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Re: (meteorobs) radio observations during enhanced meteor activity
Hallo Sirko and all.
>To my understanding, Leonids rates
>several order of magnitudes higher than in 1997 would produce a kind of
>overall ionization of the respective atmospheric layer resulting in
>continuous radio reflection.
Not necessarily. As long as no sporadic-E happens, meteors are descriminated
by frequency/phase offset, head echos, trail width and by different wind
speeds in the target area. This is not possible with FM, but with a narrow
signal beacon in SSB or CW mode, e.g. like the video carrier of a TV
transmitter. FFTDSP recording is one way to do this. Hope I meet you in
march, to show you this in detail if you are interested.
If sporadic-E happens (this is not the same as ionisation from meteors!), it
wipes out individual meteor echo signatures simply by signal strength, and
individual meteors can no longer be observed. Depending ionisation level, it
will effect (a) lower frequencies first - up to the so called "MUF" (maximum
usable frequency), and (b) longer distances first. Close by transmitters may
be uneffected, while distant channels are saturated. Again: if all this
emissions are fed into a chart recorder, to resulting "total power" will no
longer be meaningful. Donīt know if backscatter systems are saturated at all?
I tried to set a limit for my FFTDSP system: During normal routine
observation I will recognize about 1-3 / second, but depends on other
factors, too. Will look forward for next year Leonids, than I will know.
>If that happens, it wouldn't help you much to
>tune your system to another frequency or so.
You underestimate the influence of frequency here: according to the
mentioned chapter of McKinley "Meteor science..", the reflected echo power
varies with the 3rd power of the wavelength. So it will help, of course.
>Here the questions arises,
>what you can do to escape saturation.
During the Leonids I record also on 144 Mhz, but did not even process the
results from this channel (maybe 10 short reflections / hour during shower
peak), and stopped recording a few days later on this frequency, as there is
too much silence on that high frequency. The geometry is close to
backscatter, so the dynamic range will be sufficient for all Leonids
outbursts -but not if they last for only 2 seconds ;-)
During normal operation I prefer 2 channels on 53.760 Mhz to get some 20000
reflections per day.
Hope this helps
Regards, Werfried Kuneth
PS: For anyone wondering what FFTDSP is: a shareware for the PC
w/soundblaster by Mike, AF9Y, a method to show the presence of *extremely*
faint signals for moon-bounce and SETI search, by analyzing the audio
frequency of a receiver and showing the audio spectrum each 0.5 seconds on
the screen. This tool is very useful to detect and record weak meteor echos
from distant VHF TV video carriers or beacons.