US MW STATIONS - FCC TOWER HEIGHT RULES
 

http://CBC.am/ wrote:
US MW STATIONS - FCC TOWER HEIGHT RULES

In DXLD 3-144 Richard Howard inquired why so called clear channel
stations often used longer antennas than the 1/4 wavelength antennas
used by most smaller stations. Does the FCC mandate tower height
limits?

The FCC does not mandate MW tower height. They do mandate that new

This is not strictly true. 47CFR73.189 establishes minimum tower
heights for AM stations, depending on class and frequency. For example,
a Class C station above 1200KHz must use a tower at least 45m tall,
while a Class A station on 650 must use one at least 165m in height.

Under certain circumstances these requirements can be waived if the
station can meet field-strength requirements with a shorter tower.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Doug Smith W9WI wrote:

47CFR73.189 establishes minimum tower
heights for AM stations, depending on class and frequency. For example,
a Class C station above 1200KHz must use a tower at least 45m tall,
while a Class A station on 650 must use one at least 165m in height.

Under certain circumstances these requirements can be waived if the
station can meet field-strength requirements with a shorter tower.
--

The question was addressing tower height limits which I interpreted as
being maximums rather than minimums. Thanks for your clarification.

There is a company, Valcom, in Guelph, Ontario Canada that is
advertising in the US radio magazines that they are selling MW band
antennas as short as 15 meters. These look like linearly loaded
fibreglass poles with large capacity hats at the top. I wonder if any
of these have been licensed in the USA. Would not a waiver be granted
for such an antenna if the field strength requirements could be met?
It seems to me one could supply the specified field strength with any
reasonably short antenna as long as one was willing to crank up the
transmitter power output to counter the loss in efficiency. I think
that would be permissible under FCC rules but I am not sure.

The Valcom web site does not specifically call out AM broadcast
applications except for TIS stations, probably because the antennas
are only rated to 2 kW over most of the AM band.

www.valcom-guelph.com

Joe Buch

Joe Buch wrote:
It seems to me one could supply the specified field strength with any
reasonably short antenna as long as one was willing to crank up the
transmitter power output to counter the loss in efficiency. I think
that would be permissible under FCC rules but I am not sure.

I don't know a thing about it, but power in equals power out. The
problem is where it goes. A short tower sends more skyward, a tall
tower more horizontal. I'd assume that the FCC wants less skyward
and hardly care how strong the horizontal strength is because it won't
go as far; except insofar as it also indicates the skyward pattern.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

There is a company, Valcom, in Guelph, Ontario Canada that is
advertising in the US radio magazines that they are selling MW band
antennas as short as 15 meters

I believe WGCH in Greenwich, CT is planning to use one as they are being
evicted from their quarterwave site.

The Valcom is not the only short MW antenna, wasn't there an AARP (wrong but
similar acronym) type that looled like a fence?

"Joe Buch" wrote in message
...
Doug Smith W9WI wrote:

47CFR73.189 establishes minimum tower
heights for AM stations, depending on class and frequency. For example,
a Class C station above 1200KHz must use a tower at least 45m tall,
while a Class A station on 650 must use one at least 165m in height.

Under certain circumstances these requirements can be waived if the
station can meet field-strength requirements with a shorter tower.
--

The question was addressing tower height limits which I interpreted as
being maximums rather than minimums. Thanks for your clarification.

There is a company, Valcom, in Guelph, Ontario Canada that is
advertising in the US radio magazines that they are selling MW band
antennas as short as 15 meters. These look like linearly loaded
fibreglass poles with large capacity hats at the top. I wonder if any
of these have been licensed in the USA. Would not a waiver be granted
for such an antenna if the field strength requirements could be met?
It seems to me one could supply the specified field strength with any
reasonably short antenna as long as one was willing to crank up the
transmitter power output to counter the loss in efficiency. I think
that would be permissible under FCC rules but I am not sure.

Those antennas are for TIS type stations. No way to either feed them high
power or get them to tune efficiently.