Message-ID: <DA5EC04FF8D54681865FC5DE943CFA19@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <4A181EEC.5050600@btconnect.com> <9670125E608A4D63AE541048B2177A02@JimPC> <001a01c9dc5e$b6bbb040$0301a8c0@mal769a60aa920> <4A193360.9010508@btconnect.com>
In-Reply-To: <4A193360.9010508@btconnect.com>
Date: Sun, 24 May 2009 20:12:17 +0100
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Subject: Re: LF: Re: Re: First Portable Trip
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--------------------------------------------------
From: "Richard Newstead" <g3cwi@btconnect.com>
Sent: Sunday, May 24, 2009 12:45 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Re: Re: First Portable Trip

>
> mal hamilton wrote:
>> Jim
>> I did not say an inv L virtually lying on the ground as in Richards
>> case(1 METRE ABOVE GROUND), this is more like a beverage antenna.
> This is all very interesting. I have spent an hour in a darkened room
> contemplating suitable antennas (well not quite). Comments from experts
> welcome:
>
> 1) T antenna. Am I right in thinking that in the classical T
> configuration, the horizontal part of the aerial is only there to add
> capacity - i.e. it makes no contribution to the groundwave?

..........Yes

 If so, I
> assume that I can use very thin wire for the T?

.........No , depends on thin, but   I sqr  R  losses and skin losses will 
be high

>
> 2) In the more likely configuration with "horizontal" wires actually
> acting as an inverted V can I still use very thin wire without reducing
> performance?

...... As above

>
> 3) Is there any benefit to be gained by having an inductor at the top of
> the vertical section of the T?

........  I would say Yes , I use a top loading  coil on my  inverted L with 
2 wire horizontal capacity section , A centre mounted coil , when 
modelled gives slightly  more gain

 If so, will the loss of the inductor be
> relevant if the part of the antenna above it (the T wires) don't
> contribute to useful radiation?

......... would depend on the  coil , I use 40 turns of insulated   35 amp 
mains cable on a 4 inch former .. no idea of the losses  but the system 
seems to  radiate ,,,,,,  assume the  only  losses could  be dielectric 
losses or I sqr R , but with a heavy cable and polycarbonate former , I 
don't expect much ...... you  are making a series acceptor cct , max I 
should be a the  coil/cap section junction , which will be the highest point 
.

73, Graham .,.

NB  I looked into the portable antenna (for  use with a handy  fence) and 
found that a 'arrow shape'  or drooping T , with 10 mtr vertical section 
(fishing pole) with sloping  top section looked to give a reasonable 
performance, however , once the ends of the arrow , dropped to  6 feet or 
less , the radiation pattern and the performance became much reduced .. can 
only  assume it was the capacity of the  end wires to  earth



>
> 73
>
> Richard
> G3CWI
>
>
>



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