Re: NEC-LIST: induced voltages

Grant,

I believe that if the antenna is electrically short, and you make it
an active receive antenna (so that its impedance is close to an open
circuit) then you will get a voltage out of the terminals that is
approximately equal to E*length. This type of antenna is called an
electric field probe. In this case, the effective length (Le) is
equal to the actual length, where Le is defined by:

Le=V/E

By "active" I mean that the antenna drives the gate of a FET, whose
input impedance is very high. The FET is arranged as a voltage
follower, so you get the same voltage out of the FET as the voltage
into it, but the FET's output impedance is matched to the transmission
line. So the FET acts as an impedance transformer.

I believe a company called "Antenna Research Associates" makes a lot
of these electric (and magnetic) field probes. I believe they are
headquartered in either Maryland or Virginia (USA). They come with
calibration curves, so that one can use them for measurements of
fields.

Matt Taylor

Grant Bingeman wrote:

> I have a dumb question. Assume you have a linear field of one volt
> per meter. Now assume you have a wire one meter long aligned with
> that field and loaded with an impedance at its center in such a way as
> to maximize the voltage induced across that load. Is there a simple
> relationship between that induced voltage and that impinging field,
> and what restrictive circumstances must be applied? Must the load be
> the complex conjugate of the wire's self impedance? Must the wire be
> suspended in free space? Must the wire be infinitely thin? Must the
> wire be very short compared to a wavelength? When, if ever, will the
> induced voltage equal the field intensity?
>
> Grant Bingeman
Received on Tue Jun 23 1998 - 09:42:01 EDT