Message-ID: <3617AC3245C2D1118A840000F805359C01AB8CA2@pdw-mercury-1.dera.gov.uk>
From: "Talbot Andrew" <ACTALBOT@dera.gov.uk>
To: rsgb_lf_group@blacksheep.org
Subject: LF: RE: R: Formula
Date: Wed, 7 Jun 2000 12:54:34 +0100
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Ah -
I'd taken the factor of 30 outside the square root then.  Careless !!

Andy  'JNT

> ----------
> From: 	cesare tagliabue[SMTP:cestag@dada.it]
> Reply To: 	rsgb_lf_group@blacksheep.org
> Sent: 	2000-06-07 12:11
> To: 	rsgb_lf_group@blacksheep.org
> Subject: 	LF: R: Formula
> 
>             Hi Walter
>         The formula is derived from the general one that is: E =
> SQR(30*P*G)/D. Being the gain G of an half-wave dipole equal to 1.64,
> 30*1.64 = 49.2, rounded to integer and written out of the square root
> it
> becomes 7. E is the field strength in V/mt, provided that P is in
> Watts and
> D in meter; in fact the field strength is independent from frequency.
>         73  Cesare
> 
> Cesare Tagliabue   I 5 TGC
> e-mail: cestag@dada.it
> url: http://www.dadacasa.com/i5tgc
> 
> -----Messaggio originale-----
> Da: Walter Blanchard <blanch@pncl.co.uk>
> A: rsgb_lf_group@blacksheep.org <rsgb_lf_group@blacksheep.org>
> Data: mercoledė 7 giugno 2000 11.58
> Oggetto: LF: Formula
> 
> 
> >I found the following in an article recently.
> >
> >Quote:
> >
> >"The intensity E (known as the field strength) of a transmission
> >at a distance D from a source transmitting P watts of RF power via
> >a half-wave dipole in a free, unobstructed space, can be estimated
> >using the formula:
> >
> >E=(7*sqrt (P))/D.
> >
> >Thus, for a 2 watt transmitter, the theoretical field strength in
> free
> >space at one metre distance is approximately 10 V/m and at 100 metres
> >distance 0.1 V/m"
> >
> >This formula is new to me and I can't find it in any
> >textbooks I have.  Since it ignores frequency shouldn't
> >it be power flux per unit area and not field strength?
> >Can anyone tell me where it comes from?
> >
> >Walter G3JKV.
> >
> >
> >
> >
> 
> 


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