[Lf] re LF aerials]

[Andre' Kesteloot]

Alan Melia wrote:

> Hi John, your comments all noted. I see the reason why this is so
> interesting is that it 'seems' to contradict the generally agreed wisdom.
>
> I have a few thoughts on this....
>
> Could it be that it is a matter of size?
> As a comparison laying a 100m counterpoise or gound wire on 136kHz would be
> the equivalent on 80m to putting down a 10foot 'radial'. I think the general
> opinion is that that would not be very significant. Most professionals are
> dealing with bigger verticals and very few would need to go in for top-loads
> of the order of 160m (may be wrong there I have no experience in this area)
>
> Is it one of money?
> I suspect the standard NDB T aerial is an economic choice as well as a
> technical compromise. The radiation resistance does not seem to increase
> much after the arms are about equal to the height, so you stop there and
> bury lots of radials, which is much cheaper than more masts and lots of wire
> in the sky. Many seem to use umbrella format which is less than optimum
> technically but only requires one expensive mast.
>
> I am not trying to be awkward but I have worked in 'research' and know that
> cash constraints means you try what is most likely to work, not pursue all
> the variables in a pure and ideal scientific way.
>
> You are right that in some cases it is 'cost effective' to put down more
> earths, but the picture we are beginning to see is that this is for the case
> with stations on very good conductivity grounds (like Dick PA0SE, and
> probably Graham G3XTZ) Laurie already has a fairly extensive earthing system
> for his HF aerials. So he has a fair amount of copper in the ground. I
> believe with his soil resistance he may have reached the diminishing returns
> point....unless he starts putting out 136kHz quarter waves!
>
> Do these points hold any merit in your opinion? I think we could be finding
> some guides to improving the radiated signal for stations living over poor
> ground conditions, if only we can quantify what we are seeing. It could also
> have major influence on the cave radio people, who are often operating over
> granite outcrops with very little in the way of conductive soil around.
>
> I think we can also see the beginnings of an explanation why there is so
> much difference in different sites. It might be interesting to see some
> similar measuremnts to Laurie's from Oz where the ground must be quite bad.
>
> Whoops I'm getting into bore mode again! but I think this topic is going to
> run....and run.
> Cheers de Alan G3NYK
> Alan.Melia at btinternet.com