[Lf] Antennas, swamps and such

[Andre' Kesteloot]

Pierre Thomson wrote:

> Hi Mike,
>
> I used to wonder the same; it seems like AM broadcast stations are
> often built in swampy areas, and they seem to do well there.  But if
> you think about the difference between AM broadcast and Lowfer
> antennas, you will see a big difference.  A typical AM antenna is a
> full quarter wave, or approaching it.  The feedpoint impedance is 37
> ohms or so, almost purely radiation resistance.  A decent ground is
> important, but a few ohms here or there make little difference.
>
> A Lowfer antenna, on the other hand, is less than 1/100 wavelength
> long, and its radiation resistance is under 1/10 ohm. The impedance
> of the tuned system is mostly a combination of losses, and one of
> the big ones is ground loss.  Here a few ohms make a huge difference
> to the overall efficiency.  From my own experience, it seems that any
> moisture in the system increases loss; my signal drops way down in
> rain, and doesn't fully recover until the ground is dry.  Based on this, I
> would say that a fresh water swamp would not be ideal.
>
> Regards,
> Pierre Thomson
> KA2QPG / RI