QSOs between PA and 4X on 144 MHz

(2022-08-17) PE1ITR
As far as I know, a complete terrestrial radio contact on 144 MHz has never been made between the Netherlands (PA) and Israel (4X). However, signals have been spotted back and forth before. There are also unconfirmed reports of QSOs. However, that now seems to have changed. It is interesting to take a closer look at the mechanism of such radio openings.
The average distance is about 3215 kilometers. This is more than the known propagation mechanisms can support. There must be several factors that coincide.
Earlier I published on my website a similar story about radio contacts on 144 MHz between PA and EA8.

Overall, the whole path resembles the same mechanism that we also see between PA and EA8. The question is whether that is really the case? On this page, I assume it is, and we'll see if we can discover the same mechanism.

When I look in the data of cluster spots then I see from 2007 now and then a spot in which signals are observed. The validity of these spots is not always clear. 90% of these spots take place in the months of June and July.
However, in the last 2 years you see an increase in the number of observations that can also be more substantiated. This is mainly caused by 4X/OM2IB (KM72) being active on 144 MHz.
The use of digital modes and active continuous reporting on, for example, pskreporter or personal blogs also provides more insight.


On June 11, 2022, there were two time frames when PA stations spotted and even worked 4X stations. PA5Y confirmed to me that on June 11, 2022, he has worked the following stations 4X/OM2IB (17:18 UTC) and 4Z5CP (17:21 UTC). There is also confirmation that PA2CHR wkd 4X1BG, 4X/OM2IB and PA3BIY wkd 4X/OM2IB (17:12 UTC). In both cases there were several Es reflection points. The reflection point that is of interest to us seems to be above the square JN86. Through that reflection point, stations were able to reach the area around the square KN20 assuming that the angle of incidence is equal to the angle of exit. The remaining distance and 4X must then be traversed via an additional radio propagation path.

Let's take a closer look at these two events.

Below are two maps in which 144 MHz spots are plotted. In both maps an E-layer reflection can be seen above the square JN86 that enables stations for the first first hop. This is indicated by a purple ellipse. The signals then arrive approximately at the square KN20, also indicated by a purple ellipse. The two circles indicate an 1800 and 2000 km boundary where the signal is ending after the first hop E-layer reflection.
The assumption is that the path continues from there to 4X through a tropo duct. This is a 1200 - 1400 km path. Tropoducts occurs frequently in the Mediterranean, but many questions remain to determine whether this is the case.
It should also be noted that PA3BIY reports that he has received TA1BM (KN40) for a long time. The location of this station is in the 2220 km range. That could mean it has been a relatively large Es hop towards a possible shortend tropo path further to 4X. But 1000 km tropo is quite a lot without real indication of refraction.

2022-06-11 15:30 - 16:06 UTC

Fig 1: 144 MHz spots mapped between 15:30 and 16:06 UTC. The purple ellipse above JN86 indicates the E-layer reflection area. The purple ellipse above about KN20 is linked to presumably a tropo duct.

2022-06-11 17:10 - 17:30 UTC

Fig 2: 144 MHz spots mapped between 17:10 and 17:30 UTC. The purple ellipse above JN86 indicates the E-layer reflection area. The purple ellipse above about KN20 is linked to presumably a tropo duct.

The tropo propagation path

We look at the tropo refractivity map of 2022-06-11 of 18 UTC. Interesting for us is the path between 2000 and 3200 km.. I don't see a super-refractive duct that could explain the last 1200 km. It is noticeable that just above the ground some increased refraction of the radio signal is displayed, but at first sight this could not explain the 1200 km tropo path. The cross-section gives the same picture.

Fig 3:

Fig 4:


There is no clear picture for me how the propagation mechanism between PA and 4X is established. It is clear that the first part of the path Es is propagation. But the second part is unclear. The data does not indicate a strong tropo duct. That's not to say it hasn't been there.
Also, the data does also not indicate a second Es hop. So for now it is still unknown to me what the entire path looked like.

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