FAA Repair Station #QYMR098B

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MBT Electronics Offers Repair / Overhaul Service for the AN/APN-194 Radar Altimeter System.

The APN-194 radar altimeter system consists of a remotely mounted RT (receiver-transmitter), two antennas, and one or more indicators. This system has been installed in numerous aircraft, mostly large turbine types, since about 1974.

This is a pulse type radar altimeter which utilizes solid state electronics except for the transmitter which is a vacuum tube cavity oscillator. The output power is 200 watts peak. Due to the ample transmit power; the performance of the system is very good. The maximum range is 5000 feet and the system will read down to zero feet.

There are several compatible indicators available for this system which is detailed below. The difference between the indicators is mainly the scale factors and zero position. Some have zero at the top, and some have zero at the bottom. One indicator has a 1000 foot range with an expanded scale. The indicators which were used with the older AN/APN-141 radar altimeter system are also compatible.

The output of the RT unit is an analog DC voltage which the indicator converts into a pointer position. The analog voltage is electrically expanded below 400 feet by circuitry in the RT unit. The indicators have a scale which is also expanded below 400 feet. The pointer drive is a servo which is not affected by aircraft attitude or G force. The indicator servo receives a reference voltage, along with the analog range voltage, from the RT unit. This improves the accuracy of the system because the indicator does not contain a precision voltage reference which could go out of tolerance. The indicator performs a “ratio” measurement comparing the analog range voltage to the reference voltage. The indicator does not need to be calibrated with a specific RT unit. A low altitude warning lamp, controlled by a moveable pointer or “bug”, and a test function are also provided.

The aircraft 115 VAC / 400 cycle power is supplied to the indicator which has its own internal power supply. The on / off switch on the indicator also controls the power to the RT unit. With this design, the indicator has independent operating voltages and will not cause a load on the RT power supply. A failure in the indicator will not damage the RT unit.

An optional digital output module is used in the RT-1015 configuration of the APN-194. This outputs a digital form of the altitude data in addition to the analog outputs.

RT Unit Part Numbers

  • RT-1015/APN-194
  • HG7194A1
  • HG7194A3
  • 5841-00-168-7813
  • 5841-00-110-8125
    Receiver transmitter with digital module installed.
  • RT-1042/APN-194
  • HG7194A2
  • HG7194A4
  • 5841-00-165-3030
  • 5841-00-110-6262
    Receiver transmitter (most common configuration)

Remote Indicator Part Numbers

  • ID-1760/APN-194
  • JG1061AA01
  • 5841-00-168-7812

  • ID-1760A/APN-194
  • JG1061AB01
  • 5841-00-110-4883

  • ID-1760B/APN-194
  • JG1061CC01

    Indicator. Zero at bottom. 5000 foot scale.
  • ID-1768/APN-194
  • JG1073AA01
  • 5841-00-168-7811

  • ID-1768A/APN-194
  • JG1073AB01
  • 5841-00-110-4912

  • ID-1068B/APN-194
  • JG1073CC01
  • 5841-01-087-7951

    Indicator. Zero at top. 5000 foot scale.
  • ID-1811/APN-194
  • JG1082AA01
  • 5841-00-110-4130

  • ID-1811A/APN-194
  • JG1082CC01
  • 5841-01-082-1744

    Indicator. Zero at bottom. 5000 foot scale.
  • ID-1879/APN-194
  • JG1061AB02

    Indicator. Zero at bottom. 5000 foot scale.
  • ID-2206/APN-194
  • JG1091CC01

  • ID-2206A/APN-194
  • JG1091DD01
  • 5841-01-232-3104

    Indicator. Zero at bottom. 1000 foot scale.

Antenna Part Numbers

MBT Electronics offers the following services:

components of APN 194 on test bench.

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