Fixing the Transponder with Duct Tape and Aluminum Foil

[Ron Wanttaja]

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

[Richard Lamb]

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

[Gerry Caron]

"Ron Wanttaja" > wrote in message
...
> 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

[Ron Wanttaja]

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

>"Ron Wanttaja" > wrote in message
...
>>
>> 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

[Jim Weir]

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

[Tim Ward]

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

[Gerry Caron]

"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

[Cy Galley]

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
>
>

[Ron Wanttaja]

(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

[Charlie England]

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

[Gerry Caron]

"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

[Jim Weir]

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

[Jim Weir]

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

[Ron Wanttaja]

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

[UltraJohn]

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.

[Ron Wanttaja]

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

[Russell Kent]

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

[Ron Wanttaja]

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

[Richard Lamb]

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

[Jim Weir]

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

[Ron Wanttaja]

On Tue, 09 Mar 2004 03:02:57 GMT, Richard Lamb >
wrote:

>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. :-)
>
>This is just too cool for school, Ron!

After fifteen minutes fiddling with my multimeter, my guess is that the
aluminum layer is too thin to count on. Touching the probes on the shiny
exterior, the DVM readout never *did* stabilize...down to 40 ohms, back to
infinity, down to 100K, back to infinity, etc. The LCD screen spent more
time blanked than displaying any value.

I did a less-scientific test...I sliced open a balloon and inserted a cell
phone inside. The signal-strength readout did drop from full to just one
bar.

I may try it anyway, just because installation is fairly easy. But I
suspect the points of contact will rub away rapidly, losing the ground
connection and causing the noise level to rise again.

By now, I've collected material for several approaches, like the 1/2"
copper tape the RST winged-but-definitely-heterosexual-mythical-creature
left me and the aluminum window screening I shelled out $5 for last
weekend. I even got some of that "holy grail" copper tape I mentioned on
an earlier posting...it's 16" wide and 4 feet long, with a peel-off
adhesive backing. So I certainly don't lack options....

Ron Wanttaja

[John]

Every body worries about "GROUND LOOPS" but in many cases they do not
really know what they are talking about.

Antenna coax is shielded wire that is also controlled impedance wire.
You will find for every transmitter that the shield is connected at
BOTH ends of the wire and for most antennas the shield is also
grounded at both ends. If you disconnect the shield at one end and
measure the VSWR you will notice that it goes toward infinity due the
shield not being connected.

CURRENT ALWAYS HAS TO RETURN TO THE SOURCE.

The current may not flow where you want of even where you think it is
flowing but it will seek a way(s) back to the source.

LOW FREQUENCY CURRENT follows the path of least RESISTANCE.
HIGH FREQUENCY CURRENT follows the path of least INDUCTANCE.

The current will divide inversely proportional to the impedance of
each individual path among the many paths available and seek the path
of least total impedance.

Now what is the difference in low frequency and high frequency current
you might ask. The difference is the length of the connecting wire
in terms of wavelengths of the signal. If the wire is longer than
1/20 of a wavelength then the signal is considered high frequency and
you must think of the wire as a transmission line not just as a common
wire.

For LOW frequency shielding the wire shield is only connected at one
end. Low frequency in this case is defined as DC up to the top of the
audio band, 20 KHz. This keeps the magnetic coupling of near by
cables from inducing a voltage in the shield that couples to the
signal. Connecting the shield at only one end will NOT keep out high
frequency signals!

For very high frequency signals where the shield thickness is many
skin depths of the signal frequency you can have different independent
currents on both the outside and the inside of the shield. For this
reason you must have a 360 degree shield connection or the inner and
outer currents on the shield couple and mix due to the inductance of
the shield pigtail connection. To keep out, or in, high frequency
signals you must connect the shield at BOTH ends.

Here is something to think about:
How many GROUND LOOPS do you have if you place a whip antenna in the
center of a X Y grid of 10 wires by 10 wires where each wire is
connected to the crossing wire? 100?

Now we fill in the spaces between the wires with another ten wires so
we have a grid that is the same size but now has 100 wires by 100
wires. Do we now have 10,000 ground loops? Is this better?
What if we now fill in the spaces between the wires so that it is
solid metal. Do we now have an infinite number of ground loops? Is
this better? Yes, except for weight.

The answer is the current will divide among the many paths and follow
the path of least total impedance.

John Frerichs

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.

[Info]

I have noticed the clicking and chased the problem, mine comes from the
encoder..... if i turn the encoder off it coes away. Running a Microair
T2000 and ATK350

Thanks Michael

Jim Weir wrote:
> 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

[Big John]

Ron

More free advice from a long time Ham.

Have you tried a toroid? Radio Shack used to carry some that snapped
apart and then back together so you could put several turns on one
without cutting the wire(s). Price was a couple of dollars so not
expensive to try.

Also, we used to take a piece of aluminum foil from the kitchen and
just wrap around the wire(s) and then slide it back and forth to find
a spot where the interference stopped. Again, very cheap to test.

We also on occasion used some small (.02- .002) ceramic caps.

Also, any coax you use be sure it is double shielded. Some of the
cheap stuff on the market has very 'porous shielding.

Robert and my daughter are still in FL working on their boat. He could
have built another plane in the time they are spending rebuilding that
damn boat. <G> Haven't said if they are going to go by S-N-F this year
before heading back to WA?

Any words the spell checker didn't catch, I take full responsibiity
for <G>

And the best up there in the land of the every day rain.

Big John

On Sat, 06 Mar 2004 23:53:02 GMT, 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

[Ron Wanttaja]

On Tue, 09 Mar 2004 08:27:50 -0600, Big John > wrote:

>Also, any coax you use be sure it is double shielded. Some of the
>cheap stuff on the market has very 'porous shielding.

Actually, that's one thing I did wonder about. The coax I use is RG-58,
but I buy premade LAN cables from the local electronics emporium. I
shortened the one I bought for the transponder, installing a new BNC
fitting at one end. Still, the noise did exist with the old transponder,
before I went to the LAN cable stock.

But the store's bulk stock is probably the same brand, so I can't see the
LAN cable as being a second choice.

One thing that did occur to me was to take copper braid and slide some over
the transponder coax as an additional shield. Shouldn't affect the RF
characteristics, I guess, but didn't really think it would help the noise
problem.

Ron Wanttaja

[Russell Kent]

Ron Wanttaja wrote:

> One thing that did occur to me was to take copper braid and slide some over
> the transponder coax as an additional shield.

Or spiral wrap some of that copper tape that RST's winged creatures delivered.

Russell Kent

[Joe]

Why can't you just continue to use what worked? Namely the aluminum foil.

Signed,
Not Understanding, Captain of the least resistance


"Ron Wanttaja" > wrote in message
...
> 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

[John]

Ron:
The easy way to tell if the interference is coming from the radiation
of the antenna is to disconnect the antenna at the antenna and connect
a 50 ohm UHF rated dummy load in place of the antenna. If the noise
goes away it is for sure radiation from the antenna and not other
cable coupling paths or power pulse coupling through the 12 volt feed
wire.
The transponder antenna must have a ground plane that is at least 1/4
wave length in radius around the antenna. Avoid multiples of 1/2
wavelength ground planes until you have at least 5 wavelengths or
more of ground plane around the antenna since this affects the antenna
feed impedance and the amount of signal that is fed back on the
outside of the antenna coax.

If the problem is truly from the 1GHz radiation from the antenna one
of the clip on ferrites placed on the wire bundle(s) where the wires
enter the intercom and or where your audio sources come from may cure
the problem. If the coupling is from the power surges required by the
transponder from the 12 volt feed the ferrites will not do any good at
all since they only start to work above 100 MHz.
John


On Tue, 09 Mar 2004 15:10:32 GMT, Ron Wanttaja >
wrote:

>On Tue, 09 Mar 2004 08:27:50 -0600, Big John > wrote:
>
>>Also, any coax you use be sure it is double shielded. Some of the
>>cheap stuff on the market has very 'porous shielding.
>
>Actually, that's one thing I did wonder about. The coax I use is RG-58,
>but I buy premade LAN cables from the local electronics emporium. I
>shortened the one I bought for the transponder, installing a new BNC
>fitting at one end. Still, the noise did exist with the old transponder,
>before I went to the LAN cable stock.
>
>But the store's bulk stock is probably the same brand, so I can't see the
>LAN cable as being a second choice.
>
>One thing that did occur to me was to take copper braid and slide some over
>the transponder coax as an additional shield. Shouldn't affect the RF
>characteristics, I guess, but didn't really think it would help the noise
>problem.
>
>Ron Wanttaja

[Jim Weir]

If you do this, I GUARANTEE you that the noise will go away. This is a
trans-ponder. The trans part means that it responds ONLY to an input pulse. No
input pulse from a radar, no output pulse.

Wanna try again?

Jim



(John)
shared these priceless pearls of wisdom:

->Ron:
->The easy way to tell if the interference is coming from the radiation
->of the antenna is to disconnect the antenna at the antenna and connect
->a 50 ohm UHF rated dummy load in place of the antenna.
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[John]

Humm, I forgot about that Jim. However most have a self test button
that causes the transponder to transmit some pulses. I know my 20
year old Cessna ARC transponder transmits at a low rate when you push
the test button.

On Tue, 09 Mar 2004 19:56:19 -0800, Jim Weir > wrote:

>If you do this, I GUARANTEE you that the noise will go away. This is a
>trans-ponder. The trans part means that it responds ONLY to an input pulse. No
>input pulse from a radar, no output pulse.
>
>Wanna try again?
>
>Jim
>
>
>
(John)
>shared these priceless pearls of wisdom:
>
>->Ron:
>->The easy way to tell if the interference is coming from the radiation
>->of the antenna is to disconnect the antenna at the antenna and connect
>->a 50 ohm UHF rated dummy load in place of the antenna.
>Jim Weir (A&P/IA, CFI, & other good alphabet soup)
>VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
>http://www.rst-engr.com

[Ron Wanttaja]

On Tue, 9 Mar 2004 19:52:22 -0600, "Joe" > wrote:

>Why can't you just continue to use what worked? Namely the aluminum foil.

Durability and maintainability are the main issues. This isn't tucked
behind an instrument panel... the radios are mounted in an open-ended box
on the floorboards, and the area is brushed by my right foot when I get
into and out of the airplane. So it has to be something that doesn't tear
easily.

The current foil is basically just crumpled-on and duct-taped in place. If
I have to remove it, it'll just come apart and I'll have to start from
scratch. Plus, I think it was already starting to loosen, etc during the
single flight...interference seemed to be coming back by the end of the
test ride.

I'd rather have something a bit more durable held on with tie-wraps and/or
clamps. My thought is to bend up a hose clamp so it'll snug the new
shielding tight around the square cross-section of the back of the radio,
and tie-wrap it around the existing shielding on the wiring harness. Then,
to remove the radio, all I'll have to do is loosen the clamp and slide back
the shielding to get at the connectors, and slide it back into place and
tighten the clamp when I'm done. If it were aluminum foil, I'd probably
have to completely take it away and fit a new piece, every time.

Finally... since I didn't build this airplane, I have to have an A&P do the
annual inspection every year. He's eventually, essentially, going to have
to sign off my installation as part of the annual. I'd just as soon
present him with a professional-looking job.

But you're right, I'm weird. :-)

Ron "Pay no attention to Marvel Mystery Oil in the Crankcase" Wanttaja

[Jim Weir]

You may have the only known transponder of that variety that has ever been
designed. In the overwhelming predominant world, the test button tests the
receiver only by injecting microwatts of oscillator into the front end.

Jim


(John)
shared these priceless pearls of wisdom:

->Humm, I forgot about that Jim. However most have a self test button
->that causes the transponder to transmit some pulses. I know my 20
->year old Cessna ARC transponder transmits at a low rate when you push
->the test button.
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Charlie England]

So, what does the IDENT button do?

BTW, the comment about the balloon reminded me that what you really need
to do is get your wife mad at you. The roses you have to buy will come
in foil faced mylar already formed into the cone shape you need.

Charlie

Jim Weir wrote:
> You may have the only known transponder of that variety that has ever been
> designed. In the overwhelming predominant world, the test button tests the
> receiver only by injecting microwatts of oscillator into the front end.
>
> Jim
>
>
> (John)
> shared these priceless pearls of wisdom:
>
> ->Humm, I forgot about that Jim. However most have a self test button
> ->that causes the transponder to transmit some pulses. I know my 20
> ->year old Cessna ARC transponder transmits at a low rate when you push
> ->the test button.
> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
> http://www.rst-engr.com

[John]

Lets see if I got this correct. A micro power oscillator injects RF
pulses into the receiver which then thinks this is a radar
interrogation pulse and fires out a normal TX pulse out of the
transponder.
This sounds very much like what I said before: " I know my 20
year old Cessna ARC transponder transmits at a low rate when you push
the test button."

The ARC RT-359A service manual says that the self test generates 60
MHz 1us pulses that is fed to the first IF amp and that the rest of
the circuit behaves as if it was a normal radar reply. It also says
that you must use a dummy load or an antenna or damage may occur
because it is responding to the self test pulse by transmitting.

I am not sure how King and Narco do the same function since I do not
have a schematic to look at but most likely it is done the same way
which is what you said. It looks like we were both correct.

The end result is that it transmits when you push the self test
button.

On Wed, 10 Mar 2004 08:42:32 -0800, Jim Weir > wrote:

>You may have the only known transponder of that variety that has ever been
>designed. In the overwhelming predominant world, the test button tests the
>receiver only by injecting microwatts of oscillator into the front end.
>
>Jim
>
>
(John)
>shared these priceless pearls of wisdom:
>
>->Humm, I forgot about that Jim. However most have a self test button
>->that causes the transponder to transmit some pulses. I know my 20
>->year old Cessna ARC transponder transmits at a low rate when you push
>->the test button.
>Jim Weir (A&P/IA, CFI, & other good alphabet soup)
>VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
>http://www.rst-engr.com

[Ron Wanttaja]

On Wed, 10 Mar 2004 20:18:37 -0600, Charlie England >
wrote:

>BTW, the comment about the balloon reminded me that what you really need
>to do is get your wife mad at you. The roses you have to buy will come
>in foil faced mylar already formed into the cone shape you need.

Geeze, Charlie, she's ALREADY mad at me for spending $2000 for a new
transponder. Better be gold-faced mylar. :-)

Ron "Doghouse" Wanttaja

[Jim Weir]

(John)
shared these priceless pearls of wisdom:

->Lets see if I got this correct. A micro power oscillator injects RF
->pulses into the receiver which then thinks this is a radar
->interrogation pulse and fires out a normal TX pulse out of the
->transponder.

Nope. The transmitter's local oscillator (or a microfragment thereof) is
injected into the receiver's front end. The receiver tests whether or not the
microtransmitter was received.

The transmitter is inhibited by a digital signal during test.

You got it wrong. Sorry.

If you want to carry on this conversation, post your real name and real email
addy.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[sidk]

From my Terra TRT-250D repair/test manual:
*******************************************
18 Self Test.

18.1 Set interrogation RF level to -90dBm. Hold transponder "Test"
switch in test for at least 4 seconds.

18.2 Observe replies being generated by transponder on % reply meter
of the ATC-1400C/S-1403C. The replies should not exceed 75% over a 5
second period.

18.4 Also observe "T" on display indicating replies being generated.

18.5 Release "Test" switch. Replies should stop.
***********************************************

My comments to clarify some of the above:

1) The ATC-1400C/S-1403C is a transponder test-set.
2) -90 dBm is a level that is well below the receiver threashold (ie,
they don't want the transmitter to "squitter" during this test).


It seems clear to me that the transmitter is indeed transmitting.

Sid Knox
Velocity N199RS
Starduster N666SK
KR2 N24TC
W7QJQ

Jim Weir > wrote in message >...
> (John)
> shared these priceless pearls of wisdom:
>
> ->Lets see if I got this correct. A micro power oscillator injects RF
> ->pulses into the receiver which then thinks this is a radar
> ->interrogation pulse and fires out a normal TX pulse out of the
> ->transponder.
>
> Nope. The transmitter's local oscillator (or a microfragment thereof) is
> injected into the receiver's front end. The receiver tests whether or not the
> microtransmitter was received.
>
> The transmitter is inhibited by a digital signal during test.
>
> You got it wrong. Sorry.
>
> If you want to carry on this conversation, post your real name and real email
> addy.
>
> Jim
> Jim Weir (A&P/IA, CFI, & other good alphabet soup)
> VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
> http://www.rst-engr.com

[John]

Jim:
I have the Cessna RT-359A service manual in front of me. There is NO
disabling of the transmitter during self test. In fact several months
ago I watched the voltage on the cathode of the transmitter tube with
a scope and it pulses when the test switch is depressed. There are
only 4 wires and a coax cable to the TX tube. These are Cathode,
filament, anode , ground and RF out. The anode is +1400 volts DC,
the filament is +6.3 volts and ground is of course at ground. The
cathode is pulled to ground by an NPN transistor to transmit.

On page 5-9 paragraph 5-10 step 2 the manual tells you to press the
test switch to measure the TX peak power and frequency of the
transmitter.

King and Narco may or may not disable the transmitter for self test.
I do not have schematics for these transponders so I can not say one
way or the other but I see no reason to do this since it would add
extra circuits and extra cost to do this. They may do this on the
more modern units since the logic may be in an EPLD and no extra
production cost would be incurred to add this small piece of VHDL
code.

I used to have my email address as part of the post but a few months
ago I started to getting 20 to 60 bounced email messages per day that
I had not sent from people I had never heard of. Apparently the
spammers were not only using my email address to spam me at the rate
of 30 to 40 per day they were also spoofing my address on the spam
they were sending. Due to this I now no longer show even a human
readable address but if you insist here it is: frerichsATroDOTcom.
If you want my address and phone number look up airport identifier
AL10. If you email me your phone number I will give you a call and we
can talk about this.
This all started over an EMC question and I am the EMI "expert" where
I work. (The definition of expert is: A drip under pressure.)
John

On Wed, 10 Mar 2004 19:52:48 -0800, Jim Weir > wrote:

(John)
>shared these priceless pearls of wisdom:
>
>->Lets see if I got this correct. A micro power oscillator injects RF
>->pulses into the receiver which then thinks this is a radar
>->interrogation pulse and fires out a normal TX pulse out of the
>->transponder.
>
>Nope. The transmitter's local oscillator (or a microfragment thereof) is
>injected into the receiver's front end. The receiver tests whether or not the
>microtransmitter was received.
>
>The transmitter is inhibited by a digital signal during test.
>
>You got it wrong. Sorry.
>
>If you want to carry on this conversation, post your real name and real email
>addy.
>
>Jim
>Jim Weir (A&P/IA, CFI, & other good alphabet soup)
>VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
>http://www.rst-engr.com

[James M. Knox]

Charlie England > wrote in
:

> So, what does the IDENT button do?

Just sets a flip/flop so that an extra bit is set on the next reply to an
interrogation (which clears the IDENT flip flop).

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

[Jim Weir]

Jim...

As I recall, that flipflop triggers a timer (10 seconds???) that sends the ident
bit until timeout. Bose' book confirms what I remember also.

Jim



"James M. Knox" >
shared these priceless pearls of wisdom:

->Charlie England > wrote in
:
->
->> So, what does the IDENT button do?
->
->Just sets a flip/flop so that an extra bit is set on the next reply to an
->interrogation (which clears the IDENT flip flop).
->
->-----------------------------------------------
->James M. Knox
->TriSoft ph 512-385-0316
->1109-A Shady Lane fax 512-366-4331
->Austin, Tx 78721
->-----------------------------------------------



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Ed Wischmeyer]

> 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.

The inside? :-)

You get more flying time per buck than anybody I know. What do you do with
all the money you save?

Ed Wischmeyer

[Ron Wanttaja]

On Fri, 12 Mar 2004 19:30:24 -0700, Ed Wischmeyer >
wrote:

>> 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.
>
>The inside? :-)
>
>You get more flying time per buck than anybody I know. What do you do with
>all the money you save?

I sit in closet all evening, rubbing my face with dollar bills. :-)

Ron Wanttaja

[James M. Knox]

Jim Weir > wrote in
:

> As I recall, that flipflop triggers a timer (10 seconds???) that sends
> the ident bit until timeout. Bose' book confirms what I remember
> also.

That sounds likely. [Book? You have a book? <G>]

The main point, relative to this thread, is that it does NOT cause the
transponder to transmit anything in and of itself. It only controls what
gets sent upon interrogation.

jmk

[Jim Weir]

->
->That sounds likely. [Book? You have a book? <G>]

Bose, Safford, Friedman, Krause, Jasik...


->
->The main point, relative to this thread, is that it does NOT cause the
->transponder to transmit anything in and of itself. It only controls what
->gets sent upon interrogation.

That's the truth.


Jim



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[James R. Freeman]

Ron:
Most hardware stores have copper and AL screenwire. With copper you can
solder Your cage to fit.

"Ron Wanttaja" > wrote in message
...
> 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

[James R. Freeman]

Ron:
Last time I was in the local Aerospace store they had it. But You can
get it from:
http://www.twpinc.com/twp/jsp/product.jsp?type=3

"Ron Wanttaja" > wrote in message
...
> 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