There have been many articles and technical standards written on how best to verify a freshly upgraded or totally new radio system meets public safety radio coverage expectations. Far less has been written on recovering lost radio coverage in configurations that previously worked well…. or what caused the degradation in the first place. This paper describes potential impediments that sometime result as reduced coverage performance and, more importantly, what can be done to recover lost ground.
Assume for a moment that your agency has constructed a new radio system, perhaps in a different spectrum segment than your prior system. Furthermore, it had undergone a rigorous functional and coverage test plan and passed with seemingly flying colors. Users have migrated onto this gem of engineering excellence in large numbers, and with eager expectations. All is well … until the newness wears off. Over time people begin noticing coverage holes. As time wears, on more and more coverage anomalies bubble up and those once enthusiastic users are now seething mad. Sold short, they want retribution but who is to blame and what can be done – and fast!
Now is time to take a breath and begin peeling back the coverage onion. I use the onion analogy because there may be no single cause for bad system performance. The causes of degraded coverage could be layered, inter-dependent and reconciling them might involve a few tears with an occasional misstep sprinkled in along the journey. Resist the urge to blindly dive in. Take a step back, take a breath and establish a set of acceptable benchmarks. Review the system’s original procurement specification to determine if some important parameter or use case was unintentionally omitted or understated. This is an important first step since radio vendors are not mind readers. Vendor-proposed project solutions align with needs and expectations, as communicated by an Owner’s procurement specifications.
Where projects often fall off the rails is when overall completion – procurement through final acceptance - is grossly delayed. User need and expectation assumptions that made sense at the procurement’s very beginning could have gradually but dramatically changed with the passage of time. An agency may have undergone personnel changes and mission modifications that were never contemplated at the project’s onset.
Important end-user operational expectations may have changed yet the Vendor’s contract requirements remained static. Or, worse, how the users now intend to operate their portable radio equipment – well after the radio system is a reality and has been accepted by the Owner - may differ from that encompassed by the Vendor’s implementation contract. In that instance, contract-verified coverage may later fall well short of actual user needs. The Vendor is off the hook…while the Owner’s decisions and processes used in selecting the winning proposal remains in the spotlight.
As an example, a freshly commissioned radio system had easily passed its standards-compliant, contracted coverage test but was later deemed inadequate by boatloads of users. Our job was to independently determine what went wrong – although the Owner was certain the Vendor was somehow to blame. We soon discovered the Owner’s performance requirement was for field units to receive calls with their portable radios at hip level but would communicate back to the radio system with their portable radios lifted to head level. The Radio Vendor dutifully designed its system configuration to meet the Owner’s specific use case.
The Vendor provided what was in the Contract and professionally undertook its work-- only to have its reputation, at least in the eyes of the Owner, go down in flames. You see, the Owner didn’t consider, describe, or require the actual user radio operational configuration while developing its system specifications. No way the Owner could have forecast the needed configuration, though. You see, the change happened only after the users became fully aware of the Vendor’s full set of portable radio options – months after the radio system went live and fully operational.
As contract negotiations typically marched along in new radio system procurements, radio users could elect to buy the Vendor’s optional portable radio speaker-microphones and other accessories. A seemingly innocent change involving speaker microphones can instantly turned the tables on a project’s delivered coverage. The critical error often made – assuming the accessories are bought before work commences on the system’s final configuration - is when Owners fail to modify the Vendor’s coverage requirement and test methodology by change order and therefore resolve the potential coverage performance shortfall before it happens.
Use of speaker-microphones, where the portable radio’s antenna is always located on-hip, increases signal propagation losses in the talk back path by as much as 10:1. This seemingly small positioning change makes it far more difficult for low-powered portable radios to access and communicate back to distant tower sites. Yes, this Owner’s radio system test results pointed to acceptable coverage – except the test configuration no longer mirrored how the portable equipment was actually deployed. That one change made the project’s coverage maps and test results functionally invalid. Errors in defining a new radio system’s use case – and enduring the result – are costly to resolve and undermine confidence at all user agency levels. Coverage enhancements then subsequently result in additional base station tower sites or the introduction of other components such as vehicular repeater and/or building amplifier equipment.
It’s hard to lean on a Vendor for shortcoming of this sort…particularly when what was provided matched the project’s original specifications. The answer, of course, is to question each change being considered in user radio configurations and determine what effect, if any, those have on actual coverage performance. Blindly expecting no change in performance is setting one up for a very bad outcome.
Let’s move on and consider the coverage onion’s next set of layers: what outside the configuration may have changed and could be degrading radio performance. How about noise and interference?
Elevated tower site receiver noise floor levels could be your silent and non-obvious degradation contributor. Sadly, radio operations have sustained increasingly higher incidents of electrical interference due to the proliferation of switching power supplies and microprocessor-controlled devices. The good news is that these noise generators are usually found near antenna sites – often in the same equipment building. Where switching supplies are found, try briefly turning them off or replacing with a traditional linear power supply and note a change in noise level. If the noise suddenly disappears when a switcher is disabled, consider the problem ‘case closed’.
Noise floor degradation is viewed as an insidious coverage-limiting factor, particularly so for VHF radio systems but can affect even seemingly quiet 700/800MHz operations. It does no good to have a receiving system capable of detecting signals as low as 0.2 microvolts if the noise floor is 10 microvolts or higher. The incoming signal must overcome the local noise, which in cases where 10 to 20dB noise degradation is measured, can decimate any radio system’s talk-back portable coverage.
In many cases, the seriousness of an interference problem can be weighed in proportion to the number of folks complaining. Faced with a noise-limited radio system, users will typically complain they can hear calls but cannot communicate back in response… simply because their incoming signal cannot overcome the noise. Locally induced noise as caused by radio signal mixing (termed intermodulation distortion) due to loosened or corroded components on towers can often be corrected with replacement hardware and installation of proper electrical grounding attachments. Be particularly suspicious of complex cellular antenna placements on shared radio towers since poorly installed hardware in the presence of such strong composite RF levels can readily elevate a site’s noise floor. In some instances we have measured over 20dB of VHF noise degradation at co-located cellular/public safety radio sites.
Co/Adjacent channel radio interference effects may mimic an elevated electrical noise floor. The principal difference, though, is where signal desensitization and reported loss of coverage is random in lieu of continuous in occurrence. Radio users experiencing such interference might complain that from any given spot, they can communicate well one minute but have no or highly degraded communications the next.
As an example of co-channel degradation, a radio system Owner once complained about its aged analog VHF repeater system was suddenly operating strangely. Something new was going on. Its users could communicate via portable radios “full quieting” one minute and yet suddenly be shut down -- while in eyesight of the system’s repeater site! The eventually discovered cause: the region’s frequency coordinator assigned a new 350-watt paging transmitter -- 25 miles removed and at a 500ft higher elevation -- dead-on the Owner’s repeater input channel. Every time a radio page went out, the Owner’s repeater was instantly “lights out”!
Interference caused by distant (presumably licensed) radio systems unfortunately means a probable and expensive frequency change is in the cards. Yes, and in this Owner’s paging interference case, we successfully got the other guy to move. It’s only fair. The last one to the party should be the first one to leave.
In the good old analog days, radio users could often hear actual voices or call signs from distant interfering radio systems and actively participate in tracking down interference sources. Today’s trunked digital radio systems largely prevent such ongoing channel policing by users. Yet, system managers or service personnel are encouraged to monitor digital trunked system channels via the analog mode to determine if outside interference is possibly impacting normal user operations.
When users report coverage shortfalls, Owners and service technicians are tempted to conclude it’s a tower equipment problem and instinctively head that way. In some instances, it is…especially when a directional antenna is found attempting to signal-penetrate through its own metal monopole. Yes, we found such an obviously wrong installation at one Owner’s location. Worse part is it had been operating that way for several years! So, clear off another coverage onion layer by verifying to your satisfaction that tower site antennas and equipment are properly configured.
Now, what to do when the Owner dutifully investigates the installed configuration but seemingly cannot replicate the problem? This leads us to what is often the final layer of the coverage onion: inspecting and testing the as-installed user radio equipment.
It’s called two-way radio for good reason, so don’t automatically assume coverage problems are always tower-site related. User coverage complaints can distill down to poor in-field mobile and portable equipment installations or inadequate maintenance. While once assisting a client in drilling down through the various coverage onion layers, we found nearly half of the radio fleet was operating (in the loosest sense of the word) with: wrong-band antennas; no antenna at all; bad antenna connectors; cut coaxial cables; corroded primary wiring cables; poor to no electrical grounding; dead power amplifiers; noisy LED light bars; and even a bunch of bad USB cellular radio chargers that totally wiped out VHF and 800MHz in-car reception. The list was endless and, even so, not all user radio defects are hardware related.
This last layer can indeed be tricky as Today’s user radios are software driven/software defined (SDR) devices. Fortunately, performance defects and self-interference within SDR equipment can often be resolved via software. Doing so and maintaining the highest level of equipment readiness today requires a solid vendor relation that includes software refreshment and continued stewardship by system Owners. Don’t skimp on vendor software support agreements as those are key to protecting and sustaining today’s complex mission-critical network investments.
In closing, the process of identifying and resolving radio coverage shortfalls is a time-consuming investigative task. Here, a successful long-term outcome requires a technical, business-like awareness. In resolving the many potential facets of degraded radio system performance, it is essential to first understand the radio system’s fundamental design objectives; review as-built test data; and always approach one’s investigative work with an open mind. Collect true measured data and thoughtfully analyze the results. If the results make little to no sense, either the data collection process was wrong, you hadn’t considered the most likely degradation contributors, or the designer’s initial assumptions are no longer valid due to unanticipated operational or functional changes.
Keep in mind, the fly in the coverage ointment could be as simple as an 800MHz antenna attached to a VHF radio -- or a directional base station antenna aimed into a large-diameter metal pole or wall! In the field, anything is possible.
NOTICE: This document and its content, dated February 12, 2023, is the copywrite property of Central Electronics, LLC. All rights reserved. You may not, without our expressed permission, distribute or commercially exploit the content or publish/link same on any other website or electronic media.