[Lf] [Fwd: LF: Counterpoise Experiment]

[Andre Kesteloot]

James Moritz wrote:

> At 23:09 06/06/2002 +0000, you wrote:
> >What coil resistance You have? Or 37 ohm it is whithout coil resistance?
>
> The resistance values quoted are those due to the antenna alone - I have
> already subtracted the coil resistance which is about 5 ohms.
>
> >It seems to be much better if You will not use ground, conterpoise only.
> >To reduce loss all the currend should return through conterpoise.
> >In this case it is good to use ferrite  transformer betwin TX and
> >antenna to avoid HF voltage on TX box.
> >
>
> It seems to me that in this case, where most of the antenna field (and
> therefore the displacement current) is going to the ground rather than the
> counterpoise,  most of the return current will still be flowing in the
> ground, even if the counterpoise is insulated from ground. Rather than
> returning directly to the grounded terminal of the TX output, this current
> would have to flow through the capacitance between the counterpoise and
> ground. This means there must be a voltage between the counterpoise and
> ground - if the  ground-counterpoise capacitance is roughly 20 times that
> of the antenna-ground capacitance (7nF and 340pF respectively - which is
> what I estimate in this case), the counterpoise voltage would be roughly
> 1/20 of the antenna voltage. In my antenna system, this would put an RF
> voltage of about 1kV on the counterpoise when running at full power - so
> the counterpoise, antenna tuner and isolating transformer between TX output
> and tuner would all have to be insulated to withstand this voltage, making
> things quite complicated again... The advantage would be that the
> resistance of the ground path should be reduced, since the ground
> "connection" is effectively the whole area of the counterpoise, decreasing
> the loss due to this source. However, many experiments have shown that the
> resistance of the ground connection is only a minor factor in the overall
> losses in a small antenna like this one (3ohms is probably not that
> unrealistic), so I would expect little improvement overall.
>
> Cheers, Jim Moritz
> 73 de M0BMU