Do I really NEED Tropo to hear the Puerto Rican FM Broadcast Station? Or are we just close enough to do this line-of-site?

 

WIDI 99.5 FM from western Puerto Rico continues to put a full quieting signal into the eastern Dominican Republic.   The station is so regularly strong that this made me wonder if I am really using tropospheric ducting to hear it.  If I was using tropo ducting, I think there should be some variation in signal strength over the course of 24 hours right?  But it is always strong.  Why?  

I checked the distance:  97 miles.   With its antenna at 2800 feet, its visual horizon will be 64.8 miles away.  I am about 98 feet above the ocean.  This means my horizon is 12.22 miles away.  There appears to be a gap, right?  I mean 64.8 + 12.22 = 77.02 miles.   So it looks like there is a gap of about 20 miles.  

But wait!  Mike WN2A reminded me that there is a difference between radio line of sight and visual line of sight.   Radio line of sight = 4/3 of visual line of sight. 

AI explains where the 4/3 factor comes from: 

The radio horizon appears longer than the visual horizon by a factor of about 4/3 due to atmospheric refraction, which bends radio waves slightly downward. To simplify calculations, this effect is modeled by treating radio waves as if they travel in a straight line over a larger, "effective" Earth with a radius 4/3 times the actual radius. This increased effective radius allows radio waves to "see" further over the Earth's curvature, extending the line-of-sight range compared to what is seen by the human eye, which is not affected by atmospheric bending to the same degree. 

So that puts WIDI's radio horizon at 86.4 miles.  My radio horizon is 16.16 miles.   86.4 + 16.16 =  102.56 miles No gap.  We should be able to hear WIDI, even without tropospheric ducting.   

Puerto Rico -- Dominican Republic Tropo on 99.5 FM? Yes, probably

 

Our friend Todd K7TFC in Portland found this in the 1950 ARRL Handbook at an, uh, opportune moment.  TRGHS.  This seems to describe what a I am hearing, especially that "airmass boundary" in the lower left of the diagram above.  

I'm not a VHF guy, and I am a bit surprised at the persistence of this propagation path.  It is 4:30 am here and the adult contemporary rock from Puerto Rico (Kokomo by the Beach Boys!) is full quieting here in the Dominican Republic.  And it is of the same strength during daylight hours. I don't remember this from the winter months, but I may have just missed it. 

Here is what AI (Gemini) says about this: 

https://share.google/aimode/M1HvC7Y893eE5gAcn\

One other factor to consider:   The island of Mona is about halfway across the path.  There are few people there, and there is almost certainly not a repeater of any kind.  But there may be a metal tower or two... 

Gianfranco IU1DZZ and Mike WN2A  both support the tropo hypothesis.  Mike mentions the Hepburn Index.  I will have to read up on that.  Hamilton is also looking at this propagation path.  Thanks guys.  

Puerto Rico FM Broadcast Station Heard in the Dominican Republic -- But How? WIDI 99.5 FM

WIDI 99.5 FM. Booming in during daylight here on the eastern tip of the Dominican Republic. Their antenna is about 2100 feet above average surrounding terrain. That would put the horizon at about 56 miles. But the path is about 100 miles. What do you folks think is the likely propagation mode?

https://en.wikipedia.org/wiki/WIDI

The Art of Electronics #7 -- Paul Horowitz on Ham Radio, and on SETI (audio)

Radio Contact · “We didn’t find anything, so the search goes on”

Above is a seven minute audio podcast in which Paul Horowitz talks about ham radio and SETI. 

See also:  https://radiocontact.org/portfolio/paulhorowitz/

and  https://en.m.wikipedia.org/wiki/Paul_Horowitz

The Terrible Collapse of the Arecibo Dish: Climate Change, Hurricane Maria, and Funding Cuts. Also: China's New Dish

From https://www.thewrap.com/watch-crazy-footage-of-the-arecibo-observatory-collapse-goldeneye-video/  :

"Alas, over the 2010s it was battered by a series of severe, climate change-linked tropical storms and hurricanes, culminating in terrible damage inflicted by Hurricane Maria in 2017. Unfortunately the 2016 election led to a government unwilling to fund repairs. Though new sources of funding were cobbled together late in 2018, in late Nov. 2020 it was determined there was no way to safely repair the telescope and the National Science Foundation announced it would be decommissioned.

The decommissioning was supposed to proceed after NSF determined the safest possible method, but physics had other plans. So it is that on Dec. 4, the whole thing up and collapsed with almost no warning."

More info (from NSF): 

https://www.nsf.gov/news/special_reports/arecibo/index.jsp

Here is a good 2017 article that discusses the electronic and mechanical arrangements at Arecibo, and the budget cuts it was facing.  The article seems to almost predict the collapse: 

https://www.imeche.org/news/news-article/arecibo-funding-cuts-threaten-future-of-giant-radio-telescope

Here is a comment from someone who worked there and heard the collapse: 

Jonathan Friedman, who worked for 26 years as a senior research associate at the observatory and still lives near it, told the Associated Press news agency of the moment the telescope collapsed on Tuesday.

"It sounded like a rumble. I knew exactly what it was," he said. "I was screaming. Personally, I was out of control... I don't have words to express it. It's a very deep, terrible feeling."  https://www.bbc.com/news/world-us-canada-55147973?fbclid=IwAR3RuwzTfJmqInrOOFB-nctknDzyB_VSr_qdNrjg9LbbxUnAbynKBv9stPQ

Here is an interesting WIKIpedia article on China's FAST dish, with comparisons to Arecibo: 

https://en.wikipedia.org/wiki/Five-hundred-meter_Aperture_Spherical_Telescope#:~:text=The%20Five%2Dhundred%2Dmeter%20Aperture,County%2C%20Guizhou%2C%20southwest%20China.

Comparison of the Arecibo Telescope (top) and FAST (bottom) dishes at the same scale

Adios Arecibo

Arecibo Dish Antenna Seriously Damaged

https://www.sciencealert.com/a-broken-cable-smashed-a-huge-hole-in-the-arecibo-observatory

Nobel Prize winner Joe Taylor, K1JT, Talks to a Radio Club

Really great to see this session with Nobel Prize winner Joe Taylor, K1JT.
I liked his comments on his use of his retirement office at Princeton, University. 
I also liked his slide on how far below the noise level you can go with various modes. 
And then there was his reminder to 1) RTFM and 2) be sure to check the EME delay box so that your software will get the timing right when working earth-moon-earth. 

"Pulsars keep good time." 

NPR: Hams Help in Puerto Rico

I got into my car to drive home yesterday.  As soon as I turned the radio on, I heard this.  TRGHS. FB OM.  Listen.  4 minutes. 

http://www.npr.org/2017/09/29/554600989/amateur-radio-operators-stepped-in-to-help-communications-with-puerto-rico

Arecibo in Danger

http://www.extremetech.com/extreme/230637-flat-science-budgets-could-kill-the-arecibo-observatory-the-worlds-largest-telescope