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Re: LF: Re: LF antennas

To: [email protected]
Subject: Re: LF: Re: LF antennas
From: "Mike Dennison" <[email protected]>
Date: Thu, 9 Mar 2000 12:09:57 -0000
In-reply-to: <[email protected]>
References: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
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)

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