"Richard Fry" wrote in message
...
"Bill Turner" wrote
I have the same situation here in California. I'm about 100 miles from
KFI, another 50 kW station, and during the day reception is a bit weak,
but adequate. Come sundown however, reception begins fading and is
distorted. The reason is that the groundwave portion of the signal is
still present, but is now being interfered with by the skywave portion,
which is not present during the day. If I were to move farther away,
out of groundwave reception, the signal would become much clearer,
but only at night. During daytime it would not be heard at all.
______________

Various types of "anti-fade" radiators are used by many of the 50kW
stations
to try to minimize this effect.

There is a tradeoff in the electrical height of the usual AM broadcast
transmit antenna between producing the greatest groundwave and generating
an
excessive high angle skywave that can interfere with that groundwave at
night.

A 225 degree vertical is about optimum for groundwave, but has a high
angle
lobe that can cause this type of interference problem. A 195 degree
vertical has less groundwave but little/no high angle lobe, and so is used
by many full time 50kW stations. WJR, Detroit is an example of a station
using a 195 degree vertical (700 foot guyed tower).

Other antenna types also have been used for this, such as the "Franklin,"
which is a sectionalized antenna with one vertical radiator above another,
each driven separately.

Note also that the carrier frequency of the station, the conductivity
along
the groundwave path, and skywave propagation conditions will have an
affect
on the location of this zone, and the extent of interference there.

R. Fry
(WJR staff engineer, mid 1960s)


Richard,

Thanks for the response and the "inside", technical information about
Broadcast-band-AM stations. I'm happy to say that here in eastern
Pennsylvania, WJR has a beautiful night-time signal. About the only thing
that disturbs it is "local" weather-based QRM --- i.e. Mother Nature!!!. I
even recall listening to WJR in my college days in Charleston, SC in the
early 1960's (along with WLS in Chicage and WOR in NYC).

Without knowing, I would guess that WABC (770 KHz) has a rather high angle
skywave since its ground- and skywave seem in a constant "tug-of-war" at
night --- at least ~80 miles to the northwest of the xmitter.

Thanks,

Dave Pitzer
============================

"Richard Fry" schreef in bericht
...
Various types of "anti-fade" radiators are used by many of the 50kW
stations
to try to minimize this effect.

There is a tradeoff in the electrical height of the usual AM broadcast
transmit antenna between producing the greatest groundwave and generating
an
excessive high angle skywave that can interfere with that groundwave at
night.

A 225 degree vertical is about optimum for groundwave, but has a high
angle
lobe that can cause this type of interference problem. A 195 degree
vertical has less groundwave but little/no high angle lobe, and so is used
by many full time 50kW stations. WJR, Detroit is an example of a station
using a 195 degree vertical (700 foot guyed tower).

Other antenna types also have been used for this, such as the "Franklin,"
which is a sectionalized antenna with one vertical radiator above another,
each driven separately.


Have a look at this:
http://www.waniewski.de/id35.htm

The text is in German, but the diagrams and photos show an aerial system
with its feed at 90 meters above ground level, to reduce skywave.
You can click through several pages at the top (1-15).

gr, hwh

"hwh" schreef in bericht
...
Have a look at this:
http://www.waniewski.de/id35.htm

The text is in German, except when you find the small flag and choose
English :-)

gr, hwh

"Richard Fry" wrote in message
...

.................................................. ...........................
.............................................
Note also that the carrier frequency of the station, the conductivity
along
the groundwave path, and skywave propagation conditions will have an
affect
on the location of this zone, and the extent of interference there.

R. Fry
(WJR staff engineer, mid 1960s)


Richard, I think he is just too close for night time sky wave, and too far
for ground wave. When I lived in western Ohio, I had no trouble picking up
WABC with the built in loopstick. I have also picked up WABC in Bermuda and
Florida. So, I don't doubt the 27 states coverage statement. I noiced I had
trouble getting NY AM stations on the car radio in eastern PA.

BTW, You mentioned WJR. I can pick that up here in NJ, even though it is
only 10 KHz from WABC, which is about 25 miles from me. All it takes is a
receiver with *very* good selectivity. This is where the BC DX people bark
up the wrong tree when they want more antenna gain. WLW (700) became
problematic after WOR (710) went digital AM. They now broadcast hash at
least +/- 20 KHz from the carrier.

Tam/WB2TT

"Tam/WB2TT" wrote re WABC night time reception in PA:
Richard, I think he is just too close for night time sky wave,
and too far for ground wave.
_________________

Quoting the original post, "I live approx 80 miles from the xmitter of
station WABC (New York) 50,000 watts. During the day my reception is
good-to-very good. After sunset however, the signal is poor to
unlistenable -- due to fading and man-made
QRM."

WABC radiates the same power from the same radiator 24 hours a day, and
provides good daytime reception at this receive location, so it is not too
far for the groundwave.

The ground wave is more or less constant day and night, so it is likely that
the poor/unlistenable signal there at night must be the result of
interference to the groundwave from whatever high-angle skywave WABC
produces, plus the higher co- and adjacent-channel interference usually
present at night.

RF

"Richard Fry" wrote in message
...
"Tam/WB2TT" wrote re WABC night time reception in PA:
Richard, I think he is just too close for night time sky wave,
and too far for ground wave.
_________________

Quoting the original post, "I live approx 80 miles from the xmitter of
station WABC (New York) 50,000 watts. During the day my reception is
good-to-very good. After sunset however, the signal is poor to
unlistenable -- due to fading and man-made
QRM."

WABC radiates the same power from the same radiator 24 hours a day, and
provides good daytime reception at this receive location, so it is not too
far for the groundwave.

The ground wave is more or less constant day and night, so it is likely
that
the poor/unlistenable signal there at night must be the result of
interference to the groundwave from whatever high-angle skywave WABC
produces, plus the higher co- and adjacent-channel interference usually
present at night.

RF

Isn't there a zone where you tend to get cancellation between groundwave and
skywave?

Tam

"Tam/WB2TT" wrote
Isn't there a zone where you tend to get cancellation
between groundwave and skywave?
______________

Yes, that is what I have been writing in my posts on this subject line. The
RF phase of the skywave varies independently from the ground wave. Some
times it reinforces the ground wave; some times reduces it.

Further, both reinforcement and reduction can occur at the same time for
different RF frequencies across the AM channel, leading to a selective
combing effect in the program audio, and/or near loss of the carrier while
most of the sidebands are still present. Of course, that produces very high
distortion in an envelope detector. AM receivers using synchronous
detectors reduce this problem.

Most full time 50kW AM broadcast stations use an antenna system with
relatively low radiation at elevation angles above about 45 degrees in
order to reduce (but not eliminate) night time interference to their own
groundwave. I made up a simple graphic comparing the elevation patterns of
vertical antennas used in AM broadcast for four different electrical
heights: 90, 180, 195, and 225 degrees. The difference in their high-angle
radiation is apparent. Please email me if you would like a copy.

RF

Visit http://rfry.org for FM broadcast RF system papers.