---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Mon 04/11/22: 7 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:49 AM - Transponder antenna ground plane (Tom Barter) 2. 09:12 AM - Re: Transponder antenna ground plane (user9253) 3. 09:15 AM - Re: Transponder antenna ground plane (Robert L. Nuckolls, III) 4. 09:25 AM - Re: Transponder antenna ground plane (Charlie England) 5. 11:57 AM - Re: Transponder antenna ground plane (Tom Barter) 6. 12:58 PM - Re: Transponder antenna ground plane (user9253) 7. 01:44 PM - Re: Transponder antenna ground plane (Peter Pengilly) ________________________________ Message 1 _____________________________________ Time: 08:49:24 AM PST US From: "Tom Barter" Subject: AeroElectric-List: Transponder antenna ground plane Preparing to install the transponder ground plane in a tube and fabric airplane, and there seems to be a large amount of conflicting information on the size and shape needed. I have seen several references to an octagonal ground plane, and that would work well in my application. I would be using a Comant CI-105 fin style antenna. Any details on the dimensions best for the octagonal ground plane, or comments from those who have satisfactory performance from one, would be much appreciated. Tom Barter -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ________________________________ Message 2 _____________________________________ Time: 09:12:31 AM PST US Subject: AeroElectric-List: Re: Transponder antenna ground plane From: "user9253" 5.3" in diameter per: http://www.matronics.com/forums/viewtopic.php?t=16762861 Round or octagon should not matter. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=506531#506531 ________________________________ Message 3 _____________________________________ Time: 09:15:38 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Transponder antenna ground plane At 10:48 AM 4/11/2022, you wrote: >Preparing to install the transponder ground plane in a tube and >fabric airplane, and there seems to be a large amount of conflicting >information on the size and shape needed. I have seen several >references to an octagonal ground plane, and that would work well in >my application. I would be using a Comant CI-105 fin style antenna. > The 'ideal' stand alone ground plane takes two popular forms. Perfectly circular where radius of the disk is equal to 1/4 wave in free space at the operating frequency. In the case of transponders, that's 1090 Mhz. 300/1090 = 0.28 Meters for a full wave, 0.07 Meters for 1/4 wave or 2.7 inches. So a disk 5.4" in diameter is indicated. Aluminum is fine. The 'best' ground plane is an 'infinite' conductor like lots of aircraft metal skin . . . not an option in your case. Now, having described ideal ground planes, know that overall performance of the antenna isn't super critical. Ground radars can sniff out a signal REFLECTED from the metal of your airframe, it an certainly see a directly transmitted signal measured in tens if not over 100 watts. I'm unaware of any rationale for shapes other than circular. Would like to see antenna range test data that supports the suggestion. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" ________________________________ Message 4 _____________________________________ Time: 09:25:46 AM PST US Subject: Re: AeroElectric-List: Transponder antenna ground plane From: Charlie England On 4/11/2022 11:14 AM, Robert L. Nuckolls, III wrote: > At 10:48 AM 4/11/2022, you wrote: > >> Preparing to install the transponder ground plane in a tube and >> fabric airplane, and there seems to be a large amount of conflicting >> information on the size and shape needed. I have seen several >> references to an octagonal ground plane, and that would work well in >> my application. I would be using a Comant CI-105 fin style antenna. >> snip > > I'm unaware of any rationale for shapes > other than circular. Would like to see > antenna range test data that supports > the suggestion. My rationale is, two straight cuts (square) instead of lots of work cutting a circle. Then there's the mounting convenience, after fab. ;-) Charlie -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ________________________________ Message 5 _____________________________________ Time: 11:57:44 AM PST US From: "Tom Barter" Subject: RE: AeroElectric-List: Transponder antenna ground plane Forgot to ask - should the ground plane be "grounded" to the fuselage as some suggest, should it be isolated from the fuselage, or does it make any difference? Tom Barter Kesley Electric, Inc. Phone (319)-347-2462 Fax (319)-347-6607 kesleyelectric@iowatelecom.net From: owner-aeroelectric-list-server@matronics.com On Behalf Of Robert L. Nuckolls, III Sent: Monday, April 11, 2022 11:15 AM Subject: Re: AeroElectric-List: Transponder antenna ground plane At 10:48 AM 4/11/2022, you wrote: Preparing to install the transponder ground plane in a tube and fabric airplane, and there seems to be a large amount of conflicting information on the size and shape needed. I have seen several references to an octagonal ground plane, and that would work well in my application. I would be using a Comant CI-105 fin style antenna. The 'ideal' stand alone ground plane takes two popular forms. Perfectly circular where radius of the disk is equal to 1/4 wave in free space at the operating frequency. In the case of transponders, that's 1090 Mhz. 300/1090 = 0.28 Meters for a full wave, 0.07 Meters for 1/4 wave or 2.7 inches. So a disk 5.4" in diameter is indicated. Aluminum is fine. The 'best' ground plane is an 'infinite' conductor like lots of aircraft metal skin . . . not an option in your case. Now, having described ideal ground planes, know that overall performance of the antenna isn't super critical. Ground radars can sniff out a signal REFLECTED from the metal of your airframe, it an certainly see a directly transmitted signal measured in tens if not over 100 watts. I'm unaware of any rationale for shapes other than circular. Would like to see antenna range test data that supports the suggestion. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ________________________________ Message 6 _____________________________________ Time: 12:58:57 PM PST US Subject: AeroElectric-List: Re: Transponder antenna ground plane From: "user9253" The ground plane probably should be grounded to the fuselage for lightning protection. But I don't think it matters for performance. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=506535#506535 ________________________________ Message 7 _____________________________________ Time: 01:44:04 PM PST US From: "Peter Pengilly" Subject: RE: AeroElectric-List: Transponder antenna ground plane Bear in mind that the transmitter requires the braid of the coax to be connected to the ground plane and the centre conductor to the antenna blade - which must be insulated from the ground plane. Any other grounding is irrelevant to the performance of the transmitter. For a metal skinned aircraft the ground plane is the fuselage. Peter From: owner-aeroelectric-list-server@matronics.com On Behalf Of Tom Barter Sent: 11 April 2022 19:57 Subject: RE: AeroElectric-List: Transponder antenna ground plane Forgot to ask - should the ground plane be "grounded" to the fuselage as some suggest, should it be isolated from the fuselage, or does it make any difference? Tom Barter Kesley Electric, Inc. Phone (319)-347-2462 Fax (319)-347-6607 kesleyelectric@iowatelecom.net From: owner-aeroelectric-list-server@matronics.com > On Behalf Of Robert L. Nuckolls, III Sent: Monday, April 11, 2022 11:15 AM Subject: Re: AeroElectric-List: Transponder antenna ground plane At 10:48 AM 4/11/2022, you wrote: Preparing to install the transponder ground plane in a tube and fabric airplane, and there seems to be a large amount of conflicting information on the size and shape needed. I have seen several references to an octagonal ground plane, and that would work well in my application. I would be using a Comant CI-105 fin style antenna. The 'ideal' stand alone ground plane takes two popular forms. Perfectly circular where radius of the disk is equal to 1/4 wave in free space at the operating frequency. In the case of transponders, that's 1090 Mhz. 300/1090 = 0.28 Meters for a full wave, 0.07 Meters for 1/4 wave or 2.7 inches. So a disk 5.4" in diameter is indicated. Aluminum is fine. The 'best' ground plane is an 'infinite' conductor like lots of aircraft metal skin . . . not an option in your case. Now, having described ideal ground planes, know that overall performance of the antenna isn't super critical. Ground radars can sniff out a signal REFLECTED from the metal of your airframe, it an certainly see a directly transmitted signal measured in tens if not over 100 watts. I'm unaware of any rationale for shapes other than circular. Would like to see antenna range test data that supports the suggestion. Bob . . . Un impeachable logic: George Carlin asked, "If black boxes survive crashes, why don't they make the whole airplane out of that stuff?" 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