RF over Fibre FAQs

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Sentinel 3 chassis


What is the difference between Sentinel 3 and point2point?

Sentinel 3 is an intelligent RF over fibre system which allows for multiple-inputs and variable gain. A Sentinel system also incorporates ‘smart’ features such as automatic temperature compensation, self-test, remote battery control (e.g. remote power up/down) and link gain monitoring and control. Sentinel 3 has multiple connectivity options such as multi-core cross-site cables, breakout boxes and multi-channel Rx and Tx units. It is designed for complex applications such as EMC testing of aircraft, buildings and vehicles.

point2point RF over fibre links are simple, single-input, fixed (calibrated) gain links. The links are a low cost option, with fixed gain and lower complexity; offering an easier ‘plug and play’.

What are the typical applications for PPM Test products?

Sentinel 3 – Aircraft EMC (e.g. LLSF, Lightning, NEMP), EMP testing of facilities, high power RF test.

point2point AC coupled links – land-based platform testing, EMP facility test, RF distribution in harsh environments e.g. particle physics.

point2point DC coupled links – high voltage sensing, circuit breaker testing, ABS EMC test.

Fibre Optic

What type of fibre can be used for installation?

All PPM RF over fibre products require single mode fibre with APC connectors to maintain system performance (reduced return loss).

Why do you not offer a multimode fibre version for point2point / Sentinel 3?

Multimode fibre inhibits the performance of RF over fibre links, particularly for higher bandwidth systems. For this reason all our RF over fibre products use single mode only.


How does the fibre connect for each system?

Sentinel 3:

To connect the fibre to the sentinel 3 system, pull the neck of the connector towards the body to release the cap. Insert the exposed fibre into the port until a click is heard, which means the connector is now locked into the port. For more information, please review the Connections guide.


The point2point system uses an FC/APC connector and single mode fibre. To connect it remove the dust cap from the system and locate the keyway. Line the fibre up with the keyway and screw on the connector. For more information, please review the Connections guide.

In point2point equipment, is single mode or multi-mode fibre used for DC links?

All our RF over fibre products, including all point2point products, use single mode fibre. The only exception to this is the point2point power controller, which uses ST connectors and multimode fibre.


What frequency ranges are available?

point2point includes DC coupled links ranging from DC to 40 MHz and AC links ranging from 40 Hz to 3 GHz.


How do PPM RF over fibre links work?

The links can transport signals up to 1 km with negligible degradation of signal-to-noise or frequency response response, which is useful in applications such as EMC testing or monitoring in hazardous environments.

The RF signal is amplified, conditioned and converted to the optical domain for transmission over fibre. At the receiver end, the optical signal is converted back into an electrical signal. Therefore a point2point link is transparent in any system.

What is the difference between AC coupled links and DC coupled links?

AC and DC coupled point2point links perform the same function but (i) cover different frequency bandwidths and (ii) are designed for different signal levels.


AC coupled links use intensity modulation whereby an input signal is “mapped” from the electrical to the optical domain i.e. same amplitude, different domain. AC links are designed for small signals; typically less than 170 mVrms or 0 dBm and have 50 ohm inputs and outputs to match standard RF systems.


DC links convert the input into a 14-bit digital signal before optical conversion. The digitisation allows very low frequencies to be transported. DC links are designed to handle larger input signals, up to +/-150 V but have a high impedance input, like an oscilloscope. The DC output is designed to drive a 50 ohm load.

What frequency ranges/bandwidths are available?

AC links are available up to 3 GHz:

  • 40 Hz to 250 MHz (G series)
  • 2 kHz to 1.35 GHz (K series)
  • 1 MHz to 2 GHz (P series)
  • 10 MHz to 3 GHz (S series).

DC links are available up to 40 MHz:

  • 0 Hz to 2.5 MHz
  • 0 Hz to 20 MHz
  • 0 Hz to 40 MHz.

How do you perform a software upgrade on Sentinel 3?

Go to https://ppmtest.com/sentinel3-software-updates/ and enter your assigned password (please contact us if you require a password). Once you have entered the site, select the latest Sentinel 3 software and check the latest software version (a zipped file will be available). To install this, please refer to the Sentinel 3 handbook and follow the steps provided.

Is point2point equipment able to be NMS controlled?

No. – Settings are defined at manufacture and no user control settings are available.

How can I be confident that Sentinel 3’s shielding is effective?

Sentinel 3 has been designed to maximize its shielding performance and has proven this during EMP testing at field strengths greater than 250 kV/m.

How does the auto calibration feature on Sentinel 3 work?

The system gain accuracy of Sentinel 3 is fixed at time of manufacture. The relative gain accuracy is maintained by Sentinel 3’s automatic gain control (AGC) across the full operating temperature range. The AGC is an active closed loop control system that monitors and adjusts the laser temperature and optical power automatically. It is able to maintain the laser’s relative gain accuracy across the full operating temperature range.

How can I switch point2point transmitters off to preserve the battery?

Once connected to the battery,  via the linking plug, the transmitter is active and will consume power from the battery. If remote battery management control is required, a fibre optic battery switch controller is available. This enables the battery to be switched off remotely. View the Battery Switch Controller handbook for more information.

What effect does temperature have on the system gain of point2point or Sentinel 3?

point2point systems will be affected by temperature changes: the system gain can be reduced by up to 3 dB over the full operating temperature range (-20 to +60 °C).

The Sentinel 3 system is unaffected by temperature as it includes full thermal compensation and automatic gain control.

Can the systems be operated over GPIB?

Sentinel 3 supports GPIB (General Purpose Interface Bus) control through either its Ethernet or USB ports using a third party adapter.

GPIB to Ethernet external adapterEthernet to GPIB external adapter

GPIB to USB external adapterUSB to GPIB external adapter

What support is available for Labview?

A LabView driver for Sentinel 3 can be downloaded from the National Instruments website.


How do I keep the fibres clean?

To keep the fibres clean, ensure the dust and screw caps are protecting the fibres when they are not connected to the point2point or Sentinel 3 systems.

Sentinel 3 dust capsSentinel 3 dust caps

How do I clean dirty fibres?

PPM Test Fibre Cleaning Guide

Are the fibres dustproof?

All our lightweight cables are IP65 rated meaning they are dustproof when mated or when the dust caps are on. Whilst these measures do mitigate the effects of dust ingress, fibre cleaning should be undertaken on fibres when equipment is connected.


The operation light is staying red. Why is this?

It is highly probable that your fibres are not clean. Please refer to the FAQ on cleaning dirty fibres. If this does not resolve the red light then please refer to the maintenance and fault-finding guide on page 10 of the point2point handbook,  or section 6-1 of the Sentinel 3 handbook, available to download here (please contact us if you require a password for access).


What is the warranty period of each product?

point2point is offered as standard with a 3-year warranty. Sentinel 3 is offered as standard with a 2-year warranty (as of 17 July 2020).

Long term support and service agreements are available upon request.

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