3000U Altitude Serializer FAQ's
	Answers to frequently-asked questions about the 3000U ALtitude Serializer. If your question is not here please contact us.
	Q: The transponder is a Narco AT-50 or AT-50A. What do I do? A: Contact us and we will fax the solution. Q: On an Apollo GPS receiver, I get "Out of Range" on the altitude page. What's wrong? A: Generally this means that the Mode C altitude as seen by the serialzier is beyond the range for the receiver. Be sure that the C2 and C4 bits are wired properly. Be sure that pin 1 on P1 or P2 is not grounded. This is the D4 bit which comes on at 30,700 ft. Q: I don't get any altitude display on the Apollo receiver. What's up? A: Be sure that on P3 pins 3 and 8 are jumpered. Be sure that you use pin 2 on P3 for the RS-232 signal and that pin 5 goes to RS-232 ground on the receiver. Q: The serializer doesn't appear to be working. What do you suggest? A: Be sure the transponder is turned on to provide a pull up voltage for the serializer. Be sure the Mode C lines are wired properly. Be sure the serial port on the receiver is configured right. Be sure the encoder has warmed up. Be sure you looked at the first question above. Be sure that the low Mode C lines are below one volt and that the high Mode C lines are above two volts. Be sure the serializer has power. Put a scope on pin 2 of P3 and see if there is a burst of pulses once or twice a second. The signal levels are 0 to 5 volts. Q: The transponder is sending out Mode C just fine, but the serializer is acting goofy. A: If you miswire two Mode C code lines in and out of P1 and P2, but end up connecting them properly at the transponder, the transponder will work just fine, but the serializer will see an invalid Mode C value. Be very careful when wiring to the P1 and P2 connectors. Q: Why are the C2 and C4 bits out of order? A: We used the standard 15 pin encoder wiring. Everyone else wires the C2 and C4 bits this way, so we did it to be consistent! You can use a "one for one" cable between the serializer and the encoder. Q: What are the AUX pins on P1 and P2? A: All signals on P1 and P2 are wired in parallel including the AUX pins. Some encoders use one or both of these pins to enable the Mode C. We just labelled them AUX to confuse you. Q: Can I use a pulsed strobe line to the encoder? A: No, the encoder must put out Mode C data all the time. Be sure the encoder enable line is grounded at all times. If the transponder disables Mode C by ungrounding this line, the serializer will not see the Mode C data. Q: Will the serialzier work with any transponder/encoder combination? A: Virtually all combinations will work. The AT-50/50A is a problem that can be easily solved. See above. The King KXP-750 is a problem transponder, but who would put in a GPS in an airplane with a KXP-750 anyway?
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