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Fixing the Transponder with Duct Tape and Aluminum Foil



 
 
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  #1  
Old March 7th 04, 12:53 AM
Ron Wanttaja
external usenet poster
 
Posts: n/a
Default Fixing the Transponder with Duct Tape and Aluminum Foil

I'd installed my new Microair transponder a month ago, but have been having
troubles with interference. The transponder was inducing bad clicking
sounds into the comm radio receiver, making the radio difficult to
understand.

I couldn't really blame the Microair, since the Terra transponder I'd had
before did exactly the same thing. But I'd been hoping the new transponder
and installation would eliminate the problem...especially since I'd
reworked all the transponder wiring and moved the antenna to a different
location. But the interference continued.

The main suggestion I got from the avionics guys around here is that the
transponder was interfering via the cables running to the headset jacks. I
installed shielded braid over those cables, though, and the problem
continued.

All the electrical connections to the radio (except the antennas) are made
via an unshielded flat connector. Since the wires had to spread out to fit
the connector, I hadn't been able to run the braid all the way to the
radio...it terminated about two inches away, and I ran a ground wire from
the braid to the radio chassis.

It seemed to me that the most likely culprit was that last two inches of
unshielded wiring and the unshielded connector...especially since they were
the closest part of the wiring harness to the transponder.

So, today I took a roll of aluminum foil out to the airplane and wrapped
foil around the back of the radio, leading it down the wires until it
contacted the braid. Duct tape, of course, to hold it in place.

I'm happy to report that this solved the problem. Radio signals were
perfectly clear.

I figure the foil isn't worthwhile as a permanent solution. A guy at the
airport suggested using aluminum window-screen material. It appeals to the
cheap side of me. Any drawbacks, or suggestions for alternates?

Ron Wanttaja
  #2  
Old March 7th 04, 02:19 AM
Richard Lamb
external usenet poster
 
Posts: n/a
Default

Ron Wanttaja wrote:

I'd installed my new Microair transponder a month ago, but have been having
troubles with interference. The transponder was inducing bad clicking
sounds into the comm radio receiver, making the radio difficult to
understand.

I couldn't really blame the Microair, since the Terra transponder I'd had
before did exactly the same thing. But I'd been hoping the new transponder
and installation would eliminate the problem...especially since I'd
reworked all the transponder wiring and moved the antenna to a different
location. But the interference continued.

The main suggestion I got from the avionics guys around here is that the
transponder was interfering via the cables running to the headset jacks. I
installed shielded braid over those cables, though, and the problem
continued.

All the electrical connections to the radio (except the antennas) are made
via an unshielded flat connector. Since the wires had to spread out to fit
the connector, I hadn't been able to run the braid all the way to the
radio...it terminated about two inches away, and I ran a ground wire from
the braid to the radio chassis.

It seemed to me that the most likely culprit was that last two inches of
unshielded wiring and the unshielded connector...especially since they were
the closest part of the wiring harness to the transponder.

So, today I took a roll of aluminum foil out to the airplane and wrapped
foil around the back of the radio, leading it down the wires until it
contacted the braid. Duct tape, of course, to hold it in place.

I'm happy to report that this solved the problem. Radio signals were
perfectly clear.

I figure the foil isn't worthwhile as a permanent solution. A guy at the
airport suggested using aluminum window-screen material. It appeals to the
cheap side of me. Any drawbacks, or suggestions for alternates?

Ron Wanttaja



If it ain't broke (no mo!) don't fix it...


Richard
  #3  
Old March 7th 04, 03:15 AM
Gerry Caron
external usenet poster
 
Posts: n/a
Default


"Ron Wanttaja" wrote in message
news
I'd installed my new Microair transponder a month ago, but have been

having
troubles with interference. The transponder was inducing bad clicking
sounds into the comm radio receiver, making the radio difficult to
understand.

SNIP
So, today I took a roll of aluminum foil out to the airplane and wrapped
foil around the back of the radio, leading it down the wires until it
contacted the braid. Duct tape, of course, to hold it in place.

I'm happy to report that this solved the problem. Radio signals were
perfectly clear.

I figure the foil isn't worthwhile as a permanent solution. A guy at the
airport suggested using aluminum window-screen material. It appeals to

the
cheap side of me. Any drawbacks, or suggestions for alternates?


Use what the pros use -- copper tape. Call friendly neighborhood EMI
engineer or go to McMaster-Carr; www.mcmaster.com. Search for "copper
tape".

Gerry


  #4  
Old March 7th 04, 03:47 AM
Ron Wanttaja
external usenet poster
 
Posts: n/a
Default

On Sun, 07 Mar 2004 02:15:39 GMT, "Gerry Caron" wrote:

"Ron Wanttaja" wrote in message
news

I figure the foil isn't worthwhile as a permanent solution. A guy at the
airport suggested using aluminum window-screen material. It appeals to

the
cheap side of me. Any drawbacks, or suggestions for alternates?


Use what the pros use -- copper tape. Call friendly neighborhood EMI
engineer or go to McMaster-Carr; www.mcmaster.com. Search for "copper
tape".


The trouble is, to shield everything, I need to completely wrap around the
back end of the radio. It's 3.375" per side, so I'd need copper tape about
16" wide, and about the same dimension long to have some overlap on the
back of the radio and still go along the wiring harness a bit."
McMaster-Carr's got copper tape 50 feet wide, but it's only 3" long. :-)

I see M/C's got some nice copper mesh sheet. It probably would work
nicely, but they want $700 for a 11" square sheet....and I'd need two of
them. I bought a 36" square sheet of aluminum window screening for $5.
I'm hoping it'll work....

Ron Wanttaja
  #5  
Old March 7th 04, 03:48 AM
Jim Weir
external usenet poster
 
Posts: n/a
Default

Or send Jim a SASpaddedE and he'll send you what is left of a few rolls we've
used around here for "magazine projects", if y'know what I mean.

Jim



"Gerry Caron"
shared these priceless pearls of wisdom:

-Use what the pros use -- copper tape. Call friendly neighborhood EMI
-engineer or go to McMaster-Carr; www.mcmaster.com. Search for "copper
-tape".
-
-Gerry
-


Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com
  #6  
Old March 7th 04, 03:57 AM
Tim Ward
external usenet poster
 
Posts: n/a
Default


"Ron Wanttaja" wrote in message
...
On Sun, 07 Mar 2004 02:15:39 GMT, "Gerry Caron" wrote:

"Ron Wanttaja" wrote in message
news

I figure the foil isn't worthwhile as a permanent solution. A guy at

the
airport suggested using aluminum window-screen material. It appeals to

the
cheap side of me. Any drawbacks, or suggestions for alternates?


Use what the pros use -- copper tape. Call friendly neighborhood EMI
engineer or go to McMaster-Carr; www.mcmaster.com. Search for "copper
tape".


The trouble is, to shield everything, I need to completely wrap around the
back end of the radio. It's 3.375" per side, so I'd need copper tape

about
16" wide, and about the same dimension long to have some overlap on the
back of the radio and still go along the wiring harness a bit."
McMaster-Carr's got copper tape 50 feet wide, but it's only 3" long. :-)

I see M/C's got some nice copper mesh sheet. It probably would work
nicely, but they want $700 for a 11" square sheet....and I'd need two of
them. I bought a 36" square sheet of aluminum window screening for $5.
I'm hoping it'll work....

Ron Wanttaja


Have you checked www.digikey.com for a "shielded hood" for the
DB-whatever-it-is on the Microair? Their quantity 1 price will seem kind of
pricey, but it's certainly cheaper than 700 bucks -- probably more like 7.

Tim Ward


  #7  
Old March 7th 04, 04:50 AM
Gerry Caron
external usenet poster
 
Posts: n/a
Default


"Ron Wanttaja" wrote in message
...

The trouble is, to shield everything, I need to completely wrap around the
back end of the radio. It's 3.375" per side, so I'd need copper tape

about
16" wide, and about the same dimension long to have some overlap on the
back of the radio and still go along the wiring harness a bit."
McMaster-Carr's got copper tape 50 feet wide, but it's only 3" long. :-)


OTOH, 6 - 16" long pieces of tape overlapped 1/4" results in a sticky sheet
about 16" square.

I'd start by spiral wrapping the harness, making sure to contact the
overbraid on the one end and end with solid contact around the connector at
the back of the unit.

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. If
there are cover edges that don't have good metal-to-metal contact or other
openings, put a strip of tape along the gap. (Note that a gap running the
length of one side (3.375") would be just shy of 1/4 wave at 1090 MHz.)

I've sealed up much larger air transport units (big ARINC boxes) with a
couple feet of 1/2" tape.

Gerry


  #8  
Old March 7th 04, 06:45 AM
Cy Galley
external usenet poster
 
Posts: n/a
Default

Copper window screen can be soldered. The copper tape is also used by
stained glass hobbyists.

"Gerry Caron" wrote in message
. com...

"Ron Wanttaja" wrote in message
...

The trouble is, to shield everything, I need to completely wrap around

the
back end of the radio. It's 3.375" per side, so I'd need copper tape

about
16" wide, and about the same dimension long to have some overlap on the
back of the radio and still go along the wiring harness a bit."
McMaster-Carr's got copper tape 50 feet wide, but it's only 3" long. :-)


OTOH, 6 - 16" long pieces of tape overlapped 1/4" results in a sticky

sheet
about 16" square.

I'd start by spiral wrapping the harness, making sure to contact the
overbraid on the one end and end with solid contact around the connector

at
the back of the unit.

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.

If
there are cover edges that don't have good metal-to-metal contact or other
openings, put a strip of tape along the gap. (Note that a gap running the
length of one side (3.375") would be just shy of 1/4 wave at 1090 MHz.)

I've sealed up much larger air transport units (big ARINC boxes) with a
couple feet of 1/2" tape.

Gerry




  #9  
Old March 7th 04, 09:06 AM
Ron Wanttaja
external usenet poster
 
Posts: n/a
Default

(answering several responses)

On Sat, 6 Mar 2004 18:57:48 -0800, "Tim Ward"
wrote:

I see M/C's got some nice copper mesh sheet. It probably would work
nicely, but they want $700 for a 11" square sheet....and I'd need two of
them. I bought a 36" square sheet of aluminum window screening for $5.
I'm hoping it'll work....


Have you checked www.digikey.com for a "shielded hood" for the
DB-whatever-it-is on the Microair? Their quantity 1 price will seem kind of
pricey, but it's certainly cheaper than 700 bucks -- probably more like 7.


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.

Every bit of wire associated with the transponder was replaced when I
switched to the Microair...the transponder got its own circuit
breaker/power wire (the Terra shared a single breaker and a single 18-gauge
wire with the Comm radio...hey, *I* didn't install it), new encoder
harness, new coaxial cable to the repositioned antenna. So I figured the
problem was in the Narco, not the transponder.

I *am* glad I bought the unit from my friendly avionics dealer on my own
home field, instead of mail-ordering it. It gave me real-time access to
some technical advice. I emailed Microair with my problems and didn't
receive a response. I did state, in my email, that I knew the problem
wasn't with their device, but was hoping they'd have some suggestions.

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?

(Snip)

]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.

Neat suggestion, though...I might try to wrap that last couple inches of
wiring harness and shield the openings somehow.

On Sat, 06 Mar 2004 18:48:11 -0800, Jim Weir wrote:

} Or send Jim a SASpaddedE and he'll send you what is left of a few
} rolls we've used around here for "magazine projects", if y'know
} what I mean.

I was visited by the RST fairy several years back, and still have a good
bit of a roll left after doing the ground plane for my plastic-pipe-fitting
antenna.

Also, little strips of it on the edges of the suitcase work neat for
picking out your suitcase as soon as it comes off the airport luggage
carosel...subtle, but instantly recognizable. Though, from the frequency
of the "Hi, we're the TSA, and we pawed through your bag" notes I get, I
get the impression the Federales get a bit suspicious... :-)

Ron Wanttaja
  #10  
Old March 7th 04, 02:53 PM
Charlie England
external usenet poster
 
Posts: n/a
Default

Ron Wanttaja wrote:

I'd installed my new Microair transponder a month ago, but have been having
troubles with interference. The transponder was inducing bad clicking
sounds into the comm radio receiver, making the radio difficult to
understand.

I couldn't really blame the Microair, since the Terra transponder I'd had
before did exactly the same thing. But I'd been hoping the new transponder
and installation would eliminate the problem...especially since I'd
reworked all the transponder wiring and moved the antenna to a different
location. But the interference continued.

The main suggestion I got from the avionics guys around here is that the
transponder was interfering via the cables running to the headset jacks. I
installed shielded braid over those cables, though, and the problem
continued.

All the electrical connections to the radio (except the antennas) are made
via an unshielded flat connector. Since the wires had to spread out to fit
the connector, I hadn't been able to run the braid all the way to the
radio...it terminated about two inches away, and I ran a ground wire from
the braid to the radio chassis.

It seemed to me that the most likely culprit was that last two inches of
unshielded wiring and the unshielded connector...especially since they were
the closest part of the wiring harness to the transponder.

So, today I took a roll of aluminum foil out to the airplane and wrapped
foil around the back of the radio, leading it down the wires until it
contacted the braid. Duct tape, of course, to hold it in place.

I'm happy to report that this solved the problem. Radio signals were
perfectly clear.

I figure the foil isn't worthwhile as a permanent solution. A guy at the
airport suggested using aluminum window-screen material. It appeals to the
cheap side of me. Any drawbacks, or suggestions for alternates?

Ron Wanttaja

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.

Charlie

 




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