User Report: ERI Provides Total Solution for WDAV
antenna nears completion. The last section is hoisted up.
N.C. — Our phone has rung many times with word that lightning has
struck an FM antenna. In this case, one of Schropp Electronics
Services’ long-term customers, WDAV(FM), in Davidson, N.C., had the
problem. The symptom was the always-unwelcome high VSWR alarm that
had shut down the transmitter.
Schropp, my son and an engineer for Schropp Electronics Services, was
first to respond. He checked to see if the fault would clear,
rechecked for VSWR and ran the transmitter into the dummy load. It
became apparent that the antenna system was the problem. Fortunately,
WDAV has an auxiliary antenna; we were able to switch the coax
switches and return the station to the air.
we inspected everything on the ground, our next call was to the tower
climbers first did a physical inspection on the antenna. We then
disconnected the transmission line to check for soot and I swept the
line with the VNA. Fortunately, the line checked good and no soot
from the antenna had migrated into the line.
the problem was definitely the antenna. We asked the climbers to
begin to disassemble the antenna; that’s when we found melted
parts, charcoal and debris. As we looked at more of the antenna, it
became obvious it would have to be replaced.
far everything would seem to be pretty straightforward; however, this
was not the case.
WDAV has a difficult directional pattern. The old antenna had three
rows of four-basket panels, with a 13th panel added for fill. The
antenna was, in a word, huge.
wind standards for towers in the area had been upgraded over the
years; there was no way a new antenna the size of the old one could
meet the current wind standards. Adding to the wind-loading
difficulties, the tower is short-guyed at around 50 percent.
checking allocations for WDAV to see if there could be improvements
to our pattern and applying for a small improvement based on a more
accurate terrain data base, our search for a new antenna was on.
checked with various manufactures for proposals, and the best-looking
preliminary pattern fill was from Electronics Research Inc. In
addition to the custom directional antenna, ERI offered structural
analysis, tower modifications and installation. The whole package
could be purchased from one source. After careful consideration, we
chose ERI for design and installation of the antenna, along with
structural analysis and strengthening of the WDAV tower.
sent a crew down to do a full structural inspection of the tower.
Pattern development was the usual back-and-forth process of trying to
achieve the best pattern fill and market coverage for the station.
Jim added Longley-Rice coverage predictions to the materials provided
by ERI to give us a more complete look at what coverage should be
designed an antenna for us that reduced the number of elements from
13 to eight, resulting in a significantly lighter antenna while
actually gaining performance. With a smaller antenna to work with,
the structural engineers at ERI were able to design leg-strengthening
supports that would allow the tower to meet wind standards.
coverage is even better than I expected, and the tower is up to
current standards as well.
staff at ERI was great to work with throughout the project,
demonstrating a strong desire to do the best job possible for the
customer. I remember our sales representative, Carl Davis, telling me
that we were going to be happy with the results; he was very right.
information, contact Joe Meleski at Electronics Research Inc. in
Indiana at (812) 925-6000 or visit www.eriinc.com.