On Thursday, August 14, Phil Mondon, FR5DN, on Reunion Island had a successful QSO with Glen Kraut, ZS2GK, in South Africa on 2 meters. According to Dave Pedersen, N7BHC, this contact is "very likely the longest 2 meter QSO via tropospheric propagation for either country."

The 2008 ARRL Handbook defines tropospheric propagation as "radio waves [that] are refracted by natural gradients in the index of refraction of air with altitude, due to changes in temperature, humidity and pressure. Refraction under standard atmospheric conditions extends the radio horizon somewhat beyond the visual line of sight. Favorable weather conditions further enhance normal tropospheric refraction, lengthening the useful VHF and UHF range by several hundred kilometers and increasing signal strength. Higher frequencies are more sensitive to refraction, so its effects may be observed in the microwave bands before they are apparent at lower frequencies.

"Ducting takes place when refraction is so great that radio waves are bent back to the surface of the Earth. When tropospheric ducting conditions exist over a wide geographic area, signals may remain very strong over distances of 1500 km (930 miles) or more. Ducting results from the gradient created by a sharp increase in temperature with altitude, quite the opposite of normal atmospheric conditions. A simultaneous drop in humidity contributes to increased refractivity. Useful temperature inversions form between 250 and 2000 meters (800-6500 feet) above ground. The elevated inversion and the Earth's surface act something like the boundaries of a natural open-ended waveguide. Radio waves of the right frequency range caught inside the duct will be propagated for long distances with relatively low losses. Several common weather conditions can create temperature inversions."

Kraut said that on the evening of August 13, he "went to bed at about 08:30 UTC leaving the rig on and antennas pointing toward Reunion. I woke up at 00:15 UTC and heard the beacon from my shack. I went over and saw that signals were low, even with the Masthead pre-amp on. I was running CWGeT to confirm hard copy of the signal, but it was not decoding. I switched off the pre-amp and returned to bed. About an hour later, I heard the beacon again but much stronger, so I went to the shack and saw the signal at almost 1 on the S-meter. Perfect hard copy from CWGeT. I contacted Phil on his cell phone, switched the linear and pre-amp on and we logged a SSB QSO and FM QSO on 144.200 and 144.400 at 01:39 UTC on August 14 with signal reports of 5/6 both ways."

Mondon added: "At 0135 UTC on August 14, Glenn is calling me on my cell phone. That means the beacon is heard strong enough to allow a QSO. It's 0535 local time here; I speak low and run into the shack, switch off the beacon and call on 144.200 to see Glenn's signal at 55/56 with the preamp. We decide to try FM and I have clear copy on him. Time goes fast -- we stop the QSO some 20 or 30 minutes later, but the band was still nicely open! The signal was crystal clear, almost no fading, if any on my side. Whooaaaa! The first bridge is now there between South Africa and Reunion Island."

Pedersen said that trans-oceanic ducting has long been suspected around South Africa: "While operating there as ZR2BI in the late 1970s, I heard an unidentified South American station on 2 meters. Since then, having moved to the US, I was not able to pursue it any further. This last January, I started e-mailing a lot of people in Southern Africa and St Helena, but found little activity pursuing the potential tropo. Resorting to my old ways of using FM broadcast stations as beacons, I asked John Turner on St Helena Island to listen for African stations. Within days, he reported stations from Angola, then Namibia and eventually as far south as Cape Town. One February day, he logged 25 South African FM broadcasters in 30 minutes. And that was with his car radio."

Pedersen said that Ian Coverdale, ZD8I, on Ascension reported that he can occasionally hear Cape Town Harbor radio on 156 MHz, 2770 miles away; Sted Stroud, ZD8S, reported that it is fairly commonplace for Ascension Islanders to listen to Brazilian FM stations. "All those reports led to Phil Mondon putting up the beacon," Pedersen said.

According to VHF guru and conductor of QST's "World Above 50 MHz" column Gene Zimmerman, W3ZZ, VHF amateurs have long been aware of long distance tropospheric ducting across stable ocean waters. "The best known such duct is the Hawaiian duct which links the West Coast of the US, especially California with the Big Island of Hawaii. But we have also known that other such ducts exist in different places around the world, although the ham populations in these areas are often so low that we hardly ever experience two way communications. The Indian Ocean is one such place. This outstanding contact between Phil Mondon, FR5DN, on Reunion Island and Glen Kraut, ZS2GK, in South Africa confirms the existence of a path between the mainland and islands in the Indian Ocean. It follows the detection of FM broadcast stations on similar paths in the South Atlantic Ocean between the island of St Helena and Angola, Namibia and Capetown on the mainland, and reports of reception of Brazilian FM stations on Ascension Island in the South Atlantic."

Pedersen agreed: "Now that the path is proven, many South African hams are gearing up to increase the distance over the coming southern summer."