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Re: (meteorobs) Waubaushene Results
At 01:01 AM 1999-10-24 -0400, you wrote:
>During the listening period, the radio count was 153
>meteors or a rate of 127 per hour. Part of the reason for the high count
>may have been the upcoming Orionid meteor shower due to peak the following
>Thursday morning. With such a high rate, it is possible to recognize
>meteors that reflect a particular station. For example, I heard several
>bursts which contained snipits of the same song.
Over what time period did this occur? I have a regular morning two-way
high-speed meteor scatter schedule with Shelby Ennis, W8WN, of
Elizabethtown, Kentucky (my location is Shrewsbury, in central
Massachusetts), on 144 MHz. Our schedule typically lasts 15 to 25 minutes
and takes place starting at 1130 UTC (0730 eastern time). With high-speed
morse code, Shel and I alternate transmitting and receiving; he transmits
during the even-numbered minutes, and I transmit during the odd-numbered
minutes. Our morse code speed during October has been 2000 words per minute
(we record received pings using a sound blaster board in our computers, and
then while transmitting, we can play back received "pings" at more-normal
speeds of 60 to 75 words per minute so that we can "copy" what each other
was sending). So at this high speed (our signals sound like a raspy tone),
we almost always have some radio energy in the air. We point our antennas
toward each other on the horizon; the path between us is roughly WSW-ENE.
During a typical schedule, we each will hear anywhere from no pings at all
to as many as half a dozen pings... EACH MINUTE, on 144 MHz. During
October, we each have probably been hearing an average of two to three
pings each minute. This would translate to an hourly rate, over our
particular path (and if the rate held constant throughout the whole hour),
of 120 to 180 meteors. Some of these pings are very strong, and some are
quite weak to the point where we can tell they occurred, but the signal
strength is such that we cannot copy information during the slow-speed
playback.
I can't remember exactly what is the relationship of number of meteor
reflections versus frequency, perhaps Jim Bedient or Jim Richardson will
enlighten us. But it is known that both the number of meteors, and also the
strength of the reflections, increase substantially (3 to 1??) when the
radio frequency is halved. That is, if Shel and I heard 120 meteors per
hour on 144 MHz, then at 72 MHz, we might hear something like three times
that number.
You were monitoring on the FM broadcast band somewhere around 100 MHz;
presuming my assumed relationship of 3:1 meteor increase for half the radio
frequency is valid, we might assume that had Shel and I been operating at
100 MHz, we probably would have heard around 200 meteor reflections. This
is nearly twice as much as you did, Philip; but then again, Shel and I use
much larger antennas and extremely sensitive receivers, so we would be able
to hear meteors that you could not with your described setup.
Bottom line: your observation of around 120 meteors per hour doesn't sound
at all unusual to me for the sporadic background.
Now, let's consider the Orionids shower. One week before the peak, the
predicted ZHR was just 3 meteors, whereas the ZHR (as predicted by Ilkka
Yrjola's MSSOFT software) for the peak date was around 30. I believe the
predicted ZHR for Saturday was still only about 6. So, I don't think your
observation of 127 meteors in one hour was high due to the Orionids shower.
>I used the same setup as I mentioned in my message about last weekend: a
>small yagi pointed directly upwards toward the zenith feeding a pair of
>10-dB r.f. amplifiers and then the receiver. The yagi was mounted on my
>homemade 4-metre (12-ft.) mast.
In consideration of several points made by earlier posters during this last
week: the number of meteors "seen" at the zenith would be fewer than if
your antenna had been pointing at an angle of, say, 45 degrees (and
especially the horizon). In fact, however, there is more to this than that:
broadcast stations use antennas that purposely direct almost all of their
energy DOWNWARD toward their audience. If the station antenna is located on
a high hill overlooking a metropolitan area, the antenna is actually
designed and aligned such that it DOES NOT radiate toward the horizon, but
instead, DOWNWARD toward homes in the local area!
But not all broadcast station antennas are situated on high hills, and so
most stations do radiate considerable radio energy toward the horizon. But
then again, they purposely do NOT radiate UP into the sky.
If you think about this, and about where your own antenna was pointed, then
you realize that by pointing straight up, you were actually limiting the
area from which transmitters could have been located in order that they
would illuminate any meteors that happened to fall within the "sight" of
your own antenna. In addition, you were limiting the area of sky through
which meteors could fall and reflect signals directly downward to your
antenna.
This brings up a question for you experts out there: this ZHR bit: over
what field of view does ZHR apply? I mean, the zenith, at its limit, is
just a point in the sky, an infinitesimally small point in the sky.
Philip's antenna has a beamwidth, or "field of view" which can be
calculated and/or measured. I'm wondering, now, how that beamwidth might
compare to the ZHR FOV?? (Actually, I thought I'd better pose a question to
the visual experts way down near the end of this just to see how many
actually read this far!!)
There are a lot of other considerations in addition to these that I won't
get into on the reflector, some of which may tend to "tilt" your
measurements one way or another. It is interesting that you did record so
many meteor bursts that night, and I would like to hear about your future
observations, too.
SteveH
Shrewsbury, MA
Amateur Radio Station K0XP
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