Fixing the Transponder with Duct Tape and Aluminum Foil

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

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

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

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

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

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

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

"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.

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:
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
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.

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