venerdì 18 maggio 2018

Propagation News – 20 May 2018

Last week continued with zero sunspots after the 13th and a solar flux index of around 70. NOAA had forecast poorer geomagnetic conditions from Thursday, the 17th. The solar wind speed, as measured at the ACE spacecraft, did increase on Thursday morning but the K-index hadn’t got above three by Thursday afternoon.

Overall, HF conditions were average with daytime critical frequencies tending to be in the range 4 to 5MHz. This translates to an F-layer maximum usable frequency over a 3,000km path of about 15-17MHz. This means that the most reliable daytime DX band remains 20 metres, 14MHz.
As we move towards more summer-like ionospheric conditions the higher HF bands are remaining open later. The 30 and sometimes even 20 metre bands are staying open longer after sunset, although 20m is still closing by late evening.

Sporadic E is still bringing some interest to the upper HF bands, particularly 10 metres, but you can see the short-skip effects down to 20 meters as well.
The FT8 frequency of 28.074 MHz is now a good first check point for band openings. The 10m beacons are also worth checking because SR5TDM, a three watt low-power Polish beacon on 28.215MHz, was audible during the week. You can find a 10 and 6m beacon list by searching on the web for G3USF beacons.

Next week, NOAA predicts the solar flux index will remain around 70. A lack of coronal hole activity means the K-index may only reach a maximum of two.

In summary then, it’s more of the same for HF!

VHF and up:

The charts show a lot of high pressure over the next week and this means a good chance of some tropo. The best paths will be over the surrounding seas, especially the North Sea at first. There may be a trend for drier air to remove some of the low-level moisture after this weekend, so paths won’t necessarily be good all of the time. The overnight conditions under high pressure can also produce temporary nocturnal lifts over land, but these paths tend to decay quickly after sunrise, when the heating breaks down any surface inversion.

Since it looks like a largely dry spell of weather, there may be a shortage of rain scatter clouds about for the microwave bands. All is not lost and there is some hope that sporadic E will continue to put in an appearance now and again. However, one of the main ingredients, a strong jet stream over Europe, may be hard to find in this fine, settled weather. This means the fall-back option of upper ridge patterns may be the trigger to watch. Check the daily sporadic E blogs on to see the current location of jet streams and ridges.

The Moon is past perigee, but losses are still low and will fall as the week progresses. Similarly, declination is falling but still in double figures until Wednesday, so another good week for EME with moon visibility from late morning through to after midnight most days.