[BC] Re: WEEI towers (2)

[PeterH5322]

>Another interesting bit of trivia about the WEEI array is that, despite
>having an average electrical height of 207 degrees (according to CDBS), the
>efficiencies are rather low for towers of that height. If the electrical
>height really were 207 degrees, you'd expect to see efficiencies of
>approximately 400 mV/m/kW @ 1 km. Instead, the night efficiency is
>approximately 370 mV/m/kW @ 1 km and the day efficiency is approximately 386
>mV/m/kW @ 1 km. Both efficiencies are greater than the Class A minimum even
>though WEEI is a Class B, but one would expect greater efficiency than that
>listed in CDBS. I have often wondered whether the actual efficiencies are
>somewhat higher than those listed in CDBS, and if they are, why are lower
>values listed?

As is often the case, the real reason is lack of adequate (or complete) 
technical data, so the FCC estimates the performance from what (little) 
data it might have.

For years and years a well-known west coast station on a frequency in the 
high 600s had estimates, but through relentless prodding the licensee 
eventually came up with values which are now posted in the CDBS, although 
I think those numbers are a little fanciful, too.

The present posting shows 136.83 degrees with 50.32 degrees of top 
loading, for a total height of 187.15 degrees, and a efficiency which is 
the minimum for the class, 362.10 mV/m/kW at 1 km.

That putative 50.32 degrees of top loading would be about 200 feet, yet 
the actual capacitive hat is a hexagonal structure with an average 
diameter of only 50 feet.

FIM measurements by the former head of the FCC office there confirms the 
radiator does not produce 362.10. It is in the lower mid 300s, though, as 
one would expect from a 135 degree radiator.

So, what I think was done was this: an amount of top loading which would 
produce a better-than-conforming radiator was computed, and that value 
was posted, along with other data based on physical measurements.

I know a former officer at the licensee, and even they did not have the 
engineering data for that radiator, which they owned for many years, and 
the company which originally built that radiator fifty-odd years ago 
apparently didn't have it in its New York archives, either.

Just another case of lost engineering data, which may be the case at WEEI.