Propagation News – 21 May 2017

| May 19, 2017

NOAA’s prediction that the solar flux index would tend towards 80 last week turned out be wrong, as it stayed steadfastly in the low 70s. However, the prediction of poor geomagnetic conditions turned out to be right, with the K index hitting four on Wednesday, with worse to come. Nevertheless, there was DX to be had and evenings on 20 and 30 metres are proving to be useful as the bands remain open later.

Daytime maximum useable frequencies tend to be lower during the summer than they are in winter, but higher at night. This is because there is more molecular nitrogen due to heating effects in summer, and as this is harder to ionise than monatomic oxygen the Total Electron Content, or TEC, is lower. However, the TEC of the night-time F layer in summer tends to be greater than in winter, which is why night-time maximum usable frequencies can be higher.

Next week the solar flux index should remain in the mid 70s, but we are in for a turbulent time thanks to another coronal hole. A high-speed solar wind stream could push the K index up to five or six at the beginning of the week, with depressed maximum usable frequencies and noisy bands. However, the latter half of the week should be more settled and the bands could recover.

Meanwhile, we are into the Sporadic E season, which is providing good short-skip openings from 7MHz upwards at times. The strongest signals may be found on 28 and 50MHz, where noise levels are lower.

This coming week we have an emphasis on low pressure, which means tropospheric openings may be hard to find, although there could be some end of night surface-based inversions with misty dawns. These could give short-lived lifts until the day’s heating breaks down any inversion.

Low pressure in the summer often produces some large showers or thunderstorms and these are often useful for rain scatter on the GHz bands. There are plenty of weather radars online that will show where these are.

Last week brought reports of rain scatter reception of the Bell Hill Microwave Beacon cluster across Southern UK and the GB3FNY and GB3CAM 10GHz beacons further north, but no reports of UK QSOs. By contrast, a large number of QSOs were reported from stations on the continent.

Sporadic-E has been putting in an appearance recently, so check for openings from 10m up to 2m. Check clusters and beacons and set aside a few minutes late morning and late afternoon to check the VHF bands.

Random meteor scatter continues on the low VHF bands, with the Cetids shower increasing the sporadic meteor background. Monitor and call on 50.280MHz and 70.280MHz with MSK144 mode to check activity.

Moon declination goes positive overnight so moon windows will lengthen as the week progresses. Losses fall to a minimum at perigee on Thursday, when the moon is at its closest point to Earth, but note that the Sun is close to the Moon that evening so the noise levels will be high for a while.

And that’s all from the propagation team this week.

Category: GB2RS Propagation News