A number of highly experienced engineers in the critical communications field work for Tait Communications. Ian Graham is one such engineer with many years of experience, specializing in RF systems. He has also published a book on this subject and teaches courses on the technical aspects of RF systems.
Sandra Wendelken, strategy and market insights manager at Tait Communications, talked with Ian about his motivation to teach an upcoming course at the UTC Telecom and Technology Conference and to extract some tips for his fellow engineers on best practice RF site design to mitigate potential interference.
Why are you teaching this particular topic at UTC?
I have spent a very rewarding career designing reliable land mobile radio communication systems that literally save lives. And over those years I have faced a number of unexpected challenges, made mistakes, experimented and improvised, been mentored and mentored other engineers, and along that very satisfying journey I have learned a lot about best practices when designing these systems. The one area that tends to trip us up constantly is ensuring our systems do not suffer from interference. It is an area that needs conscious thought and focus early on in the design process. When you do that, you remove a lot of headaches later that may require expensive reworking.
Are there particular areas you would say engineers commonly forget to consider when designing their RF systems?
Sometimes it is easy to forget that when someone buys an LMR system, they are not just buying devices or boxes, they are also buying expected coverage. That is, the ability to communicate reliably over their entire service network during emergencies.
Customers can experience sudden and unexpected coverage loss when a site design has not fully anticipated potential aspects of interference, which can be catastrophic and even put lives at risk.We need to ensure we put sufficient focus on identifying potential interference and validating reliable coverage.
What would you say are the most common mistakes you see in RF systems design?
There are three key mistakes I often see engineers make when designing RF systems.
Mistake 1: Only consider the new system you are designing for an existing site.
When you are designing a new repeater site for deployment, it is natural to focus on that system. However, the engineer must take time to understand what other systems are already installed at that site and importantly, the resulting RF environment into which you will be installing. If you try to design a site without considering the other wireless systems that may be operating at the site, you risk interference that leads to loss of coverage.
Mistake 2: Not considering the required performance of any associated equipment, especially base stations and mobile or portable radios.
The better the RF performance of the base stations and mobile or portable radios, the greater the distance over which they will be able to communicate, which also means fewer radio sites are required to cover the service area. Importantly, the communication will be much more reliable than with cheaper radios with inferior RF performance. And what you think is interference may be poor performance of the equipment so check this as well to ensure the devices selected are of sufficient quality and will perform as you expect in the design.
Mistake 3: Assuming interference issues at existing sites are due to lack of capacity.
I witnessed this first-hand when a customer approached us for assistance. For several years whenever the customer had an issue making calls, they simply added more channels to their repeater site systems. However, reliability then got worse, not better. When my team analyzed the existing setup, we realized the problem was not capacity but was actually interference from other radio systems that shared their sites.
How would you suggest engineers who may be new to the industry upskill or learn more about interference-free mitigation?
I would suggest seeking out experienced engineers in your organization or who you are connected to and talk to them about their experiences and what has tripped them up. I have always found this community to be very generous in sharing experiences and knowledge, and that after all, is how we all learn and grow. Other options include taking training courses whenever you can.
In fact, if you are attending UTC and interference mitigation is of interest, then be sure to attend my course – you can find the conference schedule and registration here. The topic is “Designing Interference-Free RF Combining Systems for Shared Radio Sites”. It focuses on how to design interference-free antenna and combining systems at busy radio sites.
I have also attempted to distil much of what I have learned into a book that can referenced throughout your career. If you are a professional engineer or technician in the LMR industry, or a design consultant or equipment dealer, you will find this information a useful reference.
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