[BC] Changing channels

[Robert Meuser]

No one with experience should fall into that trap.  Guy wire loading 
alone will make a 225 deg tower taller. Anyone wanting to push the max 
height better do some very careful modelling and never add anything to 
the tower. Better to stick with a height a few degress smaller.

R


Dan Strassberg wrote:

>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
>
>
>
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