Perseverence pays-off in 2-metre tropo contact

Glenn Kraut, ZS2GK, in Mqandulin, a village in the Eastern Cape, made an historic contact with FR5DN on Reunion on
2 metres over a distance of 2,875 km.

On Tuesday 12 August at 10:40 local time ZS2GK heard the Reunion beacon at signal strength 1. He phoned Phil, FR5DN, on Reunion who said that he was racing home from work and would be there in 30 mins. He was unfortunately held up in heavy traffic. By the time he arrived home the band had dropped out.

On Wednesday evening ZS2GK went to bed at about 22:30 local time leaving the rig on and antennas pointing towards Reunion. He woke up at 02:15 and heard a beacon. The signal was very weak and he went back to bed. Scarcely one hour later he heard a stronger beacon signal. It was perfect copy on the CW reader.

Glenn called Phil on his cellphone, switched the linear and pre-amp on and logged a SSB QSO and FM QSO on 144,200 and 144,400 at 03:39 CAT with signal reports of 5/6 both ways. "We spoke for about 20 minutes. I also tried to access the Reunion repeater without any luck", he told SARL news. "There was no QSB on the SSB signal but a bit of fade into the noise on FM."

Listen to the QSO on www.sarl.org.za.

Glenn uses 4 x EX6OB 2 m, 9 element antennas built by ZS6OB on an H Frame at 2 m above the roof. Power used was 400 W on SSB and 200 W FM giving an ERP of about 28 100 W on SSB. On the receive side he uses a GasFet pre-amplifier, a perquisite for all serious VHF work.

VHF and UHF radio waves can propagate over the horizon when the lower atmosphere of the earth bends, scatters, and/or reflects the electromagnetic fields. These effects are collectively known as Tropospheric propagation, or tropo for short.

The most well-known form of tropo is called bending. Air reduces radio-wave propagation speed compared with the speed in a vacuum. The greater the air density, the more the air slows the waves, and thus the greater is the index of refraction. The density and index of refraction are highest near the surface, and steadily decrease with altitude. This produces a tendency for radio waves at very-high frequencies to be refracted toward the surface. A wave beamed horizontally can follow the curvature of the earth for hundreds of kilometres.

A less common, but often dramatic, form of tropo is called ducting. This occurs when there is a defined, horizontal boundary between air masses having different densities. When a cool air mass is overlain by a warm air mass, as is the case along and near warm fronts and cold fronts, radio waves at VHF and UHF are reflected at the boundary if they strike it at a near-grazing angle from beneath (within the cooler air mass).

Because radio waves are also reflected from the earth's surface, the result can be efficient propagation for hundreds or, in some cases, upwards of 1,600 km, as the waves alternately bounce off the frontal boundary and the surface.

According to Mike Bosch, ZS2FM, it is difficult to confirm whether it was tropo ducting or Sporadic E. Whichever the case, it is a great achievement.

Well-done ZS2GK and FR5DN.

Source: The South African Radio League