Most of FCL's support to clients has included a significant proportion of hardware 'hands-on' work. Laboratory based work has been necessary to verify performance to specification, to solve issues and to trial various improvement options. The following paragraphs describe some examples..
1. Microstrip and Planar Circuits
FCL has significant experience at RF and microwave frequencies with microstrip, stripline, co-planar waveguide (CPW) and combinations of these passing through various transitions. For the lower frequencies at VHF and UHF, the PCB dielectric substrate has usually been the industry standard type FR4. Many of these were multi-layer architectures, sharing RF/microwave, DC and high speed digital circuits. In fact, it has been surprising how adequate FR4 has been for many clients' hardware realisations even up to a few gigahertz. Being much cheaper to produce than the dedicated low-loss dielectric types, such as Rogers®, sometimes the small compromise in RF performance that is necessary is quite tolerable. Attention to detail and strict design of distributed features including controlled impedance lines, through hole technology, grounding and layout yields a product which works well. Where necessary, double sided PCBs have been used, with intelligent distribution of circuit function areas to each side to optimise performance generally, including isolation, EMC, ease of assembly and test.
At the higher microwave frequencies, FCL has also worked with flexible, Rogers® type low loss dielectric materials and rigid (and brittle) alumina types for space hardware applications. On circuits like these FCL has successfully solved many RF isolation, screening and EMC issues with techniques such as compartmentalisation, frequency-appropriate attention to layout and very good (low resistance and low inductance) grounding.
2. Board Bring-Up and Debugging (Excessive Loss, Noise, Spurious, Jitter etc.)
FCL is often engaged to undertake hands-on debugging work. The problems solved have ranged from initial power-up issues, simple circuit breaks, excessive loss or excessive reflections through to eliminating some unusual spurious products caused by a strange mixture of harmonics and intermodulation products. Many of these issues only manifest at temperature extremes, so hardware often needs to be set up in a thermal chamber and all of the issues of test equipment interfacing and de-embedding of the cable affects satisfactorily addressed.
Initial power-ups are of course done very cautiously. After a very detailed visual examination and verification of the connections, the voltage would normally be slowly increased whilst monitoring the current. Some circuits have non-linear DC current voltage relationships which must be allowed for. For the biggest challenges, FCL has often verified proposed solutions by building, testing and documenting temporary modifications to existing hardware and then following these through to the formal engineering changes and product improvements. The debugging process is often performed at the same time as other circuit changes, enhancements or cost saving measures.
3. Prototype Evaluation
FCL is sometimes required to support clients during the development and building of prototype hardware to tight timescales. Often this results from a commitment made to the customer by the client. The experience that FCL has acquired in similar industries enables it to rapidly provide this. FCL is familiar with many of the common types of RF and microwave test equipment such as swept CW and pulsed vector network analyzers, spectrum analyzers, noise figure meters, power meters, high speed oscilloscopes and dynamic signal analyzers. This extends to how to fully exploit their capability to produce reliable and accurate results including instrument control and data extraction over the general purpose interface bus (GP-IB/HP-IB/IEEE488) and TCP/IP (Ethernet® and Gigabit® LAN). FCL has a good grasp of what can be done realistically and at what frequencies. Evaluation assignments like these frequently embody writing or updating the associated design or test specifications. All procedures and tests described in these specifications will initially be verified hands-on by FCL's representative. FCL can sometimes find ways to make the test engineer's job easier and more productive.
4. Demonstrator Construction
Several clients have used FCL to build and verify demonstration equipment whilst they concentrate on other priorities. FCL will likely have enough previous experience with similar equipment to quickly understand what the demonstrator is intended to do. With minimal supervision FCL can treat this process as a stand-alone project: assess the priorities such as long lead items and the fulfilment of commitments that the client has made, and get to work on it. Clients have then required FCL to play a central role in describing, documenting and demonstrating the equipment to review teams and potential customers.
5. Thermal, Mechanical and Other Interfacing Issues
As well as the electrical aspects of a product, FCL also understands many of the non-electrical properties that are usually included in the product specification and have to be addressed at the same time. For example, calculations for power dissipations and heat transfer mechanisms by convection, conduction, radiation, and combinations of these. FCL is also conversant with the typical product physical properties such as mass, weight, moment of inertia, centre of gravity and centre of mass.
6. Test Equipment: Interfacing and Automation
FCL has written source code in Excel Visual Basic for Applications®, Microsoft Visual Basic 2015 Express®, Visual C/C++ 2015 Express® and Matlab 2019b® using the instrument server application. These programs and scripts have been used for controlling test equipment, extracting the data, processing it as necessary and its subsequent presentation. Physical connections have been GPIB bus connections via cards installed into PC architectures, universal serial bus (USB) and Ethernet/Gigabit®. FCL has also achieved highly effective control with various ad-hoc parallel and serial interfaces.
7. Locating Challenging Faults
Sometimes equipment fails to meet specification due to some particularly difficult parameter to achieve or perhaps something unexpected happens at an extreme end of the operating temperature range. FCL has experience of successfully finding and clearing many faults such as these. A very good understanding of the product is required: how it operates and was designed together with fully utilising the test equipment available, sometimes using unusual techniques.
In one example a frequency synthesizer was loosing lock sporadically at low temperatures. Some painstaking investigations showed that the associated voltage controlled oscillator (VCO) was coming to the end of its range prematurely. An examination of the design documents and bill of materials yielded part details of the components used. Some further research into the characteristics of the components chosen for production revealed that some had inadequate high frequency performance at the frequencies concerned. These were replaced with correctly specified components which, although slightly more expensive, allowed the VCO to work as intended. Their extra cost was insignificant compared to the full productions cost of the unit. The problem centered on the core materials used for some inductors which were magnetic and not air-cored types. The magnetic properties of many materials vary significantly over temperature and this was no exception.
8. Solar Radiation Tests
One product that FCL investigated, which was designed for operation in an external environment in the UK, was failing due to overheating at several of the customer's sites. Internal power dissipation was quite modest and convective cooling was thought to be adequate for the UK based on the predicted spread of ambient temperature. However further investigations revealed that insufficient margin had been allowed specifically for solar radiation heating, previously not thought to be of particular concern in a relatively cool climate. FCL quantified the level of solar heating expected by application of the Stefan Boltzmann 'fourth power' radiation law after making allowances for the surface emissivity, infrared spectral density, atmospheric absorption and integrated daily solar power flux. A representative unit was tested in the laboratory using solar lamps suitably orientated and calibrated for infrared content. The effects of solar radiation were found to amount to several hundreds of watts equivalent heating power thus confirming the cause of overheating. Several recommendations were made for ways of mitigating the effects.