Timing. There is a lot of information about different timing systems in "So Different Timing"
Accurate Time
To obtain accurate time, there are five receivers that provide different levels of time accuracy. They are:
- NEO-M8T
- LEA-M8F
- ZED-F9T-00
- ZED-F9T-10
- NEO-F10T
Affordable and Efficient
The most affordable way to obtain accurate time is by using the NEO-M8T receiver. It provides second-level pulses with noise (Standard deviation) up to 20 nanoseconds (under open sky) and a jitter of 11 nanoseconds. In other words, the overall dispersion will be 31 nanoseconds. There are two boards based on this receiver:
The recommended antenna is ELT0124 with 35 dB LNA amplification. This is sufficient for using a long cable.
Anti-Spoofing Protection + Reliability
For protection against time spoofing (in case of reception loss), increased stability, and other purposes, the LEA-M8F receiver is recommended. This receiver differs significantly from others in that it adjusts the frequency of its clock generator to match the accurate time from GNSS. This results in low noise, detection of spoofing, and the ability to operate for some time without satellite reception. The LEA-M8F provides second-level pulses with noise (Standard deviation) up to 20 nanoseconds (under open sky) and a jitter of 2 nanoseconds. In other words, the overall dispersion will be 22 nanoseconds. There is a board available for this receiver, the ELT0030 with an SMA connector and 12 contacts. The suitable antenna is the ELT0124.
More Accurate and Expensive
The ZED-F9T receiver offers even higher accuracy. Both variants of this receiver provide second-level pulses with noise (Standard deviation) up to 5 nanoseconds (under open sky) and a jitter of 4 nanoseconds. In other words, the overall dispersion will be 9 nanoseconds.
- If the device will be used outdoors, the most affordable solution is the ELT0090 board, which includes both the receiver and an antenna. This board has a mini-USB and a JST SH connector with 12 pins.
- If the device will be used indoors, a separate antenna on the roof or pole is required. The choice depends on whether you want to use the receiver and antenna for the L1/L2 frequency range (ZED-F9T-00) or the L1/L5 frequency range (ZED-F9T-10).
On one hand, the L1/L2 option has more satellites, while on the other hand, L1/L5 is more progressive and slightly more accurate.
For L1/L2, there are three boards with an SMA connector.
- The ELT0088 board differs in the presence of a stabilizer with an extremely low noise level. This is important if synchronization is needed for radio transmitters or other devices with a high level of power supply interference. The outputs include mini-USB and a 12-pin JST SH connector. The drawback of this board is that it only has one time stamp output.
- The other two boards, ELT0094 and ELT0113, are very similar and differ only in the presence of mini-USB on ELT0113. They have 12 contact outputs. The power stabilizer on these boards is standard, but they have two time stamp outputs.
The standard L1/L2 antenna for rooftop or mast placement is the ELT0123, which is mounted on a geodetic pole. This antenna has a very high LNA gain (40 dB). As for affordable options, there is the
- patch-antenna ELT0012 (but it requires a groundplane) with a gain of 28 dB
- helix antenna ELT0170 with a gain of 36 dB.
Both of these antennas are mounted with screws, so there may be issues with water ingress or snow accumulation when placed on a roof. It's worth noting that the longer the coaxial cable from the antenna to the receiver, the more losses it incurs. And the higher the losses, the stronger the LNA gain needed for quality reception.
For L1/L5 with boards, everything is similar, so let's repeat.
There are three boards with an SMA connector.
The ELT0141 board differs in the presence of a stabilizer with an extremely low noise level. This is important if synchronization is needed for radio transmitters or other devices with a high level of power supply interference. The outputs include mini-USB and a 12-pin JST SH connector. The only drawback of this board is the lack of multiple time stamp outputs.
The other two boards, ELT0144 and ELT0145, are very similar and differ only in the presence of mini-USB on ELT0145. They have 12 contact outputs. The power stabilizer on these boards is standard, but they have two time stamp outputs.
With L1/L2 antennas, the options are slightly worse. There are no antennas available for mounting on a geodetic pole or antennas with high-gain LNA. The most suitable antenna is the ELT0170 helix-antenna with 36 dB gain, and the affordable ELT0140 patch-antenna (but it requires a groundplane) with 28 dB gain. Both of these antennas are mounted with screws, so there may be issues with water ingress or snow accumulation when placed on a roof.
For better quality, the ELT0148 antenna (preferably with a ground plane) with 25 dB gain can be used, but a housing needs to be constructed for it. Remember that the longer the coaxial cable from the antenna to the receiver, the more signal loss it incurs. Higher LNA gain is required for quality reception when there is more signal loss.
Other Applications:
All timer configurations have already been described, so below are only the applications of the configurations described for other tasks.
Synchronization:
This task involves synchronously timestamping different receivers that are spaced apart. When using RTK, the time deviation between receivers is smaller than the receiver's time deviation from atomic time or UTC. Both L1/L2 and L1/L5 options of the F9T provide second-level pulses with noise (standard deviation) of up to 2.5 nanoseconds (under open sky) and a jitter of 4 nanoseconds. The overall deviation will be 6.5 nanoseconds.
The choice between L1/L2 and L1/L5 depends on the base receiver (in a synchronization system, all receivers should operate in the same frequency range and ideally have the same antenna and cable length). The configurations themselves are described in the "More Precise and Expensive" section.
Accurate frequency output:
- The NEO-M8T (section "Affordable and Efficient") can output frequencies from 0.25Hz to 10MHz.
- The ZED-F9T (section "More Precise and Expensive") can output frequencies from 0.25Hz to 25MHz.
- The LEA-M8F (section "Spoofing Protection + Reliability") can output frequencies from 0.25Hz to 2Hz and 30.72MHz.
Frequency measurement:
The LEA-M8F receiver is an amazing receiver. That's why its description resembles giving the same film seven "Oscars." Please refer to the configuration in the "Spoofing Protection + Reliability" section.
Time synchronization with atomic clocks:
Yes, you guessed it, it's the LEA-M8F again, and once again, it's in the "Spoofing Protection + Reliability" section.
Accurate time with rare satellite visibility:
Yes, it's the LEA-M8F again, and once again, it's in the "Spoofing Protection + Reliability" section. This receiver can provide accurate time with a deviation of no more than 100 nanoseconds even without satellite reception for a day.
© Eltehs SIA 2024
