Re: LF: Measuring earth resistance

["Dick Rollema" <d.w.rollema@freeler.nl>]

To All from PA0SE

Jan-Martin, LA8AK. wrote:


> but suppose the values of the
> noise generator are for the range 3-30MHz, the coupling capacitors must
> be increased for VLF

The noise bridge was indeed not designed for LF but there is plenty of
noise on LF and the bridge can be perfectly nulled on 136kHz. But the
X-control has hardly any effect as its range is  from  190pF
till  -155pF (means inductive reactance) and that amounts to -j6.15
kohm till  j7.54 kohm as minimum values that can be measured
in parallel with Rx.   But for measuring earth resistance the
X-control is not used because I bring the aerial  system into
resonance so that only a pure ohmic resistance has to be measured.

To make the X-control useful on LF it might be better to connect  C1
in series with R3 and C2 in series with Zx; but I have not investigated
that. I used the parallel version because at high frequencies it is
easier to compensate for the parasitic capacitances of R3 and
C2.

73, Dick, PA0SE

> -----Opprinnelig
> melding-----
> Fra: WarmSpgs@aol.com
> [mailto:WarmSpgs@aol.com]
> Sendt: 15. desember 2002 21:29
> Til: rsgb_lf_group@blacksheep.org
> Emne: Re: LF: Measuring earth resistance
>
>
> Dick Rollema's noise bridge schematic and a photo of his assembled unit
> can 
> now be downloaded from:
>
> http://lwca.org/library/articles/pa0se/earth/
>
> 73
> John Davis