X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 24 Feb 2006 21:44:03 -0500 Message-ID: X-Original-Return-Path: Received: from smtp109.sbc.mail.mud.yahoo.com ([68.142.198.208] verified) by logan.com (CommuniGate Pro SMTP 5.0.8) with SMTP id 996901 for lml@lancaironline.net; Fri, 24 Feb 2006 12:08:43 -0500 Received-SPF: none receiver=logan.com; client-ip=68.142.198.208; envelope-from=elippse@sbcglobal.net Received: (qmail 52336 invoked from network); 24 Feb 2006 17:07:56 -0000 Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@66.122.66.161 with login) by smtp109.sbc.mail.mud.yahoo.com with SMTP; 24 Feb 2006 17:07:55 -0000 X-Original-Message-ID: <000501c63964$dadb5d40$a1427a42@Computerroom> From: "Paul Lipps" X-Original-To: Subject: ground plane X-Original-Date: Fri, 24 Feb 2006 09:07:52 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0002_01C63921.CAC83420" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0002_01C63921.CAC83420 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable The purpose of the ground plane is to form a virtual antenna on the = opposite side of the monopole; this is referred to as an image antenna. = It does this by effectively inverting the polarity and reflecting the = wave up into the monopole to add to its incident energy. Metal surfaces = do not reflect energy. This apparent reflection is due to current being = generated in the ground plane surface by the incident rf wave, which = then acts as an antenna and re-radiates the signal. If the ground plane = material is a poor conductor, or is not making continuous contact = throughout, it is much less effective as a radiator. These electrically = small ground planes do not work well at low grazing angles, which is = where most of the received signal is coming from in level flight. = Patterns of monopoles over an electrically short or poorly conducting = ground plane show decreased gain normal to the monopole axis. Curved, = rather than flat, ground planes throw something else into the mix, with = hard-to-predict behaviour resulting. Look! ground-plane antennas work, = but are several dB below the gold-standard of the half-wave dipole for = horizontal radiation. If you are not worried about Tx-Rx at long = distances, live with it! If you want the best Tx-Rx, experiment with the = half-wave dipole through the horizontal stab I referred to in a previous = posting. Also, use the best low-loss, low leakage coax available, = especially to make up for the deficiencies of the monopole's ground = plane. ------=_NextPart_000_0002_01C63921.CAC83420 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
    The purpose of the ground = plane is to=20 form a virtual antenna on the opposite side of the monopole; this is = referred to=20 as an image antenna. It does this by effectively inverting the polarity = and=20 reflecting the wave up into the monopole to add to its incident energy. = Metal=20 surfaces do not reflect energy. This apparent reflection is due to = current being=20 generated in the ground plane surface by the incident rf wave, which=20 then acts as an antenna and re-radiates the signal. If the = ground=20 plane material is a poor conductor, or is not making continuous contact=20 throughout, it is much less effective as a radiator. These electrically = small=20 ground planes do not work well at low grazing angles, which is = where most=20 of the received signal is coming from in level flight. Patterns of = monopoles=20 over an electrically short or poorly conducting ground plane show = decreased gain=20 normal to the monopole axis. Curved, rather than flat, ground = planes throw=20 something else into the mix, with hard-to-predict behaviour resulting. = Look!=20 ground-plane antennas work, but are several dB below the gold-standard = of the=20 half-wave dipole for horizontal radiation. If you are not worried about = Tx-Rx at=20 long distances, live with it! If you want the best Tx-Rx, experiment = with the=20 half-wave dipole through the horizontal stab I referred to in a previous = posting. Also, use the best low-loss, low = leakage coax available,=20 especially to make up for the deficiencies of the monopole's ground=20 plane.
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