While there have been verified TEP openings at 432 MHz in Africa in the past, any reports of TEP openings on the 70cms band seem to be extremely rare.
Back on the 13th of February 1978, YV5ZZ in Venezuela reported hearing LU3AAT in Argentina on '432.1 MHz'. The distance was approximately 5,100kms.
I'm not sure of the exact locations of either stations but Buenos Aires to Caracas is about 5,100kms and seems to be the right distance.
I found two accounts about this remarkable reception reports.
Article 1) The first one appeared in the Amateur Communications column, Electronics Today International from May 1978.
"Evening-type TEP extended to 432 MHz?
Recent record-breakng contacts on the 144 MHz band apparently supported by evening-type (or Class II) trans-equatorial propagation between Australia and Japan, Puerto Rico and South America, have been hot news in amateur circles amongst those who are keen on VHF/UHF DX.
However, no sooner was the upper frequency limit of Class II TEP extended to 144 MHz, previously established as being in the 100 MHz region, than evidence of the possible extension of this ionospheric propagation mode even higher in frequency - to 432 MHz - has come to hand.
YV5ZZ, located in Venezuala, is reported to have heard an Argentinian station, LU3AAT on 432.1 MHz in February during an opening when Argentinian stations were heard working Caribbean stations and stations in the northern countries of South America.
However, two way contact was not established, but this seems only a matter of time."
Article 2) The second one appeared in an article titled 'A Newly Discovered Mode of VHF Propagation [1978]' from the QST magazine dated October 1978.
"On February 13, 1978, YV5ZZ heard weak but identifiable signals from LU3AAT, on 432.1 MHz. Two-meter and 432 propagation far exceeds the capability of the TE mode YV5ZZ was using his satellite antenna system, which is steerable in azimuth and elevation. In the direction of LU3AAT, his horizon is obstructed by a range of mountains. The lowest elevation angle which allows for clearance of the mountain range is 8 degrees.
On February 16, 1978, YV6ASU heard LU3AAT on 432 MHz, with his antenna at about the same angle of elevation. On yet another occasion, KV4FZ heard LU3AAT on 145.1 MHz. He reported that a peak in signal strength occurred when the antenna elevation angle was 8-10 degrees. This geometry suggests that single-hop F-layer reflection isn’t involved. The angle also seems high for the tilt associated with TE."
Analysis... In preparing this post, I did a search for the first 432 MHz contact with Trans-Equatorial Propagation (TEP) in South America and much to my surprise, I couldn't find anything. Despite the 1978 article saying that a 70cms contact would only be a 'matter of time', it looks as if it never happened and has yet to happen.
This raises the point that I have made in previous TEP related posts... Is there anyone in South America trying to make TEP contacts on 432 MHz??
I see many reports of TEP contacts at 144 MHz made by LU, PY, CX & ZP stations in South America and that's fine. But I think radio amateurs should also be experimenting to see what is possible, to try something new and to push the limits.
The chart about shows the progression of sunspot numbers since 1965. In 1978, the levels aren't that much higher than they are now in the Spring of 2023 and 1978 was also about two years before the peak of solar cycle 21.
Doppler... TEP propagation is well known for it's distortion of the signal due to some spreading. The higher the frequency, the higher the distortion.
I'm assuming that the distortion at 432 MHz will mean that modes like FT8, FT4 and Q65b cannot be used? But is that a correct assumption?
If nothing else, the use of modern weak signal modes will allow a weak signal to be seen on a screen even if it can't be decoded. A sign that a CW contact might be possible if only the signal was a bit stronger.
In conclusion... If anyone has any information about previous TEP contacts on 432 MHz from South America then please let me know. If not, perhaps someone would like to try for the first 432 MHz TEP contact from South America?
Acknowledgement... Thanks to Carlos, LU7MC for sending on the Electronics Today International article. If your first language is Spanish and you're reading this post via Google Translate then send your information to LU7FC if it's easier.
1) For examples of TEP contacts on 2m, see my 144 MHz page.
2) For examples of other long distance contacts on 70cms, see my 432 MHz page.
