[TowerTalk] Radial field question Single radial wires vs meshand more

[Patrick Greenlee]

Depending on mesh hole size etc vs freq of interest the mesh can begin 
to approximate a solid conductor, a reduced infinite conducting plane 
sometimes used in modeling vertical radiators.

Might give some capacitive coupling to the earth too.

Patrick        NJ5G


On 10/28/2016 1:11 PM, jimlux wrote:
> On 10/28/16 10:43 AM, Gary Schafer wrote:
>>
>> Hi Ian,
>>
>> I am wondering why even bother with mesh wire. Radials provide a return
>> current path back to the feed point so current should mainly flow 
>> along the
>> length of the radial wires. Having shorts between the radial wires as 
>> a mesh
>> provides, would seem of little benefit. Any current flowing between 
>> radials
>> via the shorts would seem to result in loss current.
>>
>
> A ground screen also provides a "shield antenna fields from the lossy 
> soil" function as well as a "provide a return path for half a dipole 
> sticking up"
>
> That is, you could run a vertical dipole above a screening layer 
> laying on the surface, with no connection between dipole and ground 
> screen, with the idea that you'll have less ohmic and dielectric loss 
> because whatever the losses in the screen are, they're less than 
> they'd be in the soil.
>
>
>
>
>> As to using any kind of steel material for radials the loss due to eddy
>> currents is going to be rather high, the same problem that steel antenna
>> wire presents.
>
> But is the eddy current loss all that high.. compared to eddy current 
> losses in soil? Are you talking about what would be called "core loss" 
> in a transformer which is a combination of eddy current and hysteresis?
>
> Skin depth at 4MHz in Iron (assuming mu=1000)is about 0.1 mil (2.5 
> micron), so the current is going to be flowing in the surface. (soft 
> iron has a mu around 4000, cold rolled steel seems to be in the 
> 1000-1500 range, depending on the alloy, heat treatment, etc.)
>
> I think hysteresis loss would be negligible - the flux is really 
> really low.
>
>
>
>
> https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19660001049.pdf
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