Topband: Ground mounted 1/2 and 1/4 wave verticals (was GAP)

[DAVID CUTHBERT]

Tim,

I ran some sims using a work-around I developed to allow NEC-2 to mimic
NEC-4 ground loss results. This sim is  for a 90 degree, 1.8 MHz vertical
over Medium ground. I get correlation within 0.06 dB between base impedance
derived loss, E-field strength at 1000', and NEC Average Gain.

More work needs to be done to see if this method gives results for other
radial and vertical lengths that overlay the N6LF results.

    Dave WX7G

On Mon, Dec 17, 2012 at 5:42 PM, DAVID CUTHBERT <telegrapher9 at gmail.com>wrote:

> Tim,
>
> I believe those are valid conclusions. Referencing *Vertical antenna
> ground system experiment #1*, by Rudy Severns:
>
> 1) Table 1 shows that going from 8 radials to 64 radials increases field
> strength by* 1.6 dB*.
> 2) Figure 4 shows the resistive part of the base impedance changing from
> 58 ohms to 43 ohms.
> 3) Using a radiation resistance of 36 ohms the radiation efficiency for 8
> radials is 62% and for 64 radials it is 84%. The difference is *1.3 dB*.
>
> Rudy's other papers confirm the correlation between the resistive part of
> base impedance and field strength.
>
>     Dave WX7G
>
>
> On Mon, Dec 17, 2012 at 4:21 PM, Shoppa, Tim <tshoppa at wmata.com> wrote:
>
>> Dave... would it be a fair extrapolation to take your last sentence, and
>> draw the conclusion that if adding radials changes feed impedance, then
>> there was actual ground loss in the near field? Or that if we add more
>> radials and feed impedance change is not seen, then we are at a minimum for
>> ground loss?
>>
>> The above statements certainly align with my gut feeling, but my gut
>> feeling is different than a mathematical proof :-)
>>
>> Tim N3QE
>>
>
>