JA-TF 160

Historically difficult JA-TF path

The path between Japan and Iceland has always been difficult, especially on 80 m and 160 m. We always hear our next neighbors in Europe work JA on the low bands giving real reports like 579, and we hear nothing! Still the atmospheric noise is lower in Iceland than most other places. We are far north with poor propagation to low latitude thunderstorm areas.

During the last sun spot minimum, around 1996, I tried very hard to work JA on 80 m CW using different antennas, like 13 m portable top loaded vertical and a half wave wire in kite or balloon. Sometimes I was /P down by the ocean, with salt water in JA direction. Once I got a reply on 80 m from a JA station, but the kite stalled to the shore before we could finish the QSO!

Why is the path so difficult?

The reason is the aurora. The solar particles causing the aurora penetrate deep into the ionosphere and cause absorption. It is like the regular D-layer that shuts off the low band DX during the daylight hours. So for us in the in the Aurora Zone, it is like having variable daylight during the dark hours also!

This absorption is approximately proportional to


That is in dB, which makes it worse!  Let us take an example:


Band                Loss

20 m                2 dB (1.6 times power)

40 m                8 dB (6.3 times power)

80 m                32 dB (1585 times power)

160 m              128 dB (6.3 million million times power)

Comparison with neighbors in Europe

The earth’s magnetic field deflects the ionized particles and forces them down in a belt around the magnetic pole, the so called Aurora Oval. The intensity of the aurora decreases both to the north and to the south of this oval. From a map in the New Shortwave Propagation Handbook (CQ Communications 1995) one can estimate the average number of days with aurora during one year as follows:

Middle of Greenland                 100

Reykjavik, Iceland                    243

Northern Scotland                    50

Middle of England                    10

North Coast of France              5

The line for 243 days is the map maximum and it passes over Reykjavik. No wonder that the low bands are often dead for DX in Iceland!

Japan is especially difficult because the path from TF goes a very long way along the aurora oval, causing maximum attenuation. Figure 1 shows the sector for the JA path from Iceland, and figure 2 shows the same path from Helsinki, Finland. The aurora map is created by VE3NEA DX-Atlas, set for Japan sun set in mid December and Aurora Index of 3 only. The difference between TF and OH is striking!


Figure 1. The TF-JA path runs a long way in the aurora belt.                    (DX-Atlas map)


Figure 2. The OH-JA path for comparison                                               (DX-Atlas map)

Why good results now?

Why have we been able to QSO JA recently with better results than before? Why did I fail many times around 1996, but now I have worked JA on both 160 m (JA7FUJ) and 80 m (JA8ISU and JR7VHZ) using 100 W to a whip antenna on my car?

I think the main reason is the unusually broad and deep sun spot minimum this time, giving us in TF some periods of low band conditions similar to those outside the Aurora Zone. Figure 3 shows a graph of past 5 solar cycles, from SIDC, Belgium. Note how the minimum now is clearly the best one. Now we are coming out of the minimum, and it is possible that such good conditions for JA-TF low band path will never occur again during our lifetime.


Figure 3. The 2009 sun spot minimum is unusually good.  (SIDC, Belgium)



Another reason that hundreds of JA stations now have TF in log on 160 m is the superstation of Thor, TF4M, in his rural valley of Otradalur. He put up a multitude of Beverage antennas and a very efficient transmitting antenna by the sea, running 1 kW. I am very glad that he was able to complete his 160 m station before the end of this sun spot minimum. Even with 2 preamplifiers, there is often no increase in noise when he connects a good RX antenna. That is how low the atmospheric QRN can be in TF. Therefore he has been able to work DX stations with low power and simple antennas.

What will happen when the sun spots come up? I am sure that TF4M will still be able to work DX in conditions that are useless for us in the city, so more JA stations will probably work him in the years to come. But we are excited to find out how often this will be possible. No station, however good, can beat aurora losses in the order of 100 dB!

When did you first QSO TF on 80 m or 160 m?

I wonder what might have been the first JA-TF QSO on 80 m and 160 m. Please send me e-mail at villik(at)hi.is with details if you know of such QSOs in the past.

NOTE:   TF4M had the first TF to JA 160 meter QSO in History with JA7NI on 31. December 2007.    

73, de Villi TF3DX

Article by Vilhjálmur Þór Kjartansson, TF3DX. Published with his permission.

Originally published in CQ HAM RADIO Japan in a wonderful article in Japanese.





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