If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
"Ron Wanttaja" wrote in message ... (answering several responses) Well, the problem isn't in the Microair's DB-25, since I had the same problem with my Terra, which had a hard-wired rack. It must be some sort of bleedover from the antenna itself, since the Microair is machined out of a solid hunk a' aluminum. So I figured the problem was in the Narco, not the transponder. On Sun, 07 Mar 2004 03:50:28 GMT, "Gerry Caron" wrote: ]OTOH, 6 - 16" long pieces of tape overlapped 1/4" results in a ]sticky sheet about 16" square. One bit of curiosity I have, about the copper tape: How does the "sticky side" affect electrical connection? Is the adhesive conductive? IIRC it's not conductive, but it's not much of a dielectric either so I imagine there's some coupling across the layers. The tape acts more as a reflector than a conductive shield. ]If the unit is metal, you shouldn't need to shield the unit itself ]with only a couple exceptions. Since we're dealing with a ]transponder (1090 MHz), the only other issue would be an aperture ]which could act as a slot antenna. This may be *exactly* the problem I have. The metal case of the radio is cut back to allow the connector to be external without grounding out... and the cutout is just shy of the full width of the case. Also, there's a wider slot orthogonal to the connector slot, where the plastic lock for the connector slides in to. That's where I would start. There are two basic EMI paths: conducted and radiated. The conducted enters thru the wiring harness. To stop this, you need to keep the EMI out of the harness. It gets into the harness either thru an e-field or m-field. The overbraid shield is the first line of defense. The second line of defense is cable routing. Cables running parallel create an opportunity for inductive coupling. Keep the Xpdr antenna cable away from comm and audio cables. If they have to be close, try to have the routes cross at 90 deg. The overbraid needs to be grounded because you can get some pretty big currents induced along a cable. The radiated path is generally blocked by the case which is designed as a shield. Any gaps in that shield let rf in. The size of the gaps will tune the susceptibility to specific frequencies. That cut out along the back for the connector sounds like a pretty good 1/4 wave slot for the transponder freq. Covering the gaps with the tape will block the rf. Grounding generally isn't an issue because the tape doesn't accumulate much of a charge. Gerry |
#12
|
|||
|
|||
I *beg* your pardon? We may be from California, but so far as I know, we are all straight here. {;-) Jim Ron Wanttaja shared these priceless pearls of wisdom: -I was visited by the RST fairy several years back Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#13
|
|||
|
|||
There are some special versions of copper tape that are specifically labeled "conductive adhesive". So far as I know, they are only made by 3M and are gawdawful expensive. And, I got bit in the butt once by assuming (terrible word) that the adhesive parts would remain adhesive over time. The "conductive adhesive" only gets its conductivity through copper dust mixed in with the stickum. If that stickum comes loose over time or temperature, you've got one hell of a good slot radiator on your hands, especially at a gigahertz or two. Jim "Gerry Caron" shared these priceless pearls of wisdom: - One bit of curiosity I have, about the copper tape: How does the "sticky - side" affect electrical connection? Is the adhesive conductive? - -IIRC it's not conductive, but it's not much of a dielectric either so I -imagine there's some coupling across the layers. The tape acts more as a -reflector than a conductive shield. Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
#14
|
|||
|
|||
On Sun, 07 Mar 2004 07:53:16 -0600, Charlie England
wrote: Try your local Home Depot 'A/C supply'. Go to the insulation section & look for 'aluminized mylar' radiant barrier insulation. It comes in various forms. Best for you would be the mylar sheet with an aluminum foil bonded to the mylar. Other types may look like either bubble wrap or foam wrap sheets for protecting delicate stuff for shipment, but will still have the aluminum foil coating. More durable than just foil; you can make a 'boot' by stitching a sheet into a cone shape. Neat idea, thanks, Charlie. Don't have a Home Depot A/C Supply real close, but Lowe's Aerospace is right across the road from the airport. :-) Ron Wanttaja |
#15
|
|||
|
|||
Gerry Caron wrote:
"Ron Wanttaja" wrote in message ... (answering several responses) an opportunity for inductive coupling. Keep the Xpdr antenna cable away from comm and audio cables. If they have to be close, try to have the routes cross at 90 deg. The overbraid needs to be grounded because you can get some pretty big currents induced along a cable. Also only one end of the cables shield should be grounded or else your open to some ground loops which can cause some of your problems. |
#16
|
|||
|
|||
On Sun, 07 Mar 2004 21:30:30 GMT, UltraJohn
wrote: Gerry Caron wrote: "Ron Wanttaja" wrote in message ... (answering several responses) an opportunity for inductive coupling. Keep the Xpdr antenna cable away from comm and audio cables. If they have to be close, try to have the routes cross at 90 deg. The overbraid needs to be grounded because you can get some pretty big currents induced along a cable. Also only one end of the cables shield should be grounded or else your open to some ground loops which can cause some of your problems. Thanks, got the same recommendation from others...and contrary advice from a few. Fortunately, with a wooden airplane, *not* grounding the other end is a lot easier than grounding it... :-) Ron Wanttaja |
#17
|
|||
|
|||
Charlie England wrote:
Try your local Home Depot 'A/C supply'. Go to the insulation section & look for 'aluminized mylar' radiant barrier insulation. It comes in various forms. Best for you would be the mylar sheet with an aluminum foil bonded to the mylar. Other types may look like either bubble wrap or foam wrap sheets for protecting delicate stuff for shipment, but will still have the aluminum foil coating. More durable than just foil; you can make a 'boot' by stitching a sheet into a cone shape. Ron Wanttaja replied: Neat idea, thanks, Charlie. Don't have a Home Depot A/C Supply real close, but Lowe's Aerospace is right across the road from the airport. :-) It probably isn't an issue in Ron's case, but having recently seen the Nova program on the investigation into the causes of the crash of SwissAir #111 I feel compelled to point out that some aluminized Mylar insulation is flammable. Russell Kent |
#18
|
|||
|
|||
On Mon, 08 Mar 2004 14:06:44 -0600, Russell Kent wrote:
It probably isn't an issue in Ron's case, but having recently seen the Nova program on the investigation into the causes of the crash of SwissAir #111 I feel compelled to point out that some aluminized Mylar insulation is flammable. Considering that there's a manly pilot leg running on the left side of the avionics box, and another manly pilot leg on the RIGHT side of the box, it's something I should keep in mind. But I actually came up with the perfect solution this afternoon...assuming the technology cooperates. I was mulling over how I'd cut the sheet, wrap it around the radio and the wiring harness, and realized that what I needed was a aluminized mylar funnel. Something very much like the bottom of a shiny aluminum toy balloon.... So I'm going to pick up a couple of (uninflated) balloons and turn my multimeter loose on them. Maybe I'll find a left-over Valentine's Day balloon on sale.. I'm really hoping they'll work out. The idea of buying an aircraft part at a store called "Party Universe" is almost irresistible. :-) Ron Wanttaja |
#19
|
|||
|
|||
Ron Wanttaja wrote:
I'm really hoping they'll work out. The idea of buying an aircraft part at a store called "Party Universe" is almost irresistible. :-) Ron Wanttaja This is just too cool for school, Ron! Richard |
#20
|
|||
|
|||
There are those fancy condoms that they sell in the mens' room at the truck
stops... {;-) Jim Ron Wanttaja shared these priceless pearls of wisdom: -So I'm going to pick up a couple of (uninflated) balloons and turn my -multimeter loose on them. Maybe I'll find a left-over Valentine's Day -balloon on sale.. Jim Weir (A&P/IA, CFI, & other good alphabet soup) VP Eng RST Pres. Cyberchapter EAA Tech. Counselor http://www.rst-engr.com |
Thread Tools | |
Display Modes | |
|
|