Why is it that I can received WCBS @ 880kc fairly well at night but WABC @
770kc suffers from phase distortion like you wouldn't believe! (I'm about
175 miles from both transmitters.) They are both 50 kwatt stations. And why
is it that both WBZ (Boston), WBT (Charlotte, NC), WJR (Detroit) and WBBM
(Chicago) come in better than either of the New York City stations?

Dave P.

Why is it that I can received WCBS @ 880kc fairly well at night but
WABC @
770kc suffers from phase distortion like you wouldn't believe! (I'm
about
175 miles from both transmitters.) They are both 50 kwatt stations.
And why
is it that both WBZ (Boston), WBT (Charlotte, NC), WJR (Detroit) and
WBBM
(Chicago) come in better than either of the New York City stations?

Dave P.
================================

Different frequencies, different directions, different sun angles
(even when below the horizon), different ionospheric layer heights,
different skip distances, different ground-path terrains and therefore
different ground-path loss.
----
Reg.

Dave P. wrote:
"Why is it that I can receive WCBS @ 880 kc fairly well at night but
WABC @ 770 kc suffers from phase distortion like you wouldn`t believe?"

I havn`t looked up the directional patterns of the two stations and
don`t know your location. If you should happen to be at the edge of a
null in the nighttime directional pattern of WABC, that would likely
cause distorted fading. WABC may be clear-channel non-directional day
and night for all I know. Not many of these remain in the U.S.A. now.

At 175 miles from both transmitters, you suffer interference between the
ground wave and sky wave from either transmitter at night, at least
occasionally. You probably have solid daytime reception from both
stations, but at night, the signal may be stronger, though variable. The
sky wave is susceptable to variations in the reflecting layers of the
ionosphere at night. These are a function of frequency, reflecting
carrier and sidebands differently at times. This can produce
overmodulation at times in the received signal. Another factor is likely
other stations on the same or adjacent channels which may fade in and
out and cause variation from your automatic volume control action even
when the interfering stations can not be readily identified. An Adcock,
loop, or other directional antenna may produce a big improvement in
reception of the desired signal.

Finally, WABC is owned by the Walt Disney company. Maybe you should
expect Mickey Mouse performance.

Best regards, Richard Harrison, KB5WZI

Richard,

Both you and Reg have given excellent answers and I thank you both.

By the way, you mention directional patterns and nulls. Is there any place I
can find polar graphs of commercial broadcast station's antenna patterns?

Thanks,

Dave P.
====================


"Richard Harrison" wrote in message
...
Dave P. wrote:
"Why is it that I can receive WCBS @ 880 kc fairly well at night but
WABC @ 770 kc suffers from phase distortion like you wouldn`t believe?"

I havn`t looked up the directional patterns of the two stations and
don`t know your location. If you should happen to be at the edge of a
null in the nighttime directional pattern of WABC, that would likely
cause distorted fading. WABC may be clear-channel non-directional day
and night for all I know. Not many of these remain in the U.S.A. now.

At 175 miles from both transmitters, you suffer interference between the
ground wave and sky wave from either transmitter at night, at least
occasionally. You probably have solid daytime reception from both
stations, but at night, the signal may be stronger, though variable. The
sky wave is susceptable to variations in the reflecting layers of the
ionosphere at night. These are a function of frequency, reflecting
carrier and sidebands differently at times. This can produce
overmodulation at times in the received signal. Another factor is likely
other stations on the same or adjacent channels which may fade in and
out and cause variation from your automatic volume control action even
when the interfering stations can not be readily identified. An Adcock,
loop, or other directional antenna may produce a big improvement in
reception of the desired signal.

Finally, WABC is owned by the Walt Disney company. Maybe you should
expect Mickey Mouse performance.

Best regards, Richard Harrison, KB5WZI

There are undoubtedly official sources from the FCC, etc.

The best hand-held guide I could recommend would be the National Radio
Club's "Night Pattern Book," a fantastic resource for MW DXers and
broadcast listeners. Basically it is a book of maps of North America
for each domestic broadcast frequency, with dots representing
transmitting locations, and the night time radiation pattern around each.

It's available from the following link:

http://www.nrcdxas.org/catalog/books/

The 5th edition is sold out, but the new 2005-06 edition is scheduled to
be out soon.

Brent Taylor
VE1JH


Dave Pitzer wrote:
Richard,

Both you and Reg have given excellent answers and I thank you both.

By the way, you mention directional patterns and nulls. Is there any place I
can find polar graphs of commercial broadcast station's antenna patterns?

Thanks,

Dave P.

There are undoubtedly official sources from the FCC, etc.

The best hand-held guide I could recommend would be the National
Radio
Club's "Night Pattern Book," a fantastic resource for MW DXers and
broadcast listeners. Basically it is a book of maps of North
America
for each domestic broadcast frequency, with dots representing
transmitting locations, and the night time radiation pattern around
each.

It's available from the following link:

http://www.nrcdxas.org/catalog/books/

The 5th edition is sold out, but the new 2005-06 edition is
scheduled to
be out soon.

Brent Taylor
VE1JH


Dave Pitzer wrote:
Richard,

Both you and Reg have given excellent answers and I thank you
both.

By the way, you mention directional patterns and nulls. Is there
any place I
can find polar graphs of commercial broadcast station's antenna
patterns?

Thanks,

======================================
Dave,

http://www.nrcdxas.org/catalog/books/
Sounds exactly what you are looking for but may take some time to
obtain.

In the meantime, the basic groundwave radiation patterns of mediumwave
broadcast antennas are either simple circles with the antenna at their
centres, or heart-shaped with the antenna at the null.

The first occurs when the antenna is a single vertical mast located
near the centre of a large populated area.

The second occurs when the antenna consists of a pair of masts, which
radiate a very broad heart-shaped beam, located on one side of the
populated area to be covered.

Contour Maps of actual measured field strengths are useful when the
basic groundwave patterns are distorted by the terrain, e.g., the
existence of mountains, forests, rivers, built-up areas, high-rise
cities, or seas, lakes or coastal regions.

Radio frequency Field Strengths are usually measured in terms of
"millivolts per meter" or in decibels relative to one volt per meter.
----
Reg.

Dave P. wrote:
"Is there any place I can find polar graphs of commercial broadcast
stations?"

I have an old book, "Map Book, 540 kc to 1600 kc" published by
"Cleveland Insritute of Radio Electronics". In it, WABC is 50 KW
non-directional day and night. It shares 770 kc with KOB Albuquerque, 50
KW day and 25 KW night. Also, KUOM Minneapolis and WCAL Nortjhfield are
both 5 KW and share the frequency on some schedule between themselves.
WNEW St. Louis is on the frequency daytimes only, as is KWA Seattle, 1
KW. XEHB in San Francisco de Oro, Mexico is a 500 watt daytimer on the
frequency, as are XELM, 150 watts at Lagos de Morens and XEDI at
Queretaro, 1 KW. There is also CMDC, 1 KW at night when it could trouble
you in Holquin, Cuba. So, at night there is possible same-channel
interderence from New Mexico and Cuba. On 760 kc, you have WJR in
Detroit 50 KW non-directional at night and on 780 kc, you have WBBM in
Chicago 50 KW nondirectional at night. These non-directional 50KW
adjacent channel stations may exercise your AVC.

On 880 kc, WCBS has no same-channel night rivals but WLS (World`s
Largest Store, Sears in Chicago) on 890 kc, onetime home of "The
National Barn Dance", could work your AVC. Also, WWL in New Orleans
occupies 870 kc with 50 KW.
Good preselection will rid you of adjacent channel interference. I lived
in Portugal for years and listened to WCBS nightly. I would rock my
tuning from 880 to 870 for WWL during fades for my version of frequency
diversity. Both stations carried the same CBS programs. My antenna was a
Beverage aimed at New York. The receiver was a Hammarlund SP-600 which
had plenty of preselection to avoid adjacent channels. Ed Murrow came in
very well.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

very well.

Best regards, Richard Harrison, KB5WZI


Slight change of subject, WCCO 830 and a couple others I've noticed, now
have a tremendous amount of digital sounding crap around them that
completely obscures stations such as KOA. Is this the new digital radio
wonder weapon that I'm supposed to love?

tom
K0TAR

"Dave Pitzer" wrote
... Is there any place I can find polar graphs of commercial
broadcast station's antenna patterns?

___________________

Dave,

Here http://www.radio-locator.com/ is a link to a website with calculated
coverage areas/contours for US AM broadcast stations. The contours are
based on their licensed radiation patterns (directional or not), AND ground
conductivities for the geographic regions concerned.

The polar radiation patterns of these stations most probably don't look much
like these plots, because of the heavy influence that ground conductivity
has on received field strength along the various azimuth bearings.

Even the real coverage contours of AM broadcast stations using omni antennas
usually are anything but omni, due to the effects of varying ground
conductivities around their various azimuth sectors and ranges.

Have fun.

RF

"Richard Fry" wrote in message
...
"Dave Pitzer" wrote
... Is there any place I can find polar graphs of commercial
broadcast station's antenna patterns?

___________________

Dave,

Here http://www.radio-locator.com/ is a link to a website with calculated
coverage areas/contours for US AM broadcast stations. The contours are
based on their licensed radiation patterns (directional or not), AND
ground conductivities for the geographic regions concerned.

The polar radiation patterns of these stations most probably don't look
much like these plots, because of the heavy influence that ground
conductivity has on received field strength along the various azimuth
bearings.

Even the real coverage contours of AM broadcast stations using omni
antennas usually are anything but omni, due to the effects of varying
ground conductivities around their various azimuth sectors and ranges.

Have fun.

Just a FYI...the contour maps at Radio-Locator.com are WRONG....the LOCAL on
FM maps is actually the distant or Service Contour (1mv or 60dbu
level)..LOCAL is defined as City Grade or 70dbu or 3.16mV level...which they
do not show..On AM, they show lower levels on the map as well...If you want
to really know what the signal level should be, draw another circle or line
inside the LOCAL one they show...about the same distance between the LOCAL
and Distant they show...Your line drawn will be local, their local becomes
Distant and their Distant becomes Finge...
Their Fringe is now DX

Chris
WB5ITT