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Thursday, June 20, 2019

Dominican Republic to UK TV DX

Mike, KA3JAW, reported that on June 19 around 1600 UTC, two UK TV-DXers in western London detected NTSC analog television channel 2 video carrier on 55.250 MHz, zero offset from callsign HIJB, Tele Antillas in the Dominican Republic. Path distance was over 4,300 miles with the half-way point over the Northern Atlantic Ocean at mid-latitude (40 N). No audio carrier was observed on 59.750 MHz.

During that time, 6 meters was open between the UK and Puerto Rico and the Dominican Republic according to a ham radio operator in the UK.

What is puzzling, but also entertaining to me is what was the mode of propagation?

My initial thought was Sporadic-E with four hops with each hop being 1,075 miles. This would be a rare case that I have never experienced in 15 years of TV-DXing. If it was, the signal path attenuation from each consecutive hop would be too high. So, this rules out that mode in my mind.

The more logical mode would be F2 with two hops with each hop being 2,150 miles. In 15 years of TV-DXing, I have received one station from Peru via single hop F2 at 2,783 miles.

On June 19, there were no sunspots, noon 10.7 cm radio flux was 68 sfu and geomagnetic activity at quiet. We are at solar minimum, one of the deepest minima of the past century. Extreme ultraviolet (EUV) radiation from the Sun is at its lowest level in a decade. How could this influence F2 ionization?

The following is from Wikipedia on F2 Propagation:
Since the height of the F2 layer is some 200 miles (320 km), it follows that single-hop F2 signals will be received at thousands rather than hundreds of miles. A single-hop F2 signal will usually be around 2,000 miles (3,200 km) minimum. [Yes in our case]
A maximum F2 single-hop can reach up to approximately 3,000 miles (4,800 km). [Not in our case]
Multi-hop F2 propagation has enabled Band 1 VHF reception to over 11,000 miles (17,700 km). [Not in our case]
Since F2 reception is directly related to radiation from the Sun on both a daily basis and in relation to the sunspot cycle, it follows that for optimum reception the centre of the signal path will be roughly at midday. [Not in our case, the Sun was between The Bahamas and Cuba.]
Clue: The DXers were not able to receive the audio carrier on 59.750 MHz. F2 has a high cut-off frequency near 60 MHz. [Yes, in our case]

Since these two propagation modes do not fit the parameters, more research is needed.

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