Mounting the Antenna. Meinberg IMS LANTIME M1000, LANTIME PTP Grandmaster
Meinberg IMS LANTIME M1000 is a modular sync system and NTP server that provides precise time synchronization and network time services. It features a GNSS timecode receiver for accurate timekeeping, LAN-CPU with USB interface, and a variety of IMS modules for customization. Meinberg IMS LANTIME M1000 is an ideal solution for applications requiring reliable and secure time synchronization in various industries, including telecommunications, financial institutions, and industrial automation.
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5 Mounting the Antenna
5 Mounting the Antenna
5.1 GNSS Signal Reception
The satellites of most Global Navigation Satellite Systems (GNSS) like GPS , GLONASS , and Galileo are not stationary but circle round the globe in periods of several hours. Only few GNSS systems like the Chinese
Beidou system work with stationary satellites. Such systems can only be received in certain regions of the Earth.
GNSS receivers need to track at least four satellites to determine their own position in space (x, y, z) as well as their time offset from the GNSS system time (t). Only if the receiver can determine its own position accurately the propagation delay of the satellite signals can also be compensated accurately, which is requirement to yield an accurate time. If the receiver position can only be determined less accurately then the accuracy of the derived time is also degraded.
GNSS satellite signals can only be received directly if no building is in the line-of-sight from the antenna to the satellite. The signals can eventually be reflected at buildings, etc., and the reflected signals can then be received. However, in this case the true signal propagation path is longer than expected, which causes a small error in the computed position, which in turn yields less accurate time.
Since most of the satellites are not stationary, the antenna has to be installed in a location with as much clear view of the sky as possible (e.g. on a rooftop) to allow for continuous, reliable reception and operation.
Best reception is achieved when the antenna has a free view of 8
◦ angular elevation above the horizon. If this is not possible then the antenna should be installed with the best free view to the sky in direction of the equator. Since the satellite orbits are located between latitudes 55 ◦ North and 55 ◦ South, this allows for the best possible reception.
Meinberg provides their own GPS receivers which operate with an antenna/converter unit and thus allow for very long antenna cables, but some devices also include GNSS receivers which support other satellite systems like GLONASS, or Galileo in addition to GPS. These receivers usually require a different type of antenna equipment which is described in chapter (4.1.2).
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5.1.1 Meinberg GPS Antenna/Converter
5.1.1.1 Introduction
The Meinberg GPS antenna/converter unit combines a standard GPS patch antenna with a frequency converter which translates the original 1.5 GHz signal received from the GPS satellites to an intermediate frequency, so a standard coaxial cable type like RG58 can be used for antenna cable lengths up to 300 meters (1000 ft). If a low-loss cable type like RG213 is used then even 700 meters (2300 ft) between receiver and antenna are possible without requirement for an additional amplifier.
Surge protectors are optionally available and should be used in the antenna line to protect the receiver from high voltages spikes e.g. due to lightning strikes close to the antenna. The antenna/converter unit is remotely powered by the connected GPS receiver via the antenna cable, so no external power supply is required near the location of the antenna if a coaxial cable is used.
If more than a single GPS receiver are to be operated then a GPS antenna splitter can be used to distribute the GPS signal from a single antenna. The GPS antenna splitter provides 4 outputs and can be cascaded to supply even more than 4 receivers with the GPS signal.
Alternatively there is also a GPS Optical Antenna Link (GOAL) available which uses a fiber optic connection between the antenna and the receiver which allows for a length up to 2000 meters (6500 ft), and provides a high level of insulation and surge protection due to the optical transmission. Since the fiber optic connection is unable to provide the antenna with DC current, an extra power supply is required in this case at the location of the antenna.
Due to the specific requirements for remote powering and frequency conversion the Meinberg GPS equipment is not necessarily compatible with GPS equipment from 3rd party manufacturers.
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5 Mounting the Antenna
5.1.1.2 Mounting and Installation of the GPS Antenna
Proper installation of the GPS antenna/converter unit is illustrated in the figure below: free view to the sky!
GPS Antenna
N-Norm female
N-Norm male
Cable Slot
N-Norm male
N-Norm female as short as possible
Ground lead to PE rail
(Protective Earth)
Cable ca. 1,5 mm Ø fastened at the surge protector
N-Norm female
N-Norm male
Meinberg GPS
N-Norm male or BNC male female female
Figure: GPS Antenna mounted on a pole with a free view of the sky. The optional surge protector keeps high voltage strikes through the antenna cable away from the receiver.
Mounting material (plastic pole and holders, clamps for wall or pole mounting) is shipped with all Meinberg GPS antennae for easy installation. A standard RG58 antenna cable of 20 meters length is included by default. If a different cable length is required then this can be ordered accordingly.
Surge protectors should be installed indoors, directly where the antenna cable comes in.
The optionally delivered protection kit is not for outdoor usage. The ground lead should be kept as short as possible and has to be connected to building’s ground rod.
Up to four GPS receivers can be fed by a single antenna/down-converter unit by using an antenna splitter which can optionally be cascaded. The total length of an antenna cable from the antenna to each receiver must not exceed the specified maximum length according to the cable type. The position of the splitter in the antenna line does not matter.
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Note:
If the antenna cable is assembled locally instead of using a cable shipped with the GPS receiver it has to be made sure that the connectors have been soldered and assembled properly, and that there is no short-circuit in the cable or in one of the connectors. Otherwise GPS reception may be degraded, or the GPS receiver can even be damaged. Mount the antenna at a distance of at least 50 cm from other antennas.
WARNING!
Antenna mounting without effective anti-fall protection
Danger to life due to fall!
- Pay attention to effective working safety when installing antennas!
- Never work without an effective anti-fall equipment!
WARNING!
Working on the antenna system during thunderstorms
Danger to life due to electrical shock!
- Do not carry out any work on the antenna system or the antenna cable if there is a risk of a lightning strike.
- Do not carry out any work on the antenna system if the safety distance to free lines and sequential circuits is exceeded.
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5 Mounting the Antenna
5.1.2 General GNSS Antennae
Some Meinberg devices use alternate GNSS receivers which support other satellite systems like GLONASS,
Galileo or BeiDou, in addition to GPS. These receivers can’t be operated directly with the standard Meinberg antenna/converter unit described in chapter "Meinberg GPS Receiver", so they require a different kind of antenna.
There are two different antenna versions available, one of which is more suited for stationary installation, while the other one should be preferred for mobile applications.
5.1.2.1 GNSS Antenna for Stationary Installation
The Multi GNSS Antenna is an active GNSS antenna which can receive the signals of the GPS, GLONASS,
Galileo and Beidou satellite systems. It is very well suited for stationary installations, operates with a 5V DC supply voltage provided by the receiver, and has an integrated surge protection.
The antenna cable length can be up to 70 meters if a H155 low-loss coaxial cable is used.
Mounting and Installation of the GNSS/L1 Antenna
Multi GNSS Antenna
free view to the sky!
Type-N female
Type-N male as short as possible
Connection to earth rail
(Protective Earth) cable diameter ca. 1,5 mm Ø
MEINBERG GNSS
Type SMA male
Figure: Schematic diagram of mounting the Multi GNSS Antenna female
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WARNING!
Antenna mounting without effective anti-fall protection
Danger to life due to fall!
- Pay attention to effective working safety when installing antennas!
- Never work without an effective anti-fall equipment!
WARNING!
Working on the antenna system during thunderstorms
Danger to life due to electrical shock!
- Do not carry out any work on the antenna system or the antenna cable if there is a risk of a lightning strike.
- Do not carry out any work on the antenna system if the safety distance to free lines and sequential circuits is exceeded.
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5 Mounting the Antenna
5.1.2.2 GNSS Antenna for Mobile Applications
The RV-76G is an active GNSS antenna which can receive the signals of the GPS, GLONASS, and Galileo satellite systems. It operates with a 5V DC supply voltage provided by the receiver, and should be preferred for mobile applications. However, the maximum length of the antenna cable is limited depending on the cable type, e.g. 5 meters with RG174/U cable, so this antenna is less suitable for stationary installations.
Figure: Installation drawing RV-76G antenna
WARNING!
Antenna mounting without effective anti-fall protection
Danger to life due to fall!
- Pay attention to effective working safety when installing antennas!
- Never work without an effective anti-fall equipment!
WARNING!
Working on the antenna system during thunderstorms
Danger to life due to electrical shock!
- Do not carry out any work on the antenna system or the antenna cable if there is a risk of a lightning strike.
- Do not carry out any work on the antenna system if the safety distance to free lines and sequential circuits is exceeded.
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5.1.3 Powering up a GNSS Receiver
If both the antenna and the power supply have been connected the system is ready to operate. Depending on the type of oscillator installed in the receiver it takes about 10 seconds (OCXO-LQ) until 3 minutes (OCXO-MQ
/ HQ) until the oscillator has warmed up and reached the required frequency accuracy.
If the receiver has some valid almanac data in its battery buffered memory and the receiver’s position has not changed significantly since its last operation the receiver can determine which satellites are in view. Only a single satellite needs to be received to synchronize and generate output pulses, so synchronization can be achieved at least one minute (OCXO-LQ) until 10 minutes (OCXO-MQ / HQ) after power-up. After 20 minutes of operation the OCXO is fully adjusted and the generated frequencies are within the specified tolerances.
If the receiver position has changed by some hundred kilometers since last operation, the expected satellites may not be in view after power-up. In this case the receiver switches to Warm Boot mode where it starts scanning for all possible satellites one after the other. Once the receiver can track at least 4 satellites at the same time it updates its own position and switches to Normal Operation .
If no valid data can be found in the battery buffered memory, e.g. because the battery has been disconnected or replaced, the receiver has to scan for satellites and collect the current almanac and ephemeris data first. This mode is called Cold Boot , and it takes at least 12 minutes until all required data have been collected.
The reason is that the satellites send all data repeatedly once every 12 minutes. After data collection is complete the receiver switches to Warm Boot mode to scan for more satellites, and finally enters Normal Operation .
In the default configuration neither pulse and synthesizer outputs, nor the serial ports are enabled after powerup until synchronization has been achieved. However, it is possible to configure some or all of those outputs to be enabled immediately after power-up.
If the system starts up in a new environment (e. g. receiver position has changed or new power supply has been installed) it can take some minutes until the oscillator’s output frequency has been adjusted properly.
In this case the accuracy of the output frequency and pulses is also reduced until the receiver’s control loops have settled again.
On the frontpanel ("Reference Time → Info GPS → GPS Satellites") as well as via the Web GUI ("Clock
→ Receiver Information") you can check the number of satellites that are in view (i.e. above the horizon) and considered good (i.e. are healthy and can be tracked).
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5 Mounting the Antenna
5.2 Long Wave Signal Reception
5.2.1 Introduction
The longwave antenna AW02 is a weatherproof and temperature resistant active antenna for outdoor use. It includes a ferrite antenna for reception of the longwave signal, and an amplifier, both assembled in a plastic housing. The standard version has been designed to receive the signal from the German longwave transmitter
DCF77 whose carrier frequency is 77.5 kHz. The DCF77 transmitter is operated by the German Physikalisch-
Technische Bundesanstalt (PTB), and is located in Mainflingen near Frankfurt / Main. Its signal can be received in Germany and adjacent countries.
The variant AW02-MSF is available for the longwave transmitter MSF which is located in Anthorn / U.K., and transmits the time and frequency maintained by the U.K. National Physical Laboratory (NPL). The signal can be received throughout the U.K., and in wide parts of Northern and Western Europe.
Another variant is the AW02-WWVB which has been adapted for the WWVB radio station which is located in the United States near Fort Collins, Colorado, and is maintained by U.S. National Institute of Standards and
Technology (NIST).
Even though these antenna variants are slightly different according to the characteristics of the associated transmitter, the basic requirements for installation are identical.
The longwave antennae can be operated with a cable length up to 300 meters (1000 ft) if standard RG58 coaxial cable is used. They are remotely powered by the receiver via the antenna cable, so no external power supply is required near the location of the antenna if a direct coaxial cable is used.
Surge protectors are optionally available and should be used in the antenna line to protect the receiver from high voltages spikes e.g. due to lightning strikes close to the antenna.
For longer distances from the antenna to the receiver an optional amplifier can be used, which requires an extra power supply. The BLV device is an amplifier with integrated surge protector.
Alternatively there is a DCF Optical Antenna Link (DOAL) available which uses a fiber optic connection between the antenna and the receiver which allows for a length up to 2000 meters (6500 ft), providing a high level of insulation and surge protection due to the optical transmission. Again, the default device has been designed for DCF77, but there are also variants for MSF and WWVB available. Since the fiber optic connection is unable to provide the antenna with DC current, an extra power supply is required in this case at the location of the antenna.
Longwave receiver equipment from Meinberg has specifically been designed for Meinberg devices and is not necessarily compatible with receivers from 3rd party manufacturers.
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5.2.2 Mounting and Installation of a Longwave Antenna
The careful selection of the antenna location should be at the beginning of each antenna installation. It determines the reception quality and therefore the availability of the DCF77 reception signal decisively. In principle, a DCF77 reception within buildings is possible, however, the DCF77 reception may deteriorate due to metallic objects (e.g. reinforced concrete walls, metal facades, heat protection glazing etc.) that shield or attenuate the reception.
For this reason we always recommend to mount the antenna outside of buildings. This has the advantage that the signal interference distance to electronic devices in buildings is usually enhances and the reliability of the synchronisation is thus significantly increased.
Proper installation of an antenna for DCF77, MSF, or WWVB is illustrated in the figure below:
DCF Antenna
Antenna aligned to the transmitter
N-Norm female
N-Norm male
Cable slot
N-Norm male
N-Norm female as short as possible
Ground lead to PE rail
(Protective Earth)
Cable ca. 1,5 mm Ø fastened at the surge protector
N-Norm female
N-Norm male
Meinberg DCF
N-Norm male or BNC male female female
Figure: Longwave antenna mounted on a wall. The optional surge protector keeps high voltage strikes through the antenna cable away from the receiver.
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5 Mounting the Antenna
The antenna has to be aligned horizontally in longitudinal direction to the transmitter, i.e. in direction to
Mainflingen near Frankfurt / Main in case of DCF77, or in direction to the location of the MSF or WWVB receiver accordingly.
If the antenna is not aligned properly then signal reception is degraded, which can result in a limited time accuracy. The antenna should be installed with a minimum distance of 30 cm away from all metal objects and possibly any microcomputers and electrical devices (engines, electricity, etc.). A distance of several meters from
TV and computer monitors should be considered as well.
The best method to align a longwave antenna is to turn the antenna slowly until the monitored signal level is minimized, and then turn the antenna by 90 o to achieve maximum reception. However, a high signal level alone is not a guarantee for good reception since it can even be caused by electrical noise in the associated frequency range. For standard longwave receivers it is important that the modulation mark is blinking exactly once per second, without intermediate flickering.
DCF77/PZF receivers use correlation techniques to decode the phase modulation provided by DCF77, and with these types of receiver the maximum interference immunity can be found by looking at the autocorrelation parameter displayed in the display menu "PZF-STATE". The displayed value should be as close as possible to
100 % for best reception.
WARNING!
Antenna mounting without effective anti-fall protection
Danger to life due to fall!
- Pay attention to effective working safety when installing antennas!
- Never work without an effective anti-fall equipment!
WARNING!
Working on the antenna system during thunderstorms
Danger to life due to electrical shock!
- Do not carry out any work on the antenna system or the antenna cable if there is a risk of a lightning strike.
- Do not carry out any work on the antenna system if the safety distance to free lines and sequential circuits is exceeded.
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5.2.3 DCF77 / PZF Receiver
If both the antenna and the power supply have been connected the system is ready to operate. After power up it takes up to three minutes for the receiver to synchronize, if reception is good enough. A high "Correlation &
Field" is an indicator for a good signal quality.
To check the field strength and the signal correlation value, select in the Front Panel "Reference Time →
Info PZF → Correlation & Field".
The correlation "State" starts in a "raw" mode, when the receiver tries to find the initial correlation. When good correlation has been found the receiver checks it 20 times: this state is labeled "check" and the correlation value is increased from 1 to 20. If the correlation quality stays good the state changes to the "fine" mode. The signal strength should be 100 or higher.
If no correlation with the incoming signal is possible then the clock changes automatically to DCF77 AM reception mode and tries to decode the second marks.
For further detailed clock configuration, please refer to the Chapter ??
".
5.3 Cable Types
Antenna Type Cable Type Maximum Cable Length
Meinberg GPS Antenna RG58
Meinberg GPS Antenna RG213
Multi GNSS Antenna
Long Wave Antenna *
Fiber Optic **
Belden H155
RG58
Fiber Optic
300 m / 1000 ft
700 m / 2300 ft
70 m / 230 ft
300 m / 1000 ft
2000 m / 6500 ft
* DCF77 (Germany, Middle Europe), MSF (GB), WWVB (US), JJY (Japan)
** Fiber Optic - GOAL - GPS Optical Antenna Link; DOAL - DCF Optical Antenna Link
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Key features
- Modular design for customization
- GNSS timecode receiver for accurate timekeeping
- LAN-CPU with USB interface
- NTP server functionality
- Supports multiple time sources
- Comprehensive web interface for easy configuration
- Compact and rack-mountable design