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Message-ID: <3.0.1.16.19990625122907.2e7ff5b8@mail.cc.kuleuven.ac.be>
Date: Fri, 25 Jun 1999 12:29:07
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: ERP Calculations
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At 10:17 25/06/99 +0100, G3XDV wrote:
>ON7YD wrote:
>> 
>> Pure mathematical the radiation resistance of a short (in wavelength)
>> vertical monopole above a perfect ground is :
>> 
>>    Ra = 40 . Pi^2 . l^2 / L^2
>> ...
>> The same vertical with a infinite top-capacitance has a radiation
>> resistance of
>> 
>>    Ra  = 160 . Pi^2 . l^2 / L^2
>> 
>
>OK, so you agree with the Admiralty Handbook figure of 160 for a 
>perfect top section (the figure 40 you quote at the start must 
>assume that L is the =actual= height of a vertical antenna as the 
>effective height is half that of a Marconi with a perfect top). Of 
>course the figure of 160 must be corrected for effective height as 
>you suggest.

The first formula (with 40) is valid for a short vertical monopole without
any topload over a perfect ground, the second formula (with 160) is valid
for a short vertical monopole with an infinite topload above a perfect ground.

>So for any practical short Marconi, ERP is:
>I^2 x 160 x pi^2 x effective height^2 divided by wavelength^2
Only if the topload is infinite, otherwise it will be less.

>You mentioned the effect of an imperfect ground. Doesn't that just 
>come into the losses that reduce the current?
That is what I thought so far, but some days ago I had a discussion about
that with someone who has been professionaly involved in this matter and
for him it was not that straightforward. So I would like know the opinions
of the LF-group members.

73, Rik


Rik Strobbe  ON7YD
rik.strobbe@fys.kuleuven.ac.be
Villadreef 14  B-3128 Baal  BELGIUM   (JO20IX)