KKXS-FM, Shingletown, CA, suffered from a problem shared by many
small FM stations in rural America: the population in this northern
California market is spread over a large area, and rough terrain
presents serious obstacles to a Class A FM station. Shingletown is too
small to support a station profitably, and most of the market’s
listeners live in Redding (27 miles away) or Red Bluff (47 miles away).
For KKXS to compete with several Class C stations in the market,
something had to be done to improve the KKXS signal. The station needed
substantial improvement at an affordable price. It was not practical to
increase power or to move closer to Redding.
When I discussed this problem with other broadcast engineers, I
learned of an FM antenna that is making a reputation of improving
coverage for small FM stations. I was skeptical at first, until I
talked to engineers and station owners who are now using single-lobe or
reduced-sidelobe antennas. Their reports were encouraging.
I was referred to SWR, which sent literature on the Illumitron FM
antenna, and also referred me to a local engineer who could look at the
coverage problems and evaluate how much improvement was possible with
the Illumitron antenna. The consulting engineer’s recommendation
was instrumental in the station’s decision to purchase a four-bay
Illumitron, which was installed in January 2002. Much of the following
month was devoted to checking the performance of the new antenna and
comparing field intensity measurements.
|Performance at a
Reduced side lobe and downward radiation
Reduced multipath effects throughout coverage area
Better field intensity variation specifications
Improved coverage area performance
Exceptional cost-per-performance ratio
While the signal is still weak compared to the Class C stations,
there is a significant improvement in coverage. Many shadows and holes
in the service area are gone. The signal is noticeably improved in
buildings and behind obstructions.
Improving signal strength
Perhaps more significant, multipath and picket fence effects are
much reduced. One listener said that “the station is more fun to
listen to” with less noise and interference. Field intensity
readings showed an average increase of almost 3dB with the new antenna,
but the consulting engineer told me that this difference is most likely
due to loss of signal from the old antenna, because of the way it was
mounted on a tapered tower. The average field intensity is related to
distance and effective radiated power (ERP), rather than the type of
antenna in use.
The major difference in signal strength (or field intensity) for the
Illumitron antenna is a remarkable stability. While most FM signals
vary ±10dB or more over short distances, this antenna’s
signal remains almost constant. Variations of 1dB or 2dB are typical,
except near overhead wires and other reflecting objects. For KKXS, the
minimum signal strength was almost 5dB higher, and maximum signal
strength was only 1.2dB higher. Receivers only care about minimum
signal strength, and this explains why the Illumitron improves coverage
and signal quality. The station had found subtle, but significant
KKXS’ antenna has not been in use long enough to have an
effect on ratings or revenue, but the station is encouraged by what it
has heard from others using a similar antenna.
We are still a Class A FM station, but we don’t feel quite so
Harry is proprietor of Sierra Broadcast Service, providing
engineering services to Northern California-area broadcast
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