General
Positioning the clock
DCF77 or TDF?
Radio clock or Internet?
NeoClock hardware
NeoClock software for Windows
NeoClock software for UNIX
General
Why are PC and server clocks inaccurate?
This is not - as often assumed - because of the hardware (i.e. the CMOS clock). It would be absurd to assume that PC manufacturers were incapable of achieving the accuracy of, for example, a cheap wristwatch.
Why do some DCF77 clocks sometimes go wrong?
These clocks can be easily implemented: simply solder a few elements together and you have a working clock. Provided these simple radio clocks have good, uninterrupted reception, they work very well. In practice, however, reception varies with environmental conditions and other factors and is affected by interference. This can produce an incorrect "apparently received time" signal, which can deviate from the correct time by minutes, hours, months or even years. Filtering these faults and (when filtering fails) recognizing them as such and suppressing them, can be difficult. The complexity of the required solution increases in proportion to the required reliability.
Why do radio clocks have to be aligned?
This is due to the nature of long-wave signals and the ferrite aerials usually used for radio clocks. Conventional, directionally less sensitive aerials, would require wires several tens of metres in length to be laid, which is impractical.
Can I align a radio clock aerial using a compass?
In theory yes, but only in an open space. In real-life situations, inside and near buildings, the lines of flux are affected by metallic objects, which change the optimum alignment.
How important is exact alignment?
At a misalignment of 90 or 270 degrees, the received signal is almost zero. A misalignment of 45 degrees is usually not critical as long as reception is good.
Why does NeoClock use the serial interface and not, for example, USB?
The V.24 serial interface is quite simply best suited for this application. Its connection cable can be extended to almost any length and does not produce long-wave interference. USB has a maximum cable length of 8 metres and high interference levels. The same goes for other interface types.
Does the slow transfer speed through V.24 not affects clock accuracy?
No, the data transfer time is constant and can therefore be accurately compensated.
A competitor claims that the serial interface limits accuracy to 1 second?
This is simply not true. See previous question. There may be radio clocks for which this applies; for the NeoClock it is not true.
The same competitor claims that the serial interface affects system performance.
This is also not true. The NeoClock, for example, requires about 1000 times less system performance than a 56k modem.
How accurate is the NeoClock?
The NeoClock hardware is accurate to within about 10 milliseconds. To answer this question, however, we need to differentiate between long-term and short-term accuracy.
The long-term accuracy is determined by the atomic clocks behind each respective time system. They are much more accurate than necessary for any real-life application.
Short-term accuracy depends on the operating system and the network properties (transfer times, system utilization, etc.) Under Windows and Netware, we are assuming an inaccuracy of no more than +/-1 second with an average of about 300 to 500 milliseconds. Under UNIX and Linux, the accuracy can be increased to an average of +/-10 milliseconds and - under some circumstances - even higher. To achieve this, the data transfer time from transmitter to receiver must be compensated, however.
GPS is much more accurate. Why is there no NeoClock for GPS?
The development of a NeoClock for GPS or Galileo is planned. In terms of short-term accuracy, GPS is unsurpassed, keeping time to within microseconds. The question is whether this level of accuracy is necessary and how accurately the time data can be transmitted from receiver to server and network. In addition, GPS has two significant disadvantages:
1. It is relatively complex and therefore expensive.
2. The aerial has to be mounted outdoors and in view of as many satellites as possible. In most cases, this means on the roof of a building, which results in high cabling costs. An additional problem is presented by the need for lightning protection: because the receiver cable is routed directly into the server room, it provides a direct lightning path to the servers.
The main advantage of GPS is its global availability. But remember that GPS is a military installation of the US Navy, made available for civil use in "peacetime".
The planned European civil alternative - Galileo - will not be operational for some time to come.
Positioning the clock
How do I choose the best location for the clock?
Because of its dual-aerial setup, NeoClock is very forgiving. A few points - to do with the nature of long waves - should be observed, however.
- Steel-reinforced concrete buildings are relatively uncritical. Rooms without outside walls and cellars should be avoided, however.
- Buildings with steel-reinforced concrete façades are critical (aluminium and copper façades less so).
- The No. 1 enemies of long wave signals are PCs and monitors. Keep a distance of at least two metres from these.
Wall mounting is ideal. The unit should be placed 2 metres above floor level on an internal wall, and about 1 metre from an external wall (for lightning protection) but near a window.
- Maintain a distance from cable ducts (at least 50 cm) and larger metal objects, such as 19" racks (at least 1 metre).
What do I need to look out for in server rooms?
Server rooms are often interior rooms without outside walls. In addition, they usually contain a high level of electromagnetic interference. If possible, use an adjacent room with windows to the outside.
Under what circumstances is an outdoor installation necessary?
- On buildings with enclosed sheet steel façades where locating the NeoClock near a window is not possible
- On buildings with a high level of electrical interference (for example production facilities)
- At long distances from the transmitter
What do I need to watch?
The NeoClock should be mounted lower down on the building. Mounting it high up on the building is not necessary and may present a risk of lightning damage. Avoid close proximity to metal façades, drainpipes and especially lightning conductors.
Are there any geographic regions with reception problems?
In theory no, although deep, narrow valleys could present a problem. Large lakes may improve or worsen the reception signal.
DCF77 or TDF?
When should I use TDF instead of DCF77?
Within Germany and most of central Europe, both systems are equally effective. Further abroad, the TDF system has a better reception.
Which system is better?
This question is difficult to answer. Both systems are much more accurate than necessary for modern IT applications, being powered by the world's most accurate atomic clocks. Their deviation lies in the range of millionths of a second. The availability of both transmitters is unsurpassed by any other system.
The DCF77 system works with amplitude modulation, while the TDF system uses phase modulation. The latter is, in theory, less sensitive to electromagnetic interference and has a slightly better short-term accuracy. But this difference does not amount to more than a few milliseconds.
The main difference is in the transmitters' power and therefore their range. TDF is clearly in the lead here.
For more information, see our transmitter comparison.
Can the NeoClock-D also receive the signals from France Inter's TDF transmitter and vice versa?
No, the two systems are not compatible. DCF77 is a dedicated time transmitter, while TDF is a radio transmitter that also sends a modulated time signal. NeoClock-D and NeoClock-F therefore have completely different receivers. Unlike the DCF77 receiver, the TDF's unit includes a demodulator. The data format transmitted through the serial interface, and therefore the NeoClock software, are the same for both models.
Radio clock or Internet?
Why do I need a radio clock if I can get the time through NTP on the Internet?
Apart from the security aspects, time retrieval through NTP and the Internet is not without problems. While lacking availability and deviations of up to one year (see quotation below) may be acceptable on stand-alone PCs, they are not good enough for commercial applications.
For a detailed overview of NTP, see the NTP FAQ page on the University of Delaware website where Dave Mills developed NTP in the 1980s.
The following quotation from a study conducted there provides an interesting insight into the accuracy of NTP: "Reality suggests that not all NTP servers work as designed in theory. In fact there was a high percentage of stratum-1 servers with a bad time: Over 30% of the active stratum-1 servers had a clock error of over 10 seconds, and a few even had an error of more than a year. The author of the survey says: "Only 28% of the stratum 1 clocks found appear to actually be useful." |
NeoClock hardware
Why are two aerials necessary?
1. Using two aerials significantly simplifies installation, removing the need to align the unit.
2. More importantly, the optimum alignment of the aerial may change with atmospheric conditions, passing vehicles and movable metal objects, such as equipment racks). The two aerials, whose signals are continually compared, are practically equivalent to a single aerial that is always perfectly aligned.
Can I extend the connection cable for the NeoClock receiver module?
Yes, the length of this cable can be increased to up to 100 meters with an extension cable. A shielded cable (as is normal for V.24 interfaces) must be used.
How can I check DCF77 signal reception?
Two LEDs indicate the operational state of the NeoClock receiver module. The red, flashing LED indicates correct function of the receiver electronics; the green LED indicates error-free reception of the DCF77 signal.
NeoClock software for Windows
Under Windows, which PCs can function as time server?
Any PC running Windows 95/98, Windows 2000 (Workstation or Server) or Windows NT 4.0 (Workstation or Server) can function as time server.
Is system time synchronized automatically or manually under Windows?
On the time server:
Both - in the NeoClock control panel, the Automatic option can be toggled on or off.
On the time client:
Synchronization is automatic. Once the synchronization program is running, it requests synchronization from the time server at regular intervals adjustable from 5 to 999 minutes.
Does the NeoClock synchronization system automatically switch to daylight saving time?
Yes, daylight saving changes are made automatically (assuming correct time signal reception) when the Daylight Saving Changes option in the NeoClock control panel is selected.
Can the NeoClock synchronization system synchronize the computer with the time of an other time zone (e.g. Greenwich)?
Yes, you can set time changes from -12 to +12 hours in the NeoClock control panel.
Can the NeoClock synchronization system synchronize several workstations or servers in a local-area (LAN) or wide-area (WAN) network?
Yes, the NeoClock synchronization system is based on a client/server architecture; any workstation or server can function as time server. The other workstations or servers can then be synchronized at regular intervals with the time server. (The number of possible time clients depends on the license purchased).
What protocols are used by the NeoClock synchronization system?
The programs (or services) support the "routing-enabled" TCP/IP and IPX/SPX protocols.
Is synchronization also possible when the time server can be accessed only through a router?
Yes, because the programs and services use the "routing-enabled" TCP/IP and IPX/SPX protocols.
At what interval can a time client be synchronized with a time server?
Under Windows, this period can be adjusted from 5 to 999 minutes in the NeoClock control panel. Under Novell, a synchronization is performed at every login.
Can synchronization of the computer continue even when the DCF77 signal reception is temporarily interrupted (e.g. by electromagnetic interference or thunderstorms)?
Yes, if the Crystal Clock option is selected in the NeoClock control panel. In this case, the computer will be synchronized with the NeoClock receiver's built-in crystal clock. When reception is good, the atomic time is, of course, used.
How can I check time synchronization?
After starting the synchronization program, a clock icon appears on the taskbar. As long as time synchronization is running correctly, the clock background is green. If you click the icon, the NeoClock atomic clock window opens with green letters on black background. If time synchronization is not correct, the clock icon background and the associated NeoClock window are red.
How can I tell whether the time server program (or service) has been started?
After the time server program (or service) is started, a small circle containing an "S" symbol appears on the Taskbar. If the program or service is functioning correctly, the background of this circle is green; if it is not functioning correctly, the background is red.
What programs or services do I have to install on the time server and clients?
On the computer acting as time server, two programs (or services) will be installed: the first receives data from the NeoClock receiver module and synchronizes the time server's clock; the second makes the date and time available to any time client querying the time server. Time clients require the installation of one program (or service), which performs regular time synchronization with the time server. Installation is automatic with an installation program.
How can I tell, how many time clients have been synchronized with the time server?
When the time server service is started, a clock icon with an "S" appears on the Taskbar. You can click this icon to open the NeoClock time server window, which displays the number of connected time clients.
Can I view statistics about DCF77 signal reception?
Yes, a program NeoStat.Exe is included in the software, which provides a statistical overview of DCF77 signal reception.
NeoClock software for UNIX
In progess ...
