CDIs and interfaces

Couldn't find much help with google. Can someone give me a short course on
Course Deviation Indicators (CDIs) and their interfaces to the equipment that
drives them?

Looking at a couple of web sites, there appear to be tens of unique models of
the CDIs, a different model for each possible NAV radio or GPS (LORAN, etc) to
be used with it. Is the interface really proprietary and unique to each radio?

Specifically, considering migrating my setup from a KX-155/KX-170B combination
to a GNS530/KX-155 combination and trying to figure out whether my existing CDIs
(King KI-2??) can or should be used with the new setup.

More generally, I'd just like to understand a little more about these interfaces
and what the choices are.

....and what does a "serializer" do?

Thanks!

Dave
Remove SHIRT to reply directly.

Dave Butler wrote:
: Couldn't find much help with google. Can someone give me a short course on
: Course Deviation Indicators (CDIs) and their interfaces to the equipment that
: drives them?

There are 2 main types of VOR CDIs, those that have a NAV converter, and
those that do not. This is about LOCALIZER information, not GLIDE
SLOPE information.

1. Those that have a nav converter: Used with KX-155, for example. The
computation of which radial the airplane is on is done in the CDI. The
signal from the radio is usually called "VOR Video". Advantages: fewer
wires from radio to CDI.

2. Those that do not have a nav converter: Used with KX-165, and Collins,
for example. The computation of which radial the airplane is on is done
in the radio. This requires sending the OBS setting back to the radio
from the CDI. Advantages: more universal. These CDIs use an "OBS Resolver".
Most HSI units operate in this mode, with the exception of the Narco DGO-10.

3. Weird types. Old Cessna/ARC and Narco used a potentiometer instead of
a resolver. These are usually not compatible with anything except what they
were sold for.

GLIDE SLOPE: All glide slope info is sent to the CDI in a mostly standard
manner. The computations of where the airplane is on the glideslope are
done in the radio.

The Garmin GPS units require a CDI with an OBS resolver. The best source
of these in used condition is Collins GLS350. The KX-155 uses a CDI with
a nav converter built-in (KI-209), which can't be used with a GPS. King
makes a KI-209A that can be used with a GPS, as it contains a switch to
change modes between nav converter and OBS resolver.

: ...and what does a "serializer" do?

A serializer reads the code put out by your altitude encoder and makes it
into a serial data stream that can be fed into an IFR GPS. Many GPS units
can also read the encoder lines direcly.

--
Aaron Coolidge

Aaron, excellent! Thanks. That's just the level of information I was looking
for. Dave

Aaron Coolidge wrote:
Dave Butler wrote:
: Couldn't find much help with google. Can someone give me a short course on
: Course Deviation Indicators (CDIs) and their interfaces to the equipment that
: drives them?

There are 2 main types of VOR CDIs, those that have a NAV converter, and
those that do not. This is about LOCALIZER information, not GLIDE
SLOPE information.

1. Those that have a nav converter: Used with KX-155, for example. The
computation of which radial the airplane is on is done in the CDI. The
signal from the radio is usually called "VOR Video". Advantages: fewer
wires from radio to CDI.

2. Those that do not have a nav converter: Used with KX-165, and Collins,
for example. The computation of which radial the airplane is on is done
in the radio. This requires sending the OBS setting back to the radio
from the CDI. Advantages: more universal. These CDIs use an "OBS Resolver".
Most HSI units operate in this mode, with the exception of the Narco DGO-10.

3. Weird types. Old Cessna/ARC and Narco used a potentiometer instead of
a resolver. These are usually not compatible with anything except what they
were sold for.

GLIDE SLOPE: All glide slope info is sent to the CDI in a mostly standard
manner. The computations of where the airplane is on the glideslope are
done in the radio.

The Garmin GPS units require a CDI with an OBS resolver. The best source
of these in used condition is Collins GLS350. The KX-155 uses a CDI with
a nav converter built-in (KI-209), which can't be used with a GPS. King
makes a KI-209A that can be used with a GPS, as it contains a switch to
change modes between nav converter and OBS resolver.

: ...and what does a "serializer" do?

A serializer reads the code put out by your altitude encoder and makes it
into a serial data stream that can be fed into an IFR GPS. Many GPS units
can also read the encoder lines direcly.



--
Dave Butler, software engineer 919-392-4367