AM Aux sites / towers (WCBS)

[Dave Doherty]

Well, let's check out the actual app.  It is available online at 
http://svartifoss2.fcc.gov/prod/cdbs/pubacc/prod/app_sear.htm. Search for 
apps for WCBS and select BXP-20020816AAO.

They proposed a new 300' non-top-loaded tower. Presumably, although I did 
not check this out, the 200' tower it replaced was top-loaded, or they would 
not have mentioned this.

There is not a complete ground system for this tower. It was proposed to use 
a square ground mesh bonded to the copper radials of the main tower that 
pass through the area. Although not specifically stated, that would go a 
long way toward explaining the 35kW daytime maximum. The AM License app form 
302 is still a paper app, so nothing is available online that would indicate 
what the final base resistance was.

As for night operations, the two stations studied are a new 870 in Reading, 
PA (still unbuilt, as far as I can tell) and WBPS (now WAMG) in Dedham, MA. 
Both are first adjacents, and in neither case does the proposed operating 
power of 26kW increase the nighttime limit.

The main night power limit appears to be Dedham. At 26kW, the predicted 
skywave at Dedham is 0.2373mV/m. The main WCBS facility is 0.2374mV/m, and 
the previous aux was 0.2373mV/m.

According to 73.31, in the range from 10 to 50kW, you must specify power to 
the nearest kW, so there is no option for, say, 26.1kW.

At 27kW, the nighttime skywave would be 0.2373 * (27/26) ^ 0.5 = 0.2418mV/m, 
which would be an increase in nighttime interference at Dedham.

So that explains the 26kW night power limitation.

-Dave Doherty
 Skywaves, Inc.
 97 Webster Street
 Worcester, MA 01603
 508-425-7176