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Re: LF: ERP calculations / measurements

To: [email protected]
Subject: Re: LF: ERP calculations / measurements
From: Brian Rogerson <[email protected]>
Date: Sat, 06 Dec 2008 10:19:49 +0000
In-reply-to: <[email protected]>
References: <[email protected]> <001e01c94a77$cc1fa780$a402a8c0@Inspiron> <004e01c94a9c$dddbe860$0900a8c0@AM> <[email protected]> <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Rik and LF

Your email below prompted me to carry out another afternoon of measurements from higher ground for the station FS/ERP survey.  The results seem spectacular though I am unsure of what they mean.  I hope to place the data on my web site later.

73, Brian CT1DRP



At 09:36 20/11/2008, you wrote:
Hello group,

it seems to be generally accepted that a small vertical antenna has a gain of 3 (4.77dBi / 2.62dBd), due to the radiation pattern in the vertical plane.
But in very few cases this gain seems to be measured when doing ERP measurements.
As far as I understand this gain of 3 is based on a perfect ground (endless conductivity) that acts as a (perfect) mirror and thus creates the "mirror image" needed for radiation.
But what about a short vertical antenna above a not-so-perfect ground?
I have done some simulations with MMANA-GAL (15m high vertical at 500kHz) and over a perfect ground I get the expected 4.77dBi and a take-off angle of 0 degrees.
If the conductivity is not endless the gain drops and the take-off angle rises:
1000mS/m (salt water) = 4.5dBi / 9 degrees
500mS/m (clay) = 4.4dBi / 10 degrees
50mS/m (marsh) = 3.9dBi / 14 degrees
15mS/m (loam) = 3.5dBi / 17 degrees
5mS/m (wet sand) = 2.9dBi / 21 degrees
0.05mS/m (dry sand) = -1.5dBi / 32 degrees

Could this explain (a part of) the missing dB's ?

73, Rik  ON7YD - OR7T


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