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challgren(at)mac.com
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 Posted: Wed Sep 09, 2009 8:45 am Post subject: VHF & Transponder separation requirements on 701 |
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Listees:
I am in the process of ordering my Garmin SL40 radio and GTX 330 Transponder and am unable to find minimum separation distances between the two antennas. John at Stein Avionics seemed to think that 24" would be sufficient. As I sit on my creeper in the hellhole I realize that placing the antennas much more than arm's length away would not be advisable. I also have to consider the location of the Magnetometer for the Grand Rapids EFIS Sport.
I thought Bingelis would have the answer. If he did, I could not find it. I also thought The AeroElectric Connection would have the answer. Again, if it did; I could not find it. I remember reading about radiating planes around antennas and needing them for maximum communication distances but can't find the reference. I googled Aircraft Antenna Locations and found "Mount the antennas at least 36 inches away from obstructions and as far as possible from other antennas." It also said "On fabric covered aircraft...,it will be necessary to provide a flat metallic surface or "ground plane" extending at least 12 inches in all directions from the center of the antenna."
Given the above background, I am considering mounting the VHF radio antenna on the far starboard side of the tail section within arm's reach of the Maintenance Access Opening (hellhole). I would mount the transponder antenna on the other side, again right up next to the vertical bulkhead. I would put the magnetometer between the two antennas. The two antennas would be about 24" apart.
My question then is, from those who are flying their 701's: Is what I suggest feasible, or; are you using a different plan that works?
All comments would be appreciated.
Confused in Colorado.
Stan Challgren
701/3300
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craig(at)craigandjean.com
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| Posted: Wed Sep 09, 2009 9:04 am Post subject: VHF & Transponder separation requirements on 701 |
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In general the comm. antenna goes on top and the transponder antenna goes on the bottom (where the RADRA can “see” it and it can see the RADAR). On the 601 plenty of people have mounted the transponder antenna on the cabin floor a bit behind the nose gear tube.
-- Craig
From: owner-zenith701801-list-server(at)matronics.com [mailto:owner-zenith701801-list-server(at)matronics.com] On Behalf Of Stanley A Challgren
Sent: Wednesday, September 09, 2009 10:36 AM
To: zenith zenith701801-list
Subject: VHF & Transponder separation requirements on 701
Listees:
I am in the process of ordering my Garmin SL40 radio and GTX 330 Transponder and am unable to find minimum separation distances between the two antennas. John at Stein Avionics seemed to think that 24" would be sufficient. As I sit on my creeper in the hellhole I realize that placing the antennas much more than arm's length away would not be advisable. I also have to consider the location of the Magnetometer for the Grand Rapids EFIS Sport.
I thought Bingelis would have the answer. If he did, I could not find it. I also thought The AeroElectric Connection would have the answer. Again, if it did; I could not find it. I remember reading about radiating planes around antennas and needing them for maximum communication distances but can't find the reference. I googled Aircraft Antenna Locations and found "Mount the antennas at least 36 inches away from obstructions and as far as possible from other antennas." It also said "On fabric covered aircraft...,it will be necessary to provide a flat metallic surface or "ground plane" extending at least 12 inches in all directions from the center of the antenna."
Given the above background, I am considering mounting the VHF radio antenna on the far starboard side of the tail section within arm's reach of the Maintenance Access Opening (hellhole). I would mount the transponder antenna on the other side, again right up next to the vertical bulkhead. I would put the magnetometer between the two antennas. The two antennas would be about 24" apart.
My question then is, from those who are flying their 701's: Is what I suggest feasible, or; are you using a different plan that works?
All comments would be appreciated.
Confused in Colorado.
Stan Challgren
701/3300
[quote][b]
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n752ms(at)softcom.net
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| Posted: Wed Sep 09, 2009 11:52 am Post subject: VHF & Transponder separation requirements on 701 |
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Stan.
I have mounted my com antenna on top at the front part of the baggage area and the ELT antenna on top behind the baggage area and the transponder on the bottom just behind the seat. I just had the transponder checked and it tested just fine. The com radio works great with the ELT antenna about 30 inches away.
Mark S.
[quote] ---
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bobkat
Joined: 07 Sep 2008
Posts: 143
Location: Bismarck, ND
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| Posted: Thu Sep 10, 2009 6:17 pm Post subject: VHF & Transponder separation requirements on 701 |
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You want to seperate your com antenna from the elt (assuming a 121.5 elt - a 406/121.5 would be similar) by at least 1/4 wavelength at the com frequencies. A rule of thumb is approximately the length of the antenna, though farther away is better. I mounted mine as far rearward on the top of the fuselage as I could comfortably reach through the bottom of the 'hell hole!'
A transponder antenna is best on the belly of the plane, usually as far forward as you can mount it, though anywhere as much out of the way of obstructions like gear, etc. is OK. It is interrogated by ground stations (excluding TCAS) so works better on the belly!
My 701, (like most) has a fiberglass cowling so I mounted it behind where the aluminum on the belly starts, actually quite a way back come to think of it......Actually I put it under the seat so as not to worry about the connectors and coax being underfoot. Also, theoretically at least, the transponder antenna should not be where it would be able to radiate RF energy directly to you or especially your family jewels! The aluminum seat bottom does a fine job of shielding any radiation in or around the antenna base, so I put it there. The metal gear doesn't interfere with radiation/operation of the XPDR.
My ELT antenna (406/121.5) I put halfway between the plastic BRS blowout panel and rear of the windscreen to separate it far enough from the VHF com antenna and to have the aluminum skin act as a ground plane. Also, I'm a ham radio operator and so I put my 146 mhz 2 meter antenna on the right side of that panel, and the ELT on the left.
The tail is supposedly better for an ELT as an antenna mounted on the tail is generally a bit more clear to radiate than one mounted elsewhere in most crashes. I always wonder why some company doesn't make two antennas with one hookup to the ELT - one for the top, one for the bottom of the fuselage, so you would always have one antenna to radiate. With the CAP I once saw a crash that had flipped over and the elt antenna was on the bottom and couldn't be heard until you flew over it very low, and even the, barely.
Of course, with multiple antennas your airplane might look like a porcupine with all those antennas and you might lose 40 of your blazing 60 knots! Hah!
[quote] ---
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