The great state of Texas
is where I make my home. It is a
big state and the saying goes, “Everything is bigger in Texas.” It is a place
with a colorful and sometimes controversial history. The open range
to the horizon was once big enough for farmers, ranchers and hunters to coexist
without encroaching on each other. By the late 1800s however, good pasture and
water had become scarce, coveted resources
. That, and the invention of barbed
wire, contributed to the heated and often violent battles known as the Fence Wars
The legendary Texas Rangers
were called upon to settle the dust.
That same time period also saw the first attempts at
wireless communication. The radio pioneers had access to any spectrum they
needed as all of it lay fallow. Interfering with other users was of no concern.
Fortunately so, since their spark gap transmitters could create a good deal of Out-Of-Band
Emissions (OOBE) even when skillfully tuned.
We can usually count on history to repeat itself and
consequently, frequency spectrum is now a precious commodity. Everyone needs to
stay within their licensed boundaries without trespassing upon the neighbors. In
certain situations, avoiding such infringement requires the use of Interference Mitigation Filters (IMF). One typical case for IMFs is where one user’s
transmit (downlink) band is too close in frequency to another’s receive
Not so long ago I was called upon to help solve a case here
in the heart of Texas. In this instance a cellular carrier had installed a Distributed Antenna System (DAS) on a university campus. When the DAS was turned up,
it was discovered that the uppermost carrier with downlink close to 894 MHz was
interfering with public utility uplink radio channels near 896 MHz. Those
radios suffered a degradation of at least 15 dB due to OOBE from the cellular
transmitters. The emission levels complied with regulations – the two radio
systems were just too close to each other in location and in frequency.
Because modern-day Texans are known for civility, the two
radio operators did not reach for their six-shooters to settle this territorial
conflict—they reached out to CommScope. Their situation was not unlike what we
encounter in a number of countries around the world using a varying mix of 850
and 900 MHz cellular spectrum. Because of the variability, we developed a
flexible IMF design platform that was, in this case, adapted to provide over 30
dB rejection of the offending signals. An on-site trial confirmed the solution
was 100 percent effective. This was of course a relief for the “victim” but no
less so for the cellular carrier who could now safely turn up that top channel
and regain much needed traffic capacity.
Across the world, spectrum is being reallocated to meet
capacity demands. At CommScope, we are ready to pin that tin star on our chest
and help make peace along the fence lines—in Texas and elsewhere. Job done, we
can all mount up together and ride off into the sunset.
Have you considered where new interference scenarios can
occur with broadcast and two-way operators, on co-location sites and in