Message-ID: <002201c34524$0b6407b0$ee9bfea9@oben>
From: "dj9dw" <dj9dw@t-online.de>
To: rsgb_lf_group@blacksheep.org
References: <5.1.0.14.0.20030707113252.025bf530@gemini.herts.ac.uk>
Date: Tue, 8 Jul 2003 09:39:20 +0200
Subject: Re: LF: Field strength calcs.
Sender: <owner-rsgb_lf_group@blacksheep.org>
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Content-type: text/plain; charset=windows-1252; format=flowed
MIME-Version: 1.0
Content-transfer-encoding: 8bit

Hello James,
thanks for your enlighting explainations on fs-calc via loop. Now I know how
to and give my new toy, SNA-1 analyzer, its first serious task measuring my
neighbour in Mainflingen.

vy 73, Peter, dj9dw.

----- Original Message -----
From: "James Moritz" <j.r.moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Monday, July 07, 2003 1:14 PM
Subject: Re: LF: Field strength calcs.


> At 17:26 06/07/2003 +0100, you wrote:
> >When making the signal strength measurements using a loop antenna should
> >this be resonated or aperiodic?
> >
> >I made measurements under both conditions but the results are puzzling -
> >even allowing for my peripatetic decimal point!
>
> Dear Ian, LF Group,
>
> The voltage induced in a loop is:
>
> V = 2.1x10^-8 (fNAE)
>
> where f = frequency (Hz)
>          N = number of turns
>          A = area (m^2)
>          E = field strength (V/m)
>
> Always assuming that the antennas are far enough apart for the loop to be
> in the "far field" (>1 - 2km seems to be enough)
>
>  From the circuit point of view, the loop behaves as a voltage source of
> the value given by the formula, in series with the inductance and
> resistance of the loop winding. If a high impedance load is connected to
> the loop terminals, the measured voltage will be more or less that given
by
> the formula. If the  load impedance is relatively low, the output voltage
> will be reduced by the potential divider action of the loop
> inductance/resistance and the load resistance. For single-turn loops less
> than a few metres in diameter, the inductive reactance is only a few ohms,
> so even a 50ohm load on the loop will have little effect on the signal
> voltage - this is one reason single-turn loops are popular for
> measurements; few variables affect the measurement. A multi-turn loop with
> higher inductance can be series-tuned; the reactance of the loop is
> cancelled by the capacitor reactance, eliminating this loading effect. A
> parallel-tuned loop could be used with a high impedance load - in this
> case, the voltage will be stepped up by a factor equal to the loaded Q of
> the loop - but since this depends on a number of variables, it introduces
> greater uncertainty into the measurements.
>
> If you turn the formula round, you get E by measuring the signal voltage:
>
> E = V/(2.1x10^-8 x fNA)
>
> Then ERP (relative to a dipole) is:
>
> Perp = (Ed)^2 /50 (d is distance in metres, E is fs in V/m, Perp in watts)
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>