How are upgrades handled and what do they cost?
Software upgrades for all our products are freely available for download from our website at:
www.endruntechnologies.com/download.htm.
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How does the Daylight Saving Time (DST) change in 2007 affect me? (US only)
The main purpose of DST (called "Summer Time" in many places in the world) is to make
better use of daylight. We change our clocks during the summer months to move an hour of
daylight from the morning to the evening. Countries have different change dates. Today,
approximately 70 countries utilize DST in at least a portion of the country.
Japan and India are the only major industrialized countries that do not observe some form of daylight
saving time.
In the United States, DST has been starting at 2 a.m. on the first Sunday in April
and ending at 2 a.m. the last Sunday in October. In 2005, Congress passed an energy bill that
included extending the DST period by about a month. Beginning in 2007, DST will
start the second Sunday of March and end on the first Sunday of November.
How Does This Affect Your EndRun Equipment?
EndRun products can operate in three different time modes: Local Time, UTC and GPS. The only time
mode that is affected by DST is Local Time. Therefore, if you operate your
equipment in either UTC or GPS time modes you are not affected by this change in DST.
NTP Users: The Network Time Protocol (NTP) uses UTC time only so it is not affected by DST.
There is nothing you need to do to the NTP Server and there is nothing you need to do to the NTP client
software running on each workstation. It is the operating system (Windows, Linux, etc.)
of the clients that handles the conversion from UTC to Local Time. You will need to update the operating system rules
for timekeeping on each computer/workstation, etc. Refer to the appropriate operating system vendor for more information on the DST change.
If your time server is a Tempus LX then you may be displaying Local Time on the front-panel display. If so,
then you can change the DST settings inside the Tempus LX so that the Local Time will be displayed properly. To do this navigate
to the Main Menu, then to the Clock Menu, then select DST. You can then change the start and stop days for Daylight Saving Time.
All Others: If you are operating your EndRun equipment in Local Time mode then all you need to do
is change the start and stop dates for DST. One way to do that is through the console port.
Use the "xxxxtimemode" command to see what the current time mode of your equipment is.
(xxxx is either gsys, csys, gntp, or cntp, depending on your equipment - see your User Manual).
Use the "xxxxtimemodeconfig" command to change the time mode and DST start/stop dates.
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How far can I install the antenna from the GPS receiver?
The standard antenna cable length is 50 feet. If you need more we offer antenna lengths of up to 250 feet
without a GPS preamplifier. If you need more than 250 feet of cable then a preamp is required.
You can run an additional 200 feet of cable for every preamp installed and you can have up to
3 or 4 preamps. This will allow you to run a total of 850 to 1050 feet of cable. For more information on our GPS preamplifiers
click here.
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Will GPS work inside?
Unlike CDMA, GPS will not work inside buildings. To receive GPS signals the antenna must
have a view of the sky. The best location is on a roof-top with the antenna in view of
a maximum amount of sky. However, our GPS products have the ability to operate
in a single-satellite mode. This lets you avoid the trouble and expense of a rooftop installation
by allowing you to mount the antenna in a window of your building with only a partial view of the sky.
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I don't have roof-top access. What do I do?
You have two choices:
1. Mount your GPS antenna in a window (see the question above), or
2. Purchase a CDMA-synchronized product which works very well
inside buildings (assuming your area has CDMA coverage).
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Do your CDMA products work with PCS or cellular and what is the difference?
The difference between PCS and cellular is the frequency band. PCS frequencies are at 1960 MHz and
cellular frequencies are at 881 MHz. Our newest rackmount products
use a dual-band CDMA receiver and can receive either cellular or PCS signals.
Some of our earlier products use CDMA at
cellular frequencies only (Praecis Ct, Cf, Ce).
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How do I know if I am in a CDMA coverage area?
CDMA coverage is worldwide, extensive, and growing daily. If you are in the
United States and not in the middle-of-nowhere then you most likely have CDMA coverage.
The best way to know if you have CDMA coverage is to find someone with a CDMA
cellular or PCS phone and see if it indicates any signal level at all. Our
products work in very poor signal level conditions.
An alternative is to check the on-line CDMA coverage
database. The CDMA Development Group keeps a database on coverage at
www.cdg.org/worldwide/index.asp.
As you scan the lists keep in mind that the cities stated actually
describe very large regions of coverage. For example, the San Francisco, CA
region includes coverage extending nearly 100 miles to the north, east, and
south of San Francisco.
If you are unsure that you have the appropriate CDMA coverage call us.
Also, since we offer a money-back guarantee
there is no risk in trying it out. We have shipped
many units throughout the United States and overseas and our return rate has been less than 1%.
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Do I have to pay a monthly cell phone service fee to use your products?
No. Our CDMA products merely receive the timing signals that are freely transmitted from basestations
and which are used by the mobile handsets for synchronization. Since our units only receive the timing data and do
not transmit any information, no subscriber fee is required to use our instruments.
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Does weak signal level affect timing accuracy?
No. If the unit is able to acquire and
decode the data, the accuracy is just as good as with a strong signal
level. There is no gradual degradation of timing accuracy.
The time data encoding scheme ensures that if the data is decodable, it
will be valid.
The unit is able to receive and decode data even with very poor signal levels. It only
has to be able to decode one low-speed CDMA channel, unlike cell phones that need to decode multiple high-speed data channels.
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Are your CDMA products traceable to UTC?
The ISO definition for traceability is: "The property of the result of a
measurement or the value of a standard whereby it can be related to stated
references, usually national or international standards, through an unbroken
chain of comparisons all having stated uncertainties."
The CDMA specification ANSI/TIA/EIA-95-B states in Section 1.2 CDMA System Time:
"All base station digital transmissions are referenced to a common CDMA system-wide time scale that uses the Global Positioning System (GPS) time scale,
which is traceable to and synchronous with Universal Coordinated Time (UTC)".
Each CDMA base station has one or more GPS receivers that maintains the time for
the cell phone system. The GPS receivers at these base stations are usually redundant, of very high quality, and
more thoroughly tested than the typical GPS receiver on the market.
The CDMA specification mandates that the accuracy of each base station's time
be maintained to within +/- 10 microseconds of GPS time, even during
periods of GPS unavailability lasting as long as twenty-four hours. Such
GPS outages would arise from damage to the GPS antenna
or its downlead, and would be considered rare events. If such an outage should occur the GPS receiver would
drift away from perfect time very slowly, at microseconds per day. Once it got to over 10 microseconds then the
base station would be taken off-line as it would start to cause problems for the overall cell phone system.
Our CDMA products are
synchronous with the transmissions from these base stations to typically within +/-
10 microseconds of accuracy. Therefore, CDMA-synchronized products are, for all practical purposes,
traceable to UTC (or NIST).
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Why does the timing accuracy vary?
CDMA basestation transmissions must be
synchronous with UTC to within 10 microseconds, typically much better -
less than 1 microsecond. This variation is due to the possibility
that a basestation might have a GPS outage, a rare occurrence.
Under these conditions the basestation must stay within 10 microseconds
of UTC for as long as 24 hours. This ensures the smooth operation
of the CDMA telecommunications system.
Our products are synchronous with the CDMA basestation transmissions from one to tens of microseconds, depending on
location. This variation depends on the propagation delay from our
receiver to the basestation. The propagation delay is about 5
microseconds per mile (about 3 microseconds per kilometer). In an
urban environment, there are many basestations and you would probably
be within a mile of one. Therefore the accuracy of the unit would
be within 5 microseconds of the CDMA transmissions and typically within
6-7 microseconds of UTC. Our main facility is located in an urban
environment and our products test here to within 2 microseconds of UTC.
This is very typical for an urban environment.
In suburban or rural areas the basestations are spaced further apart. This increases the propagation delay and
therefore the accuracy of the unit degrades. At our suburban test
facility the units are synchronous with UTC to within 20-25
microseconds. At our rural test facility the best-case accuracy we
have seen is 30 microseconds and the worst-case is nearly 90
microseconds. That would put the received basestation at nearly
18 miles away!
If you know approximately how far away the basestation is from your location you can eliminate this propagation delay
component by using the CAL command via the serial I/O port. Refer
to the user's manual for more details.
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Since
the timing accuracy varies why is the frequency so stable?
Unlike the timing outputs, the 10 MHz frequency output is not affected by propagation
delay. Since both the basestation and the EndRun unit are
stationary (they don't move in relation to each other) the frequency is
extremely accurate, to parts in 10 to the 12th over
24-hour averaging times. On rare occasions, a basestation might
experience a GPS outage, as when the GPS antenna is damaged. Under these
conditions the basestation's GPS receiver would go into a holdover mode and its
frequency could drift up to about a part in 10 to the 10th over 24 hours.
An outage is rare, and one lasting 24 hours would be very rare.
Note that the requirement to maintain basestation synchronization during
long GPS outages requires that each basestation have at least one high
performance GPS time receiver controlling either an ultra high stability
quartz oscillator or a rubidium vapor atomic frequency standard. Since it is
very difficult to meet this performance using quartz oscillators, most base
stations have rubidium units and redundant GPS receiver/oscillator units are common.
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Can you
tell if the basestation you are receiving is in a holdover mode?
No.
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How accurate is NTP?
Over WANs (Wide Area Networks), up to 100
milliseconds is typical. It depends on how far away the public time
server is, or more specifically, how many hops between you and the server. Within a LAN (Local Area Network) using a
dedicated NTP Time Server, 0.5 to 2 milliseconds is typical. The
internal accuracy of the CDMA Network Time Server is on the order of 10
microseconds. It can easily keep all clients on a LAN synchronized
to typically within 0.5 to 2 milliseconds.
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Where can I get NTP client software?
NTP client software is widely available as freeware and shareware. Setting up an
NTP or SNTP client is relatively simple once you have installed the software on your
workstation and communicated with the time server over the network. For a list
of client software click here.
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How long will the time server deliver Stratum 1
performance if the signal is lost?
Exclusive EndRun oscillator-control algorithms provide extended Stratum 1 holdover performance when
the unit is not locked to the synchronization signal (GPS or CDMA). Typical NTP Stratum 1 holdover periods are:
24 hours - TCXO (standard)
35 days - OCXO (upgrade)
140 days - Rubidium (upgrade)
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Why do I need a time server?
When two or more computers are involved, accurate time keeping is
difficult, especially if they are not in the same physical
location. A dedicated time server inside your network
perimeter is the most accurate, reliable and secure way to ensure
accurate timekeeping for all computers on your network. Accurate
timekeeping is necessary to support eBusiness and other applications
such as Stock Trades, Logs, B2B Transactions, File Operations, Packet Time Stamps,
Software Configuration Management, Database Accuracy, Telecommunication Call Billing, etc.
For a more detailed response to this question click here.
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Why not use the network time
services available over the Internet?
There are many public time servers available over the Internet. Access to these public time servers is free of charge.
While public time servers are certainly less costly - accurate, reliable
and secure time is best provided by a dedicated time server that
resides under your control inside your network security
perimeter. Using public time servers available over the Internet
is not recommended for the following reasons:
1. Setting up your firewall to accept NTP packets (which is based on UDP/IP) introduces a security risk that many Network
Administrators are not willing to take.
2. Time accuracy degrades because of indeterminate network latency, up to 100 milliseconds is typical.
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What is Stratum?
Stratum is a term that means different things depending on the context. In the
telecommunications industry stratum level is indicative of oscillator performance.
It refers to the holdover performance of the oscillator in the event of loss of synchronization.
A Stratum 1 clock has an accuracy of 1.0 x 10-11, Stratum 2 has an accuracy of 1.6 x 10-8,
Stratum 3 has an accuracy of 4.6 x 10-6, and Stratum 4 has an accuracy of 3.2 x 10-5.
In the world of NTP, Stratum is defined in RFC 1305. NTP uses a hierarchical structure
in which Stratum 0 is the reference clock, linked via a time signal, to a reliable source of UTC.
Stratum 1 is the time server with a direct link to the reference clock. Stratum 2 is a client
that receives time over a network connection from a Stratum 1 clock. Stratum 3 is a client that receives
time from a Stratum 2 clock. And so on, up to Stratum 15. For more details on strata in
the NTP world, click
here.
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Will the Præcis Ct work on a Novell network?
Yes. There is some easily configurable software available at www.polygon.com
which can be used to synchronize a Novell network by using various hardware time sources. The software is called Cadence Time
Services, however it is not free.
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