The Question Of Narrowband Performance


By Thor Wiegman - Posted on 15 January 2010

There has been local discussion recently regarding performance of narrowband systems versus legacy systems.  It is wise to discuss this so that everyone understands what is happening and why.

Scientists and engineers can make your head spin with mathematics that prove, beyond the shadow of a doubt, that narroband system coverage is less than with legacy systems.  They will provide you with measurable amounts (you can expect 5 or 6 Decibels less performance on narrowband).  I don't think anyone among us is qualified to debate this with the eggheads, so we can simply accept what they tell us as fact.

Oddly enough I do not know of any example in the real world where a narrowband system performed less than the legacy system it replaced.  You've also heard from several vendors that all of their other customers who are using narrowband have found the performance to be the same or better.

So how is it that we are experiencing the same or better performance with narrowband when the eggheads tell us we should be seeing a decrease in performance?  How is this possible?

It's magic of course.  The magic of maintenance and system improvements.  Quite often a system that is converted to narrowband hasn't really received a thorough, system wide maintenance check.  This is almost always done during the conversion.  Technicians will often find and correct minor defects in the system that were previously unnoticed.  Sometimes equipment will be replaced with more modern equipment that incorporates gains made in technology.  This attention to the system will often result in 6 Decibels or more of improvement in the system which magically counters the decrease the eggheads told us to expect.

Another reason we often don't notice a difference in performance is what we call "terrain limiting".  This simply means that the signals from our systems are limited by the terrain long before they run out of oomph.  Imagine you are going to fire a missile from your office to any single point within your area of responsibility.  I give you a missile that can fly a maximum of 100 miles.  That should be enough to do the job, right?  So there would be no advantage in me giving you instead a missile that could fly 1000 miles.  You'll hit the end of your jurisdiction with either missile before they run out of oomph.  Our radio systems are exactly like this. 

Finally there is the fact that we are taking this opportunity to improve the system and the way we operate.  One example is the recent addition of several new channels to the primary law enforcement system.  In the past all radios talked only through a single repeater located on Sandpoint Baldy Mountain.  That site provides poor coverage of such places as Sandpoint, Priest River and Ponderay.  So, even before converting this system entirely to narrowband, we've added channels at the county courthouse and Priest River Junior High that dramatically improve coverage in those areas.  Similar improvements are being implemented on the few EMS & Fire dispatch system.  So even if we did see a minor decrease in performance of the old systems, the new systems are being installed with an eye on overall improvement in coverage and reliability.