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: [email protected]
[mailto:[email protected]] On Behalf Of Gary - G4WGT
Sent: 12 August 2006 16:48
To: [email protected]
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: [email protected]
[mailto:[email protected]]On Behalf Of Rik Strobbe
Sent: 11 August 2006 22:10
To: [email protected]
Subject: Re: LF: Re: antenna: how to get max. capacity
Quoting captbrian <[email protected]>:
> 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
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