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11 STANDARDS FOR
ELECTRONIC POSITION FIXING EQUIPMENT
11.1 LORAN-C
System
-
11.1.1 Application
11.1.1.1 These standards for LORAN-C, required by the Navigating
Appliances and Equipment Regulations, apply to the following types of
receivers:
TYPE I - Fully Automatic Acquisition, Cycle Selection,
Settle, and Track
Denotes that equipment which, after the initial selection,
automatically acquires the master and at least two secondaries, settles,
cycle selects, tracks the signals and periodically updates the time
differences.
TYPE II - Semi-Automatic Acquisition, Fully Automatic Cycle
Selection, Settle, and Track
Denotes that equipment, which automatically acquires the master
signal, may require operator assistance to acquire the secondaries and
then automatically settles, cycle selects, tracks the signals and
periodically updates the time differences.
11.1.1.2 These Standards are based on the receiver being used with an
antenna and antenna coupler having electrical characteristics equivalent
to that for which the receiver is designed.
11.1.2 ACCURACY ^
-
11.1.2.1 All Loran-C receiving equipment is required to meet a
combined accuracy of 0.3 microsecond or better throughout the reference
signal conditions stated in this Standard. Combined accuracy is defined
as:
Combined accuracy = (MTDE)2 + (s TDE)2)1/2
11.1.2.2 Combined accuracy shall be met independently on each time
difference indicated by the receiver.
11.1.3 DYNAMIC RANGE ^
- 11.1.3.1 The receiver must meet the accuracy and lock on requirements
of paragraphs 11.1.2 and 11.1.4 throughout the range of reference signal
conditions referred to in this Standard.
11.1.3.1 When differential signal amplitude is in excess of 60 dB, or
when signal amplitude exceeds 110 dB/1m v/m,
it is permissible that the combined accuracy of the Loran-C receiving
equipment be degraded. Accordingly, the receiving equipment handbook
shall include the following information:
- Maximum signal level at which correct lock-on is attained,
combined accuracy at the signal level, and the equivalent minimum
range to a station, based on an assumed signal level of:
- 3 v/m at 1 km range, and varying inversely with distance
(400 kw station)
- 7.5 v/m at 1 km range, and varying inversely with distance
(2500 kw station)
Differential signal level to be less than 60 dB.
- Maximum signal level at which tracking is continued after
lock-on, the combined accuracy at that signal level, and the
equivalent minimum range to a station (based on the assumed signal
levels above). Differential signal level to be less than 60 dB.
- Maximum differential signal level at which lock-on is
attained, the combined accuracy at that limit, and the equivalent
minimum range to a station, based on an assumed remote signal level
of 25 dB/1m v/m.
- Maximum differential signal level at which tracking is
continued after lock-on has been completed, the combined accuracy at
that limit, and the equivalent minimum range to a station, based on
an assumed remote signal level of 25 dB/1m
v/m.
11.1.4 SIGNAL LOCK-ON ^
-
11.1.4.1 Maximum lock-on time shall be 7.5 minutes or less throughout
reference signal conditions. Lock-on time does not include time to tune
filters. Unless all secondaries are tracked, it shall be possible to
select which secondaries are to be locked-on and tracked.
11.1.4.2 When the available signal conditions degrade from the
reference signal conditions, but lock-on may still be achieved, lock-on
times shall be a maximum of 20 minutes.
11.1.4.3 For maximum lock-on time beyond 7.5 minutes, the receiving
equipment handbook shall state the maximum lock-on time for the
following extensions of reference signal conditions applied
individually:
-
- With a SNR between 0 and minus 10 dB
- With ECD's between plus 2.4 to 3.8 m
s or between minus 2.4 to 3.8 m s.
- With a signal level between 110 and 120 dB/1m
v/m or between 14 and 25 dB/1m v/m
- With a differential signal level between 60 and 80 dB
11.1.5 CONTINUOUS WAVE INTERFERENCE (CWI) ^
11.1.5.1 Paragraphs 11.1.5.1.1 to 11.1.5.1.3 below define types of
CWI to which the receiver shall be subjected. Paragraph 11.1.5.1.4
presents the actual signal and interference conditions under which the
receiver shall provide specified performance. Paragraphs 11.1.5.1.5 and
11.1.5.1.6 present conditions under which the level of receiver
performance shall be stated in the receiving equipment handbook. When a
frequency band is referred to, the receiver shall provide stated
performance when subjected to interference throughout that band unless
otherwise specified. It is neither intended nor required that CWI levels
in excess of 120 dB 1m v/m be addressed for
paragraphs 11.1.5.1.1 through 11.1.5.1.6; such levels may be
appropriate, however, under paragraph 11.1.5.1.7.
-
- Two near-synchronous near-band interfering signals, each with
a SIR of 0 dB (with respect to the lowest amplitude Loran-C signal
in use). One signal shall be odd-synchronous and the other signal
shall be even-synchronous.
- One non-synchronous near-band interfering signal with a SIR of
-20 dB with respect to the lowest amplitude Loran-C signal in use.
- Two non-synchronous interfering signals, each with a SIR of
-60 dB with respect to the lowest amplitude Loran-C signal in use.
One signal shall have a frequency lower than 50 kHz and the other
signal shall have a frequency higher than 200 kHz.
- This section presents the conditions under which the receiver
shall provide specified performance. The non-CWI signal conditions
shall be defined as the reference signal conditions in this
standard. The combinations of CWI signal conditions are given in
Table I following:
|
CWI
Conditions
|
11.1. 5.1.1
(two near-sync near-band, 0 db) |
11.1.5.1.2
(one non-sync, near-band, -20 dB) |
11.1.5.1.3
(two out of band,
-60dB) |
|
1
2
3
4 |
X
X*
|
X
X |
X
|
Table I
CWI Performance Conditions
* One of the two near-synchronous interfering signals may be eliminated.
- The receiving equipment handbook shall state the minimum
allowable SIR of one near-synchronous (even or odd) near-band
interfering signal under which the receiver shall provide specified
performance. Reference signal conditions shall apply.
- The receiving equipment handbook shall state the minimum
allowable SIR of one non-synchronous near-band interfering signal
under which the receiver shall provide specified performance.
Reference signal conditions shall apply.
- The Loran-C receiver must continue to operate with specified
performance in the presence of nearby transmissions from
communications equipment. The receiving equipment handbook shall
include antenna installation information as to minimum and preferred
separation between communications transmitting antennas in the
frequency range of 410 kHz to 25 MHz for typical nominal power
levels, and Loran-C receiving antennas. Particular attention shall
be given to the field from the 410-512 kHz main telegraph antenna.
- Minimum and preferred antenna separation data (with
geometrical configuration where applicable) shall be given for the
following performance:
- specified combined accuracy and lock-on time (paragraphs
11.1.2 and 11.1.4) .
- the point beyond which the Loran-C receiving equipment
(including the antenna system) may be permanently damaged.
11.1.6 SKYWAVE REJECTION ^
-
Skywave delays (time between corresponding points on groundwave and
skywave) decrease with greater distance from the transmitter. Relative
skywave signal level is defined as the ratio, in dB, between a point
(e.g. the peak) on the skywave to a corresponding point on the
groundwave. The receiver shall lock-on in the presence of skywave
interference with delays from 32.5 m s to 45 m
s and with relative skywave signal levels from 12 dB to 26 dB
respectively. Nothing in this standard implies that skywave levels in
excess of 94dB/1m v/m need be considered.
11.1.7 CROSS-RATE INTERFERENCE (CRI) ^
The receiver shall provide the required accuracy and lock-on time in
the presence of CRI at a level as high as the strongest signal being
used. Receiver performance shall be demonstrated by tracking simulated
Southeast U.S. chain signals (7980 - SL2) in the presence of CRI at the
Northeast U.S. chain rate (9960 - SS4). This is a respresentative sample
of real world CRI conditions.
11.1.8 ALARMS ^
-
11.1.8.1 General Explanation
11.1.8.1.1 The alarms described in this section may indicate their
function individually or they may be combined into one or more general
alarms. The definition of the threshold of each type of alarm condition
shall be stated in the receiving equipment handbook. As a minimum, alarm
conditions must be detected and displayed for all secondaries from which
displayed time differences are derived.
11.1.8.1.2 The alarm actuate time is the time between the
commencement of the alarm condition and the alarm indication. The alarm
reset time is the time between the termination of the alarm condition
and the alarm indicator returning to normal status. In the case of a
latched alarm, the alarm indicator shall remain actuated after the alarm
condition is eliminated. A latched alarm shall have the capability of
manual reset. If manually reset while the alarm condition still exists,
the alarm shall re-energize.
11.1.8.2 Blink Alarm
11.1.8.2.1 The receiver shall detect secondary blink and energize the
blink alarm within the following time limits after the Loran-C secondary
initiates blink:
11.1.8.2.1.1 Within 60 seconds when the received blinking signal has
a SNR or 0 dB and greater;
11.1.8.2.1.2 Within 90 seconds when the received blinking signal has
a SNR over the range 0 to -10 dB.
11.1.8.2.2 After the Loran-C secondary stops blink, the receiver
shall detect absence of blink and reset the blink alarm (see paragraph
11.1.8.2.3) within the following time limits:
11.1.8.2.2.1 Within 60 seconds when the received secondary signal has
a SNR of 0 dB and greater;
11.1.8.2.2.2 Within 90 seconds when the received secondary signal has
a SNR over the range 0 to -10 dB.
11.1.8.2.3 If the receiver does not provide a continuous cycle alarm
(see paragraph 11.1.8.4), the blink alarm shall latch after detection of
a blink condition.
11.1.8.2.4 It is possible that a receiver may indicate a blink
condition when there is no blinking on the received signals. This is
called false blink and shall not occur more frequently than one
occurrence per 5 days when the SNR of the weakest secondary signal
tracked is -10 dB and greater.
11.1.8.2.5 The receiver is not required to detect or display master
blink or to indicate which secondary is blinking. For a receiver which
detects and displays blink on a common indicator for (one or more)
secondaries whose time differences are not displayed, it shall be
possible for the operator to disable blink display for those secondaries
whose time differences are not displayed.
11.1.8.3 Lost Signal Alarm
11.1.8.3.1 The receiver shall detect loss of signal and energize the
lost signal alarm within 60 seconds when the affected signal had a SNR
of -10 dB and greater immediately proceeding the lost signal condition.
11.1.8.3.2 The receiver shall detect restoration of the signal and
reset the lost signal alarm (see paragraphs 11.1.8.3.3) within the
following time limits:
11.1.8.3.2.1 Within 15 seconds when the restored signal has a SNR of
0 dB and greater;
11.1.8.3.2.2 Within 60 seconds when the restored signal has a SNR
over the range 0 to -10 dB.
11.1.8.3.3 If the receiver does not provide a continuous cycle alarm
(see paragraph 11.1.8.4), the lost signal alarm shall latch after
detection of a lost signal condition.
11.1.8.3.4 It is possible that a receiver may indicate a lost signal
condition when it does not exist. This is a false alarm and shall not
occur more frequently than one occurrence per 5 days when the SNR of the
weakest signal tracked is -10 dB and greater.
11.1.8.3.5 The receiver is not required to display which signal has
been lost. For a receiver which displays lost signal alarm on a common
indicator for (one or more) secondaries whose time differences are not
displayed, it shall be possible for the operator to disable the lost
signal display for those signals whose time differences are not
displayed.
11.1.8.4 Cycle Alarm
11.1.8.4.1 If a cycle alarm is required (due to lack of latching per
paragraphs 11.1.8.2.3 or 11.1.8.3.3) the receiver shall indicate any
settle error. The receiving equipment handbook shall state the threshold
levels, duration, and response time associated with this alarm.
11.1.8.4.2 It is possible for a receiver to indicate an alarm
condition when none exists or to fail to indicate an alarm condition
when one does exist. Neither of these false indications shall occur more
frequently than one occurrence per 5 days when the SNR of the weakest
signal tracked is -10 dB and greater.
A cycle alarm indication during selection, acquisition, or settle
operations shall not be considered an indication of receiver error.
11.1.8.4.3 For a receiver which detects and displays a cycle alarm
condition on a common indicator for (one or more) signals whose time
differences are not displayed, it shall be possible for the operator to
disable the cycle alarm display for those signals whose time differences
are not displayed.
11.1.9 DYNAMIC TRACKING ^
-
11.1.9.1 The receiver shall provide the specified performance when
mounted on a platform performing motions as specified in this paragraph.
(Motion is specified in both geographical and Loran-equivalent
time-difference coordinates.)
11.1.9.1.1 At speeds up to 16 kt (3.2 microseconds/minute
time-difference rate of change) in any horizontal direction, and at
accelerations up to 3 kt/minute (0.6 microsecond/minute/minute
time-difference acceleration), and with additional ordinary ship motion
perturbations in roll, pitch and yaw, the receiving equipment shall
provide the combined accuracy and other performance parameters specified
elsewhere in this Standard.
11.1.9.1.2 At speeds between 16 and 20 kt (4 micro seconds/minute
time-difference rate of change), and with ship motion and acceleration
conditions as in 11.1.9.1.1, the receiving equipment shall provide
combined accuracy of 0.45 microsecond or better and all other
performance parameters specified elsewhere in this Standard.
11.1.9.1.3 In addition, the receiving equipment handbook shall state
a range of speeds and accelerations throughout which the receiver meets
all requirements of this standard, except that combined accuracy may be
relaxed to 0.6 microsecond.
11.1.10 DISPLAYS ^
-
11.1.10.1 The receiver shall be capable of displaying, either
simultaneously or sequentially, the time differences between the master
and at least two secondaries with a resolution of 0.1 m
s or better. Each time difference shall update every 15 seconds or less.
After lock-on, it shall not be possible to disable the indication of any
alarm associated with any time difference being displayed.
11.1.11 COMBINATIONS OF CONDITIONS ^
11.1.11.1 In addition to the independent application of requirements
cited in this Standard, the receiver shall meet the following
performance requirements throughout the range of the following
conditions:
11.1.11.1.1 Conditions
| SNR |
0 dB and greater
|
| Signal Level |
25 to 110 dB/1 m
v/m |
| Differential Signal Level |
0 to 60 dB |
| ECD |
-2.4 m s
£ ECD £
+2.4 m s
|
| Skywaves skywave delay |
32.5 to 45 m
s |
|
relative skywave |
|
| signal level |
12 dB (maximum) |
| CWI |
one near-band near-synchronous signal at +10 dB SIR
(minimum) one near-band non-synchronous signal at -10 dB SIR
(minimum)
|
| CRI |
one crossing rate signal (either master or secondary)
with a level no greater than that of the largest signal in use and
with CRI selection as per paragraph 11.1.7.
|
| Dynamic Tracking |
as per paragraph 11.1.9.1.1. |
| Noise Level |
12 to 75 dB/1m
v/m |
|
11.1.11.1.2 |
Performance Reguirements
|
| |
|
| Combined Accuracy |
0.31 m
s or less |
| Maximum Lock-On Time |
20 minutes or less |
| Alarms |
as per paragraph 11.1.8. |
11.1.12 MINIMUM TEST STANDARDS ^
-
11.1.12.1 This section describes the minimum test standards a
receiver must meet in full to be considered acceptable under this
Standard.
11.1.12.1.1 Effects of Tests
11.1.12.1.1.1 Unless otherwise provided, the application of the
specified tests must produce no condition which would be detrimental to
the continued performance of the equipment.
11.1.12.1.1.2 If the results of a test are statistical in nature
(e.g. mean, standard deviation, etc.), all trials shall be used in the
computation. If a test is designed as pass/fail at a specified minimum
or maximum level or a particular level is to be determined, 90% of the
trials shall be required to meet the pass criteria (for less than 10
trials, round off number to pass).
11.1.12.1.1.3 Where a test procedure evaluates the receiver master
channel and not all of the secondary channels, the test shall be
repeated, with half the number of trials, so that all secondary channels
shall be evaluated.
11.1.12.1.1.4 Unless otherwise specified, receivers shall meet the
combined accuracy and lock-on time required in paragraphs 11.1.2 and
11.1.4 respectively for all standards and all GRI's pursuant to this
Standard for which the receiver is designed. Unless otherwise specified,
the performance standards must be met throughout the full range of
reference signal conditions which shall be defined as: signal levels
from 25 to 110 dB/lm 4v/m, differential
signal level 0 to 60 dB, ECD between plus and minus 2.4 m
s, and a minimum SNR of 0 dB with the noise level within the range 12 to
75 dB/1m v/m.
11.1.12.1.2 Power Input Voltage
11.1.12.1.2.1 Unless otherwise specified, all tests shall be
conducted with the power input voltage adjusted to nominal design
voltage ± 2%. The input voltage shall be measured at the receiver input
terminals.
11.1.12.1.3 Power Input Frequency - Alternating Current
11.1.12.1.3.1 In the case of receivers designed for operation from an
AC power source of essentially constant frequency, the input frequency
shall be adjusted to design frequency ± 2%.
11.1.12.1.4 Adjustment of Equipment
11.1.12.1.4.1 The circuits of the equipment shall be properly aligned
and otherwise adjusted in accordance with the manufacturer's recommended
practices (including warmup time) prior to the conduct of the specified
tests.
11.1.12.1.5 Test Instrument Precautions
11.1.12.1.5.1 Due precautions shall be taken to prevent the
introduction of errors resulting from the improper connection of volt
meters, oscilloscopes and other test instruments to the equipment during
these tests.
11.1.12.1.6 Ambient Conditions
11.1.12.1.6.1 Unless otherwise specified, all tests shall be
conducted under conditions of ambient room temperature, pressure and
humidity. However, the ambient room temperature shall be not less than
10° C.
11.1.13 INTERNATIONAL STANDARD ^
-
11.1.13.1 Radio Technical Commission for Marine Services (RTCM) Paper
12-78/D0-100 dated 20 December 1977 "Minimum Performance Standards
(MPS) Marine Loran-C Receiving Equipment" section 1.2(e) TYPE I and
II only, section 1.3 and sections 2.0 to 2.10 inclusive.
11.1.14 EFFECTIVE DATE ^
-
11.1.14.1 This Standard comes into force on 1 September 1985.
11.2 SATELLITE NAVIGATION SYSTEM (SATNAV) ^
11.2.1 The satellite navigation receiver must have:
-
- automatic acquisition of satellite signals after initial
operator settings have been entered; and
- position updates derived from satellite information obtained
during each usable satellite pass.
11.2.2 INTERNATIONAL STANDARD ^
11.2.2.1 This Standard is based on the United States NM 1/82
Section 3.
11.2.3 EFFECTIVE DATE ^
11.2.3.1 This Standard comes into force on 1 September 1985.
11.3 DIFFERENTIAL
OMEGA ^
11.3.1 INTRODUCTION ^
-
11.3.1.1 Receivers for differential Omega intended for navigational
purposes on ships with maximum speeds not exceeding 35 knots shall
comply with the following minimum performance standards.
11.3.1.2 Differential Omega requires both Omega signals and
differential correction signals for correct operation. Receivers used
for the reception of the differential correction signals should
preferably be combined with the receivers used for reception of the
Omega signals. Where separate receivers are used, care shall be taken to
ensure that the installation meets the overall system performance
standards.
11.3.2 PERFORMANCE STANDARDS FOR THE RECEPTION OF OMEGA SIGNALS
^
-
11.3.2.1 Signal reception
11.3.2.1.1 The system shall provide for reception of Omega
transmissions on the frequency of 10.2 kHz. It may additionally provide
for the reception of one or more of the other Omega frequencies.
11.3.2.1.2 The antenna shall be capable of receiving Omega signals
from any direction in the horizontal plane at all times.
11.3.2.2 Positional information extraction
11.3.2.2.1 Means shall be provided for synchronizing the system to
the Omega transmission format. Automatic or manual means may be used but
in any case it shall be possible to monitor the synchronization state
continuously.
11.3.2.2.2 The system shall be capable of processing information from
at least four Omega stations simultaneously.
11.3.2.3 System performance
11.3.2.3.1 When a ship is stationary, the instrumental error
introduced by the receiver to the measurement of uncorrected phase
difference (line of position) on any selected pair of Omega signals
shall not exceed 0.02 lane widths (2 centilanes). When sailing on a
constant heading at speeds up to 35 knots, instrumental error shall not
exceed 0.04 lane widths (4 centilanes).
11.3.2.4 Display of positional information
11.3.2.4.1 Equipment which gives positional information in terms of
lines of position (LOPs) shall be capable of displaying at least three
operator-selected LOPs either simultaneously or sequentially with the
following facilities:
-
- a display of at least two whole lane digits and providing a
read-out to 0.01 lane width for each pre-selected pair of stations;
- means for setting up initially the whole lane digit counts;
- identification of the selected Omega stations;
- where LOP information is displayed sequentially, provision
shall be made for holding any one pair of stations on display for as
long as required without interruption to the continuous up-dating of
LOP counts. Separate visual indication that the display is in the
"hold" condition shall be provided; and
- where provision is made for manually entering corrections in
order to display corrected LOP counts, the applied correction with
its polarity sign shall be separately displayed at the same time as
the corrected LOP.
11.3.2.4.2 An alternative method of displaying the positional
information may be used, provided that such method conforms in principle
to the recommendations of paragraph 11.3.2.4.1. In the case where a
latitude and longitude display is used, presentation shall be as a
minimum in the form of degrees, minutes and tenths of minutes. The
display shall also clearly indicate north, south, east and west. The
read-out values of latitude and longitude should be based on the World
Geodetic System 1972 (WGS-72).
11.3.2.4.3 Means may be provided to transform the computed position
based on WGS-72 into data compatible with the datum of the navigational
chart in use. Where this facility exists, positive indication shall be
provided to indicate that the facility is currently in use and means
shall be provided to indicate the transformation correction.
11.3.2.4.4 When a system is designed for operation on a single Omega
frequency only it shall be provided with means of identifying lane slip
sufficient to assist the re-establishment of the correct lane
information.
11.3.2.5 Displays and indicators
11.3.2.5.1 The brilliance of all illumination, except for any warning
light, shall be adjustable; a common control may be used. The range of
adjustment shall be such that the display of positional information is
clearly readable in bright diffused daylight and at night the brightness
is the minimum necessary to operate the equipment.
11.3.2.5.2 Where the figures of a digital display are built up of
individual parts (e.g. segments) then a facility shall be provided
which makes it possible to check all the segments of each figure. During
such checking the operation of the equipment, except for the display,
shall not be interrupted.
11.3.2.6 Power supply
11.3.2.6.1 It shall be possible to supply the receiver from the usual
power supplies available on board ships: alternating current
100-115-220-230V ± 15%, 50 or 60 Hz; direct current 24-32V ±
15%.
11.3.2.6.2 The receiver shall be fitted with a built-in emergency
supply which shall be capable of being automatically substituted with no
break to the normal supply described in 11.3.2.6.1 above. This emergency
supply shall be capable of supplying the equipment during at least 10
minutes.
11.3.2.7 Warning devices
11.3.2.7.1 If the receiver is of the type which requires the operator
to select the Omega stations whose signals will be employed to generate
position information, a warning device shall be provided to indicate the
absence of a signal from a selected station.
11.3.2.7.2 If the receiver is of the type which automatically selects
the most suitable Omega signals from those received, a warning device
shall be provided to indicate the lack of sufficient usable signals for
normal equipment operation.
11.3.2.7.3 Provision may be made to indicate which Omega signals are
being received at a strength sufficient to be employed in position
fixing.
11.3.2.7.4 The equipment shall be fitted with a warning device for
indicating main power supply failure which remains active until reset by
the operator.
11.3.2.8 Controls
11.3.2.8.1 All controls shall be of such size as to permit normal
adjustments to be made easily. The control shall be clearly identified.
11.3.2.8.2 Where the inadvertent operation of a control could lead to
failure of the equipment or false position-fixing information, the
control shall be protected from accidental operation.
11.3.2.9 Human errors
11.3.2.9.1 The number of manual calculations needed to transform the
uncorrected Omega signals into a charted position shall be kept to a
minimum. Reliable automatic correction of Omega data is preferable. For
navigational purposes, a reliable automatic transformation of Omega
information into geographical co-ordinates is preferable. In this case
due regard shall be taken of possible additional errors which may be
introduced by this process.
11.3.2.10 Auxiliary equipment
11.3.2.10.1 Single frequency (10.2 kHz) receivers shall, and other
receivers may, have an output to peripheral equipment, e.g. LOP or
co-ordinate recorder, or path plotter. For this output, position data
should be in digital form according to the format defined in CCITT
Opinion V24.
11.3.3 ADDITIONAL PERFORMANCE STANDARDS FOR THE RECEPTION OF
DIFFERENTIAL OMEGA ^
11.3.3.1 Reception of signals
11.3.3.1.1 The system shall provide the reception of differential
Omega corrections for the basic frequency of 10.2 kHz. It may
additionally provide for the reception of corrections for one or more of
the other Omega frequencies.
11.3.3.1.2 The receiving equipment for differential Omega corrections
shall be able to receive corrections transmitted in accordance with the
performance standards for differential Omega correction transmitting
systems (resolution A.425(XI)) and shall indicate the Omega
transmissions for which differential corrections are available. (Copies
of this resolution may be obtained from Superintendent Navigation
Safety, Canadian Coast Guard, Place de Ville, Ottawa, Ontario, K1A ON7)
11.3.3.1.3 Correction receivers shall operate satisfactorily when the
electric field received from the transmitting station is 10 microvolts
per metre or greater, day and night, in the conditions for atmospheric
noise as defined by CCIR for the band 285-415 kHz. Correction receivers
shall have a selectivity, or protection devices, allowing acceptable
reception of correction information when interfering signals are
present. Operation shall also be possible when the interfering signal is
a non modulated carrier frequency, at a level 20 dB above the wanted
signal, on any frequency outside a band of ± 200 Hz centred on the
nominal frequency of the correction transmitting station.
11.3.3.1.4 The antenna for the reception of differential Omega
corrections may be combined with the antenna described in 11.3.2.1.2.
The antenna for the reception of differential Omega corrections (whether
the same as the one described in paragraph 11.3.2.1.2 or not) shall
provide satisfactory reception of correction signals in the conditions
described above and from any direction in the horizontal plane.
11.3.3.2 Extraction of position data
11.3.1.2.1 Means shall be available for the synchronization of the
system with the differential Omega correction transmission format. It is
possible to use automatic or manual means but, in any case, it shall be
possible to monitor the state of synchronization.
11.3.3.2.2 The system shall be capable of processing information
relating to at least four Omega stations simultaneously.
11.3.3.3 System operation
11.3.3.3.1 Instrumental errors introduced by the correction receiving
equipment shall not be greater than those accepted for Omega receivers,
according to paragraph 11.3.2.3 above.
11.3.3.4 Position information display
11.3.3.4.1 The system Omega and differential Omega may be in two
forms:
- Separate Omega and differential Omega receivers.
- .1.1 The user may only add the differential Omega corrections to
the raw data from his Omega receiver before plotting his position on
the chart.
- .1.2 The user may enter differential Omega corrections into the
Omega receiver under the conditions described in paragraph
11.3.2.4.1.5.
- Combined Omega and differential Omega receivers.
- .2.1 The combined receiver may separately display Omega and
differential Omega data. The user may combine them as described in
paragraph 11.3.3.4.1.1.
- .2.2 The combined receiver may, under the control of the user,
automatically add differential Omega corrections to raw Omega data.
11.3.3.4.2 Where the differential Omega receiver gives correction
information for LOPs, it shall be able to display the corrections for at
least 3 LOPs selected by the user, either simultaneously or sequentially
in the following manner:
-
- Display of from 0 to 99 centilanes of correction, providing
reading for 1 centilane for each station pair selected.
- If found necessary display combined with the display described
in paragraph 11 .3.3.4.2.1 of the integer part of the correction.
- Identification of the selected Omega stations.
- Where LOP information is displayed sequentially, provision
shall be made for holding any one pair of stations on display for as
long as required without interruption to the continuous up-dating of
LOP counts. Separate visual indication that the display is in the
"hold" condition shall be provided.
- Where provision is made for manually entering corrections in
order to display corrected LOP counts, the applied correction with
its polarity sign shall be separately displayed at the same time as
the corrected LOP. In addition the user shall be clearly advised
whether corrections are applied or not.
- Where means are provided for automatically entering the
differential Omega corrections, the user shall be clearly advised
whether corrections are applied or not.
- Means shall also be provided to ensure that differential Omega
corrections can only be applied to raw Omega data.
11.3.3.4.3 Alternative methods of displaying the positional and
correction information may be used as mentioned in paragraphs 11.3.2.4.2
and 11.3.2.4.3, provided that such methods conform in principle to the
recommendations of paragraphs 11.3.2.4.1 and 11.3.3.4.2.
11.3.3.4.4 Where automatic receiving systems are used:
-
- The selection of Omega stations in such a system shall be
automatic. The system shall be capable of evaluating the quality of
Omega signals directly received as well as that of the corrections
for each Omega station. It shall establish the position information
through the use of all available information from the various
stations while taking account of the quality of each one. The
operator shall however have the possibility to control the choice of
stations manually.
- Position data shall be automatically obtained when a position
estimated from dead-reckoning or another means has been introduced.
The acceptable uncertainty on the estimated initial position is
essentially related to the number of Omega frequencies that the
system may directly receive on board. This acceptable uncertainty
shall be clearly known by the operators.
- Even if it uses Omega corrections only on the frequency 10.2
kHz, an automatic receiver should preferably be capable of directly
receiving Omega signals on the frequencies 10.2 and 13.6 kHz. It
could also, although it is not essential, work with the frequencies
11.33 and 11.05 kHz.
- An automatic system of differential Omega should preferably be
capable of correcting the dispersion which results, at a distance
from the correction transmitting station of more than 200 nautical
miles, from variations of the propagation velocity of Omega waves
between day and night.
- An automatic system shall be so designed that differential
Omega corrections can only be applied to raw Omega data.
- It is desirable for the system to give an indication of
quality of the positional data displayed.
-
11.3.3.5 Displays and indicators
11.3.3.5.1 Indication and display devices shall conform with the
recommendations of paragraph 11.3.2.5.
11.3.3.6 Power supply
11.3.3.6.1 Power supply devices shall conform with the
recommendations of paragraph 11.3.2.6.
11.3.3.7 Warning devices
11.3.3.7.1 The Omega and differential Omega systems shall be fitted
with the warning devices mentioned in paragraph 11.3.2.7.
11.3.3.7.2 Warning shall be given:
-
- when the correction transmitting station transmits no
correction for any of the selected stations;
- when correction information for any of the selected stations
is not correctly received on board;
- when correction information has not been updated during the
last period of six minutes for any of the selected stations.
11.3.3.7.3 A warning may be given when the 8 Hz modulation is not
present.
11.3.3.7.4 For those receivers mentioned in paragraph 11.3.3.4.4, the
recommendation of paragraph 11.3.3.7.2 is replaced by an alarm if the
quality of position data is unacceptable.
11.3.3.8; Controls
11.3.3.8.1 Controls shall conform with the recommendations of
paragraph 11.3.2.8.
11.3.3.9 Human errors
11.3.3.9.1 The number of manual calculations needed to transform the
uncorrected Omega signals into a charted position shall be kept to a
minimum.
11.3.3.9.2 Differential Omega correction shall be directly applied to
raw Omega data, excluding the usual corrections applicable to Omega use.
11.3.3.9.3 Automatic correction of raw Omega data by the corrections
received from differential Omega stations is preferable. As for Omega
alone, due consideration shall be given to possible additional errors
resulting from the transformation into geographical co-ordinates.
11.3.3.10 Auxiliary equipment
11.3.3.10.1 Omega and differential Omega systems may be fitted with
an output for connection with peripheral equipment such as LOP or
co-ordinate recorders, or path plotters.
11.3.3.10.2 Such a facility is desirable with receivers working only
with frequency 10.2 kHz and with automatic equipment. On this
output position data shall be in the form of a digital message according
to the format defined in CCITT Opinion V24.
11.3.3.11 INTERNATIONAL STANDARD ^
-
11.3.3.11.1 The International Maritime Organization Resolution
"A.479(XII) Performance Standards for Shipborne Receivers for use
with Differential Omega" is the adopted standard.
11.3.3.12 EFFECTIVE DATE ^
11.3.3.12.1 There is no effective date for this Standard as the
fitment is strictly voluntary.
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