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Locating Transponder Antenna on top of the fuselage instead of under it.



 
 
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  #11  
Old December 28th 19, 07:36 PM posted to rec.aviation.soaring
[email protected]
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Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

Regarding performance only, is there any study indicating that top of the fuselage location is worth than the normal under fuselage location?
Dan
  #12  
Old December 28th 19, 07:44 PM posted to rec.aviation.soaring
George Haeh
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Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

"You are bathing all the other avionics with high-energy RF pulses from the transponder... A L2 type wave antenna for mounted inside a non-conductive fuselage should normally be mounted back in the fuselage away from the pilot and avionics. And things like PowerFLARM 1090ES In are designed to work by seeing somewhat reduced power leakage of your transponder signal, not being blasted by the direct high-energy signal."

The avionics, except for the Oudie, are all in metal enclosures.

"You may be operating the FLARM antennas closer to a transponder antenna than a good idea (~30cm minimum recommended by FLARM... but that's when both externally mounted, this may be worse mounted inside). I'm not even sure something as close as 30cm is a good idea externally.
Does ownship PowerFLARM transponder identification work OK? Or do you have to disable PCAS etc.? FLARM range checks all look good?"

The PF Flarm and ADS-B antennas are mounted on the sides of the canopy quite some distance from the xpdr antenna which itself is about a foot forward of the instrument panel. The PF range is better than the four other gliders I've checked. No PF problem with own glider xpdr.


"How do you know if the Transponder is working OK until you check/ask?. You also might be flying in a remote enough area that you get few transponder interrogations, so things seem to work OK. A close encounter with a TCAS equipped aircraft might result in a chirp of ~1kHz transponder interrogations.. Even if things are are working OK now who knows what that will do to your electronics, PowerFLARM, traffic display, etc. when you might need to most rely on it."

Will be doing another transponder check in the spring.

"You likely have lots of conductive objects within the antenna RF near field near field (including the Schleicher panel support brass rod, all the usual wiring and conductive instrument cases). That can significantly affect the radiation pattern in ways unlikely to be obvious."

Most of the unshielded wiring is in the bottom of the instrument enclosure directly below the L2 antenna where the radiated energy may be lower. But so far, everything seems to be working.

"And you are possibly exposing yourself to excessive RF radiation."

My lower legs are about a foot away while the rest of me is 2 to 4 feet away. I found a research paper that showed the radiation hazard was low.
  #13  
Old December 28th 19, 09:10 PM posted to rec.aviation.soaring
Darryl Ramm
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Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

On Saturday, December 28, 2019 at 10:44:46 AM UTC-8, George Haeh wrote:
"You are bathing all the other avionics with high-energy RF pulses from the transponder... A L2 type wave antenna for mounted inside a non-conductive fuselage should normally be mounted back in the fuselage away from the pilot and avionics. And things like PowerFLARM 1090ES In are designed to work by seeing somewhat reduced power leakage of your transponder signal, not being blasted by the direct high-energy signal."

The avionics, except for the Oudie, are all in metal enclosures.

"You may be operating the FLARM antennas closer to a transponder antenna than a good idea (~30cm minimum recommended by FLARM... but that's when both externally mounted, this may be worse mounted inside). I'm not even sure something as close as 30cm is a good idea externally.
Does ownship PowerFLARM transponder identification work OK? Or do you have to disable PCAS etc.? FLARM range checks all look good?"

The PF Flarm and ADS-B antennas are mounted on the sides of the canopy quite some distance from the xpdr antenna which itself is about a foot forward of the instrument panel. The PF range is better than the four other gliders I've checked. No PF problem with own glider xpdr.


"How do you know if the Transponder is working OK until you check/ask?. You also might be flying in a remote enough area that you get few transponder interrogations, so things seem to work OK. A close encounter with a TCAS equipped aircraft might result in a chirp of ~1kHz transponder interrogations. Even if things are are working OK now who knows what that will do to your electronics, PowerFLARM, traffic display, etc. when you might need to most rely on it."

Will be doing another transponder check in the spring.

"You likely have lots of conductive objects within the antenna RF near field near field (including the Schleicher panel support brass rod, all the usual wiring and conductive instrument cases). That can significantly affect the radiation pattern in ways unlikely to be obvious."

Most of the unshielded wiring is in the bottom of the instrument enclosure directly below the L2 antenna where the radiated energy may be lower. But so far, everything seems to be working.


Yes with wires running into them, and power cables, and metal construction is not perfectly RF tight, all of which will leak some RF power into the enclosures. And none of which are designed to be close to high power transponder signals.

That you can't find any problem so far does not make this a good idea for others.

  #14  
Old December 29th 19, 12:14 AM posted to rec.aviation.soaring
2G
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Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

On Saturday, December 28, 2019 at 12:10:29 PM UTC-8, Darryl Ramm wrote:
On Saturday, December 28, 2019 at 10:44:46 AM UTC-8, George Haeh wrote:
"You are bathing all the other avionics with high-energy RF pulses from the transponder... A L2 type wave antenna for mounted inside a non-conductive fuselage should normally be mounted back in the fuselage away from the pilot and avionics. And things like PowerFLARM 1090ES In are designed to work by seeing somewhat reduced power leakage of your transponder signal, not being blasted by the direct high-energy signal."

The avionics, except for the Oudie, are all in metal enclosures.

"You may be operating the FLARM antennas closer to a transponder antenna than a good idea (~30cm minimum recommended by FLARM... but that's when both externally mounted, this may be worse mounted inside). I'm not even sure something as close as 30cm is a good idea externally.
Does ownship PowerFLARM transponder identification work OK? Or do you have to disable PCAS etc.? FLARM range checks all look good?"

The PF Flarm and ADS-B antennas are mounted on the sides of the canopy quite some distance from the xpdr antenna which itself is about a foot forward of the instrument panel. The PF range is better than the four other gliders I've checked. No PF problem with own glider xpdr.


"How do you know if the Transponder is working OK until you check/ask?. You also might be flying in a remote enough area that you get few transponder interrogations, so things seem to work OK. A close encounter with a TCAS equipped aircraft might result in a chirp of ~1kHz transponder interrogations. Even if things are are working OK now who knows what that will do to your electronics, PowerFLARM, traffic display, etc. when you might need to most rely on it."

Will be doing another transponder check in the spring.

"You likely have lots of conductive objects within the antenna RF near field near field (including the Schleicher panel support brass rod, all the usual wiring and conductive instrument cases). That can significantly affect the radiation pattern in ways unlikely to be obvious."

Most of the unshielded wiring is in the bottom of the instrument enclosure directly below the L2 antenna where the radiated energy may be lower. But so far, everything seems to be working.


Yes with wires running into them, and power cables, and metal construction is not perfectly RF tight, all of which will leak some RF power into the enclosures. And none of which are designed to be close to high power transponder signals.


Well, they BETTER be! Any aircraft can be expected to have a transponder with an antenna at a unknown location, so it must be assumed that the antenna is close to the particular avionics. The transponder response is only 25 microsec long, so you are being exposed to an RF pulse that averages 1 to 2 mW, depending upon the code and altitude being transmitted (1202 has only 3 ONEs out of a possible 12, and each ONE bit has power on for one third of the bit time). By way of comparison, a cell phone transmits at 600 mW, and as much as 3 W - and you are holding that thing right next to your head and think nothing of it.

Tom

  #15  
Old December 29th 19, 12:34 AM posted to rec.aviation.soaring
Darryl Ramm
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Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

Any aircraft can be expected to have the transponder antenna stuck amongst equipment in the instrument panel? What RF shielding requirements/standards do you think typical glider cockpit avionics, including all the non-regulated, non-certified devices are built against.

In typical ras fashion somebody asking a reasonable question
has degenerated to nonsense. There are perfectly good documents from glider manufacturers that recommend where/how to install transponder antennas. None describe stuffing it in the instrument panel.
  #16  
Old December 29th 19, 01:10 AM posted to rec.aviation.soaring
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Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

"Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
Dan
  #17  
Old December 29th 19, 01:28 AM posted to rec.aviation.soaring
Richard Pfiffner[_2_]
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Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

On Saturday, December 28, 2019 at 4:10:30 PM UTC-8, wrote:
"Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
Dan


Yes,

http://www.craggyaero.com/antennas.htm



Richard
www.craggyaero.com
  #18  
Old December 29th 19, 01:39 AM posted to rec.aviation.soaring
Dan Marotta
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Default Locating Transponder Antenna on top of the fuselage instead of under it.

The ground plane in my glider is mounted to the inside of the carbon
skin and I'm told my transponder is quite visible.Â* My installation also
passed the ADS-B test with flying colors.

On 12/28/2019 5:10 PM, wrote:
"Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
Dan


--
Dan, 5J
  #19  
Old December 29th 19, 03:02 AM posted to rec.aviation.soaring
2G
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Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

On Saturday, December 28, 2019 at 3:34:09 PM UTC-8, Darryl Ramm wrote:
Any aircraft can be expected to have the transponder antenna stuck amongst equipment in the instrument panel? What RF shielding requirements/standards do you think typical glider cockpit avionics, including all the non-regulated, non-certified devices are built against.

In typical ras fashion somebody asking a reasonable question
has degenerated to nonsense. There are perfectly good documents from glider manufacturers that recommend where/how to install transponder antennas. None describe stuffing it in the instrument panel.


I didn't say IN the panel, but near it. I once had a transponder antenna in a DG-400 that was mounted just below my right knee. Everything in the panel worked fine. There is, at times, good reasons for putting the antenna in the nose. You can always do a compatibility test on your own with a temporary antenna mount, or just hand-hold the antenna and move it around near the panel.

Tom
  #20  
Old December 29th 19, 03:43 AM posted to rec.aviation.soaring
Darryl Ramm
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Posts: 2,403
Default Locating Transponder Antenna on top of the fuselage instead ofunder it.

On Saturday, December 28, 2019 at 4:10:30 PM UTC-8, wrote:
"Pay attention to the proper ground plane installation with any of the standard external transponder 1/4 wave antenna. That is very important."
Can the ground Plane be inside a carbon fibre fuselage for an external blade type antenna ?
Dan


The ground plane you install would normally be inside the CF fuselage. And the antenna manufacture or glider manufacturer should provide instructions on how to do this properly. A part of the point of that aluminium plate or foil tape ground plane is to help with a good connection to the coax cable ground. In some cases you might scuff the inside of the fueslage to help make additional electrical connection to the carbon fibre weave. *Follow the directions your glider manufacturer provides.* A plate especially can also help provide a good solid surface for antenna lock washers to engage with. Clearly here the CF will act in part as a ground plane (even without a good direct electrical connection, but by backing it with a better conductor with good connection to the coax you are helping things along).

 




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