Re: LF: Question about ground impedance at 8.97 KHZ Stefan.

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

I wondered that, but 500pF as measured, if genuine at 10kHz, works out at -j 32000, which is close to the 70k Real term.   The series equivalents are therefore 12k - j26.5k  -   which still doesn't seem right.

 

Andy
www.g4jnt.com

On 26 March 2010 20:48, Alan Melia <alan.melia@btinternet.com> wrote:

Hi Johan, an Impedance bridge measures the reactance and resistance is
parallel I believe....doe sthat make a difference  to what he is seeing??

Alan G3NYK

----- Original Message -----
From: "Johan H. Bodin" <jh.bodin@telia.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, March 26, 2010 8:32 PM
Subject: Re: LF: Question about ground impedance at 8.97 KHZ Stefan.


> Hi Paul,
>
> it sounds like your impedance bridge is measuring the absolute impedance
> (that is Z = (R^2 + X^2)^0.5 where R is the real part, resistance, and X
> is the imaginary part, reactance). R is probably a 10 to a few hundred
> ohms, most of it is ground resistance - it can be neglected - the major
> part of your impedance is the capacitive reactance of the antenna (Xc).
> At 9 kHz, where C = 1/(2*Pi*9000*Xc), 70 kOhms means 253pF which is in
> the ballpark for your 170' wire (about 5pF/m).
>
> 73
> Johan SM6LKM
>
> ----

>
> Paul A. Cianciolo wrote:
> >
> > Hello All,
> >
> > Below is a quote from the Stefan's web page concerning his latest
"Dreamers Band" DX contact Congratulations again Stefan.
> >>From this information alone is it possible to calculate or know the
antenna system impedance.
> >
> >
> >
> >
> > "100m Vertical wire antenna, coil/antenna voltage was abt 15kV rms,
average antenna current about 480mA, giving up to 1,7mW ERP. Applied power
was up to 250W."
> >
> > Pertaining to the coil "Technical and mechanical data: L=553mH, Q=82,
R(DC)=283 Ohm; 0,4mm diameter enameled copper wire, about 1200 turns!
Average diameter 0,55m, height abt 0,5m. So, about 2000m wire! :-)"
> >
> >
> >
> > I have built a small impedance bridge that operates at 10 KHZ and shows
my sloping 170' wire as 70K Ohms. I can also see approx 500 PF that can be
nulled out using the bridge?
> >
> > Can the 70K value possibly be correct?   (3) 6' ground rods about 6'
apart are the ground... plus the electrical ground of the house.
> >
> > I am hoping to attempt a local transmission on 9KHZ
> >
> > Any information would be helpful.
> >
> > Thank you
> >
> > Paul
> >
> > W1VLF
> >
> >
> >
> >
> >
>