Return-Path: Received: (qmail 14666 invoked from network); 12 Oct 1999 13:59:43 +0100 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by guiness.force9.net with SMTP; 12 Oct 1999 13:59:43 +0100 Received: from majordom by post.thorcom.com with local (Exim 3.02 #1) id 11b1Hv-0005Em-00 for rsgb_lf_group-outgoing@blacksheep.org; Tue, 12 Oct 1999 13:44:19 +0100 Received: from [143.179.236.31] (helo=Iguanodon.big-orange.net) by post.thorcom.com with esmtp (Exim 3.02 #1) id 11b1Ht-0005Eh-00 for rsgb_lf_group@blacksheep.org; Tue, 12 Oct 1999 13:44:17 +0100 Received: from w8k3f0 ([143.179.151.162]) by Iguanodon.big-orange.net (Netscape Messaging Server 3.6) with SMTP id AAA50BA; Tue, 12 Oct 1999 14:44:06 +0200 Message-ID: <000f01bf14b0$b923e440$a297b38f@w8k3f0> From: "Dick Rollema" To: "LF-Group" Cc: "John Devoldere, ON4UN" , "Koos Fockens, PA0KDF" , "Koos Fockens, PA0KDF" , "Jaap Kroon, PA0IF" , "Ger van Went, PA0GER" , "Hans Peltzer, PA0HRP" Subject: LF: Directivity of inverted-L antenna Date: Tue, 12 Oct 1999 14:52:05 +0200 MIME-Version: 1.0 Content-Type: text/html; charset=windows-1252 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 4.72.3110.5 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Content-transfer-encoding: 8bit
To All from PA0SE
 
A question by Jaap, PA3GUC, prompted me to investigate the directivity of an Inverted L-antenna.
 
I modeled by computer an antenna with 10 m vertical and a horizontal part of different lengths; made of 1.5 mm diameter (16 SWG) copper wire.  .
 
"Front" in F/B ratio is along the top wire in the direction of the open end.
 
The impedance at the feed point is calculated over  perfect earth. For gain, F/B ratio and take-off angle real ground is used.
 
Gain is expressed in dBd; gain over a halfwave lossless dipole in free space.
 
Rrad is the radiation resistance; Rloss  the resistance of the wire; X the reactance at the feedpoint. The minus sign indicates capacitive reactance.
Zant = Rrad + Rloss + jX.
 
Length of    Rrad      Rloss     Xant      F/B  Sky wave   F/B surface wave     Max. gain    Take-off angle
top (m)         Ohm      Ohm       Ohm               dB                             dB                       dBd          for max. gain
                                                                                                                                                               degrees
 
 10                  0.0176   0.130     -9659             0,17                             0                       -7.76              18
 
 20                  0.0221    0.198    -6609             0 .41                            0                       -8.39              18
 
 50                  0.0276    0.403    -3386             1.16                             0.02                 -10.00            18 
 
 100                0.0297    0.752    -1835             2.34                             0.05                 -11.49            18
 
 200                0.0337    1.496    -885               4.14                             0.11                  -12.74            20
 
 400                0.0383     3.44     -256                4.40                             0.23                 -13.21            30
 
 537.57           0.051       5.63       0                   1.99                             0.29                  -12.92            58
 
 
During daylight contacts over a few hundred kilometres are made by the surface wave and the Inverted
L-antenna shows no useful directivity.
 
After dark the skywave appears and some directivity can be obtained, but only by long top wires.
 
The decreasing maximum gain with longer top wires is caused by a widening vertical arc within which radiation takes place.
In the case of a resonant antenna  (last line) the gain is  constant within 1 dB over elevations from
about 15 to 100 degrees!
 
73, Dick, PA0SE
JO22GD
D.W. Rollema
V.d. Marckstraat 5
2352 RA Leiderdorp
The Netherlands
Tel. +31 71 589 27 34