Propagation: Meteor Scatter (MS)

   
 
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25 April 2017, 1:57 UTC 


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Propagation:
  Sporadic E skip (Es)
  Backscatter
  Tropo
  Meteor Scatter (MS)
  F2 Skip
  Aurora
  Trans-equatorial scatter (TE)
  Lightning scatter (LS)

Propagation
by Glenn Hauser 
News

Meteor Scatter (MS)

MS is the one mode of propagation that is somewhat predictable. We've all seen "shooting stars"; these bright trails in the sky are also capable of reflecting VHF signals (even in the daytime when they cannot be seen). Astronomical studies abound showing in which days of the year one can expect the greatest frequency of "random" meteors (as the earth sweeps through meteor debris in its orbital path); and on certain dates meteor showers occur year after year, peaking within a couple of days of the same date. Consult almanacs or astronomical magazines for dates of predicted shower peaks.

Like Es, MS affects the lowest channels most, but more often than Es, MS can be noted on FM, channel 7, and above. Signal strengths are seldom great enough to produce MS observable with an indoor antenna. Some external antenna is a must, and the bigger, the better. Above FM you'll need to squeeze every dB (decibel, a unit of signal strength) possible out of the system (such as by amplification and stacking antennas). As the radiant point crosses the sky, the most favorable directions of MS DX change with it. Tables can give you a good idea of where to point your antenna during a shower at any given time. Then, you can actually plan what stations you want to try for, by finding out their schedules, and setting up for their direction. Dxing MS is a great way to fill in the gaps left by Es and tropo Dxing --- often in the 400-800 mile range --- and to hear/see new states at any distance up to 1400 miles.

Semi-local and tropo stations are anathema to MS DX'ers. For this reason, it may be reasonable to limit your MS DX'ing to the wee hours --- westerly stations lte at night, after nearby locals are off the air, or easterly stations in the morning before the locals return.

The true peak of a shower is determined by when your part of the world sweeps through the heaviest concentration of meteorites. But this time is skewed by the fact that around 6 a.m. local means the time your part of the world is meeting the debris head-on; the speed of the earth's rotation is added to the speed of the earth's revolution. Thus, other things being equal, MS peaks at 6 a.m. and reaches a low point at 6 p.m., when the reverse occurs. The combined rotation and revolution speed means the meteors come in at greater speeds, burn brighter, and produce more ionization --- and more DX, on the average.

MS is for the pure DX'er; it's impossible to watch or listen to a program by this propagation, for it may last from a split second to a little more than a minute. An individual "burst" may be on the order of a second or so, but sometimes larger meteors, or swarms of small ones may overlap, producing a very "choppy" assortment of signals. Swarms may cause bursts many seconds long.

Fortunately for the MS DX'er, the diurnal 6 a.m. peak coincides with the time of day when many TV stations are running continuous test patterns with their call letters displayed. This makes identification possible even in a split second. A video tape recorder or even a movie camera can be very helpful in the later identification of short bursts.

FM DX'ers often note MS overriding stations normally received with a weak signal. This DX should NOT be considered a nuisance! On TV one may occasionally identify more than one station during a single "long" burst, by rapidly flipping channels. Naturally, your TV receiver must be quite stable, with all the controls pre-set. But on FM one can often log several stations during one burst. The first rule is never stay on a frequency where the MS burst brings music; hardly ever will music provide any way to ID the station. Keep tuning until you hear talk. Again, a tape recorder can be helpful.
On the 88-92 MHz band, which is a bit more subject to MS than the higher channels, one can occasionally make ID's by paralleling different frequencies with the same programming. Since FM receivers are more sensitive than TV's, you can also choose a good clear frequency, sit on it, and hear dozens of "pings" --- occasionally lengthening into a burst with some identifiable information.

 


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