KLN-89B GPS xponder compatibility

I have installed a KLN-89B installed but the altitude comming from the
xponder is not working. The xponder is an old Narco AT50. I wonder if
other pilots have another model of xponder installed that actually
interfaces with the GPS.

I have installed a KLN-89B installed but the altitude comming from the xponder
is not working. The xponder is an old Narco AT50. I wonder if other pilots have
another model of xponder installed that actually interfaces with the GPS.


I thought the altitude information would come from the encoder or serializer.
Get a sandia aerospace SA35 encoder serializer (encoder with 2 rs-232 ports,
altitude information in 10' increments).

I think another possibility is that you might need to look at the wiring
diagram of the install, what was connected and how. A KLN89b is an OK gps
navigator but not a great one. I don't know who did the installation but
perhaps the avionics shop has the work order and that would explain what was
supposed to be done.

Best situation would be the Garmin GTX327 transponder which will accept the
serializer input and display the pressure altimeter with 10' increments.


paul k. sanchez, cfii-mei
on eagles’ wings
2011 south perimeter road, suite g
fort lauderdale, florida 33309-7135
305-389-1742 wireless
954-776-0527 fax
954-965-8329 home/fax

Victor wrote:
: I have installed a KLN-89B installed but the altitude comming from the
: xponder is not working. The xponder is an old Narco AT50. I wonder if
: other pilots have another model of xponder installed that actually
: interfaces with the GPS.

This assumes that the KLN-89B is reading the parallel (gray-code)
transponder output that the transponder is connected to.

You need to use isolation diodes on all lines from the Narco transponder
to the encoder, and from the GPS to the encoder. If you don't do this, the
GPS will read the encoder incorrectly. You'll also need pull-up resistors
on the outputs of the encoder.

ASCII schematic:
+V
|
(kln89B) -------|--- 10K
| |
--------------- (Encoder)
|
(AT50) -------|---

^^
Diode

--
Aaron Coolidge (N9376J)

Aaron Coolidge wrote:
: You need to use isolation diodes on all lines from the Narco transponder
: to the encoder, and from the GPS to the encoder. If you don't do this, the
: GPS will read the encoder incorrectly.

That's not quite true. So long as the power is on for both of them,
they'll both read fine. The problem is when power's turned off on either,
to grounds all the lines for the other.


You'll also need pull-up resistors
: on the outputs of the encoder.

This shoulnd't be necessary, unless either the KLN-89B or AT50 are
very weird. All the transponders and GPSs I've dealt with have their own
pullup internally. They're all open-collector outputs and have their own
rail.

-Cory

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* - learn what you don't know, *
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Older AT50's and some AT60A's strobe the output from the encoder, and unless
the transponder is modified the output is not always present as required by
the GPS. There is a Narco service bulletin that addresses this problem.

"Victor" wrote in message
m...
I have installed a KLN-89B installed but the altitude comming from the
xponder is not working. The xponder is an old Narco AT50. I wonder if
other pilots have another model of xponder installed that actually
interfaces with the GPS.

This sounds quite likely. I remember now reading about the
strobe, but it didn't apply to my applications so I promptly forgot...
I'd imaging you can just tie it high? Dunno

-Cory

Jerry wrote:
: Older AT50's and some AT60A's strobe the output from the encoder, and unless
: the transponder is modified the output is not always present as required by
: the GPS. There is a Narco service bulletin that addresses this problem.




--
************************************************** ***********************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
************************************************** ***********************