The IEEE P1641 default Test Signal Framework Library for compatable IEEE716-95 Signals This XML instance file is specified in IEEE Std 1641-20XX, "IEEE Standard for Signal and Test Definition." This schema is a World Wide Web Consortium (W3C) Extensible Markup Language (XML) binding of Annex E Test signal framework (TSF) for ATLAS Clause E.2 TSF library definition in XML" The purpose of this XML file is to provide unique TSF definitions inline with legacy ATLAS 716 signals.This files uses the W3C XML Schema definition language as the encoding. This allows for interoperability and the exchange of TSF component instances between various systems.This file shall not be modified but may be included in derivative works. Copyright (c) 2009 Institute of Electrical and Electronics Engineers, Inc. USE AT YOUR OWN RISK A sinusoidal time-varying electrical signal. AC Signal amplitude DC Offset AC Signal frequency AC Signal phase angle For this signal, the allowable types are Voltage, Current and Power. All types must be consistent, thus for example, if ac signal amplitude is specified in volts then the dc offset must also be specified in volts. A continuous sinusoidal (carrier) wave whose amplitude is varied as a function of the instantaneous value of a second (modulating) wave. Carrier amplitude Carrier frequency Modulation frequency Depth of modulation Modulation amplitude

The output is given by the equation:

e = Ec (1+maEm sin(ωmt))sin(ωct)

where

Ec is the carrier amplitude (unmodulated)

Em is the modulation amplitude )

ma is the depth of modulation (≡ modulation index)

ωm is 2π x modulating frequency

ω c is 2π x carrier frequency

An unvarying electrical signal with an optional ac component. DC Level AC Component amplitude AC Component frequency AC Component phase angle For this signal, the allowable types are Voltage, Current and Power. All types must be consistent, thus for example, if dc level is specified in volts then the ac component amplitude must also be specified in volts. A parallel digital source that creates a digital logic signal in which the physical values for logic 1, logic 0 and high impedance data values are determined by the logic threshold values specified. Data Value Clock period Logic One level Logic Zero level The width of the signal (and hence the minimum associated connection width) is implied by the number of logic elements in each array element. The default condition for clock period (clock_period = 0) denotes infinite time for static digital data. A high impedance is generated when the digital signal value character is "Z", i.e., no digital signal is present. A logic 1 (output voltage is equal to logic_one_value) is generated when the digital signal value character is "H". A logic 0 (output voltage is equal to logic_zero_value) is generated when the digital signal value character is "L". An unknown value cannot be generated by the digital source model. When the digital signal value character is "X" the model may generate a logic one or a logic zero. The output values are held at the defined levels for the duration of the clock_period. For this signal the data values are transmitted via the parallel connections. Data received via these connections will be available when the signal is used in a measurement. A serial digital source that creates a digital logic signal in which the physical values for logic one, logic zero and high impedance data values are determined by the logic threshold values specified. Data Value Clock period. Zero denotes infinite time for static digital data. Logic One level Logic Zero level The default condition for clock period (clock_period = 0) denotes infinite time for static digital data. The Serial TSF deals only with serial data where the data value is conveyed as the value of the signal rather than any transition of the signal. A high impedance is generated when the digital signal value character is "Z", i.e., no digital signal present. A logic 1 (output voltage is equal to logic_one_value) is generated when the digital signal value character is "H". A logic 0 (output voltage is equal to logic_zero_value) is generated when the digital signal value character is "L". An unknown value cannot be generated by the digital source model. When the digital signal value character is "X" the model may generate a logic one or a logic zero. The output values are held at the defined levels for the duration of the clock_period. For this signal the data value supplied is transmitted via the serial connections. Data received via the serial connections will be available when the signal is used in a measurement. Generate and measure digital data on the same pins. By default, this TSF defines a pin monitor capability on pins that are being STIMmed, in order that faulty pin drivers may be detected. If this feature is not required, then the script in the data value of the ParallelDigital BSC DT_Sense should be modified so that 'H' and 'L' are both substituted with 'X' instead of being passed unchanged. The duration of the digital step. Value of logic High in the output stream (voltage or current). Value of logic Low in the output stream (voltage or current). Threshold value of logic Low in the measurement (voltage or current). Threshold value of logic High in the measurement (voltage or current). The digital data to be generated or measured. A radio aid to air navigation that provides distance information by measuring the time of transmission from an interrogator to a transponder and return. The DME system is composed of a transponder in the ground based unit and an interrogator in the airborne unit. The interrogator on the aircraft emits a pulse signal that, once received by the DME transponder on the ground, starts a response sequence that sends a return pulse signal on a different (paired) channel to the aircraft. The aircraft equipment receives the response from the ground station, computes the elapsed time between interrogation and response, subtracts 50 µs (to cover ground station processing time), and divides the result by 2. This result is then displayed on the DME indicator. The DME operates on the UHF band in the range 962 MHz to 1213 MHz with a step of 1 MHz. The frequencies used by the interrogator are between 1025 MHz and 1150 MHz, and the transponder on the ground replies using two set frequencies: the first from 962 MHz to 1024 MHz and the second from 1151 MHz to 1213 MHz. The number of available frequencies is 252, making 126 available channels. Each channel has 2 frequencies: one for interrogation and the other for the response from the ground station. On each pair of frequencies, the difference between the interrogator frequency and the response frequency is always 63 MHz. For the channels between 1 and 63, the interrogation frequency is 63 MHz higher than the response frequency and for channels from 63 to 126 the response frequency is 63 MHz higher than the interrogator frequency. Carrier Amplitude Interrogator Frequency Interrogation Rate This model has limited functionality. It does not provide for the variation of some of the parameters (such as the pulse timing and level). The model may be modified by the user to include such parameters in the interface properties. A radio aid to air navigation that provides distance information by measuring the time of transmission from an interrogator to a transponder and return. The DME system is composed of a transponder in the ground based unit and an interrogator in the airborne unit. The interrogator on the aircraft emits a pulse signal that once received by the DME transponder on the ground, starts a response sequence which sends a return pulse signal on a different (paired) channel to the aircraft. The aircraft equipment receives the response from the ground station, computes the elapsed time between interrogation and response, subtracts 50 µs (to cover ground station processing time), and divides the result by 2. This result is then displayed on the DME indicator. The DME operates on the UHF band in the range 962 MHz to 1213 MHz with a step of 1 MHz. The frequencies used by the interrogator are between 1025 MHz and 1150 MHz, and the transponder on the ground replies using two set frequencies, the first from 962 MHz to 1024 MHz and the second from 1151 MHz to 1213 MHz. The number of available frequencies is 252, making 126 available channels. Each channel has 2 frequencies: one for interrogation and the other for the response from the ground station. On each pair of frequencies the difference between the interrogator frequency and the response frequency is always 63 MHz. For the channels between 1 and 63, the interrogation frequency is 63 MHz higher than the response frequency; and for channels from 63 to 126 the response frequency is 63 MHz higher than the interrogator frequency. Transponder Frequency Carrier Amplitude Slant Range Range Rate Rate of Change of Range Rate

Slant range of DME is dependent on aircraft height, transponder location and its associated environment, and geographical topography. Maximum range in ARINC 568 is quoted as up to 300 nmi up to an altitude of 75000 ft. The delay range quoted will allow for a transponder transmission range of approximately 400 nmi and its lower value is 0 nmi,(the default 50 µs usually allowed from receipt of an interrogator signal to the transponder response within the transponder itself). These values must not be exceeded.

This model has limited functionality. It does not provide for the variation of some of the parameters (such as the pulse timing and level). The model may be modified by the user to include such parameters in the interface properties.

 A continuous sinusoidal (carrier)wave generated when the frequency of one wave is varied in accordance with the amplitude of another (modulating)wave. Carrier amplitude Carrier frequency Frequency Deviation Modulation frequency Modulation amplitude

e = Ec sin (ωct + mf sin (ωmt) )

mf = kf (Em /ωm )

where:

Ec = carrier amplitude (unmodulated)

Em = modulation amplitude

ωc = 2πx carrier frequency

mf = deviation ratio (≡ modulation index)

ωm = 2π x modulating frequency

kf = frequency deviation

The glide slope is the vertical guidance portion of an ILS. At present, 40 glide slope channels exist with 150 kHz channel separation in the frequency range from 328.6 MHz to 335.4 MHz. The carrier is amplitude modulated at 90 Hz and 150 Hz in a spatial pattern, with the 90 Hz modulation predominant when the airplane is above the glide path, and the 150 Hz modulation predominant if the airplane is below the glide path. This glide slope signal is achieved by transmitting 2 beams with equal offset about the correct glide slope angle. The upper beam is modulated to a depth of 40% with a 90 Hz tone, and the lower beam is modulated to a depth of 40% with a 150 Hz tone. The carrier of both beams is phase-locked so that any receiver will treat them as a single-carrier signal with two modulating tones. If the aircraft is positioned off the glide slope, the ILS receiver will detect one signal as stronger than the other. As a result, the demodulated amplitude (or apparent depth of modulation) of one tone will be greater than that of the other. If the receiver is exactly on the glide slope, it will receive an RF carrier where the 90 Hz and 150 Hz modulation depths appear exactly the same. The greater the deviation from the glide slope, the greater will be the difference in amplitude of the tones. Carrier amplitude Frequency 150 Hz attenuation depth 90 Hz attenuation depth This model has limited functionality. It does not provide for the variation of some of the parameters (such as the tone frequencies). The model may be modified by the user to include such parameters in the interface properties. For this signal, the allowable types for carrier amplitudes are Voltage and Power. The localizer is the lateral guidance portion of the ILS, giving azimuth guidance with reference to the runway centre line. It operates using the same principles as the Glide Slope but with forty channels in the VHF band 108.0 MHz to 112.0 MHz. Each localizer channel is paired with a glide slope channel. The carrier is modulated with 90 Hz and 150 Hz tones in a spatial pattern that makes the 90 Hz tone predominant when the aircraft is to the left of the course and the 150 Hz tone predominant when the aircraft is to the right of the course. The localizer carrier contains a Morse coded signal identifying the runway and approach direction and also may carry a ground-to-air communication channel. Carrier Amplitude Carrier frequency 150 Hz attenuation depth 90 Hz attenuation depth This model represents a limited implementation of the signal. It only represents the two tone directional signal and does not allow for inclusion of coded information. It does not provide for the variation of some of the parameters (such as the tone frequencies). The model may be modified by the user to include such parameters in the interface properties. For this signal, the allowable types for carrier amplitudes are Voltage and Power. Two or three marker beacons operate at 75 MHz to give range with reference to the touch-down point. The outer marker is modulated with a 400 Hz tone to a depth of 95%. It is located 3.5 nmi to 6 nmi (6 km to 11 km)from the end of the runway where the glide slope intersects the procedure turn altitude ± 50 ft (15 m)vertically. It radiates a fan shaped pattern vertically and normal to the localizer and activates a marker receiver when the aircraft passes through. The middle marker is a second fan shaped marker similar to the outer marker. It is located approximately 0.5 nmi to 0.8 nmi (1 km to 1.5 km)from the ILS approach end of the runway and modulated at 1300 Hz. The inner marker, when used for category II approaches, intercepts the glide path at about the 100 ft (30 m)height to mark the over-shoot decision point (if the runway is still not visible). The marker is recognized by its 3000 Hz modulation. Category II approaches allow operation down to 100 ft (30 m)and 1300 ft (400 m) visibility. Marker Frequency Carrier Frequency This model represents a limited implementation of the signal. It does not provide for the variation of some of the parameters (such as the carrier frequency). The model may be modified by the user to include such parameters in the interface properties. For this signal, the carrier amplitudes can only be expressed in terms of power. A continuous sinusoidal wave (carrier) whose phase is varied in accordance with the amplitude of another wave. Carrier amplitude Carrier frequency Phase Deviation Modulation frequency Modulation amplitude

e = Ec sin (ωct + kpEm sin (ωmt) )

where:

Ec = carrier amplitude (unmodulated)

Em = modulation amplitude

ωc = 2πx carrier frequency

ωm = 2π x modulating frequency

kp = phase deviation

A signal characterized by short duration periods of (sinusoidal) ac electrical potential. AC Signal amplitude AC Signal frequency DC offset Initial delay Pulse width Pulse repetition frequency Number of pulses Default condition (where p_repetition = 0) is for continuously repeating pulses. This model represents a pulsed ac signal with a permanent dc offset. An alternative model may be created where only the pulses have a dc offset.

For this signal, the allowable types are Voltage, Current and Power. All types must be consistent, thus for example, if the ac signal amplitude is specified in volts then the dc offset amplitude must also be specified in volts.

 A signal, characterized by a train of pulses of sinusoidal electrical ac activity with different durations and amplitudes. AC amplitude AC frequency DC offset Pulse train This model represents a pulsed ac train with a permanent dc offset. An alternative model may be created where only the pulses have a dc offset. For this signal, the allowable types are Voltage, Current and Power. All types must be consistent, thus for example, if the ac signal amplitude is specified in volts then the dc offset must also be specified in volts. A signal characterized by a train of pulses of electrical dc activity with different durations and amplitudes with an optional ac component. DC level AC component amplitude AC component frequency Delay before first pulse Pulse width Pulse repetition frequency Number of pulses Default condition (where p_repetition = 0) is for continuously repeating pulses. This model represents a pulsed dc signal with a permanent ac component (ripple). An alternative model may be created where only the pulses have an ac component. l. For this signal, the allowable types are Voltage, Current and Power. All types must be consistent, thus for example, if a dc level is specified in volts then the ac component amplitude must also be specified in volts. A signal, characterized by a train of different, short duration periods of dc electrical activity. DC level Pulse train AC Component amplitude AC Component frequency For this signal, the allowable types are Voltage, Current and Power. All types must be consistent, thus for example, if dc level is specified in volts then the ac component amplitude must also be specified in volts. This model represents a pulsed dc train with a permanent ac component (ripple). An alternative model may be created where only the pulses have an ac component. An appropriately delayed signal response to an input radar signal. Atten Range of simulated target Rate of change of rate change Rate of change of target range Proportion of Tx pulses returned This annex describes a transmitted signal as a reference. Thus, the TSF library provides a description for both the transmitted (i.e., Radar_TX_Signal) and received (i.e., Radar_RX_Signal) signals. The Radar_RX_Signal, takes an input Radar signal and delays the signal response. In addition, the signal does not respond to all transmitted radar pulses (a feature that gives rise to a reply efficiency). To achieve reply efficiency, the Radar_RX_Signal must detect the incoming radar pulses and suppress some individual pulses. To detect a radar pulse an RMS monitor is used with a selected gate_time. This monitoring provides an event while the continuous rms value is greater than a nominal threshold value. This rms monitor is used solely to detect a signal. The default values for range_rate and range_accn (i.e., range_rate = 0 and range_accn = 0) represent a stationary target. For this signal, the allowable types are Voltage, Current and Power. However, for this signal the type is determined by the RADAR_TX_SIGNAL to which it is referenced. A pulsed ac signal used as a reference for received radar signals (i.e., Radar_RX_Signal). Tx signal amplitude Tx signal frequency Initial delay Pulse duration Pulse repetition frequency Number of pulses Default condition (where repetition = 0) is for continuously repeating pulses

For this signal, the allowable types are Voltage, Current and Power.

 A periodic wave whose instantaneous value varies alternately and linearly between two specified values (i.e., initial and alternate). Ramp signal amplitude DC offset Ramp signal period Ramp signal time to rise

For this signal, the allowable types are Voltage, Current and Power. All types must be consistent. Thus for example, if the ramp signal amplitude is specified in volts then the dc offset must also be specified in volts.

 Transient disturbances occurring unpredictably, except in a statistical sense. Noise signal amplitude Pseudo random noise frequency Pseudo random noise seed The default for random noise is white noise (characterised by a flat frequency spectrum in the frequency range of interest). White noise needs only noise signal amplitude to be defined. For repeatable pseudo-random noise, both the frequency upper bound and seed need to be specified. Specifying the frequency upper bound provides noise in the frequency band bounded by the frequency value. If no seed is specified, this signal may not be repeatable.

For this signal, the allowable types are Voltage and Power.

 Two ac sine wave voltages whose relationships of amplitude represent the rotation of a shaft position of an electro-mechanical transducer, Shaft angle Reference amplitude Reference frequency Zero index Shaft angle rate Transformer Ratio This model does not consider the effects of angular velocity of the rotor and the quadrature voltages generated in the secondaries.

The outputs of the resolver secondaries are given by the following two equations:

Sine output

es1 = KEr sinθ sin(2πfrt+φ)

Cosine output

es2 = KEr cosθ sin(2πfrt+φ)

or

es2 = KEr sin(θ+π/2)sin(2πfrt+φ)

where

K is the transformer ratio (trans_ratio), assuming K to be the same for both secondaries

E r is the reference amplitude in the primary (ampl)

q is angular displacement of the rotor (angle)

fr is the reference frequency of the signal in the primary (freq)

j is the zero index position of the rotor (zero_index)

Thus the operation of the resolver may be modeled as the product of two signals for each output.

Sine output

es1 = (Er sin(2πfrt+φ)) x (Ksinθ)

Cosine output

es2 = (Er sin(2πfrt+φ)) x (Ksin(θ+π/2))

 A serial databus signal that transmits and receives strings of characters and operates according to the specification TIA-232. Data Word Baud Rate Data Bits Parity Stop Bits Flow Control When using the RS_232 TSF model, only the active data connection (and its ground) are considered, i.e., the connections hi and lo may be used. Some or all of the other control connections required by the TIA-232 specification may need to physically connected, but are not considered by this TSF. For this signal the data word supplied is transmitted via the serial bus connections according to the rules specified in TIA-232. Data received via the serial bus connections will be available when the signal is used in a measurement. A periodic wave that alternately assumes one of two fixed values of amplitude for equal lengths of time. Square wave amplitude Square wave period DC offset

For this signal, the allowable types are Voltage, Current and Power. All types must be consistent. Thus, for example, if the square wave amplitude is specified in volts then the DC Offset must also be specified in volts.

 Secondary Surveillance Radar (SSR) provides information to supplement the information obtained from a primary radar. Governing documents for civilian air traffic control (ATC) are ARINC Specification 572 and ARINC Specification 711 and for the military's identification, friend or foe system (IFF), STANAG 4193. An aircraft on-board transponder will sense an interrogation from a ground (or airborne) station on a specific frequency (i.e., 1030 MHz) and responds with coded signals on another frequency (i.e., 1090 MHz). P1 Amplitude Interrogation mode P3 Start Time P3 level SLS Deviation SLS Level The interrogation signal comprises three pulses, called P1, P2, and P3, respectively. The normal spacing between P1 and P2 is 2 µs. Normal spacing between P1 and P3 depends on the choice of mode. While interrogators will repeat the interrogation sequence approximately every 2 ms and are capable of interlacing several modes alternately (most commonly 3-A and C, known as Mode 3-C), the model is set up for a single interrogation thus allowing each mode to be interrogated individually to ensure the correct response.

SSR_pulses = (0 us ,0.8 us, 1),

({0.000002+sls_dev}, 0.8 us, {sls_level}),

({p3_start}, 0.8 us, {p3_level})

where

sls_dev is the SLS Deviation from the interface properties

sls_level is the SLS Level from the interface properties

p3_start is the P3 Start Time as determined by the value of Interrogation Mode from the table below.

p3_level is the P3 Level from the interface properties

Interrogation mode (mode)

P3 Start Time (p3_start)

1

3µs

2

5µs

3

8µs

A

8µs

B

17µs

C

21µs

D

25µs

For this signal, the allowable types are Voltage, Current and Power.

 The transponder response to a valid SSR interrogation. It consists of an encoded pulse train. Each pulse train consists of a number of data pulses. The number and position of these data pulses (after the start pulse) are determined by the mode selected. There are 16 pulse positions in the pulse train; however, the code or (height) information carried by the response will determine which pulses are present. Carrier Amplitude P3 pulse start time SSR Response Pulse Train

The response is initiated 3 us after the third pulse of a valid interrogation is received.

The parameters of the array of pulses are defined in the table. Pulses F1 and F2 must be present. Pulse X is not currently used and should be omitted, other pulses may be specified as required.

 

Pulse

Start_Time

Pulse_Width

Level_Factor

F1

0

0.45ms

1

C1

1.45 ms

0.45ms

1

A1

2.9 ms

0.45ms

1

C2

4.35 ms

0.45ms

1

A2

5.8 ms

0.45ms

1

C4

7.25 ms

0.45ms

1

A4

8.7 ms

0.45ms

1

X

10.15 ms

0.45ms

1

B1

11.6 ms

0.45ms

1

D1

13.05 ms

0.45ms

1

B2

14.5 ms

0.45ms

1

D2

15.95 ms

0.45ms

1

B4

17.4 ms

0.45ms

1

D4

18.85 ms

0.45ms

1

F2

20.3 ms

0.45ms

1

P1

24.65ms

0.45ms

1

 

 

For this signal, the allowable types are Voltage, Current and Power. The type selected must agree with the type of the SSR_INTERROGATION signal that triggers the SSR_RESPONSE. A change of dc electrical potential from one level to another, either positive or negative. Step size DC offset Step time An amplitude modulated signal in which the carrier is suppressed. Carrier amplitude Carrier frequency Modulation frequency Depth of modulation

e = (EmEc /2)cos(ωc +ωm )t+(EmEc /2)cos(ωc -ωm )t

where

Em is the modulation signal amplitude

E c is the carrier amplitude (unmodulated)

ωm is 2π x modulating frequency

ωc is 2π x carrier frequency

 Three ac sinusoid voltages whose relationship of amplitudes represent the rotational shaft position of an electro-mechanical transducer. Shaft angle Reference amplitude Reference frequency Zero index Shaft angle rate Transformer Ratio This model does not consider the effects of angular velocity of the rotor and the quadrature voltages generated in the stator windings.

The outputs of the synchro stator windings are given by the following equations:

S1

 

Es1 = KEr sin(θ-2Π/3)sin(2πfrt+φ)

S2

 

Es2 = KEr sinθ sin(2πfrt+φ)

S3

 

Es2 = KEr sin(θ+2π/3)sin(2πfrt+φ)

where

 

K                 is the transformer ratio (trans_ratio), assuming K to be the same for all stator windings

Er                                is the reference amplitude in the primary (ampl)

q                  is angular displacement of the rotor (angle)

fr                  is the reference frequency of the signal in the primary (freq)

j                   is the zero index position of the rotor ( zero_index)

Thus the operation of the synchro may be modeled as the product of two signals for each output.

S1

 

Es1 = (Er sin(2πfrt+φ)) x (Ksin(θ-2π/3)

S2

 

Es2 = (Er sin(2πfrt+φ)) x (Ksin(θ))

S3

 

Es3 = (Er sin(2πfrt+φ)) x (Ksin(θ+2π/3))

Tactical air navigation (TACAN ) is a complete UHF polar coordinate navigation system using pulse techniques. The function operates identically as a DME and the bearing function is derived by rotating the ground transponder antenna so as to obtain a rotating multi-lobe pattern for coarse and fine bearing information, as defined in MIL-STD-291B The model defines a subset of the TACAN X signal concerned with bearing, rather than the complete signal, as test requirements dealing with TACAN distance can be refined using the DME model. The transponder emits RF pulses that are amplitude modulated to provide bearing information. The amplitude modulation is produced by rotating a parasitic reflector array about the antenna radiating element. The array consists of one 15 Hz and nine 135 Hz reflectors. As the pattern from the 15 Hz reflector passes through the magnetic east azimuth, a main reference burst (MRB) is transmitted. As the pattern from the 135 Hz reflectors passes through east, an auxiliary reference burst (ARB) is transmitted, except when the pattern is coincident with the 15 Hz pattern. This produces a total of one MRB and eight ARB bursts per antenna rotation. The airborne receiving equipment determines the aircraft bearing from the ground station by measuring elapsed time, first, from the MRB to the 0° phase of the 15 Hz component and second, from the ARB to 0 ° of the 135 Hz component. The TACAN beacon also generates a 2 or 3 letter Morse identification signal every 37.5 s. Transponder Frequency Modulation Index Magnetic Bearing er Amplitude The transponder generates 2700 pulse pairs per second but with a jittered PRF. The rotating antenna modulates this signal at 15 Hz and 135 Hz using the same principles as the variable phase in a VOR signal. The MRB and ARB comprise 12 and 6 equally spaced pulse pairs, respectively. Spacing has been assumed to be 30 s in the model. MRB and ARB pulse trains take priority over interrogator and randomly generated pulse-pairs; therefore the model suppresses these pulse pairs at the appropriate time. This model is a limited implementation to provide the basic TACAN signal. Many properties have been included as fixed parameters and have not been made externally accessible to the user. Some parameters, such as the beacon identification signal (comprising 2 or 3 Morse letters) and speed (i.e., variable pulse width and spacing) have not been addressed in model. A periodic wave whose instantaneous value varies alternately and linearly between two specified values (i.e., initial and alternate). The interval required to transition from the initial value to the alternate value is equal to the interval to transition from the alternate value to the initial value. Triangular wave signal amplitude Trianglar wave signal period DC offset For this signal, the allowable types are Voltage, Current and Power. All types must be consistent, thus for example, if the triangular wave signal amplitude is specified in volts then the dc offset must also be specified in volts. VHF omnidirectional range (VOR) is a system combining ground based and airborne equipment to provide bearing to or from a ground station, as defined in ARINC Specification 579-2. The VOR radiates an RF carrier in the band 108.0 MHz to 117.975 MHz, with which are associated two separate 30 Hz modulations. The phase of one of these modulations is independent of the point of observation (i.e., reference phase). The phase of the other modulation (variable phase) is such that, at a point of observation, it differs from the reference phase by an angle equal to the bearing of the point of observation with respect to the VOR. The two separate modulations consist of the following: A sub-carrier of 9960 Hz, frequency modulated at 30 Hz, modulating the carrier to a nominal depth of 30%. This 30 Hz component is fixed independent of the azimuth and is termed the reference phase. A 30 Hz component, modulating the carrier to a nominal depth of 30%. This 30 Hz component is caused by a rotating antenna producing a change in phase with azimuth and is termed the variable phase. Carrier amplitude Carrier frequency Radial bearing This model has limited functionality. It does not provide for the variation of some of the parameters (such as the tone frequencies). The model may be modified by the user to include such parameters in the interface properties.