Guest Post: Some thoughts on VHF paths across the South Atlantic ...by Dave, N7BHC

Dave N7BHC (Also PJ4VHF & ZR2BI) left a comment on a post recently about VHF propagation in the South Atlantic. There was so much interesting info in it that I have put it up here as a guest post. There is plenty in there as food for thought.

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Back in 2007-2010, I was trying to drum up trans-Atlantic tropo ducting interest. I am very pleased to see more progress now. A contact from ZD7 (St.Helena Is) to PY (Brazil) on 144 MHz (2m) is 100% probable. 

I introduced John Turner at Saint FM, the local FM radio station, back in 2008-2010 to tropo ducting on the FM broadcasting band. He successfully logged many Angolan, Namibian, and Cape Town FM stations. One December he emailed that he was unsuccessful identifying an Angolan FM radio station as he had interference from a Brazilian station on the same frequency. This was using just a car radio with its whip antenna. 

Back in March 2008, ZD8I on Ascension Island reported that they sometimes heard Cape Town Marine Radio (ZSC) on 156.8 MHz FM. That is an omni antenna to an omni antenna on FM at a range of 4400 km. 

ZD8S on Ascension Island reports listening to Brazilian FM stations with indoor portable radios. 

Since then, I spent the next ten years on Bonaire as PJ4VHF. My biggest tropo ducting success across the North Atlantic was the initial reception of D4C/b on the Cape Verde Islands at a range of 4,694km. I strongly encourage any stations on ZD7 and ZD8 to be active on both 2m and 70cm. 

I have been studying trans-ocenic ducting for many decades (I started out as ZR2BI in East London). The South Atlantic may be the BEST location worldwide for long-haul ducting, both for range and how often the openings occur. FM vertical polarization works well bit SSB or FT8 on horizontal is even better.

Maybe someday we may be allowed to and able to travel again, and I can afford to visit ZD7 in person. Until then, all I can do is strongly encourage others. 

73, Dave N7BHC/PJ4VHF/ZR2BI dpedersen AT drasticom DOT com

New 144 MHz beacon on St Helena Island heard over 3000kms away in South Africa - 1st March 2021

Back in February of 2021, I had a post up about the new 144 MHz on St Helena Island in the South Atlantic. Now we have the first reception report!

On the 1st of March 2021, Charles ZS1CF in Cape Town heard the ZD7GWM beacon on St Helena Island over a distance of approximately 3145 kms. The beacon operates on 144.475 MHz with 25 watts on CW into a vertical antenna.

The tropo prediction map above from Pascal, F5LEN shows path and it is believed that the propagation mode was via a maritime duct just above the ocean.

This marine path from South Africa to St Helena is a relatively common occurrence and successful contacts have been made on 2m and 70cms in the last few years. It is hoped that the new beacon will give a better picture of just how often this 3000km+ path opens and encourage others to have a listen as well.

As outlined in the original beacon post, there may be a possibility of a 144 MHz trans-Atlantic path to Brazil or via TEP to Europe.

Link...

1) Update on the new 144 MHz beacon on St Helena Island (ZD7) - Feb 16th 2021

3000km plus contact made on 433 MHz from St.Helena to South Africa - 16th Oct 2020

On the 16th of October 2020, there was a remarkable 3000+ km contact made on the 70cms band between South Africa and St.Helena in the South Atlantic.

The contact at 433 MHz was made between Garry, ZD7GWM on St.Helena Island and Tom, ZS1TA in South Africa. The distance was approximately 3136 kms and what was even more amazing was that the contact was made on FM!

The power used for the contact was a modest 35 watts into a vertical antenna. This was a new distance record for a contact between South Africa and St.Helena on the 70cms band.

The mode of propagation was probably a marine duct as shown by this tropo forecast map from Pascal, F5LEN.

This 3000km+ tropo path between South Africa and St.Helena opens up on a reasonably regular basis. Back in November of 2018, there was an opening on 144 MHz as outlined in this previous post.

In June of 2020, the 2m path opened up again and the most recent opening on 2-metres was on the 23rd of September 2020 when ZD7GWM was worked by no fewer than five ZS stations... ZS1TA, ZS3CVB, ZS1CF, ZS3JPY and ZS1FC.

To put these remarkable contacts on 144 MHz and 433 MHz into context, the 3136 km distance is equivalent to the path across the North Atlantic between Newfoundland and Ireland.

Link...

1) Cape Town Amateur Radio Centre: ZS1TA & ZD7GWM Set New 70cm Distance Record - 16 Oct '20