weird FM signals
 

Today while driving, I was listening to WDOD 96.5 near Chattanooga,
somehow they were off the air..and instead there was a Mexican station
taking over the signal, very strong signal, fading and coming back,
then there was another Mexican station in the same channel.By the city
and frequency I found it to be XHRN-FM in Veracruz.It was the same on
other frequencies, like 94.5FM, there were 2 or 3 Spanish stations(One
of those was from Mexico City, Insituto Mexicano de la Radio
XHIMER,playing classical music). Then I moved to 101.7 and there were
another 2 spanish stations there.
Why does that happens and how often? I think it has to do with the
weather being hot and humid.
Any comments about that?

"Antonio" wrote in message
...
Today while driving, I was listening to WDOD 96.5 near Chattanooga,
somehow they were off the air..and instead there was a Mexican station
taking over the signal, very strong signal, fading and coming back,
then there was another Mexican station in the same channel.By the city
and frequency I found it to be XHRN-FM in Veracruz.It was the same on
other frequencies, like 94.5FM, there were 2 or 3 Spanish stations(One
of those was from Mexico City, Insituto Mexicano de la Radio
XHIMER,playing classical music). Then I moved to 101.7 and there were
another 2 spanish stations there.
Why does that happens and how often? I think it has to do with the
weather being hot and humid.
Any comments about that?

Fairly common in late spring and early summer.

http://home.swbell.net/pjdyer/
http://www.qsl.net/wa5iyx/index.html

http://dxworld.com/tvfmlog.html Use the "Look Back" feature near the bottom
of the page to see earlier posts.

Within Europe, 100 MHz Es occurred on at least 25 successive days in
June/July.

Sounds like trophospheric ducting, where vhf and uhf signals propagate
beyond line of sight (do a search on google for tropospheric ducting for
more info that you care to know).

"Antonio" wrote in message
...
Today while driving, I was listening to WDOD 96.5 near Chattanooga,
somehow they were off the air..and instead there was a Mexican station
taking over the signal, very strong signal, fading and coming back,
then there was another Mexican station in the same channel.By the city
and frequency I found it to be XHRN-FM in Veracruz.It was the same on
other frequencies, like 94.5FM, there were 2 or 3 Spanish stations(One
of those was from Mexico City, Insituto Mexicano de la Radio
XHIMER,playing classical music). Then I moved to 101.7 and there were
another 2 spanish stations there.
Why does that happens and how often? I think it has to do with the
weather being hot and humid.
Any comments about that?

I encountered this same phenomenom while driving through South Carolina
during the last week of June. I picked up signals from Kansas and Texas.

There are two types of "weird signals":
Troposheric ducting, which allows ground signals to extend for hundreds
of miles
Skip, in which the signals are bounced off an ionized layer in the
atmosphere. Signals over 1000 miles away are propagated this way.

"RandyP" wrote in message
...
Sounds like trophospheric ducting, where vhf and uhf signals propagate
beyond line of sight (do a search on google for tropospheric ducting for
more info that you care to know).

"Antonio" wrote in message
...
Today while driving, I was listening to WDOD 96.5 near Chattanooga,
somehow they were off the air..and instead there was a Mexican station
taking over the signal, very strong signal, fading and coming back,
then there was another Mexican station in the same channel.By the city
and frequency I found it to be XHRN-FM in Veracruz.It was the same on
other frequencies, like 94.5FM, there were 2 or 3 Spanish stations(One
of those was from Mexico City, Insituto Mexicano de la Radio
XHIMER,playing classical music). Then I moved to 101.7 and there were
another 2 spanish stations there.
Why does that happens and how often? I think it has to do with the
weather being hot and humid.
Any comments about that?

"umarc" wrote in message
...
(Antonio) writes:

Today while driving, I was listening to WDOD 96.5 near Chattanooga,
somehow they were off the air..and instead there was a Mexican station
taking over the signal, very strong signal, fading and coming back,
then there was another Mexican station in the same channel.By the city
and frequency I found it to be XHRN-FM in Veracruz.

It's called tropospheric ducting. When a layer of warm air forms above
a layer of cooler air, the boundary can reflect radio waves. This
can temporarily extend the range of FM signals. It is especially
common in summer months and over water. To broadcasters on the coast
it can be annoying, especialy when somebody's country station a
hundred miles away regularly wipes out one's classical station in
its home town.

Fine explanation of tropospheric ducting.

But that ISN"T the type of propagation involved in this report.

The propagation heard these past few weeks has been Ionospheric, by means of
the sporadic E layer, about 100 km (60 miles) above the Earth's surface. Go
back and read the information on the WA5IYX pages. Here are URLs again:

http://home.swbell.net/pjdyer/
http://www.qsl.net/wa5iyx/index.html

Antonio wrote:
Today while driving, I was listening to WDOD 96.5 near Chattanooga,
somehow they were off the air..and instead there was a Mexican station
taking over the signal, very strong signal, fading and coming back,
then there was another Mexican station in the same channel.By the city
and frequency I found it to be XHRN-FM in Veracruz.It was the same on
other frequencies, like 94.5FM, there were 2 or 3 Spanish stations(One
of those was from Mexico City, Insituto Mexicano de la Radio
XHIMER,playing classical music). Then I moved to 101.7 and there were
another 2 spanish stations there.
Why does that happens and how often? I think it has to do with the
weather being hot and humid.
Any comments about that?

Sporadic-E. (see R.J. Carpenter's links)

On occasion, one of the atmospheric layers responsible for long-distance
reception on shortwave becomes briefly capable of supporting MUCH higher
frequencies, like FM broadcasts. There are many theories as to why this
happens but none are proven.

Weather is not a cause. Sporadic-E is more prevalent from late May
through mid-July (and again around Christmas). It's also more prevalent
in mid-morning and early evening.

The tropospheric ducting mentioned by other posters is almost certainly
NOT responsible for this DX. Tropospheric propagation is almost never
able to cross mountains, and the 1400-mile distance to Mexico City would
be VERY, VERY unlikely. Sporadic-E, on the other hand, doesn't have
much grief with mountains. 1400 miles is on the long side, but
certainly possible.

(I had several Mexico City stations in just this morning at my place in
Cheatham Co. about 30mi. northwest of Nashville)

Keep an eye on channels 5 and 6 on a TV with an antenna. (also 2 and 4
if you're far enough out that WRCB doesn't spill over too much) The
skip will hit TV first.

Take a look at http://www.anarc.org/wtfda for more information.


--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com