Return-Path: Received: (qmail 83531 invoked from network); 4 Jan 2004 14:59:01 -0000 Received: from unknown (HELO ptb-mxscan02.plus.net) (212.159.14.236) by ptb-mailstore01.plus.net with SMTP; 4 Jan 2004 14:59:01 -0000 Received: (qmail 1032 invoked from network); 4 Jan 2004 14:59:01 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Priority: 3 X-MSMail-Priority: Normal X-Spam-detection-level: 11 Received: from ptb-mxcore02.plus.net (212.159.14.216) by ptb-mxscan02.plus.net with SMTP; 4 Jan 2004 14:58:58 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore02.plus.net with esmtp (Exim) id 1Ad9iT-000Pyb-Vk for dave@picks.force9.co.uk; Sun, 04 Jan 2004 14:58:58 +0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Ad9hx-0001kz-R1 for rs_out@blacksheep.org; Sun, 04 Jan 2004 14:58:25 +0000 Received: from [213.218.75.231] (helo=smtp02.freeler.nl) by post.thorcom.com with esmtp (Exim 4.14) id 1Ad9ho-0001kq-P4 for rsgb_lf_group@blacksheep.org; Sun, 04 Jan 2004 14:58:16 +0000 Received: (qmail 21987 invoked from network); 4 Jan 2004 14:58:13 -0000 X-Fake-Domain: unknown Received: from unknown (HELO w8k3f0.freeler.nl) ([62.21.138.3]) (envelope-sender ) by smtp02.freeler.nl (qmail-ldap-1.03) with SMTP for ; 4 Jan 2004 14:58:11 -0000 Message-ID: <6.0.1.1.2.20040104145328.038a80d0@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl (Unverified) X-Mailer: QUALCOMM Windows Eudora Version 6.0.1.1 Date: Sun, 04 Jan 2004 15:29:15 +0100 To: rsgb_lf_group@blacksheep.org From: "Dick Rollema" In-reply-to: <006401c3d21e$16191420$03c828c3@captbrian> References: <6.0.1.1.2.20031229161651.027e8660@POP3.freeler.nl> <000001c3d009$acf7a620$c7e47f50@Smisan> <6.0.1.1.2.20040103121138.0280f960@POP3.freeler.nl> <006401c3d21e$16191420$03c828c3@captbrian> MIME-Version: 1.0 Subject: Re: LF: Re: "T" versus "L"aerial Content-Type: text/html; charset=windows-1252 X-Spam-Checker-Version: SpamAssassin 2.60 (1.212-2003-09-23-exp) on post.thorcom.com X-Spam-Status: No, hits=0.0 required=5.0 tests=HTML_MESSAGE autolearn=no version=2.60 X-SA-Exim-Scanned: Yes Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SPAMFiltered: yes X-Spam-Rating: 1 Content-transfer-encoding: 8bit To All from PA0SE

Bryan, G3GVB wrote:

Then the simulation must surely be wrong.!
I spent a long time reading a 160/80 m antenna book by ON4 ?? before
realising that the performance of various antenna configurations confidently
reported as if they actually existed, were in fact only the result of
computer simulations.

The simulation is certainly right under the conditions used as input. One of the conditions I used was that no resistance existed in the aerial system. This is certainly not realistic; but the effect of resistance is that the actual power radiated is less than the simulation indicated because power is lost in the resistance of the wire and in the earth that forms part of the return path for the aerial current. But this does not affect the shape of the radiation pattern.

That you can get vertically radiated horizontally polarised radiation for
_nothing_ using the simulation program has to tell you something about its
limitations .

I had a look at the radiation pattern of the horizontally polarised field. In the case of the "L" there is maximum under 90 degrees elevation: straight up.
For the "T" there is a minimum under 90 degrees. But the pattern is split into two lobes with maxima under 45 and 135 degrees, so there is no complete cancellation.

The radiation pattern for the vertically polarised field over both perfect and real ground is identical for "L" and "T". When you consider the top load wires as capacitors to earth it is reasonable that the total capacitance is the same for a single wire of 40 m or two wires of 20 m in opposite directions. So the "extra" current in the vertical leg due to the top loading "capacitors" is also the same. And because the current in the vertical part of the aerial generates the vertically polarised field it is logical that the radiation patterns of "L" and "T" are identical.

Both the book and the programs are very good indicators but not _absolute.
truths_

Very true. But both are still very useful as long as the limitations inherent in the modeling of an aerial are kept in mind and the results make sense.

73, Dick, PA0SE

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

>
> 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.****
>