How much longer will WBZ stay at 1170 SFR?

Dale H. Cook
Mon Jun 13 21:35:54 EDT 2011

At 08:35 PM 6/13/2011, Dan.Strassberg wrote:

>But I have to ask this question: WBZ's towers are only about 1/4
>wavelength apart. Assuming the phasor were set up to ground either
>tower and send substantial power (say 25 kW) into the other tower,
>wouldn't someone working on the grounded tower--say, at a height at
>which the active tower's RF current were maximum--be exposed to a
>hazardous RF magnetic field?

Especially with towers over 90 degrees in height (WBZ's towers are 
188.5 degrees tall) and often with shorter towers the normal 
practice, in my experience, is to anti-resonate the undriven tower so 
it will not re-radiate energy from the driven tower during non-D 
operation. I have had to do that in a 5-tower array so that the three 
towers not used in the day pattern would not re-radiate and disturb 
the day pattern. Anti-resonating undriven towers also protects a crew 
working on one of them.

For those curious about such things, this was WLVA, Lynchburg, VA, 
which was built in 1948 with four self-supporting towers (later 
top-loaded) in an endfire array, 1 kw night and day with different 
patterns. A fifth tower, much shorter than the four originals and 
guyed, was added for a 1986 CP to increase day power from 1 kw to 5 
kw (the fifth tower was used with the third original tower for the 
new cardioid day pattern). Since the fifth tower was relatively short 
and about a half-wave from the 1948 array, it could be floated at 
night without disturbing the night pattern. After I was brought in 
towers 1, 2 and 4 were anti-resonated during the day to avoid 
disturbing the day pattern, as 2 and 4 in particular were picking up 
a lot of energy from 3 during the day (3 was getting about 2/3 of the 
power in the 5 kw day pattern). Although the CP was granted in 1986 
the owners went through nearly a decade of CP extensions without 
getting things to work, until I was brought in with another engineer, 
we rebuilt both phasors and all 6 ATUs (3 had differnt day and night 
ATUs). I rebuilt the night phasor and the four night ATUs almost 
single-handed. We got it working - the license to cover was granted 
in 1996. Because we rebuilt so much we had to proof 12 radials, with 
some of those common to both patterns.

As noted upstream I've sometimes made arrangements to have two non-D 
configurations ready to go for tower work (easy in most of my career 
because most of the stations I have worked for in the last 30+ years 
have had two tower arrays).

Dale H. Cook, Contract Engineer, Roanoke/Lynchburg, VA 

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