on
both the strength of that reflection and the electrical height of the
antenna, taking skin depth into account. Lousy soil where that
reflection is formed would weaken its strength.
I'd be interested to hear Frank's thoughts on this from an analytical
point of view. But the bottom line for situations such as yours (and
mine when I lived in Chicago) is that any antenna is better than no
antenna, but the reason we study how antennas work is to make the most
of our situation, which includes, but is not limited to, real estate,
our surroundings, available or possible skyhooks, local noise, and our
resources (money, friends to help, physical and mental abilities).
73, Jim K9YC
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