[BC] Changing channels

[Dan Strassberg]

Xen Scott wrote:
Some others that may still be directional Class C stations are WOLF in
Syracuse, NY on 1490khz, <snip>

Not WOLF. I visited the site almost five years ago and the tall tower (half
wave at 1490) that had been part of WOLF's two-tower DA-D was long gone. The
shorter tower was still there and WOLF was using it, but the owner, Craig
Fox, held a CP to move his 1540 (licensed to E Syracuse) to that tower. 1490
and 1540 are generally thought to be too close in frequency for a practical
diplex, so Fox planned to move 1490 to a different tower that he had
constructed at the same site. BTW, Fox's 1540 is a two-site Class D AM; the
night and day sites are both inside of the Syracuse city limits. The night
site is a rooftop installation on a fairly tall building; the antenna is a
76' Valcom Fibreglass whip.

Fox had constructed a 412', grounded, uniform cross-section, guy-supported
tower at the WOLF site. That tower was loaded with antennas for FM
translators and LPTVs. Also on it was a folded unipole. It was Fox's plan to
move WOLF to that antenna, but he had been having BIG problems. The
efficiency, which was supposed to be 440 mV/m @ 1 km, was WAY low--not even
up to the Class C minimum of 241.5. He had already gone through a couple of
consulting engineers trying to figure out what was the matter. It took about
four more years, but he finally got WOLF onto the 412' tower. A few weeks
before Fox got WOLF onto the 412' tower, Craig Healy had suggested to me
that the problem might well have been use of aluminum wire for the folded
unipole. The higher resistance wire slows the propagation velocity in the
folded unipole, increasing the antenna's electrical length, which would have
been bad news with an antenna whose length had been calculated to be 225
degrees assuming a propagation velocity close to that of free space, which
was the case with Fox's folded unipole (412' = 225 degrees at 1490). The
high resistance also does a separate number on the efficiency. Craig Healy
told me to recommend to Fox that, if he had used aluminum wire, he should
replace it with copper-coated steel. I passed on the recommendation through
a mutual friend. Just weeks later, WOLF was on the air from the 225-degree
tower. Whether Craig Healy's recommendation was the key, I don't know and
probably will never find out.

--
Dan Strassberg, dan.strassberg at att.net
eFax 707-215-6367