Re: LF: Re: Re: "T" versus "L"aerial

["Dick Rollema" <d.w.rollema@freeler.nl>]

Dear Bryan,

Because the aerial  system is very small, expressed in wavelength,
the voltage on all wires "above" the loading coil will be the
same; unless there is another loading coil between the vertical and
horizontal parts of the "T".  When the two horizontal
parts have equal capacitances to earth the current distribution on these
wires will be similar and that will also be the case for the two vertical
wires of the "double L".  In case of unequal capacitances
the current in the vertical wires will be different. But because the
wires are very near to each other they act as a single radiator carrying
the sum of the currents in the two wires.
So for all practical purposes there is no difference in performance of
the "double L" and a real "T".

I use the "double L" instead of a real "T" because
the aerial is also used as a multiband dipole with open line feeder on
160m and the HF bands.

73, Dick, PA0SE 

At 22:04 28-12-03, you wrote:
> I find it difficult to believe that
> there is any different loading seen at
> the bottom of two L's in parallel but with opposing horizontal parts
> from
> that seen by a single wire vertical to the Tee or that there is any
> different current distribution or radiated pattern.
>
> If there are those that do not then I ask::
> what is the voltage difference between the two vertical wires at
> their
> respective junctions with their own horizontals ?
>
> Bryan G3GVB
>
>
>
> ----- Original Message -----
> From: "hamilton mal" <g3kev.ham@virgin.net>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: 28 December 2003 18:04
> Subject: LF: Re: "T" versus "L"aerial
>
>
>
>   ----- Original Message -----
>   From: Dick Rollema
>   To: LF-Group
>   Sent: Saturday, December 27, 2003 2:09 PM
>   Subject: LF: "T" versus "L"aerial
>
>
>   To All from PA0SE
>
>   Further to my e-mail of 26 December I measured the field strength
> as
> radiated by the aerial in
>   Inverted L-configuration. From this I found EMRP = 57
> milliwatt.
>
>   This confirms the benificial effect of top loading. The T-aerial
> radiated
> 140 milliwatt.
>
>   So going from a single 20m top load wire for the "L" to
> 2 x 20m for the
> "T" resulted in an improvement by a factor 2.46 (3.9dB) in
> radiated power.
>
>   The vertical part of the "T" consisted of an open wire
> feedline of 11m
> with the two wires connected in parallel in the attic shack. For the
> "L" one
> of the feedline wires was removed. I assume this did not appreciably
> affect
> the EMRP.
>   HI Dick
>   From your explanation using open wire feeder you are using an inv
> L with
> one feeder wire connected and with the 2 feeders strapped at the shack
> end
> then you have two inverted  L antennas in parallel. A true T antenna
> has
> both feeder wires connected at the top as well as the bottom, in fact do
> not
> use open wire feeder, connect one wire to the centre of your T horizontal
> at
> the top and the bottom of your single wire to the loading coil and
> matching
> unit.
>   73 de Mal/G3KEV
>
>                            
> .
>
>   73, Dick, PA0SE