On the Statistics of Random Meteors.

From Six News Feb 1998

Reply-To: Palle Preben-Hansen, OZ1RH

Hi again,

Now I got my manuscript. Note it is written with 50 MHz in mind. Here is quote from Six News Feb 1998:

The statistics on RANDOM meteors says the reflections comes from two "hot spots" about +/- 10 degrees from the great circle bearing to the other station. Which hot spot is most active is dependent on the path (North-South or East-West) and the time of the day. The different activity of the hot spots is caused by the earth rotation and its movements around the sun towards the meteors. No reflections come directly from the great circle bearing as the geometry does not fit. Most amateurs beam great circle bearing and get success, because our beamwidth is wide enough to cover both hot spots.

The MS "hot spots" move closer and closer to on-path as the distance gets greater, and there is but a single hot spot at path midpoint when you reach the geometric propagation distance limit at about 2.300 km.

These "hot spots" are often mentioned in the literature, but all sources I have read use the same drawing, which seems to come from: Hines, C.O, Journal of Atmospheric and Terrestrial Physics, 1956, pp.229-232. This drawing below shows predicted diurnal variations in random meteor counts for a path length in the order of 1.000 km. The following is for middle latitudes in the northern hemisphere. If you are south of the equator reflections from the north and south side of an east-west path would be interchanged.

For a north-south path the west side is the most productive from 18H to 06H local and it peaks at 03H. The east side of a north-south path is better from 06H to 18H and peaks at 10-11H. Max. meteor reflection counts on a north-south path is not at 06H local time!
For an east-west path the north side is best from 00H to 12H and it peaks at 06H. The south side is best from 12H to 24H, but is on a quite even and low level.

This only applies to random meteors, in fact some assumptions were made in the 50'ties on isotropic distribution of meteor velocities in a heliocentric system and a line density of trail ionization which is independent of meteor speed. I have no idea to what extend these assumptions are valid, and I do not care either, as it is possible to make QSO's anyway.

The afternoon and early evening has fewer meteors, but the reflections should be longer, as the trails tend to form at lower heights, where the trails persist longer. Longer reflections are no disadvantage to making QSO's, so there is no reason to give up making QSO's in the evening.

With help from OH5IY I have realized this 'hot spot' stuff is only for random meteors, and not valid for showers. Unless your antenna is very narrow this +/- perhaps 10 degrees in azimuth is not important. However if you beam off great circle bearing using lower angle of radiation, you better pick the best side of the path, that is the best hot spot.

The meteors of a shower seem to come from a circle with a diameter of about 10 degrees. So your beam should not be narrower than this. On 144 MHz a H-stack of 4x18-XXX M2 longboomers will be about 13 degrees wide, so we are talking about quite big antennas if it should be too narrow for 144 MHz meteor scatter. On 50 MHz no amateur antenna will be too narrow. A high gain antenna will not give more meteors, but the reflections will be audible longer. An improvement from S5 to S6 will not matter, only going from S0 to S1 will.

My conclusion is if you use an EME antenna for meteor scatter it should have a beamwidth of more than 10 degrees. You need to know where to point your beam, and the same applies to your QSO partner. If you both have a sharp EME antenna you should agree on which hot spot to use.

Vertical radiation pattern seems to be more important than azimuth for random meteor QSO's. Elevation control should be considered for the shorter distances, and is well described many places like OH5IY's fine MS-program with documentation. 1.200 km requires about 6 degrees radiation angle. Radiation angle is not the same as the elevation angle of your antenna. The radiation angle depends on height over reflecting ground and the terrain slope. You need YTAD from ARRL or K6STI's Terrain Analyzer to estimate your radiation angle.

73, Palle, OZ1RH (OZ5W-OZ9EDR contest team) oz1rh@dialip.csc.dk

50.160 MHz /144.280 MHz / 432.180 MHz in major contests

The Statistics of Random Meteors on 50 MHz by OZ1RH