Envelope-to: dave@picks.force9.co.uk
Delivery-date: Sun, 05 Feb 2006 10:33:33 +0000
Message-ID: <200602051131570102.0488A03E@smtp.wanadoo.fr>
In-Reply-To: <007001c62a34$97e808b0$2101a8c0@AUG2004>
References: <007001c62a34$97e808b0$2101a8c0@AUG2004>
Date: Sun, 05 Feb 2006 11:31:57 +0100
From: "John RABSON" <john.rabson@wanadoo.fr>
To: rsgb_lf_group@blacksheep.org
Cc: r.gill@bcra.org.uk
Mime-Version: 1.0
Subject: Re: LF: {Spam?} Active_antennas
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

G8DSU has been doing some measurements on height gain at UHF and is also interested in active antennas at LF for cave radio purposes.  I will copy this to him because I'm not sure whether he is currently reading this list.

John G3PAI

*********** REPLY SEPARATOR  ***********

On 05/02/2006 at 09:14 Walter Blanchard wrote:

>The theory behind the "height gain" observed using small LF active
>antennas at different heights has to do with compression of the near-earth
>LF potential gradient caused by the grounded "mast" holding the antenna.
>The essential bit is that there is a grounded connection between the
>antenna and receiver, which may be just the outer of the co-ax cable. It
>would be an interesting experiment to repeat the "height gain" experiment
>without any connection to ground. This could be done by building an active
>antenna with a little transmitter to re-radiate the received LF signal (on
>2.4 GHz?) and poking it up using a fibreglass mast. If the theory is right
>then there wouldn't be any height gain. Might do it myself sometime but
>anyone else interested?
>
> Walter G3JKV.