Rb/GPS: use with Frequency Converter (opt 133) and Paragon-neo

The Calnex Rb/Gps Frequency Reference Unit (opt 132) can be used to provide a Paragon-neo with a 1PPS and 10MHz reference. When used with a Calnex 1PPS/ToD/Frequency Converter (opt 133) it can also provide a ToD reference to the Paragon-neo. The three scenarios below represent likely use cases and their setups.

For best accuracy, Calnex recommend using direct unbalanced reference signals (BNC connections) whenever possible. This is especially important for 1PPS where a clean rising edge is required. For example, Scenario 2 presented here allows for a direct BNC connection from the Rb/GPS to the Paragon-neo, whereas Scenario 3 requires a conversion of the unbalanced 1PPS BNC signal to a balanced signal, which will cause degradation.

As per ITU-T G.703 Section 19.2, coaxial cables with BNC connectors for 1PPS measurements should be 50 ohm impedance cables with a maximum length of 3 meters. The specification for unbalanced measurement cables is tighter than for the balanced RJ45 alternative (ITU-T G.703 Section 19.1), therefore providing a higher quality signal.

Scenario 1: 1PPS and 10MHz references (no ToD)

When using the Rb/GPS unit to provide only 1PPS and 10MHz references, the devices should be set up as shown in Figure 1. The 1PPS and 10MHz signals are unbalanced and connected with short coaxial cables following the requirements of G.703 section 19.

Connect the 1PPS and 10MHz reference outputs from the Rb/GPS unit directly to the corresponding 1PPS and 10MHz reference inputs on the Paragon-neo. The port mappings are given in the table below.

To configure this in the Paragon-neo GUI, select both BNC reference inputs for 1PPS and 10MHz (Figure 2).

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Figure 1: Scenario 1 Setup

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Figure 2: Scenario 1 GUI

Scenario 2: 1PPS, 10MHz, and ToD references (unbalanced 1PPS to Paragon-neo)

Use the Opt 133 Frequency Converter together with the Opt 132 Rb/GPS Reference unit when Paragon-neo tests require a ToD reference in addition to 1PPS and 10MHz references. In this scenario, the Opt 133 converts the RS232 ToD signal to a RS422 signal and a standard RJ45 cable connects ToD to Paragon-neo. The unbalanced 1PPS and 10MHz reference signals connect to Paragon-neo the same as shown in Scenario 1.

Figure 3 shows this setup - the Rb/GPS unit ToD output is connected to the opt 133 frequency converter ToD input. The ‘1pps + ToD, RS422’ output from the frequency converter is then connected to the ‘1PPS | ToD’ RJ48 input on the Paragon-neo. In this instance only ToD is carried on this connection.

The 1PPS and 10MHz signals are connected directly from the Rb/GPS unit to the Paragon-neo as shown in Scenario 1. The table below shows the port mappings.

To configure this in the GUI only the ToD half of the RJ48 port should be selected, along with both BNC reference inputs for 1PPS and 10MHz (Figure 4).

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Figure 3: Scenario 2 Setup

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Figure 4: Scenario 2 GUI selection

Scenario 3: 1PPS, 10MHz, and ToD references (balanced 1PPS to Paragon-neo)

An opt 133 frequency converter is required to provide balanced 1PPS, 10MHz, and ToD reference signals to the Paragon-neo from an Rb/GPS unit. This should be setup as shown in Figure 5.

The 10MHz signal connects directly from the output port on the Rb/GPS unit to the input reference connector on the Paragon-neo.

The ToD output from the Rb/GPS unit is connected directly to its respective input on the frequency converter. The 1PPS output from the RB/GPS unit requires a BNC → RJ48 converter to allow for connection to the 1PPS RJ48 input on the frequency converter. If using a Calnex provided BNC → RJ48 converter (shipped with the frequency converter) the BNC 1PPS should connect to the converters black BNC connector.

The ‘1pps + ToD, RS422’ output from the frequency converter can then be connected to the ‘1PPS | ToD’ RJ48 input on the Paragon-neo. The table below shows the port mappings.

To configure this in the Paragon-neo GUI the BNC reference input for 10MHz should be selected, along with the RJ48 input for 1PPS and ToD (Figure 6).

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Figure 5: Scenario 3 setup

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Figure 6: Scenario 3 GUI selection