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Old December 28th 03, 11:20 PM
Reg Edwards
 
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Default Broadcast Station Field Strengths..

Could someone please give me an idea of the field strength, in terms of
volts/meter, which broadcasters expect will provide a MINIMUM SATISFACTORY
service in various sorts of service areas.


Obviously, satisfactory field strength depends on broadcasters' estimates of
noise levels, typical antennas, and types of receivers. I am not interested
in noise levels. Only in what field strength broadcasters consider
necessary to provide a satisafactory grade of service.

It would be nice to have 4, admittedly crude numbers, for -

MF and HF in densely populated, city areas.

MF and HF in rural areas.

Somebody in broadcasting must surely have some ideas about this.

(I am not interested in sand deserts, antarctica and oceans because nobody
lives there.)
----
Reg, G4FGQ



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Old December 29th 03, 12:29 AM
David Robbins
 
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"Reg Edwards" wrote in message
...
Could someone please give me an idea of the field strength, in terms of
volts/meter, which broadcasters expect will provide a MINIMUM SATISFACTORY
service in various sorts of service areas.


Obviously, satisfactory field strength depends on broadcasters' estimates

of
noise levels, typical antennas, and types of receivers. I am not

interested
in noise levels. Only in what field strength broadcasters consider
necessary to provide a satisafactory grade of service.

It would be nice to have 4, admittedly crude numbers, for -

MF and HF in densely populated, city areas.

MF and HF in rural areas.

Somebody in broadcasting must surely have some ideas about this.

(I am not interested in sand deserts, antarctica and oceans because nobody
lives there.)
----
Reg, G4FGQ



there is a lot of info he http://www.uwasa.fi/~jpe/voacap/ but no quick
answer.


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Old December 29th 03, 01:57 AM
Jack Smith
 
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On Sun, 28 Dec 2003 22:20:17 +0000 (UTC), "Reg Edwards"
wrote:

Could someone please give me an idea of the field strength, in terms of
volts/meter, which broadcasters expect will provide a MINIMUM SATISFACTORY
service in various sorts of service areas.


With respect to MW broadcasting in the US, the FCC has established a
complex set of values. Here's a quick summary. These are found at 47
C.F.R. Sect. 73.182 if you want more detail.

The four classes of AM broadcast stations (Class A,B,C and D; these
relate to power and frequency) have in general three types of service
areas, i.e., primary, secondary and intermittent. (See Sec. 73.14 for
the definitions of primary, secondary, and intermittent service
areas.) Class A stations render service to all three areas. Class B
stations render service to a primary area but the secondary and
intermittent service areas may be materially limited or destroyed due
to interference from other stations, depending on the station
assignments involved. Class C and Class D stations usually have only
primary service areas. Interference from other stations may limit
intermittent service areas and generally prevents any secondary
service to those stations which operate at night. Complete
intermittent service may still be obtained in many cases depending on
the station assignments involved.

(d) The groundwave signal strength required to render primary
service is 2 mV/m for communities with populations of 2,500 or more
and 0.5 mV/m for communities with populations of less than 2,500. See
Sec. 73.184 for curves showing distance to various groundwave field
strength contours for different frequencies and ground conductivities,
and also see Sec. 73.183, ``Groundwave signals.''

(e) A Class C station may be authorized to operate with a
directional antenna during daytime hours providing the power is at
least 0.25 kW. In computing the degrees of protection which such
antenna will afford, the radiation produced by the directional antenna
system will be assumed to be no less, in any direction, than that
which would result from non-directional operation using a single
element of the directional array, with 0.25 kW.

(f) All classes of broadcast stations have primary service areas
subject to limitation by fading and noise, and interference from other
stations to the contours set out for each class of station.

(g) Secondary service is provided during nighttime hours in areas
where the skywave field strength, 50% or more of the time, is 0.5 mV/m
or greater (0.1 mV/m in Alaska). Satisfactory secondary service to
cities is not considered possible unless the field strength of the
skywave signal approaches or exceeds the value of the groundwave field
strength that is required for primary service. Secondary service is
subject to some interference and extensive fading whereas the primary
service area of a station is subject to no objectionable interference
or fading. Only Class A stations are assigned on the basis of
rendering secondary service.


Primary service area. Means the service area of a broadcast station in
which the groundwave is not subject to objectionable interference or
objectionable fading.


Secondary service area. Means the service area of a broadcast station
served by the skywave and not subject to objectionable interference
and in which the signal is subject to intermittent variations in
strength.

Intermittent service area. Means the area receiving service from the
groundwave of a broadcast station but beyond the primary service area
and subject to some interference and fading.



In addition, Section 73.24 of the FCC's Rules require that applicants
for MW broadcast licenses must demonstrate that their daytime 5mV/m
contour covers 80% of the population of the entire principal community
to be served, relaxed to 50% for stations in the 1605-1705 KHz band.


Jack K8ZOA
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Old December 29th 03, 03:54 AM
Richard Harrison
 
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Reg, G4FGQ wrote
"It would be nice to have 4, admittedly crude numbers for - MF and HF in
densely populated city areas. MF and HF in rural areas ."

In the USA, the Federal Communications Commission defines three
different types of service area for medium wave broadcasting stations.
The primary service area is the area where groundwave from the station
is not subject to fading. The secondary service area is served by the
station`s skywave such that there is no objectionable groundwave
interference. Nevertheless, skywave signals are subject to fading. The
third service area lies between the primary and secondary service areas.
It is subject to interference and fading. It is called an intermittent
service area. Assignments are made in an attempt to keep primary and
secondary service areas clear of objectionable interference.

FCC defines local channels as those frequencies reserved for stations of
1 KW daytime, and 250 watts nighttime, or less. Primary service is
limited by interference.

Regional channels are reserved for stations of 5 KW or less. Directional
patterns are often used by new stations to avoid interference in service
areas of existing stations.

Clear channels no longer are the sole domain of some high power lonely
US broadcast station. Clear channels are now often shared with one or
more high powered stations, and perhaps also shared with lower powered
stations during daytime hours, in an attempt to make better use of the
frequency while the high powered stations still serve wide areas.

The FCC specifies the following minimum field intensities:

City business or factory area------10 to 50 mV/m

City residential area------------------2 to 10 mV/m

Rural--all areas during winter or northern areas during
summer----------------------0.1 to 0.5 mV/m

Southern areas during summer 0.25 to 1.0 mV/m

The FCC has published additional guidelines for signal strengths in
towns of certain populations, to overcome often encountered noise:

Up to 2500 inhabitants----------0.5 mV/m

2500 to 10,000 inhabitants---2.0 mV/m

The needed signal intensity depends on interfering signal levels and all
other noise.

At higher frequencies, groundwave propagation goes away but noise
declines too. The FCC field intensities needed for satisfaction at
mediumwave broadcasting may be more than required for amateur
communications.

The information above is provided by John E. Cunningham in "The Complete
Broadcast Handbook".

The answer to Reg`s questions are incomplete, but I hope they help.

Best regards, Richard Harrison, KB5WZI



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