Topband: Low Dipoles

[Jim Brown]

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