In this three part series of posts, I am going to look at the 2020 logs of a very active Band 2 DXer and what they might suggest about propagation on the 88 to 108 MHz FM band. The posts are broken up into three parts... 1) Tropospheric Propagation, 2) Sporadic-E & 3) Meteor Scatter.
First off, a big thank you to Paul Logan who very kindly shared his 2020 Band 2 logbook with me and answered numerous questions that I had. Outside of his usual 'local' FM radio stations which he can hear under flat conditions, he logged and identified roughly 5,500 long distance signals on Band 2 in the year 2020.
Profile of Paul Logan... Paul is a very active listener of Band 2 radio (88-108 MHz) signals and has been logging stations that he has heard for about 30 years. He lives in Lisnaskea in Co.Fermanagh in Ireland and his location is shown in the map below.
Paul's location is far from ideal for listening to distant VHF signals. He has some local hills to the east as well as the hills and mountains in Scotland, England and Wales as a further obstruction.
Equipment... For the 2020 logs, Paul used an SDRPlay RSP1 & RSP1A.
In recent years, software defined receivers have transformed FMDX listening as signals can now be seen on a computer screen as well as being heard. This allows a user to visually check for any unusual signals and can then go investigate it. One of the most impressive features is the ability to record sections of the spectrum and a user can then go back later to listen for anything unusual.
For an antenna, Paul is using a Korner FM9 from Antennenland in Germany.
This antenna which is mounted 8 metres above ground level is highly regarded by many FMDXers in Europe.
2020 Tropo Log... During the year 2020, Paul heard and identified around 86 signals that were heard via tropospheric propagation. This mode of propagation occurs when signals are bent over the horizon by sharp changes between air layers with different temperatures and moisture content.
I have picked out 5 groups of signals of note which I have marked from A to E. Refer to the map below and then the horizon profile further down.
A - This group of signals from the north-west corner of Spain are in the region of 1200 to 1300 kms. The sea path from the south coast of Ireland to the north coast of Spain is very good for VHF propagation with marine ducting happening several times a year. These sea paths are usually the best for very long paths in excess of 500kms and sometimes the signals can be amazingly strong.
In the video below, Paul shows how he was able to hear a Spanish radio station on a small portable radio when the opening was at its strongest. With his main directional antenna, he was able to hear the Spanish signals for most of the day.
In the horizon plot below, you can see that the path to NW Spain at Paul's location is largely unobstructed with only a 1 degree elevation. This allows very low angle signals to arrive at his location.
B - This path to Brittany and Cornwall is similar in that the sea path helps and the hills on the horizon are quite low at about 1 degree elevation.
C - This interesting batch of signals came from Norfolk in the east of England, a distance of 600kms. These signals had a few obstacles to overcome including Paul's local hills as well as the Pennines running down the centre of England.
With the signals arriving at least 3.5 degrees above the horizon, the means of propagation may have been via an elevated duct in the region of 500m to 2000m above the earth's surface. While higher frequency VHF & UHF signals tend to propagate better inside of ducts, it went as low as 89.7 MHz in this example.
D - This cluster of signals from the Netherlands and Germany were interesting for a number of reasons. First off is the sheer distance... about 1000kms which is unusual for Band 2 tropo. I suspect that the sea path over the North Sea may have helped for a large part of the journey.
If you examine the horizon plot below, you'll notice that there is a gap in the hills due east (90 degrees) where the horizon has an elevation of about 2.5 degrees.
What's really interesting is that the paths from the four transmission sites fit exactly in the gap. The signal from the most northerly German transmitter is exactly at the left hand side of the gap. The signal from the most southerly Dutch transmitter is exactly at the right hand side of the gap. The four signals fit exactly like a glove which suggests that they are coming in just barely above 2.5 degrees above the horizon.
E - These signals from the Newcastle area were at a distance of about 370kms and again are coming in from an obstructed path. This one has the highest angle as it had to clear a local hill that was 4 degrees on the horizon.
