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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <405452.30291.qm@web86408.mail.ird.yahoo.com>
Date: Sat, 5 May 2007 18:43:58 +0100
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Subject: LF: Re: Field Strength Meter
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Status: O

Hi Chris Dick usually monitors the group but I am sure he would not mind me
passing his emal address to you. I am sure he will be keen to help you adapt
his instrument to 500kHz
E-mail Address(es):
  dickrollema@casema.nl

Cheers de Alan G3NYK


----- Original Message -----
From: CHRISTOPHER OSBORN <c.cjo@btinternet.com>
To: LF group <rsgb_lf_group@blacksheep.org>
Sent: 05 May 2007 18:29
Subject: LF: Field Strength Meter


> Has anyone built the field strength meter from the 'LF Experimenter's
Handbook' (p 83) ?
> I intend to make a similar one but for the 500 kHz band, however a couple
of things in the artical are confusing me:
> (1)
> The formula (3) for a Helmholtz coil pair gives  H = I / (1.40 * r )
> where I is the coils' current in Amperes and r the coils'  radii in
metres.
> Looking on the internet the Helmholtz formula also includes the
permeablility of free space  -  4 * PI * 10 ^ -7  !!    so is there a
misprint ?
> (2)
> The artical gives the required magnetic field to equate to an electric
field strength of  5 mV / m as being 13.3 uA / m
> I follow the working for this ok but if the Helmholtz coils are being fed
from a signal generator with a series 50 ohms resistor surely the output
voltage setting would be impracticably low  -  about  540 uV ( I think )
>
> I can make the Helmholtz coils as per the artical (i.e. with radii of
0.292 m) so what signal generator setting would I need to generate the
required field strength of 13.3 uA / m and how would I achieve this ?
> Any lessons learned by members of LF Group while making this meter would
be much appreciated.
>
> 73 Chris G3XIZ
>
>
>
>
> ---------------------------------
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