Message-ID: <000601c3d2c3$2bd34e70$b733f7c2@johnb5a82ea1a4>
From: "John Rabson" <word.factory@zetnet.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <6.0.1.1.2.20031229161651.027e8660@POP3.freeler.nl> <000001c3d009$acf7a620$c7e47f50@Smisan> <6.0.1.1.2.20040103121138.0280f960@POP3.freeler.nl>
Date: Sun, 4 Jan 2004 09:39:06 -0000
MIME-Version: 1.0
Subject: Re: LF: Re: "T" versus "L"aerial
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Sender: <owner-rsgb_lf_group@blacksheep.org>
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

How much horizontally polarised skywave is there and how well does it
propagate?

Would it be worth constructing an aerial that favoured skywave?

73
John Rabson G3PAI

----- Original Message ----- 
From: "Dick Rollema" <d.w.rollema@freeler.nl>
To: <rsgb_lf_group@blacksheep.org>
Sent: Saturday, January 03, 2004 11:30 AM
Subject: RE: LF: Re: "T" versus "L"aerial


> To All from PA0SE,
>
> Mike,  PC4M, wrote:
>
> At 02:50 1-1-04, you wrote:
> >Dear Dick / Bob and Lofers,
> >
> >Does the computer calculate the earth losses in the return path from the
> >aerial system to the transmitter? If it would then the earth losses in a
T
> >should have been significantly less then the L alternative. There are two
> >separate return currents
> >(parallel resistance) and each with a smaler physical length (lower
> >R-earth)  in a T system resulting in more ERP if compared to an L system.
>
> In the computer simulation no resistances were included. That means that
> the 1 kW fed to the aerial is completely radiated. Even an extremelly
short
> vertical with no top load would do so and produce the calculated 29.9mV/m
> at 10km
>
> Bu the point raised by Bob, ZL2CA, was that the current in the single wire
> topload  of the "L" would generate a horizontally polarised field. In the
> "T" the currents  in the two topload wires flow in opposite directions so
> the horizontally polarised fields caused by these currents would at least
> partially cancel each other.
> The horizontally polarised field is radiated as a sky wave and the power
in
> it detracts from that in the vertically polarised field of the ground
wave.
> If the above reasoning were correct it could be expected that the "T"
would
> produce a stronger ground wave than the "L" because less power disappears
> in the horizontally polarised sky wave.
> The simulation has shown that this is not the case.
>
> The subject of losses in the earth  and surrounding objects has been
> treated very well by Jim, M0BMU, in his e-mail.
>
> 73, Dick, PA0SE
>
>
> >-----Oorspronkelijk bericht-----
> >Van: owner-rsgb_lf_group@blacksheep.org
> >[mailto:owner-rsgb_lf_group@blacksheep.org] Namens Dick Rollema
> >Verzonden: maandag 29 december 2003 16:37
> >Aan: rsgb_lf_group@blacksheep.org
> >Onderwerp: Re: LF: Re: "T" versus "L"aerial
> >
> >To All from PA0SE
> >
> >Bob, ZL2AC wrote:
> >
> >
> >
> >Dick PA0SE,
> >
> >Fine on the test result.  As you stated, the tested T has twice the
amount
> >of top loading wire (2x 20 metres) than the L (1x 20 metres).
> >
> >It would be interesting to know if a T is better than an L for constant
> >length top loading i.e. what the difference is if the upwire joins at the
> >end or the middle of the horizontal top wire (theory suggests the T is
> >better as there is minimal horizontally polarised component).
> >
> >Bob,  I cannot answer your question by a practical experiment but used
> >computer simulation instead by means of K6STI's program Antenna
Optimizer.
> >
> >I modeled two antennas with a vertical element of 20m.  One an Inverted
> >L-antenna with a horizontal top load wire of 40m. The other a T-antenna
> >with a top load of 2 x 20m.
> >Both antennas  without losses, over perfect ground and fed with 1kW.
> >
> >At a distance of 10km (so well outside the near field region) and over
> >perfect ground both antennas produced a vertically polarised field of
> >29.9mV/m. The horizontally polarised field was zero; but this is to be
> >expected because over a perfect conducting ground a horizontal field
> >component cannot exist.
> >
> >73, Dick, PA0SE
> >
> >Original message:
> >
> >
> >To: <mailto:rsgb_lf_group@blacksheep.org>LF-Group
> >Sent: Sunday, December 28, 2003 3:09 AM
> >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.
> >73, Dick, PA0SE
>