Re: LF: G8IMR - stronger? ...and G3XBM on 136kHz WSPR this evening

[Andy Talbot <andy.g4jnt@gmail.com>]

We put it down to an increase in lossy paralle resistance.

In dry conditions, the reactive (out of phase) near field current terminates on ground radials without passing through too much (relatively speaking) lossy ground material.

 

When everything is covered in water, the reactive field is conducted away into lossy ground material before entering the radials.  Being resistive, the current moves into phase with the E-field and ,starts to introduce added I^2R loss.  Most significantly here, walls and roof tiles the top-hat passes close to become more conductive, extracting noticably in-phase currents from the E field.

 

The result is a decreased resistance in parallel with the antenna capacitance, and when you plug decreased parallel R into the equation for parallel-to-serial transform, voila, an increased series term.

 

The tuning shifts marginally, but it was far worse when the effect was first discovered on 73kHz.

Was that really well over a decade ago - time flies!

 

Andy

www.g4jnt.com

 

 

 

On 5 January 2011 23:28, Alan Melia <alan.melia@btinternet.com> wrote:

Yes that is what my aerial measurements said as well in rain....increased
loss resistance.....not sure though whether it is a ground effect or the
film of water on the wire.

Alan G3NYK

----- Original Message -----
From: "Andy Talbot" <andy.g4jnt@gmail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, January 05, 2011 3:33 PM
Subject: Re: LF: G8IMR - stronger? ...and G3XBM on 136kHz WSPR this evening


> No - no changes at all.
>
> The only difference is that it is raining now.which - by the way these
> things work - has *increased* the antenna resistance and reduced power
> output by a dB or two.
>
> Andy
> 'JNT / 'IMR
>
>
>
> On 5 January 2011 14:53, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:
>
> > Hi Andy,
> >
> > Your 136kHz WSPR beacon is coming in very well today at around -6/-7dB
S/N
> > at 188km. Have you made some further ERP improvements?  PA0A is also a
very
> > good signal too.
> >
> > I hope to be TXing on 136kHz WSPR this evening ....but with a rather
weaker
> > signal than these two. Any reports (at all) would be very much
appreciated.
> >
> > 73s
> > Roger G3XBM
> > --
> > g3xbm-qrp.blogspot.com/
> > www.g3xbm.co.uk
> > www.youtube.com/user/g3xbm
> > <http://vlf_grabber/>G3XBM   GQRP 1678    ISWL G11088
> >
>