Return-Path: Received: (qmail 21508 invoked from network); 3 Jan 2004 12:39:58 -0000 Received: from unknown (HELO ptb-mxscan03.plus.net) (212.159.14.237) by ptb-mailstore02.plus.net with SMTP; 3 Jan 2004 12:39:58 -0000 Received: (qmail 54998 invoked from network); 3 Jan 2004 12:39:57 -0000 X-Filtered-by: Plusnet (hmail v1.01) X-Priority: 3 X-MSMail-Priority: Normal X-Spam-detection-level: 11 Received: from ptb-mxcore03.plus.net (212.159.14.217) by ptb-mxscan03.plus.net with SMTP; 3 Jan 2004 12:39:57 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore03.plus.net with esmtp (Exim) id 1Acl4O-000ECU-MS for dave@picks.force9.co.uk; Sat, 03 Jan 2004 12:39:56 +0000 X-Fake-Domain: majordom Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Acl42-000453-BC for rs_out@blacksheep.org; Sat, 03 Jan 2004 12:39:34 +0000 Received: from [213.218.75.232] (helo=smtp03.freeler.nl) by post.thorcom.com with esmtp (Exim 4.14) id 1Acl41-00044u-2o for rsgb_lf_group@blacksheep.org; Sat, 03 Jan 2004 12:39:33 +0000 Received: (qmail 6301 invoked from network); 3 Jan 2004 12:39:32 -0000 X-Fake-Domain: unknown Received: from unknown (HELO w8k3f0.freeler.nl) ([62.21.149.32]) (envelope-sender ) by smtp03.freeler.nl (qmail-ldap-1.03) with SMTP for ; 3 Jan 2004 12:39:30 -0000 Message-ID: <6.0.1.1.2.20040103121138.0280f960@POP3.freeler.nl> X-Sender: FRE0000086604@POP3.freeler.nl (Unverified) X-Mailer: QUALCOMM Windows Eudora Version 6.0.1.1 Date: Sat, 03 Jan 2004 12:30:09 +0100 To: rsgb_lf_group@blacksheep.org From: "Dick Rollema" In-reply-to: <000001c3d009$acf7a620$c7e47f50@Smisan> References: <6.0.1.1.2.20031229161651.027e8660@POP3.freeler.nl> <000001c3d009$acf7a620$c7e47f50@Smisan> 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=0.2 required=5.0 tests=HTML_FONTCOLOR_BLUE,HTML_FONT_BIG,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,

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: 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