Attempting 2 meter contact, Dominican Republic to Puerto Rico

It is about 100 miles across the Mona Channel.  That is a longshot on 2 meters, but I got the idea when, this past summer, I regularly heard WIDI 99.5 FM in the Dominican Republic from western Puerto Rico.  So over the fall I gathered 2 meter gear, and got a directional antenna and sent all of this gear to the DR.  

Here is the antenna.  Seven elements. I got it through Amazon.  It came kind of incomplete and without any written or on-line instructions.  AI told me to do exactly the WRONG thing with what they assumed was a reflector.  Fortunately I ran into this YouTube video and learned that it was in fact a "ZL Special" antenna, and that it has, in fact, TWO driven elements.  It was through that video that I learned how to assemble this thing.  

My "station" consists of a Heathkit HM-2109.  It is a VHF wattmeter/SWR meter that I bought by mistake.  But I kept it, and it proved very useful in this 2 meter Mona Channel project.  There is a Baofeng UV-5R (boo! hiss!) and a Yaesu FT-470 that KD4EBM gave me.  I have a Communication Concepts 2 meter amplifier -- I must have picked this up at a hamfest.  It promises 35 watts with 5 watts of drive.  The old CCI amp gives the rig good juju. 

This morning I wrote to the hams of western Puerto Rico: 

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Saludos desde el otro lado del canal de la Mona! 

Soy radio aficionado:  Hi7/N2CQR.   Vivimos en República Dominicana en Cap Cana seis meses cada año.

He notado que puedo escuchar WIDI 99.5 FM aquí.  Parece que hay Tropospheric ducting. 

Como radioaficionado, me gustaría averiguar si podemos hacer contacto en 2 metros usando la misma propagación. 

Tengo: 

Dos transceptores de FM

Un amplificador a 35 vatios. \

Un antenna directional de 7 elementos con un gain de 11.5 db. 

Estoy a una elevación de 7 Pisos.  Puedo ver el canal de Mona. 

Hay alguien en la costa oeste de PR (tal vez cerca de Mayagüez) quien puede hacer un schedule para probarlo? 

O hay un repetidor en la zona que puede usar para averiguar si puedo -- por lo menos -- "kerchunk"  el repetidor?  

Gracias por su ayuda! 

73  Bill  Hi7/N2CQR

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Greetings from the other side of the Mona channel!

I am a radio amateur: Hi7/N2CQR.   We live in the Dominican Republic in Cap Cana six months every year.

I've noticed that I can listen to WIDI 99.5 FM here.  There seems to be Tropospheric ducting.

 As a radio amateur, I would like to find out if we can make contact in 2 meters using the same propagation.

 I have:

Two FM transceivers

An amplifier at 35 watts. \

A 7-element directional antenna with a gain of 11.5 db.

I am at an elevation of 7 Stories.  I can see the Mona's channel.

 Is there someone on the west coast of PR (maybe near Mayagüez) who can make a schedule to try it out?

 Or is there a repeater in the area that you can use to find out if I can -- at least -- "kerchunk" the repeater?

 Thank you for your help!

 73  Bill  Hi7/N2CQR

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Stay tuned! 

Maybe it is Tropospheric Ducting After All -- 99.5 FM WIDI Puerto Rico Received in the Dominican Republic

 

Invest 94L moved arcoss the Mona Passage yesterday, lowering temperatures, bringing lots of rain and relatively high winds to the area.   I happened to check on reception in the DR of WIDI 99.5 FM (near Mayaguez, Puerto Rico), and was surprised to find that the signal had weakened considerably.  This morning, after the storm passed, signal levels were back to their normal full quieting. This would support the idea that tropospheric ducting is playing a big role in bringing this signal into the Dominican Republic.  I had been surprised by the persistence of the signal -- for weeks it had been full quieting here.  I thought that perhaps I was just receiving it directly, line-of-sight, without the benefit of tropo ducting.  But Invest 94L has made me question this idea. 

I asked Google Gemini AI about the persistence of tropospheric ducting on FM broadcast signals in the tropics.  Here is what it said: 

AI Overview

In the tropics, tropospheric ducting is a frequent, persistent, and often strong phenomenon, especially over and around large bodies of water. Unlike mid-latitudes where ducting is a seasonal event, the meteorological conditions in the tropics are favorable year-round.
Why ducting is persistent in the tropicsHigh temperatures and humidity: Tropical climates are characterized by consistently high temperatures and abundant moisture. These conditions are the primary drivers of atmospheric ducting.

Temperature inversions: Stable high-pressure systems common in the tropics can create temperature inversions, where a layer of warm, moist air sits above cooler air. The sharp change in temperature and humidity with altitude creates the "duct" that traps and bends radio waves over long distances.

Dominance of water paths: Large tropical ocean regions are ideal for ducting. A common ducting phenomenon called the "evaporation duct" is ever-present over the sea surface due to a sharp humidity gradient and is particularly effective for trapping frequencies above 3 GHz. While the FM broadcast band (87.5–108 MHz) is at a lower frequency, coastal areas and islands frequently experience ducting over sea paths.

Atmospheric stability: The general stability of high-pressure systems in the tropics allows ducting conditions to persist for many months at a time. This is observed in areas like the Caribbean and the Persian Gulf, where long-distance radio reception is a common occurrence.

Impact on the FM broadcast band (VHF Band II)Favorable frequencies: The FM broadcast band (VHF Band II) is particularly susceptible to tropospheric ducting. While ducting can occur across a range of frequencies, signals above 90 MHz generally propagate more favorably during ducting events than lower frequencies.

Signal interference: The most noticeable effect of this regular ducting is co-channel interference, where distant stations can override local ones. During an event, a listener may pick up two different stations on the same frequency, or experience temporary loss of reception from a nearby transmitter.

Extended reception: For radio hobbyists, this high frequency of ducting means that signals from FM stations hundreds or even thousands of kilometers away can be received clearly.

Diurnal cycle: Ducting events in the tropics often peak during the evening and overnight hours when surface cooling creates a stable nocturnal boundary layer. Conditions may "burn off" after sunrise, but ducting is common throughout the day during periods of stable weather.

In summary, the specific meteorological and geographical conditions found in tropical regions—consistent heat, humidity, and the presence of large bodies of water—make persistent tropospheric ducting on the FM broadcast band not just possible, but highly probable throughout the year.

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 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