FAQ

In the United States, we expect CDMA service to sunset by the end of 2022. For background and details, click here.

The difference between PCS and cellular is the frequency band.  PCS frequencies are at 1960 MHz and cellular frequencies are at 881 MHz.  All our current CDMA-synchronized 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.

CDMA coverage is throughout the USA, China, Korea, India, Japan and elsewhere.  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.

If you are unsure that you have the appropriate CDMA coverage contact us.  Also, since we offer a 60-Day Money-Back Guarantee there is no risk in trying it out.  We have shipped thousands of units throughout the world and our return rate has been less than 1%.

No.  Our CDMA-synchronized 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.

The answer is positive because there is a delay between the antenna and the receiver.

Think about it like this: The antenna receives the time data x nanoseconds before the receiver.  Therefore, the receiver is behind the antenna by x nanoseconds.  By entering a positive delay, the clock will be advanced x nanoseconds to compensate.

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.

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.

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.

No.