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Radio Altimeter Test Sets

BASIC PRODUCT DETAILS

Radio Altimeter Test Set:-About, Application, Types, and Selection:

Radio Altimeter test set is a flight-line test set instrument used to test the Radio altimeters by linear altitude simulation. A Radio Altimeter is used to measure the distance between the ground terrain and the aircraft. It is also known as a radar altimeter, the instrument will analyze the frequency drift and time of reflected radio waves to provide crucial flight navigation data.  

  • Radio Altimeter providing ongoing altitude data to the cockpit, for instrument landings, ground proximity warning systems (GPWS) and Radio Altimeter test set will help to check and verify the correctness of the measured data during the installation and regular checkup of Radio Altimeters. 

Radio altimeter test set will make sure the performance and accuracy of the radio altimeters where sustained low altitude flight paths and rapid ascent or descent is required. The latest Military Radio Altimeter Test Set will support the accuracy requirements for military applications with high-resolution programmable flight simulation at high altitudes.

To learn more about RF communication systems, we recommend you check the following RF and microwave bestsellers articles.

To understand the Radio Altimeter test set in a better way, we recommend you to check to understand more about the following components, which are associated with testing.

In this Radio Altimeter test set article, we will cover,

  • What is the Radio Altimeter test set?
  • Types of  Altimeter and Different types of Radio Altimeters.
  • Application of Radio Altimeter test set.
  • Main specifications need to consider in the selection of the Radio Altimeter test set:
  • RF and microwave Radio Altimeter test set manufacturers.

Design and Application

Types of Altimeter:

The altimeter is one of the elemental instruments in modern air crafts to determine the altitude of aircraft during the operation. Nowadays radio altimeters are prime altimeters used in aircraft and are primarily categorised as pulsed altimeters and FMCW altimeters. The other type of altimeters is barometric altimeters, laser altimeters, GPS and GNSS altimeters, which are commonly used to identify the altitude of aircraft.

Radio Altimeter:

A Radio altimeter (RALT) or a radar altimeter (RA) or electronic altimeter, is an instrument used in flights to measures altitude above the terrain. It utilizes a beam of radio waves by sending it to the ground, and analyzers the reflected wave to the craft to calculate the distance between the antenna on the aircraft and the ground directly below it.

Radar altimeter utilizes the simple radio detection and ranging principle to calculate the altitude above the ground it is flying by analyzing the travel time of the signal and the speed of light. Radar altimeter sends a frequency modulated signal, which can change its frequency over time within its range. This signal is mixed with the radio frequency carrier signal and then sent to the ground by using a transmission antenna.

  • In Radio Altimeter, the reflected signal frequency will be slightly delayed relative to the signal being sent out, corresponding to the time it took to reach the ground and return. By using a frequency mixed, these frequency differences can be extracted and the altitude of the terrain can be calculated. This technique is also known as Frequency Modulated CW radar.

Radar altimeters normally work in the S-band frequency range for a more advanced level of measurement. Radar altimeters also provide accurate and reliable height measurements even above the water body. A radar altimeter is basically used to measures the absolute altitude of the commercial and military aircraft above the underlying terrain.

Each radio altimeter consists of a transmitter and receiver as well as discrete transmit (TX) and receive (RX) and associated antennas. The ultra-high speed of the transmitted signal from the altimeter helps to avoid significant radio altimeter errors. Radio altimeters are classified as Pulsed & FMCW Radio Altimeter.

Pulsed & FMCW Radio Altimeter:

The pulse radio altimeter sends and receives a radio pulse signal to interpret round trip time as a function of distance, like in a pulsed radar operation. In the FMCW method, the deviation in frequency of send and receive signal is used to determine the altitude of the aircraft.

  • FMCW is a prevalent radio altimeter option for most military and commercial aviation, due to the advancement of digital signal processing technology. 

Barometric altimeter:

The barometric altimeter measures the altitude based on air pressure and it is predated to the radio altimeter. Even though barometric altimeter, is not taking direct altitude measurement it is still used to determine altitude above 2,500 feet. It works on the principle that atmospheric pressure drops proportionally to the increase in altitude.

  • As weather conditions can influence air pressure, barometric altimeter readings can be varied during bad weather conditions.  

Laser Altimeters:

The laser altimeters use infrared light waves to determine the altitude of the flying objects. The laser altimeter sends the infrared light waves and receives the reflected lights to determine the heights of the lower altitude aircraft.

GPS or Global Navigation Satellite System-based altimeter:

GPS or Global Navigation Satellite System (GNSS) altimeters are based on modern navigational technology and are mainly used for applications such as hobbyist drones, small UAVs and mountaineering applications.

Radio Altimeter Test Set:

Radio Altimeter test set is an instrument used to test and evaluate the specification of the Radio altimeter at the time of installation and the regular field evaluation.

The radio altimeter test set will be a simulation instrument to simulate the flight conditions like altitude and range. These test sets will have programmable RF delay lines and control software to simulate the RF time delay over a specific range of frequencies.

Most of the Radio altimeter test sets can simulate the altitude up to 60,000 feet and appropriate RF signal propagation losses for the accurate simulation of various environmental and atmospheric conditions.

  • Radio Altimeter test set will have a front panel display and control keypads or digital communications interface to set and incrementally change the specific parameters needed for the test and evaluation.
  • This test set will have the Power and frequency measurement accurate within ±2 dB and ±10 MHz and will have a self-test routine for guaranteeing reliable test performance. 

High-end military Radio altimeter test sets are available to meet the demanding military applications with features to simulate the unique military flight profiles with flexible altitude and duration. These test sets are capable of simulating the rapid ascent and descent rates of the flights. The altitude measurement range for these test sets can be extended up to 8,000 ft as per the requirements. These military radio altimeter test sets will have internal delay calibration for maintaining the accuracy of the test and measurements of the altimeters. 

Application of Radio Altimeter Test Set:

Real-time aircraft altitude data is requisite for safe instrument landings, Decision Height Alerts, Gear Warning, and it is needed for ground proximity warning systems (GPWS). It is important to check the accuracy of the altimeter during the installation and periodically during the operation for the safety of the commercial and military air crafts. Radio Altimeter test set is one of the prime test instruments used to test and verify the accuracy and functionality of these altimeters.

The radio altimeter is an important tool in helicopters during vertical descent in darkness as well as to minimize the risk during the autopilot mode of operation. An accurately tested Radio altimeter by using a radio altimeter test set can provide an independent and unambiguous warning, even if the barometric altimeter is failed during operation.

Few of the Applications of Radio Altimeter test set:

  • Test and installation of Terrain Awareness Warning System (TAWS).
  • Test and simulate complete landing, takeoff and departure approach.
  • Profile creation to control dynamic altitude simulations.
  • Replicate actual and real-time airborne conditions.

Basics & Selection Feature

Main specifications need to consider in the selection of the Radio Altimeter Test Set

When selecting a radio Altimeter test set for the testing Radio Altimeter, the Linear Altitude simulation range, frequency and its accuracy are the prime specifications needed to consider. Below are the specifications need to check for the selection decision.

Linear Altitude Simulation of Radio Altimeter test set:

The liner altimeter Range required for commercial aircraft is in the range of 20 to 6000 ft with a resolution of 1 ft for the normal test requirements. For the military applications range extension required is up to 8000 ft. Need to select as per the test requirements.

Fixed & Variable Delay and Delay Accuracy:

The Delay requirement is corresponding to the altimeter range requirements. Need to select a test set with the options to set the customer specified delay up to the range of about 100us for the normal operation. The accuracy of 0.5 % of set value can be considered for the general test requirements.

RF Input Frequency:

Most of the altimeter test sets will have a frequency range of 4.20 to 4.40 GHz. Accuracy of ±5 MHz with frequency Stability ±1 ppm will be an ideal requirement for most of the test requirements.

Display and front panel control:

LCD display with touch-screen or keypad controls will help to set and read the delay and other parameters needed for the test requirements. Need to select as per the test requirements.

SWR of Radio Altimeter test set:

The standing wave ratio of both the Tx and Rx connectors need to consider for confirming the suitability of the operation.

RF TX Power Input Tracking & Measurement for CW & Pulsed signal:

RF TX Power and Input Tracking Range of the test set need to match with the DUT requirement. It needs to consider for the pulsed and CW signal test.

Environmental:

Environment parameters like operational and storage temperature, humidity need to select as per the test conditions. For normal operations operating temperature of -20° to 55°C will be good enough.

Physical Characteristics & Emissions & Immunity standards:

Physical characteristics like dimensions and weight need to consider as per the test requirements. Emissions & Immunity standards need to verify to confirm the suitability of the test instruments.

Eg: MIL-PRF28800F Class 2 EN 61326:1998 Class A etc.

Conclusion:

A radar altimeter is an instrument used to measures altitude above the terrain directly beneath a flying spacecraft (The distance between the ground directly below the antenna of the aircraft). The Radio altimeters are used to test both pulse and frequency-modulated continuous-wave (FMCW) Radio altimeters.

In the manufacturer section, you can check the list of top-rated Radio Altimeter test set manufacturers registered with the RFMWC website. These altimeter test sets can be used directly to measure the parameters of the most popular altimeter manufacturers like Rockwell Collins, Honeywell, etc. 

  • You can select a suitable Radio Altimeter test set for your test requirements directly from these manufacturers or contact us for further support.

If you would like to add additional details of Radio Altimeter test set or manufacturers to www.rfmwc.com website, please feel free to contact us over the contact page.

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