Received-SPF: neutral (gmail.com: 193.82.116.20 is neither permitted nor denied by best guess record for domain of owner-rsgb_lf_group@blacksheep.org)
Message-ID: <7D653C9C42F5D411A27C00508BF8803D06B4628F@mail.dstl.gov.uk>
From: Talbot Andrew <ACTALBOT@mail.dstl.gov.uk>
To: rsgb_lf_group@blacksheep.org
Date: Mon, 14 Aug 2006 10:18:55 +0100
MIME-Version: 1.0
Subject: RE: LF: Re: antenna: how to get max. cap	acity
Content-Type: text/plain
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

The 198kHz transmitter at Droitwich has four wires forming the vertical,
with a four wire top hat.  When I first put up my LF antenna I thought "they
must know what they're doing" and copied the multiple vertical wire concept
and chose with 3 up and top wires, although with a spacing of only 300m.
At 7m high, and a top hat of 14 m length (x 300mm) with a plethora of ground
rods in heavy clay, I manage typically 100 ohms antenna resistance at 137kHz
- although it increases by 20 - 50% in wet weather due to extra absorbtion
of the reactive E filed in foliage and wet roof tiles.  Originally I only
had 150mm spacing, and going to 300mm did make a noticeacbe improvement, but
I was never serious enough about getting loadsa mega-erp to try making it
any larger.

The vertical element tapers from a single point about 2m above the groung to
the full width at the top.  I could try bunching the vertical conductors
together to test, but thst would then involve going on the air (!) and
actually getting some measured signal reports.

Andy  G4JNT
www.scrbg.org/g4jnt/

 
-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Gary - G4WGT
Sent: 12 August 2006 16:48
To: rsgb_lf_group@blacksheep.org
Subject: RE: LF: Re: antenna: how to get max. capacity

Hi Rik & LF,

I remember seeing a multi top wire LF antenna with multi wire vertical
conductors somewhere & I found it in the 'Low Frequency Experimenters
Handbook' in an article written by Peter G3LDO. He shows a 4 wire top with a
4 wire vertical feed & describes it as a 'Traditional T LF Antenna'. What I
am curious about is that if it is detremental to have this multi wire
vertical arrangement as you stated, why has Peter shown it in his article? I
have an Admiralty book 'Handbook of Wireless Telegraphy' (1938) which shows
the same type of T antenna with a multi wire vertical section.  I have also
seen articles elsewhere (maybe on internet) regarding multi wire verticals &
tops were the wires are in a  circular arrangement/format & are presented as
'Cage Antennas & Cage Dipoles' although I believe to increase bandwidth.

The reason I am interested is that I have thought about a similar
arrangement because of my small garden area like Dick.

Comments invited please.

Gary - G4WGT.


-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org]On Behalf Of Rik Strobbe
Sent: 11 August 2006 22:10
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: antenna: how to get max. capacity


Quoting captbrian <captbrian@ukonline.co.uk>:

> Make the vertical of three parallel conductors , each to the centre of
each
> top wire

Using multiple vertical wires will increase the antenna capacitance but also
decrease the radiation resistance. I guess that a thing you don't want.

73, Rik  ON7YD - OR7T


Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm


"This e-mail is intended for the recipient only.  If you are not the
intended recipient you must not use, disclose, distribute, copy, print,
or rely upon this e-mail. If an addressing or transmission error has
misdirected this e-mail, please notify the author by replying to this e-mail."

"Recipients should note that all e-mail traffic on MOD systems is
subject to monitoring and auditing."