Re: LF: Re: E-Field Probe calibration question

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

Hi Alan + All...

 

Actually its a bit more complicated on its own...   The physical length of the element is 0.75m, which is appreciably longer than the electrical effective length.   And I'm betting a chunk of that difference is made up by having a series resistor in the output circuitry to give a 50 ohm source impedance and help stability but reducing voltage gain to below unity.  If 50R in series, there is an immediate -6dB  halving the length.    If my original dipole concept were to apply, then the other half of the leg caused by the car would also be affected by the attenuation.

 

But it appears from your comments so far the argument doesn't apply in which case the 0.15m length still holds.   How do the EMC measurement community do it, as their measurements have to be valid in law and could be held up to scrutiny?

 

Now, what was the voltage from an untuned loop, again ;-?

 

Andy

www.g4jnt.com

Mostly retired inguneer

 

 

On 1 April 2010 12:44, Alan Melia <alan.melia@btinternet.com> wrote:

Hi Andy maybe I dont read it right, but if that is an E-field probe it is
not a "dipole" The input capacitance senses the voltage at two points on the
wavefront. The ground plane is, I believe, irrelevant. You just need another
capacitance separated from the "probe" to reference to voltage to. See
Renato's balanced probe (www.vlf.it)  In your case this is the car.....but
it could be the size of a dinky toy.The area of the wavefront intercepted by
the probe or the ground reference does not affect the terminal
voltage.....as I see it.................of course I might just be wrong cos
i am really a scientist not an enjuneir!!
 :-))
Alan