X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 07 May 2014 07:53:50 -0400 Message-ID: X-Original-Return-Path: Received: from bar01.comporium.net ([208.104.2.35] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTP id 6862110 for lml@lancaironline.net; Wed, 07 May 2014 07:28:24 -0400 Received-SPF: neutral receiver=logan.com; client-ip=208.104.2.35; envelope-from=snopercod@comporium.net X-ASG-Debug-ID: 1399462068-07cf4e4cf0635400001-yPXFKn Received: from rg20.comporium.net (rg20.comporium.net [208.104.2.10]) by barracuda. with ESMTP id GviHaALt6EeR0XxG for ; Wed, 07 May 2014 07:27:48 -0400 (EDT) X-Barracuda-Envelope-From: snopercod@comporium.net X-Barracuda-Apparent-Source-IP: 208.104.2.10 Received: from 33.225.235.68.dsl.brvdnc.dynamic.citcom.Net (EHLO _127.0.0.1_) ([68.235.225.33]) by rg20.comporium.net (MOS 4.3.4-GA FastPath queued) with ESMTP id BCB67311 (AUTH snopercod); Wed, 07 May 2014 07:26:48 -0400 (EDT) X-Original-Message-ID: <536A1873.5020303@comporium.net> X-Original-Date: Wed, 07 May 2014 07:26:43 -0400 From: John Cooper User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 X-Original-To: Lancair Mailing List Subject: [LML] Re: Antennas for 406 MHz ELTs References: X-ASG-Orig-Subj: [LML] Re: Antennas for 406 MHz ELTs In-Reply-To: Content-Type: multipart/alternative; boundary="------------050004080302050608070404" X-Barracuda-Connect: rg20.comporium.net[208.104.2.10] X-Barracuda-Start-Time: 1399462068 X-Barracuda-URL: http://208.104.2.35:8000/cgi-mod/mark.cgi X-Virus-Scanned: by bsmtpd at comporium.net X-Barracuda-BRTS-Status: 1 X-Barracuda-Spam-Score: 0.00 X-Barracuda-Spam-Status: No, SCORE=0.00 using global scores of TAG_LEVEL=1000.0 QUARANTINE_LEVEL=1000.0 KILL_LEVEL=5.0 tests=HTML_MESSAGE X-Barracuda-Spam-Report: Code version 3.2, rules version 3.2.3.5610 Rule breakdown below pts rule name description ---- ---------------------- -------------------------------------------------- 0.00 HTML_MESSAGE BODY: HTML included in message This is a multi-part message in MIME format. --------------050004080302050608070404 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Ron and Tom-- But don't the "whip" antennas supplied with the 406 MHz ELTS require a ground plane? The antenna that comes with the ACK E-04 is clearly dedigned for external mounting on a metal skin. See: http://www.aircraftspruce.com/pages/av/elts_zack/whipantennaE04.php What I am looking for is either a quarter-wave "rubber duck" antenna that mounts directly to the ELT, or preferably a copper foil half-wave dipole that I can bond to the inner surface of my aircraft. Being a Ham Radio operator in a former life, I know that a quarter wave whip antenna is cut for _one specific frequency_ and performance is degraded at all other frequencies unless some kind of "trap" or impedance-matching device is installed. Theoretically, a quarter-wave antenna for 406 MHz should be somewhere around 7" long. For 121.5 MHz it should be around 23" long. Clearly the whip antennas that come with the ELT units are cut for some intermediate frequency which is a compromise that works "OK" at both 406 and 121.5. And what about polarization? The 121.5 and 243MHz signals should be vertically polarized like your COMM antenna(s), but technically the 406 MHz should be _circularly _polarized which would either require a helical antenna or two crossed dipoles. Of course the polarization would depend upon whether your aircraft was upright or not :-( > Subject: > Re: [LML] Re: Antennas for 406 MHz ELTs > From: > Ron Galbraith > Date: > 5/6/2014 7:40 AM > > > I just installed an ME406 ELT. The antenna is around 12-14"long thin whip and is for 121.5/243.0/406mhz. Installs easily inside a glass airframe. > > Ron --------------050004080302050608070404 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit
Ron and Tom--

But don't the "whip" antennas supplied with the 406 MHz ELTS require a ground plane? The antenna that comes with the ACK E-04 is clearly dedigned for external mounting on a metal skin. See: http://www.aircraftspruce.com/pages/av/elts_zack/whipantennaE04.php   What I am looking for is either a quarter-wave "rubber duck" antenna that mounts directly to the ELT, or preferably a copper foil half-wave dipole that I can bond to the inner surface of my aircraft.

Being a Ham Radio operator in a former life, I know that a quarter wave whip antenna is cut for one specific frequency and performance is degraded at all other frequencies unless some kind of "trap" or impedance-matching device is installed. Theoretically, a quarter-wave antenna for 406 MHz should be somewhere around 7" long. For 121.5 MHz it should be around  23" long. Clearly the whip antennas that come with the ELT units are cut for some intermediate frequency which is a compromise that works "OK" at both 406 and 121.5.

And what about polarization? The 121.5 and 243MHz signals should be vertically polarized like your COMM antenna(s), but technically the 406 MHz should be circularly polarized which would either require a helical antenna or two crossed dipoles. Of course the polarization would depend upon whether your aircraft was upright or not :-(

Subject:
Re: [LML] Re: Antennas for 406 MHz ELTs
From:
Ron Galbraith <cfi@instructor.net>
Date:
5/6/2014 7:40 AM		 

I just installed an ME406 ELT.  The antenna is around 12-14"long thin whip and is for 121.5/243.0/406mhz.  Installs easily inside a glass airframe. 

Ron

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