Message-ID: <20100123151204.tm00cc8fmogkc80g@webmail6.kuleuven.be>
Date: Sat, 23 Jan 2010 15:12:04 +0100
From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
References: <9afca2641001230502q45fb0825n3ee7dca1774c95eb@mail.gmail.com>
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Subject: Re: LF: G3XBM's ERP on 500kHz
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Roger,

I simulated the antenna based on your description (with MMANA) and the =20
current through the vertical wire seems to be quite constant. So the =20
tophat works well and the effective height will be more or less the =20
physical height.
The simulation gives a radiation resistance of 0.074 Ohm, so with 0.12 =20
A a radiated power just over 1mW EMRP (1.75mW ERP).
In the real world it will be some dB's less (as Jim stated recently), =20
probably something like 0,5 to 1mW ERP.

Very impressive that it covers over 1200km.

73, Rik  ON7YD - OR7T

Quoting Roger Lapthorn <rogerlapthorn@gmail.com>:

> All,
>
> Yesterday I did a recalculation of the G3XBM ERP based on the  =20
> classic formula and re-measurements of my antenna current. My  =20
> antenna is a 5m long vertical with a spiral top hat of about 7 turns =20
>  about 1.5m x 1.5m. Not being clear how to model the top hat I  =20
> assumed effective heights of 5, 4 or 3m. The measured antenna  =20
> current is 0.12A.
>
> My results are as follows:
>
> Assumed effective height 5m     ERP =3D 1.53mW
> Assumed effective height 4m     ERP =3D 0.98mW
> Assumed effective height 3m     ERP =3D 0.55mW
>
> So, I believe my 1mW ERP previously calculated is not a bad  =20
> estimate, and it may indeed be lower than this figure.
>
> 73s
> Roger G3XBM
> --
>
> http://g3xbm-qrp.blogspot.com/
> http://www.g3xbm.co.uk
> http://www.youtube.com/user/G3XBM
> G3XBM    GQRP 1678      ISWL G11088
>