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.
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