Topband: radial length

[Herb Schoenbohm]

Richard (Rick) Karlquist (by way of Bill Tippett 
<btippett at alum.mit.edu>) wrote:

>So I think the answer to this "paradox" is that you
>need very close radial spacing close to the antenna
>where the current density is highest.  Farther out it
>is OK to have greater spacing.
>
>Rick N6RK
>
>_______________________________________________
>  
>


Rick,

That has been the belief in the broadcast industry for as long as I can 
remember.  Every presentation at NAB and IEEE I have ever listened to or 
read seem to support the thesis that a 50x50 or 100X100 piece of 
expanded copper mesh under a 90 degree tower AM broadcast tower 
establishes the near field FSM normallty made at one mile from the 
tower.  Adding 30 or 60 radials, so I have read, will make little or no 
significant difference to this reading.  But as the man said topbanders 
seldom use FSM readings of ground wave levels as a determination of what 
works best for sky wave propagation requirements. So IMHO if you have 
limited options for a location a  large screen of expanded copper mesh 
(I know its expensive and chicken wire will work in the short term) you 
will not be disappointed with the screen as a viable substitute for 
limited space or other long radial restrictions.


Herb, KV4FZ