3000U Altitude Serializer Installation
REV 2.5 (May 1998)
STC and FAA PMA
Model 3000U Connections
The Model 3000U is connected in parallel with the existing code lines from the encoder. Use the primary encoder if there is more than one in the aircraft.

The two 15 pin connectors (P1 and P2) on the serializer are wired in parallel (pin for pin) using the defacto standard encoder pin out. In many cases, you will be able to plug the cable that now goes to the encoder directly into the serializer. You can then make a short cable between the other 15 pin connector and the encoder. Be sure to check that the encoder wiring matches the pinouts on the Model 3000U.

Note that power is also bussed through the two connectors. Power to the encoder will be on either the 28 vdc pin or the 14 vdc pin, but not both. The serializer gets its power ( only 20 ma.) from one of the two pins supplying power to the encoder. The encoder's circuit breaker can be used since the serializer uses only 20 ma.

The two AUX pins are wired through from one connector to the other and are not used in the Model 3000. Sometimes the encoder enable (strobe) line is in the harness so that the encoder output can be enabled by grounding this line. The AUX pins can be used to pass this signal through.

The 3000U must see the encoder output at all times, even if Mode C is turned off. The transponder must be on to provide a pull-up voltage for the encoder open collector transistors; otherwise the 3000U will not function.  [Return]
Model 3000U Pin Signals
  1. D4 (If encoder does not go above 30,700 ft leave this pin open)
  2. A1
  3. A2
  4. A4
  5. B1
  6. AUX (wired thru)
  7. AUX (wired thru)
  8. Power input 28 VDC at 125 ma must be fused or protected with circuit breaker and go to avionics bus, not master bus
  9. B2
  10. B4
  11. C1
  12. C4 this is correct despite illogical order
  13. C2 this is correct despite illogical order
  14. Power input 14 volts DC (must be fused or CB protected)To aircraft ground.[Return]

Note: the C1, C2, and C4 code lines are not in a logical order, but that happens to be the way many encoders are configured so we kept the same pinout to be consistent! Most installation problems relate to miswired connections to the serializer. If you see-2500 feet on the GPS receiver as the encoder altitude, the 3000U is seeing an invalid gray code from the encoder. Check your wiring and that the transponder is on.

  • Serializer will not work with transponders using a pulsed strobe line. Most modern transponders do not use a pulsed strobe. The serializer must "see" Mode C data at all times.
  • Serializer will not function with King KXP-750 transponder.

Consult factory if transponder is Narco AT-50 or AT-50A or Wilcox 1014. There are two mods for these Narco units that are required.

If a separate dedicated encoder is used to drive the serializer, pullup resistors must be provided on all code lines. A 33K 1/4w resistor to buss voltage will work fine. These resistors can be located either at the encoder or at the serializer. They may be placed inside a DB15 hood and plugged into P1 pr P2. [Return]

How to use 3000U with various receivers
 The Model 3000U will function as an altitude input for Trimble, Northstar, Garmin 150, Magellan, and the Apollo FlyBuddy and 2001 GPS receiver.

To connect the 3000U to a Northstar GPS, see the Northstar GPS installation manual. Note that pins 8 and 9 on P3 of the serializer must be jumpered for the Northstar configuration. Pins 2 and 7 on P3 supply the RS-422 data to the receiver.

Trimble GPS receivers (models 1000, 2000, and 3000)

Use the RS-422 input pins on the #1 serial port on the Trimble GPS receiver.

GPS Receiver Port 1 RS-422 INPUTS Serializer RS-422 OUTPUTS P3

RXD1- pin 4 ----------------------------- T- pin 2

RXD1+ pin 16 ----------------------------- T+ pin 7

Altitude Source must be set for ENCDR INPUT. See Trimble manual for details. [Return]
Apollo FlyBuddy and 2001 GPS Receiver
 To connect the serializer to the Apollo receivers, jumper pins 3 and 8 on P3 (the DB-9). Connect pin 2 on P3 to the RS-232 Altitude Input on the GPS. Pin 5 on P3 should be connected to ground on the receiver. A shielded cable is recommended. 

The 3000U will completely emulate the Apollo Altitude Converter. It will also function as a replacement for the Apollo Encoder, but with 100 foot increments since the raw data is coming from the aircraft's encoder. The jumper on pins 3 and 8 will cause the 3000U to produce the Apollo compatible data stream at 1200 baud for any Apollo GPS equipment. [Return]
Garmin GPS Receiver
For Garmin (Model 150/155) receivers, no jumpers are required for 9600 baud. For 2400 baud, jumper 8 and 9 on P3. See Garmin manual for details.

How to test installation
Turn on the encoder, transponder, and GPS receiver. Look at the altitude page. The source should show that it is from the encoder and the altitude should correspond roughly with field elevation. The altitude shown is the raw encoder output uncorrected for the local altimeter setting. [Return]
Model 3000U Specifications
Specifications:
Weight 5 oz
Operating temperature -20C to +55C
Power requirements 10 to 30 vdc at 20 ma. (must be fused)
Mounts in any orientation uses four screws
 Converts altitude from -1200 feet to 62,000 feet
Impedance on all code lines Greater than 100K input
Baud rate: 9600/2400/1200 baud One reading per second
Data Format: RS-422 balanced output and TTL output suitable for RS-232
Protocols: Trimble, Northstar, Garmin, and Apollo GPS receivers
Pin configuration P1 on unit DB15M, P2 on unit DB15M, P3 on unit DB9M
Size: 4.2" by 3.00" by 1.00"
 [Return]

Adobe Acrobat (PDF) file containing information and notes available here.