From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Thu, 9 Mar 2000 12:09:57 -0000
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Subject: Re: LF: Re: LF antennas
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ON7YD wrote:
> Now we take the real-world case and assume a loss of 100 Ohm (environement
> + coil). If we put 100W into this system we will have an antennacurrent of
> 1A and radiate 8.2mW (-42dB compared to the 'perfect case'). The question
> is if we can take the directivity of a perfect vertical (2.6dB) into
> account ? My opinion is that we have to take this gain into account, as
> the enviromental losses already played their part by limiting the
> antennacurrent. But the only way to find out what really happens is to
> measure the radiation pattern of the antenna, is the anyone with acces to
> a small airplane or helicopter ?

Hmmm. Well I think we do have to take earth losses into account 
twice. This is because it not only affects the ERP because of the 
effective resistance in series with the source (which is also affected 
by any resistance in the connection to the earth), but it also affects 
the 'ground gain' which is the result of reflection from the ground 
after the signal has left the antenna. I am inclined to think that in a 
practical amateur LF station there is little or no ground gain by 
reflection, except perhaps where the station is very near the sea. 
By 'ground' I am including any radial system which in a commercial 
station dramatically improves the real ground resistance close to 
the antenna, but is usually very inefficient in an amateur station.


Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm