Using GPS Receiver 1PPS Output to Verify Time Stamp Accuracy and Measure Propagation Delay

A simple pulse overlay circuit using a logic OR gate was developed to overlay a precise leading edge 1 pulse per second time reference marker from a global positioning system receiver onto a non-return -to- zero-level pulse code modulation telemetry data stream to validate time stamp accuracy and measure propagation delay in telemetry equipment.

A pulse overlay (PO) circuit was designed to produce a time reference marker within a pulse code
modulation (PCM) telemetry data stream that was recorded and analyzed to validate an IRIG
Standard 106-17 Chapter 10 recorder’s time stamp accuracy [1]. A manufacturer of a newly
purchased Chapter 10 recorder claimed the time stamp accuracy to be better than 10 microseconds
(μs) with only IRIG-B120 (IRIG-B) input and better than 1 μs with IRIG-B and one pulse per
second (1PPS) inputs. The PO circuit and a Chapter 10 recorder test setup were used to verify the
vendor’s data-time synchronization claims and to justify infrastructure upgrade costs to connect
additional cables to each purchased recorder. The circuit was also used to measure the propagation
delay (PD) of a long distance Telemetry multiplexer/demultiplexer telecommunication system
which the manufacturer did not provide a PD specification.

Using the one pulse per second time reference marker of the global positioning system receiver
and the pulse overlay circuit to overlay the one pulse per second variable pulse width signal into a
pulse code modulation telemetry stream provided an excellent means to validate time stamp
accuracy within a Chapter 10 recorder and to measure propagation delays within a normal
telemetry operating environment. The positive results from the Chapter 10 recorder tests validated
the vendor’s claims and justified the implementation to add the one pulse per second signal to the
range Chapter 10 recorders. The pulse overlay circuit and test setups defined in this paper can
easily be used to measure other telemetry equipment.