Paragon-neo Option 133: how to measure 1PPS propagation delays
Knowing the propagation delays of 1PPS signals passing through the Option 133 1PPS/ToD/Frequency Converter is critical when setting the Paragon-Neo 1PPS reference and measurement compensation values.
To minimise the effect of variation between individual converters, users can measure the propagation delays of a specific Option 133 converter device using the test sequence described here. The yellow dots in picture below shows the location of 1PPS propagation delays in the Rev C and Rev D Option 133 Converter.
Propagation delays on the ToD message paths through the converter are small enough not to affect ToD measurements.
The functionality of the 1PPS paths between ports is given in the table below.
Input Port | Output Port | Notes | ||
Port 1 Balanced 1PPS In | RJ45 pins 3+6 | Port 2 Unbalanced 1PPSOut | RJ45 pins 1+2 |
|
Port 1 Balanced 1PPS In | RJ45 pins 3+6 | Port 7 Unbalanced 1PPS Out | BNC | Rev D only |
Port 3 Unbalanced 1PPS In | RJ45 pins 1+2 | Port 4 Balanced 1PPS Out | RJ45 pins 3+6 |
|
Port 3 Unbalanced 1PPS In | RJ45 pins 1+2 | Port 7 Unbalanced 1PPS Out | BNC | Rev C only |
Measuring the propagation delay between two ports of the Option 133 Converter is done using the Paragon-neo 1PPS Time Error Measurement function. Connect the two ports that you want to measure the propagation between the relevant neo 1PPS reference port (RJ45 or BNC) and the relevant 1PPS measurement port (BNC or RJ45).
An example connection is shown below for measuring the Option 133 Converter port 3 to port 4 propagation delay. All cables must be kept as short as possible and the length of the cables must be measured precisely. To avoid temperature effects, ensure that the Option 133 Converter propagation delays are measured at the same temperature as will occur during final measurement tests.
Once connected, run a 1PPS Time Error measurement with the Delay Compensation set to compensate for the total cable length. Please measure the cable lengths accurately and then compensate at a rate of 5.1ns per metre, plus an additional 0.5ns if the Calnex RJ45 to BNC adaptor cable is used. The measured Time Error (reported in CAT) is the propagation delay between two ports of the Option 100 Converter.
The example screenshots below show the Paragon-neo 1PPS Time Error Measurement application with appropriate delay compensation, and the Time Error results in CAT. The cables used in this example were 0.64m length at 5.1ns/m gives a Delay Compensation of 3.26ns. The red arrows highlight the relevant status indicators. CAT show the delay through this example Option 133 Converter port3 to port 4 is 18.6ns
For future use, ensure that the measured Option 133 delay compensation value is included in the cable delay compensation value when making measurements with it in the signal path e.g. for the above example the cable del value would be the actual cable delays + 18.6ns.