Envelope-to: dave@picks.force9.co.uk
Delivery-date: Sun, 05 Feb 2006 10:49:22 +0000
Message-ID: <001901c62a41$ae6c45d0$2101a8c0@AUG2004>
From: "Walter Blanchard" <blanch@pncl.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <007001c62a34$97e808b0$2101a8c0@AUG2004> <200602051131570102.0488A03E@smtp.wanadoo.fr>
Date: Sun, 5 Feb 2006 10:48:06 -0000
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Subject: {Spam?} Re: LF: {Spam?} Active_antennas
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John,

"Height gain" at LF/MF is caused by quite a different mechanism from the 
"height gain" at VHF.
VHF observations are irrelevant, I'm afraid.

Walter G3JKV.

----- Original Message ----- 
From: "John RABSON" <john.rabson@wanadoo.fr>
To: <rsgb_lf_group@blacksheep.org>
Cc: <r.gill@bcra.org.uk>
Sent: Sunday, February 05, 2006 10:31 AM
Subject: Re: LF: {Spam?} Active_antennas


> 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.
>
>
>
>
>
>