Topband: Measuring field strength

[David Gilbert]

Tom Rauch wrote:
>> resistance. In actual use the feedpoint resistance will be 
>> higher. The difference is
>> due to losses. The radiation efficiency is then 
>> calculated. As the GND system
>> is improved the base resistance will decrease. I use this 
>> method and it is
>> convenient. It has confirmed simulations and articles that 
>> say that many short
>> radials is not much better than a few short radials.
>>     
>
> I measured dozens of systems and that method will not work 
> except by pure luck.
>
> As an example just a few moths ago Roy Lewallen and I 
> measured a series of 40 meter vertical radial system. We had 
> a very low base impedance with four elevated radials (about 
> 40 ohms) but about 16 buried radials produced identical FS 
> with a base impedance of about 60 ohms.
>
> I've found the same to be true when measuring FS on 160 and 
> 80 meters, as well as the BC band.
>
> I also think Rudy Severns posted something on here a month 
> or two ago agreeing with this.
>
> If you want to know  FS change you really have to measure 
> the FS.
>
> 73 Tom 
>
>   

It is even quite easy to create models in EZNEC that support Tom on 
this.  The relative base impedance of a vertical monopole fed against 
ground does not accurately predict relative field strength in either 
theory or practice.

Dave  AB7E

-- 

Subvert the dominant paradigm.