"Impossible" FM radio signals in Peruvian Andes?

p1879

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18 years back I was in a small bus ("Combi" Van) that traversed the route Leimebamba- Celendin in the northern Amazonas region, that crossed the massive Mara~non gorge. At the bottom of the gorge, in Balsas, you cross the river into Cajamarca region.

At the top, on the Amazonas side, is the 3500 Meter-high Calla Calla Pass. This is in itself not remarkably high in Peru, but the view from this spot is extremely dramatic, even by Andean standards. I was riding up front with the driver, and I asked him about radio reception along this high spot. He told me it was amazing, and said you could hear Lima radio stations from there; he turned on the radio, tuned around, and demonstrated a station from Lima on the ordinary dashboard radio.

Google Earth says this is 610 KM to the Morro Solar TX site used by almost all Lima stations.

I would call BS on this assertion on the surface, but Peru is really a land of many mysteries and miracles, as well.

Many major radio outlets, like RPP Noticias, and Radio Nueva Q, do have stations all over the country that carry their programming, but he said you could hear numerous stations from that high point , that actually were in Lima. I got to know the gentleman, and his son-- who also owned the hotel I stayed in during my stay in Celendin-- and they were very honest and trust-worthy folks. The only place that had any radio stations in possible line-of-sight from there were below in Balsas, about 30 KM downhill. Even then, the river bottom at Balsas is not visible from up top.

The stations listed on the Peru Ministerio de Transporte y Communicaciones website in Balsas have 100W, and 50W respectively. I am sure he knew them well, from years on this route.These folks drove this route both ways, once a week, and were familiar with every curve, and knew all the folks we encountered along the route. I feel certain his statement about the Lima stations was true.

Now, map direct-lines and radiogoniometric plots can differ, depending on the type of map. On the Google Earth map (which I am having difficulty pasting here) shows the path to Lima from Calla Calla passes over the Cordillera Blanca, which has Peru's highest peak-- Huascaran,-- at 6700 Meters high. Huascaran, for example, has a 2000 Meter snow and ice wall on it, and many adjoining peaks have huge snow and ice ramparts.

The distances, and obstacles, sound insurmountable.

I realize this must sound like a radio fairy tale, but I have to seriously wonder if Calla Calla gets some type of signal refraction from the Cordillera Blanca, or has an unusual climatic condition that somehow creates frequent ducting into it. Yes, I fully understand the curvature of the planet over this enormous distance, and the other factors, as well.

Not offended if you don't believe it, just my true experience.
Enough of my wordiness. How could this be?
p1879
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mmckenna

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None of that really surprises me, but it is always fun to see it happen in real time and in the real world.

FM broadcast is in an interesting part of the spectrum where ducting can absolutely happen. Lots of stories about people in the UK picking up US FM broadcast, TV, etc.

Altitude obviously helps.
RF can reflect of things.
Ducting happens.
Good antennas.

I've experienced some interesting FM broadcast stuff, but not quite that good. Enough for me to think it's entirely possible.

If this part of Peru experiences this all the time, not just periodically, then it's probably not ducting, unless ducting happens all the time down there.

Another factor here may be that there just aren't that many FM broadcast stations, so co-channel interference isn't a thing. With a good clear frequency, amazing things can happen.
 

p1879

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The explanation of this phenomena is beyond me. Admittedly, if such a miraculous propagation path did exist, you would think it would be a well-known and studied affair. It is always possible it was indeed some other city that carried programing from Lima, and my "chofer" was not correct about direct reception. But I feel he did know what he was talking about. It seems unbelievable, but there are many strange things in that marvelous place.

I mentioned ducting to cover that base, but my indication was this is a common occurrence at that place. I am including a link to a fantastic Adventure Motorcycle Riding Blog by a Danish couple who recently passed through the Calla Calla pass. They have a picture that shows the view from an overlook at the Canyon. The geography there is most impressive. I was 100 meters off on the pass elevation. It is at 3600 M. It was still a dirt road when I was there.....

Speaking of Nevado Huascaran, Peru's highest point, 6768 Meters is 22,205 feet.

 

mmckenna

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Stunning scenery.

It's entirely possible it is the same broadcast transmitted from different locations, that's a common practice.

But like I said, if there isn't a lot of frequency reuse in a mostly rural area, FM can carry quite far.
 

RFI-EMI-GUY

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"he turned on the radio, tuned around, and demonstrated a station from Lima on the ordinary dashboard radio. "

Radio propagation has at its basics, statistical probability. Had he said, I receive this very station every single day, I would be skeptical. It may occur 5%, 25% or 50% of the time. But he would probably have been able to receive a distant station from some other direction a day later.

I was amazed decades ago, to receive MILSAT communications from the pacific northwest on my Regency MX5000 using a simple discone antenna in Miami Florida. Of course a satellite was involved. But then years later the same receiver picked up TV audio and FM Police transmissions from Cuba. My Sony TV with outside antenna was able to receive TV channels up to 13 from Cuba at same time.
 

krokus

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Ducting can be interesting. I once received a small town FM station from New Mexico, on my vehicle radio, in southeast Michigan. I figured that someone was using a low power transmitter, from an online feed. I called the station, and the DJ said that they have no streaming of their signal.
 

KB2GOM

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Not to hijack the thread, but FM DXing fascinates me, yet I am a total newb regarding FM DX.

So, my dumb@ass question for the day: is there such a thing as "graveyard frequencies" or perhaps certain frequencies where one ought to look for FM DX, or can it happen anyway on the FM broadcast spectrum?
 

KB2GOM

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Not to hijack the thread, but FM DXing fascinates me, yet I am a total newb regarding FM DX.

So, my dumb@ass question for the day: is there such a thing as "graveyard frequencies" or perhaps certain frequencies where one ought to look for FM DX, or can it happen anyway on the FM broadcast spectrum?
Perhaps someone could point me in the right direction.
 

nd5y

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Perhaps someone could point me in the right direction.

Here is a list of all US FM broadcast frequencies.
See the links below the table for looking up US stations.

You won't be able to hear DX on frequencies used by your local FM stations.
Depending on your receiver it might not be able to receive weak DX stations on channels adjacent to your local stations.
 

KB2GOM

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