I, WILLIAM BRUCE BYRON, Director of Aviation Safety, on behalf of CASA, make this instrument under subregulation 21A (1) of the Civil Aviation Regulations 1988.
[Signed Bruce Byron]
Bruce Byron
Director of Aviation Safety and
Chief Executive Officer
17 December 2007
Civil Aviation Order 103.26 Instrument 2007
1 Name of instrument
This instrument is the Civil Aviation Order 103.26 Instrument 2007.
2 Commencement
This instrument commences on the day after it is registered.
3 New Civil Aviation Order 103.26
Civil Aviation Order 103.26 is repealed and a new Civil Aviation Order 103.26 substituted as set out in Schedule 1.
Schedule 1 Civil Aviation Order 103.26
Equipment standards — automatic direction finding receiving equipment
Note: This Order is to be read in conjunction with Civil Aviation Order 103.21.
1 Application
1.1This Civil Aviation Order specifies standards for airborne automatic direction finding receiving equipment operating within the frequency range from 200 to 1 750 kHz.
1.2These standards apply to the approval of equipment for use in Australian registered aircraft for the purpose of providing information for the navigation of the aircraft.
2 Design requirements
2.1The equipment must automatically indicate the direction relative to aircraft heading from which radio waves, at a selected frequency, are being received. The design of the equipment must make provision for compensation of quadrantal error.
2.2The frequency range must be at least from 200 to 415 kHz, but should extend from 200 to 1 750 kHz with satisfactory operation of the equipment in all intended modes of operation.
2.3For all I.F.R. and limited I.F.R. classifications, the equipment must provide some means which will assist in establishing correct tuning, e.g. tuning meter BFO, crystal control.
2.4For all I.F.R. and limited I.F.R. classifications, the equipment must incorporate a means to rotate the loop antenna (or equivalent) from the indicated bearing for an ADF function check.
2.5There is no requirement in Australia for manual direction finder operation but, when this facility is provided, it must function in accordance with characteristics approved by the Director for that specific type of equipment. As applicable, performance standards for functions using the loop antenna only should be substantially similar to comparable operation of the ADF system.
2.6Controls not intended for use during flight must not be readily accessible to the flight crew.
Section 1 - Civil Aviation Order 103.26 Instrument 2007 - Civil Aviation Order 103.26 Instrument 2007 | Zoe
2.7All indicators, controls and test points must be clearly marked or readily identifiable as follows:
(a) indicators and controls for in-flight operation must be marked in English symbols;
(b) indicators, controls and test points for maintenance adjustments to installed equipment must be marked in English or recognised technical symbols;
(c) controls and test points used only during maintenance at the test bench must be identifiable by means of suitable markings or by other means of providing unambiguous identification, e.g. overlays, photographs.
2.8The equipment must be designed so that any possibility of incorrect mating of connectors is minimised. Plugs and sockets without positive means to prevent incorrect mating must be suitably marked or readily identifiable with their function or suitable circuit reference.
2.9The equipment must be so designed that the possibility of electric shock to passengers or crew is negligible.
2.10The equipment must be so constructed that normal methods of mounting and the application of vibration and shock under the most severe conditions likely to be encountered by the equipment will not cause detuning or other malfunctions to occur or otherwise damage the equipment.
2.11The equipment must be designed so that the rating of each component with appropriate derating is not exceeded in any localised component environment which may occur during operation of the equipment in any over-all environment implied by its classification.
2.12The attachment of components and the restraint of plug-in components, adjustment and tuning devices, must be adequate to ensure their security and permanence of adjustment under the vibration conditions within which the equipment may be operated.
2.13The performance characteristics of the equipment must be unaffected by operation of panel and indicator lamps incorporated in the equipment.
Note It is recommended that lamps be fitted with a dimming device or provision made for their connection into a suitable dimming circuit.
2.14The manufacturer must describe acceptable standards for the sense antenna and lead-in cables.
Note The circuit constants to be used as an artificial aerial between the signal generator and the receiver sense-aerial input should also be published. In the absence of such data, the artificial aerial specified in Appendix 1 must be used.
3 Conditions of test
3.1Compliance with this Civil Aviation Order must be substantiated by tests conducted on 1 or more sets of equipment to the extent appropriate to the desired classification.
Note 1 The Director may allow some departure from certain individual requirements provided that, in his opinion, overall performance is consistent with the intended purpose of the equipment and generally satisfactory throughout the range of environmental conditions mentioned in this Order.
Note 2 The Director may require additional tests to be conducted if particular designs or performance characteristics appear to warrant special assessment.
3.2During, and subsequent to the application of, the specified tests, the equipment must not exhibit evidence of any condition which would be detrimental to its continued satisfactory performance.
3.3Unless otherwise specified or required, tests must be conducted under room ambient conditions.
Note Room ambient conditions should be:
Note: atmospheric pressure — 810 to 1050 mb or 24 to 31 inches Hg;
air temperature — +10 to +40C;
relative humidity — less than 85%.
3.4Unless otherwise specified or required, the equipment must be operated at normal rated power supply voltage and frequency. Variations up to ±2% of voltage and ±2% of frequency will be accepted.
Note 1 Normal rated voltages and frequencies are those specified by the manufacturer for continuous or stated duty cycle operation of the equipment. Usual ratings will be 13.75 or 27.5 volts for dc and 115 volts at 400 Hz for ac operated equipment.
Note 2 For equipment designed to operate on a variable frequency ac supply, the terms “selected test frequency” and “critical test frequency” should be used and noted in the test reports.
3.5Measurement of performance requirements for which input signal levels are specified in field strength units (e.g. microvolts per metre) must be conducted with the loop antenna positioned in a shielded enclosure equipped with a calibrated test transmission line (as described in Appendix 1) producing a signal field at the loop antenna, and the appropriate input to the sense antenna terminal, to accurately simulate the conditions in a free-space radiated field.
If the measurement of any performance requirement which requires that the input signal be applied only to the sense antenna terminal is conducted without using the shielded enclosure and calibrated transmission line, a standard test antenna must be used as described in Appendix 1.
3.6Where a voltage level at radio frequency (other than an input signal level) is specified, it must be interpreted as the voltage actually occurring between the points stated or the point and equipment frame, as appropriate.
3.7Unless otherwise agreed by the Director, equipment covered by these Equipment Standards must be capable of continuous operation.
3.8Accepted test procedures must be used for the conduct of the performance tests required by these Equipment Standards. Unless otherwise agreed by the Director, the same procedures must be used for the conduct of similar tests under environmental, low voltage and normal test conditions.
Note Suggested test procedures are contained in Appendix 1.
3.9Evidence that test equipment is properly calibrated and checked must be made available at the Director’s request.
3.10Minor modifications to correct deficiencies noted as a result of the tests may be made at any stage of the tests providing that such tests as the Director considers necessary are repeated.
Note Results of repeated tests should be identifiable with the specific modification.
4 Minimum performance requirements under normal test conditions
Note Unless otherwise stated, these requirements are applicable at all receiver frequencies throughout the range from 200 to 415 kHz. It is desirable that similar standards should apply at all other frequencies to which the receiver may be tuned.
4.1Frequency indicator accuracy
4.1.1For equipment capable of continuously tunable frequency selection, the frequency of maximum response must be within 1% (for ratings I) or 1.2% (for ratings L and V) of the indicated frequency.
4.1.2For equipment in which the frequency is selected in discrete increments, the frequency maximum response must be within 0.1% of the selected frequency.
4.2Sensitivity (MCW and CW)
The field strength of the signal required to produce a signal-plus-noise to noise ratio of 6 dB at 20% of reference output (see Note) must not exceed 70 microvolts per metre (for ratings I and L) or 100 microvolts per metre (for ratings V) when:
(a) the signal is modulated 30% at 1 020 ±50 Hz or 400 ±25 Hz and the BFO is not in operation; and
(b) the signal is unmodulated, the BFO is in operation and the receiver is tuned to produce a beat note at approximately 1 000 Hz.
Note Reference output is that audio output porter obtained when the gain controls are set to produce maximum receiver gain and a 10% increase in the level of an input signal modulated 30% at 1 000 Hz produces a 5% increase in audio output power. (It is permissible to adjust the RF gain control just enough to permit determination of reference output as otherwise specified.)
Note: For equipment without an RF gain control, reference output may be alternatively defined as that audio output power produced by an input signal field strength of 100 microvolts per metre with the same audio gain control setting as that which produces maximum audio output with no more than 25% distortion with an input signal field strength of 500 millivolts per metre when the input signals are modulated 30% at 1 000 Hz.
4.3Audio output
The audio output capability must be not less than the rated output power published by the manufacturer when the field strength of a signal modulated 60% at 1 000 Hz is 70 microvolts per metre (for ratings I) or 100 microvolts per metre (for ratings I and V).
Note To ensure satisfactory performance in a wide variety of installations, an audio output capability not less than 50 milliwatts for the headset output circuit and 3 watts for the speaker output circuit (if provided) is recommended.
4.4Distortion
The combined noise and distortion in the receiver output must not exceed 25% at reference output when the input signal is modulated 85%. This requirement must be met for modulating frequencies from 350 to 1 400 Hz and signal levels from 3 dB above the minimum at which reference output can be achieved to 500 millivolts per metre.
4.5Audio frequency response
With the RF signal level and receiver gain controls adjusted to produce 20% of reference output and at least 25 dB signal-plus-noise to noise ratio at the maximum response frequency, the audio level must not vary more than 10 dB as the modulating frequency is varied over the range of 350 to 1 400 Hz.
Note The response should decrease below 350 Hz and above 2 000 Hz.
4.6Manual gain control
The control range of the manual gain control must be at least 24 dB for any signal field strength from 70 microvolts per metre to 500 millivolts per metre.
4.7Audio output regulation
The manufacturer must declare the effect of variation of audio load impedance on audio output power or voltage.
Note Although no specific values of acceptability are set down for this requirement, the information is necessary to the design and approval of aircraft audio installations. The information should cover load impedance variations from 0.25 to 2RL for headphone circuits and 0 5RL for speaker circuits.
4.8Selectivity
4.8.1The level of an input signal required to produce constant audio output must not vary more than 6 dB when its frequency is varied above and below the frequency of maximum response by 0.6 kHz (for ratings I and L) or 0.5 kHz (for ratings V).
4.8.2The level of an input signal required to produce constant audio output as its frequency is varied above and below the frequency of maximum response must be not less than the values tabulated:
Operational ratings
kHz above and below the Frequency of Maximum Response
Signal level relative to that at Frequency of Maximum Response (dB)
IL2
02367
06206580
L1
0369
0124055
Note Although a minimum requirement for selectivity has not been specified for rating V equipment, a standard equivalent to that for rating L1 is recommended. The Director may not approve, or may withdraw approval for use in certain areas, equipment with selectivity below the standard specified for L1.
4.9Cross modulation
This requirement is applicable only to equipment for which an I rating is desired.
With the simultaneous application of an unmodulated (wanted) signal at the frequency to which the receiver is tuned and a signal (unwanted) modulated 30% at 1 000 Hz at another frequency as specified below and with the receiver gain controls set for maximum output, the receiver output due to cross modulation must not exceed 20% of reference output when:
(a) the wanted signal is at any level from 100 microvolts per metre to 500 millivolts per metre; and
(b) the unwanted signal is:
(i) at any level between 100 microvolts per metre and 200 millivolts per metre for signals between 50 and 550 kHz, excluding frequencies within 12 kHz of the selected frequency; and
(ii) at any level between 100 microvolts per metre and 1.0 volt per metre for signals between 500 kHz and 20 MHz, excluding frequencies within 12 kHz of the selected frequencies; and
(iii) at any level between 100 microvolts per metre and 400 millivolts per metre for signals between 20 and 150 MHz.
4.10Intermodulation
This requirement is applicable only to equipment for which any rating is desired.
With the receiver gain controls set for maximum output, the receiver output must not exceed 20% of reference output when any combination of signals 1 and 2, as defined in the following table, are simultaneously applied:
Signal
Frequency
Signal level
Modulation
1
(a) 50 to 550 kHz excluding frequencies within 12 kHz of the selected frequency(b) 550 kHz to 20 MHz excluding frequencies within 12 kHz of the selected frequency(c) 20 to 50 MHz
100 microvolts/metre to 200 millivolts/metre100 microvolts/metre to 1.0 volt/metre100 microvolts/metre to 400 millivolts/metre
NoneNoneNone
2
(a) 50 to 550 kHz excluding frequencies within 12 kHz of the selected frequency(b) 550 kHz to 20 MHz excluding frequencies within 12 kHz of the selected frequency(c) 20 to 150 MHz
100 microvolts/metre to 200 millivolts/metre100 microvolts/metre to 1.0 volt/metre100 microvolts/metre to 400 millivolts/metre
30% at1 000 Hz30% at1 000 Hz30% at1 000 Hz
4.11Spurious responses
The response (relative to maximum response) at any frequency between 50 kHz and 150 MHz, excluding frequencies within 6 kHz of the frequency of maximum response, must be at least:
minus 60
minus 50
minus 40
dB
I
L2
L1:V
4.12ADF sensitivity
4.12.1Threshold sensitivity must be such that when the direction of arrival of a signal, at a level not exceeding the appropriate value specified below, is abruptly changed through 175 degrees, the equipment must, within the time and accuracy limits shown, produce the bearing indication obtained after the signal has remained on for 20 seconds:
Operational ratings
Threshold signal level(microvolts/metre)
Time (seconds)
Accuracy (degrees)
I
70
7
2
L
70
9
3
V
100
10
5
4.12.2The performance must be as specified in 4.12 (1) for any signal level between the threshold signal level and 500 millivolts per metre.
4.13Bearing indication accuracy
The bearing indication, after allowance for quadrantal error compensation must not differ from the simulated relative bearing of the signal source by more than the tolerance specified for any signal input level within the range specified in the following table:
Operational ratings
Tolerance (degrees)
Signal input level range
I
3
70 microvolts/metre to 500 millivolts/metre
L
4
70 microvolts/metre to 500 millivolts/metre
V
5
140 microvolts/metre to 500 millivolts/metre
4.14ADF operation with BFO operating
This requirement is applicable only to equipment for which an I or L rating is desired.
If a beat frequency oscillator is incorporated in the equipment, no observable bearing error must result from its use when the input signal field strength is varied throughout the range from 70 microvolts per metre to 100 millivolts per metre.
4.15ADF selectivity
The change in indicated bearing must not exceed that specified when an unmodulated interfering signal from a source bearing 90 degrees to the wanted signal source is applied simultaneously and has the frequency and level relative to the wanted signal tabled below.
The wanted signal must be modulated 30% at 1 000 Hz.
Note Although a minimum requirement for ADF selectivity has not been specified for rating V equipment, a standard equivalent to that for rating L1 is recommended. The Director may not approve, or may withdraw approval for use in certain areas, equipment with ADF selectivity below the standard specified for rating L1.
4.16Effect of detuning on ADF bearing indication
With a signal field strength of 1 000 microvolts per metre, modulated 30% at 1 000 Hz, and the RF gain control, if provided, set to produce maximum receiver gain, the stabilised bearing indication must not change by more than 1 degree (for ratings I and L2) or 2 degrees (for rating L1) when:
(a) the sense antenna input circuit is detuned above and below resonance sufficiently to cause the receiver audio output to decrease by 3 dB from 20% of reference output; and
(b) the loop antenna input circuit is detuned above and below resonance sufficiently to cause the receiver audio output to decrease by 3 dB from 20% of reference output; and
(c) the sense antenna and loop antenna input circuits are detuned simultaneously as in (a) and (b) above; and
(d) in the case of a tunable receiver, it is detuned above and below resonance sufficiently to cause the receiver audio output to decrease by 6 dB from 20% of reference output.
4.17Automatic gain control
When the signal field strength is increased from 100 microvolts per metre to 500 millivolts per metre, the audio output must not vary more than 8 dB (for ratings I), 12 dB (for ratings L) or 14 dB (for ratings V).
4.18Operation of tuning indicator
If a tuning indicator is incorporated in the equipment, it must have sufficient sensitivity to clearly indicate correct tuning to signals at threshold sensitivity (as determined in paragraph 4.12.1).
The tuning indicator must not present spurious or doubtful indication as the field strength is varied throughout the range from threshold to 500 millivolts per metre.
4.19Operation of mechanical devices
Mechanical devices must perform their intended function. Marginal operation must be avoided.
4.20Spurious emissions
Note 1 Equipment which complies with the requirements of either Category A or B equipment specified in Appendix A to RTCA DO-186 or later amendment will be taken to comply with this paragraph.
Note 2 The omission of spurious radio frequency energy of a transient nature resulting from the manual operation of switches, but not including emissions from circuits operating as a result of that manual operation, may exceed the limits mentioned in this paragraph if its duration does not exceed 1 second.
4.20.1Emissions from antenna
The RF signal level across a dummy antenna of capacitance equal to the nominal capacitance of the sense antenna, with otherwise normal use of RF transmission line, couplers, etc, in the sense antenna circuit, must be not greater than 200 microvolts.
4.20.2Emissions from interwiring
This requirement is applicable only to equipment for which an I rating is desired.
Unwanted radio frequency energy on any cable must be of such level, or must be contained in such manner, that the level of signals on discrete frequencies from 190 kHz to 450 MHz induced in another cable run with it does not exceed 1 000 microvolts. (Refer to Appendix 1 for suggested test procedure.)
Note Although this requirement does not apply to receivers with L or V ratings, a similar standard is desirable. Particular attention should be given to minimising spurious emissions within the frequency ranges from 190 kHz to 20 MHz and 108 to 136 MHz in order to provide reasonable assurance that mutual interference limits mentioned in other Civil Aviation Orders can be met. Transistorised inverters in power supply circuits are frequently responsible for unacceptable emissions.
4.21Variation of primary power frequency
The equipment must comply with this Equipment Standard when the primary power frequency is varied throughout the range for which the equipment has been designed. For equipment designed for operation from a nominally constant frequency supply, it must be assumed that the frequency will vary by at least ± 5%.
4.22Application of conducted voltage transients
This requirement is applicable only to equipment for which an I rating is desired.
Note 1 Although specified for I rating equipment only, it is desired that this requirement be applied, where practicable, to all equipment, especially that which incorporates solid state devices susceptible to damage by voltage transients.
Note 2 This requirement is expressed in this interim form pending further investigation of the magnitude and effects of aircraft electrical system transients.
4.22.1Intermittent transients
After application of intermittent transients as specified in RTCA DO-186 or later amendment, the equipment must not exhibit evidence of damage and must continue to function without degradation.
4.22.2Repetitive transients
When the equipment is subjected to the repetitive transients test specified in RTCA DO-186 or later amendment, the requirements of paragraphs 4.2 (Sensitivity — MCW and CW) and 4.13 (Bearing indication accuracy), both of this Order, must be met.
4.23Conducted and radiated interference susceptibility
These requirements are applicable only to equipment for which an I rating is desired.
Note Although these requirements do not apply to equipment with L or V ratings, a similar standard is desirable, especially for the former, in order to provide reasonable assurance that mutual interference limits, mentioned in other Civil Aviation Orders, can be met.
4.23.1Conducted audio frequencies
The requirements of paragraphs 4.2 (Sensitivity — MCW and CW) and 4.13 (Bearing indication accuracy) must be met when the equipment is subjected to the test specified in RTCA DO-186 or later amendment.
4.23.2Audio frequency magnetic fields
The requirements of paragraphs 4.2 (Sensitivity — MCW and CW) and 4.13 (Bearing indication accuracy) must be met when the equipment is subjected to the test specified in RTCA DO-186 or later amendment.
4.23.3Radio frequencies (radiated and conducted)
The requirements of paragraphs 4.2 (Sensitivity — MCW and CW), 4.12 (ADF sensitivity) and 4.13 (Bearing indication accuracy) must be met when the equipment is subjected to the tests specified in RTCA DO-186 or later amendment.
5 Minimum performance requirements at low primary voltage
5.1When all primary power input voltages are simultaneously reduced to 80% of normal rated for DC and 90% of normal rated for AC supplies:
(a) threshold sensitivity when tested under the conditions mentioned in paragraph 4.12.1 must be such that the time required to produce the specified bearing indication accuracy is not more than 1.5 times that mentioned in paragraph 4.12.1; and
(b) the bearing indication accuracy specified in paragraph 4.13 must be achieved over the signal level range from 6 dB above the minimum to the maximum level mentioned in paragraph 4.13; and
(c) mechanical devices must perform their intended functions.
6 Minimum performance requirements under environmental test conditions
Note Environmental test procedures are mentioned in Civil Aviation Order 103.21.
6.1Altitude test
When the equipment is subjected to this test:
(a) there must be no evidence of arcing, burning or other deleterious effect; and
(b) the requirements of paragraphs 4.2 (Sensitivity — MCW and CW), 4.12 (ADF sensitivity) and 4.13 (Bearing indication accuracy) must be met.
6.2Depressurisation test
6.2.1When the equipment is subjected to this test, it must continue to function as intended. Some degradation of performance may be permitted providing that the bearing indication accuracy mentioned in paragraph 4.13 is achieved when the pressure is restored to that equivalent to 20 000 feet and lower altitudes.
6.2.2There must be no evidence of any condition occurring as a result of this test which may cause complete failure of the equipment.
6.3Short time operating high temperature test
When the equipment is subjected to this test:
(a) there must be no evidence of overheating of any component or exudation of grease or other compounds; and
(b) the equipment must continue to function as intended. Some degradation of performance, within the following limit, is permitted:
(i) the bearing indication accuracy must be within 3 degrees of that mentioned in paragraph 4.13 over the input signal level range from 6 dB above the minimum to the maximum mentioned in paragraph 4.13.
6.4High temperature test
When the equipment is subjected to this test:
(a) there must be no evidence of overheating of any component or exudation of grease or other compounds; and
(b) the requirements of paragraphs 4.2 (Sensitivity — MCW and CW), 4.12 (ADF sensitivity), 4.13 (Bearing indication accuracy), 4.18 (Operation of tuning indicator) and 4.19 (Operation of mechanical devices) must be met, with input signal levels not more than 1.5 times the minimums mentioned in the respective paragraphs.
6.5Temperature variation test
When the equipment is subjected to this test, the requirements of paragraphs 4.1 (Frequency indicator accuracy), 4.2 (Sensitivity — MCW and CW), 4.12 (ADF sensitivity) and 4.13 (Bearing indication accuracy) must be met.
6.6Low temperature test
When the equipment is subjected to this test:
(a) the requirements of paragraphs 4.2 (Sensitivity — MCW and CW), 4.13 (Bearing indication accuracy) and 4.19 (Operation of mechanical devices) must be met with input signal levels not more than 6 dB greater than the minimums mentioned in the respective paragraphs; and
(b) threshold sensitivity, when tested under the conditions mentioned in paragraph 4.12.1 must be such that the time required to produce bearing indications within 2 degrees (rating I) or 3 degrees (rating L2) of the corresponding bearing indications under normal test conditions must not exceed 14 seconds.
6.7Humidity test
6.7.1After the equipment has been subjected to this test, and immediately following the 15 minute warm-up period, the requirements of paragraphs 4.2 (Sensitivity — MCW and CW) and 4.13 (Bearing indication accuracy) must be met with input signal levels not more than 12 dB greater than the minimums mentioned in the respective paragraphs. The requirements of paragraph 4.19 (Operation of mechanical devices) must be met.
6.7.2Within 4 hours from the time the primary power is applied, the requirements of paragraphs 4.2 (Sensitivity — MCW and CW), 4.12 (ADF sensitivity), 4.13 (Bearing indication accuracy) and 4.19 (Operation of mechanical devices) must be met.
6.8Resonance search
When the equipment is subjected to the resonance search, there must be no evidence of excessive flexure of the chassis or mounting and components must not develop independent movement which would be likely to result in failure of the component or its attachment to the equipment.
6.9Anti-vibration mounting attenuation test
When the equipment is subjected to this test:
(a) the mountings must not attain their limit of displacement in any direction; and
(b) magnification of vibration amplitude must be confined to frequencies below 20 Hz.
6.10Vibration test
When the equipment is subjected to this test:
(a) there must be no evidence of detuning, upset of adjustments or other malfunction; and
(b) the requirements of paragraphs 4.2 (Sensitivity — MCW and CW), 4.12 (ADF sensitivity), 4.13 (Bearing indication accuracy), 4.18 (Operation of tuning indicator) and 4.19 (Operation of mechanical devices) must be met.
6.11Acceleration test
After the equipment has been subjected to this test, there must be no evidence of it breaking free from its mountings.
Appendix 1
Test procedures
1 It is recognised that compliance with some of the minimum performance requirements mentioned in this Civil Aviation Order may be determined using alternative test procedures. However, paragraph 3.8 states that “accepted” test procedures are to be used and the Director may require a full description of the procedures actually used should there be any doubt as to the validity of the results of any test.
2 Procedures suitable for the conduct of most of the tests mentioned in this Civil Aviation Order are contained in Appendix A to RTCA DO-179 or later amendment. In some instances, suitable test procedures may be determined from the wording of the requirement.
3 For the convenience of manufacturers who do not have ready access to RTCA DO‑179 or later amendment, or certain of the test equipment mentioned in it, the following information on acceptable test procedures may, be useful.
4 Description of special test facilities
4.1 Standard test antenna
Image unavailable in extracted text 4.1.1 If details of an artificial antenna providing similar characteristics to the sense antenna are not specified by the equipment manufacturer, the following must be used:
Figure 1
where:
Cs = HeCa 10% (pf)
Cs + Cp = Ca ± 10% (pf)
Ca = capacitance of antenna for which equipment is designed (pf)
He = effective height of antenna for which equipment is designed (metres).
4.1.2 When the artificial antenna is used in the conduct of tests mentioned in this Civil Aviation Order, the voltage “e” is the receiver input signal level mentioned and is equivalent to the field strength at the antenna with which the receiver is designed to operate.
4.2 Screened test room
4.2.1 The measurement of performance characteristics requiring an RF signal input to the loop antenna must be conducted with the equipment in a screened room or with the loop in a special test facility in which an RF field of known strength can be produced. The loop antenna must operate as it would in a free space radiated field.
4.2.2 A screened room is recommended with inside dimensions not less than:
length 2.74 metres
width 2.13 metres
height 2.28 metres.
4.2.3 The room should be double screened with 12 mm mesh galvanised steel wire netting or single screened with copper sheet. The screen should be earthed at a single point only. If double wire mesh screens are used, these should be connected together at the earth point only. Contact strips must be fitted around the door to ensure that continuous screening is provided when the door is closed.
4.2.4 Power supplies should enter the room at the point of ground connection and be filtered to exclude interfering signals and RF noise. Power cables within the room should be run in metal conduit bonded to the screening.
4.2.5 A test transmission line must be provided. This should be of 16/22 SWG tinned copper wire and stretched across the width of the room between short strain insulators. It must be horizontal and parallel to and midway between the end or side walls. The distance of the line below the ceiling will depend on the height of the room and other factors. For the minimum room size recommended, it will probably be about 0.30 metre; it will be greater for rooms with higher ceilings. A suitable distance for the centre of the loop below the transmission line will have to be determined. These distances affect the attenuation constant “K” of the room and test transmission line.
(a) Connect signal generator to transmission line through low capacity co-axial line as shown in Figure 2. Do not connect resistors R1 and R2.
(b) Connect a RF VTVM between each end of the transmission line and the inner screen of the room.
(c) Vary the signal generator output frequency until the VTVM at the feed end of the transmission line indicates a dip and that at the other end a peak reading. At this frequency, the transmission line is at ¼ wave resonance.
(d) Without altering the signal generator output frequency, determine by trial and error the value of non-inductive resistor which, when connected between the end of the transmission line remote from the feed end and the inner screen of the room, produces equal readings on the 2 VTVMs.
(e) With the selected value of terminating resistor connected, determine that the VTVM readings remain equal (or very nearly so) when the signal generator output frequency is varied through the range from 100 kHz to 5 MHz.
(f) The selected value of resistor R2 thus determined is equal to the characteristic impedance of the transmission line, i.e. R2 = ZL.
For the minimum room size recommended, the value of ZL will probably be between 250 and 500 ohms.
4.4 Termination of co-axial feeder line
(a) The value of resistor R1 may be determined from:
R1 = ZL x ZG
Image unavailable in extracted text ZL – ZG
where:
ZL = characteristic impedance of transmission line determined in 4.3 above.
ZG = output impedance of signal generator (usually 50 or 70 ohms).
(b) Connect resistor R1 of the calculated value between the feed end of the transmission line and the inner screen of the room.
(c) After terminating resistors R1 and R2 have been properly installed re-check that equal voltages are obtained on the 2 VTVMs connected at each end of the transmission line over the frequency range from 100 kHz to at least 5 MHz.
Note If a discrepancy is found, it may be due to the signal generator output impedance varying from the nominal value. Adjustment of R1 will probably enable the proper result to be obtained.
4.5 Calculation of field strength at loop centre due to test transmission line
The following formulae enable the field strength at a known distance from the line to be calculated:
E = E1 + Ef – Ec
where E = field strength at given position
(i.e. loop centre refer Figure 2)
E1 = field strength due to current in line
= Image unavailable in extracted text
EF = field strength due to current in floor
= Image unavailable in extracted text
EC = field strength due to current in ceiling
= Image unavailable in extracted text
and
EG = voltage input to co-axial line from signal generator
ZL = characteristic impedance of transmission line
Note (A) = 0.06 when dimensions d1, d2, d3 are in metres; or
Note: (A) = 2.36 when dimensions d1, d2, d3 are in inches.
4.6 Attenuation constant “K”
(a) The attenuation constant “K” is the ratio of signal generator output voltage to field strength at loop centre:
i.e. K = Image unavailable in extracted text
and can be used to readily determine the signal generator setting required to produce the desired field strength at the loop centre for a given test set-up.
(b) If desired, the dimensions d1, d2 and d3 can be selected to make “K” a whole number.
(c) If suitable field strength measuring equipment is available, the results should be checked by actual measurement.
4.7 Sense antenna coupling circuit
(a) In all ADF tests, it is necessary to feed a signal to the receiver sense antenna input terminal at a level equivalent to that which would be provided by the sense antenna which is to be simulated. A capacitive voltage divided can be arranged, as shown in Figure 3, so that the same attenuation constant “K” as already established for the test transmission line and loop test set-up can be applied to the sense input.
(b) If appropriate values for sense antenna capacity and effective height are known, the required capacitor values can be calculated using the formulae that follow:
C1 = HeCa (pf)
C2 = Image unavailable in extracted text (pf)
C3 = Image unavailable in extracted text (pf)
where He = effective height of sense antenna to be simulated (metres)
Ca = capacitance of sense antenna to be simulated (pf).
Note: Image unavailable in extracted textNote HeCa = sensitivity product (in metre pf) of the sense antenna to be simulated.
Figure 3
Screened room layout showing capacitive voltage divided and connections for sense antenna input
5 Cross modulation (paragraph 4.9 refers)
(a) Connect the equipment as shown in Figure 4.
Image unavailable in extracted text
Figure 4
(b) The wanted signal is supplied by SG.1 and the unwanted signal by SG.2.
(c) Set SG.2 output to zero.
(d) Set SG.1 output to 100 microvolts modulated 30% at 1 000 Hz.
(e) Tune the receiver and adjust its gain to produce 20% of reference output.
(f) Remove the modulation from SG.1.
(g) Set the output of SG.2 to the frequencies and levels mentioned in paragraph 4.9 and check for cross modulation.
Note If cross modulation is occurring, the receiver output will decrease when the output of SG.1 is decreased.
6 Intermodulation (paragraph 4.10 refers)
(a) Connect the equipment as shown in Figure 4.
(b) Set SG.2 output to zero.
(c) Set SG.1 output to 100 microvolts modulated 30% at 1 000 Hz.
(d) Tune the receiver and adjust its gain to produce 20% of reference output.
(e) Vary the output levels and frequencies of SG.1 and SG.2 throughout the ranges mentioned in the table in paragraph 4.10 and search for any combinations which produce intermodulation products resulting in a receiver output greater than 20% of reference output.
Note 1 Intermodulation products are likely to occur when:
f1 f2 = f
f1 2f2 = f
2f1 f2 = f
Note: etc
where:
f1 = frequency of SG.1 output
f2 = frequency of SG.2 output
f = resonant frequency of receiver.
Note 2 Intermodulation products may also occur when series or parallel resonances in the receiver input circuits, e.g. transmission lines, RF transformers, etc, coincide with 1 of the unwanted frequencies. Care should be taken to ensure that such possibilities are covered by the search.
7 ADF selectivity (paragraph 4.15 refers)
This test must be conducted in a screened room or other suitable test facility in which 2 RF fields oriented at 90 degrees can be produced.
The test would normally be conducted in a screened room having 2 calibrated test transmission lines arranged at right angles to each other. Each line must be set up and calibrated as described in paragraphs 4.1 to 4.6 inclusive of this Appendix.
The isolation between the test transmission lines must be not less than the null depth of the loop antenna.
8 Spurious emissions (paragraph 4.20 refers)
8.1 Emissions from antenna
(a) Connect an artificial antenna having characteristics similar to the sense antenna specified for use with the equipment, or as described in paragraph 4.1 of this Appendix, to the receiver using a transmission line, couplers, etc, as specified for a normal installation.
(b) Operate the receiver at representative frequencies in all modes while measuring the RF voltage across Cp.
8.2 Emissions from interwiring
(a) The test conditions should simulate a typical installation in an aircraft.
(b) Mount the equipment by its normal means, approximately centrally, on a copper, brass or aluminium groundplane measuring at least 0.76 metre wide and having an area of at least 1.1 square metres.
(c) This test should preferably be conducted in a screened room with the groundplane connected to the room shielding by low reactance paths from at least both ends of the groundplane.
(d) Where the length of interconnecting cables is not specified by the manufacturer, these should be at least 1.52 metres long and arranged as in a typical installation. Cables should be raised about 50 mm above the groundplane to reduce shunt capacitance effects. Only those cables so specified by the manufacturer in wiring diagrams applicable to the equipment may be screened.
(e) Bonding straps across vibration isolators, etc should be fitted where these would be used in a normal installation. Bonding must not be used in any place where it would not normally be used in an installation.
(f) Tie in with each bundle of cables in the simulated installation an 18 or 20 gauge insulated cable, unterminated at both ends. Connect a suitable tunable receiver — such as a field intensity receiver — to this “pick-up” cable.
(g) Tune the tunable receiver across the specified frequency range and note the presence and level of signal indications. A signal generator may then be used to determine the levels of noted signals.