Topband: Antenna analysers in close proximity to BC station.

[Richard Fry]

Tim N3QE wrote:
>And I think clear channel stations do not cut back power at night... do 
>clear channel stations actually still exist?

There are about 116 AM broadcast stations in the U.S. using 50 kW 
transmitter power during the day. Some of them reduce power at night, 
however KFMB (760 kHz) San Diego operates with 5 kW non-directional days, 
and 50 kW directional at night.

Some of these 116 stations are directional day and night, and some of those 
have different patterns for day and night.

The directional patterns used by some of these 116 stations may have an ERP 
of around 500 kW at the center of their major lobe.

The stations using 50 kW non-directional day and night are:

KFI  640 kHz  Los Angeles
WSM  650  Memphis
WFAN  660  NYC
WSCR  670  Chicago
KNBR  680  San Francisco
WLW  700  Cincinnati
WGN  720  Chicago
WSB  750  Atlanta
WJR  760  Detroit
WABC  770  NYC
WBBM  780  Chicago
WGY  810 Schenectady
WBAP  820  Ft. Worth
WCCO  830  Minneapolis
WHAS  840  Louisville
KOA  850  Denver
WCBS  880  NYC
WLS  890  Chicago
KDKA  1020  Pittsburgh
WHO  1040  Des Moines
KNX  1070  Los Angeles
WTAM  1100  Cleveland
KMOX  1120  St. Louis
KSL  1160  Salt Lake City
WHAM  1180  Rochester
WOAI  1200  San Antonio
WPHT  1210  Philadelphia

WBZ 1030 Boston and WWL 870 New Orleans use 50 kW day and night, but with 
directional arrays to favor radiation over land areas.

A groundwave field intensity of 2.5 V/m or more can be present at a radius 
of 1 km from the stations in the above list.  That can rise to more than 7 
V/m in the main lobe of a directional station with 500 kW ERP.

The original concept of a clear channel meaning that only one 50 kW, 24/7, 
non-directional station was authorized on that frequency at night is gone. 
The FCC has allowed nighttime service on all of them by stations located far 
enough away from those on the list above when using fairly low power (some 
less than 1 kW), and usually, directional arrays.

The stations listed above are given protection to their nighttime 
(secondary) service areas for interference to their 0.5 mV/m-50% skywave 
contour from stations on the same channels.

RF